JP6971748B2 - Radioactivity measuring device - Google Patents

Description

The present invention relates to a radioactivity measuring device.

Conventionally, for example, a radiation detection device is described in Patent Document 1. When measuring surface contamination by β nuclides, this radiation detector targets the surrounding background γ-ray components for correction and compensation. Specifically, the detection layer on the radiation incident surface side is the first layer, the next detection layer is the second layer, the first layer mainly detects both β rays and γ rays, and the second layer mainly detects both β rays and γ rays. Detects gamma rays. Then, when measurement is performed for a certain period of time and the count rate detected in the first layer is (β + γ) and the count rate detected in the second layer is γ', β = (β + γ) -c1 · γ', c1 is As a correction coefficient, a β-ray count rate obtained by correcting the γ-ray component is obtained.

Japanese Patent No. 5060410

By the way, when the inspection device for inspecting the radioactive contamination on the surface of the storage container containing radioactive waste detects β-rays which is the radioactive contamination on the surface, the radiation amount of γ-rays inside the storage container is high. In some cases, the effect of this γ-ray cannot be ignored. Therefore, as described in Patent Document 1, it is conceivable to detect both β-ray and γ-ray count rates and subtract the count rates mainly detected for γ-rays from the count rates, which is described in Patent Document 1. As described above, it is difficult to accurately detect β-rays because a correction coefficient is required and an error occurs. Further, if the counting rate of γ-rays is higher than the counting rate of β-rays, the error becomes large, and it becomes more difficult to detect β-rays accurately.

The present invention solves the above-mentioned problems, and an object of the present invention is to provide a radioactivity measuring device capable of accurately measuring β rays by reducing the influence of γ rays.

In order to achieve the above object, the radioactivity measuring device according to one aspect of the present invention is a radioactivity measuring device for measuring the radioactivity contamination on the surface of the measurement target, and is relative to the surface of the measurement target. The radioactivity detection unit is provided with a radioactivity detection unit that is movably provided to detect radioactivity, and a signal processing unit that processes the detection signal detected by the radioactivity detection unit. The radioactivity detection unit mainly contains β-rays. The β-ray detection unit to be detected is arranged along the surface of the measurement target, and the γ-ray detection unit that mainly detects γ-rays is stacked and arranged on the side of the β-ray detection unit away from the measurement target. Then, the signal processing unit counts when the detection signal is input from the radioactivity detection unit and the detection signal is input only from the β-ray detection unit for each predetermined pulse.

In the radioactivity measuring device according to one aspect of the present invention, in the radioactivity detection unit, the β-ray detection unit is configured to have a plastic scintillator, and the γ-ray detection unit is configured to have an inorganic scintillator. It is desirable that it is done.

In the radioactivity measuring device according to one aspect of the present invention, in the radioactivity detecting unit, the β-ray detecting unit is configured to have a plastic scintillator having a thickness of 0.1 mm or less, and the γ-ray detecting unit is configured. It is desirable that the scintillator has an inorganic scintillator having a higher density than the plastic scintillator having a thickness of 20 mm or more.

In the radioactivity measuring apparatus according to one aspect of the present invention, in the radioactivity detection unit, the inorganic scintillator of the γ-ray detection unit is GSO (gadrinium silicate), LSO (lutetium silicate) or LaBr ₃ (smelting). It is desirable to use either lantern) or YAP (yttrium orthoaluminate).

In the radioactivity measuring device according to one aspect of the present invention, the radioactivity detecting unit has a protective cover that covers the plastic scintillator in the β-ray detecting unit, and the protective cover is attached to the measurement target side of the plastic scintillator. It is desirable that a slit-shaped incident window that exposes the detection side surface is formed.

In the radioactivity measuring device according to one aspect of the present invention, in the radioactivity detecting unit, the β-ray detecting unit is laminated on the long plate-shaped plastic scintillator and the side of the plastic scintillator away from the measurement target side. It has a long plate-shaped light guide and photomultiplier tubes connected to both ends in the length direction of the light guide, and the signal processing unit outputs signals from each of the photomultiplier tubes. It is desirable to count when the signal is output and not when the signal is output from only one of the photomultiplier tubes.

In the radioactivity measuring device according to one aspect of the present invention, in the radioactivity detecting unit, the light guide is formed so that the end portion in the length direction protrudes longer than the plastic scintillator, and the light guide is formed from the measurement target side. It is desirable that it is curved so as to be separated.

In the radioactivity measuring device according to one aspect of the present invention, in the radioactivity detection unit, a shielding cover formed of a radioactivity shielding member is provided at a position facing the measurement target side of each photomultiplier tube. Is desirable.

In the radioactivity measuring device according to one aspect of the present invention, in the radioactivity detecting unit, the γ-ray detecting unit includes the long plate-shaped inorganic scintillator, the light guides arranged at both ends of the inorganic scintillator, and the said. It has a photomultiplier tube connected to each end of the light guide, and the signal processing unit counts and counts when a signal is output from each of the photomultiplier tubes of the γ-ray detection unit. It is desirable not to count when a signal is output from only one of the photomultiplier tubes.

In the radioactivity measuring device according to one aspect of the present invention, the measuring object is formed in a cylindrical shape, and while being rotated around a vertical axis in an upright position, the radioactivity is measured on its side surface, upper surface, and lower surface. The radioactivity detection unit is configured to measure radioactivity along the detection unit, and the radioactivity detection unit includes a side surface detection unit arranged longitudinally so as to correspond to the vertical dimension of the side surface of the measurement target, and the side surface detection unit. An upper surface detection unit arranged longitudinally so as to correspond to the diameter dimension of the upper surface of the measurement target, and a lower surface detection unit arranged longitudinally corresponding to the diameter dimension of the lower surface of the measurement target. , Is desirable.

According to the present invention, an inverse coincidence counting method capable of recognizing and excluding the detection pulse of the β-ray detection unit as γ-rays when detected by the γ-ray detection unit is applied. Therefore, the influence of γ-rays can be minimized, and only β-rays can be detected. As a result, β-rays can be measured accurately without causing an error in the measured value due to the influence of γ-rays.

FIG. 1 is a block diagram of inspection equipment including a radioactivity measuring device according to an embodiment of the present invention. FIG. 2 is a block diagram of the radioactivity measuring device according to the embodiment of the present invention. FIG. 3 is a schematic configuration diagram showing a radioactivity detection unit and a signal processing unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 4 is a side view of the radioactivity detection unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 5 is a front view of the radioactivity detection unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view of a radioactivity detection unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 7 is a diagram showing the relationship between γ-ray sensitivity and β-ray detection efficiency depending on the thickness of the plastic scintillator of the β-ray detection unit in the radioactivity detection unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 8 is a diagram showing the relationship between the thickness of the inorganic scintillator of the γ-ray detection unit and the γ-ray sensitivity in the radioactivity detection unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 9 is a block diagram showing a signal processing unit of the radioactivity measuring device according to the embodiment of the present invention.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment. In addition, the components in the following embodiments include those that can be easily replaced by those skilled in the art, or those that are substantially the same.

FIG. 1 is a block diagram of inspection equipment including a radioactivity measuring device according to the present embodiment.

The inspection equipment 100 of the present embodiment performs inspection while transferring, for example, a storage container 200 containing radioactive waste generated in a nuclear power plant. The storage container 200 is a measurement target in the present embodiment and is standardized for storing the stored radioactive waste, and a sealable, for example, a cylindrical drum can having a capacity of 200 liters is used. .. The radioactive waste stored in the storage container 200 is a uniform solidified body obtained by solidifying concentrated waste liquid and used resin, and radioactive waste such as metal and plastic is solidified in the storage container 200 by a filler (mortar or the like). There is a filled solidified body.

The inspection equipment 100 has a plurality of units 101, 102, 103, 104, 105, 106, 107 and an inter-unit transfer mechanism 110.

Units 101, 102, 103, 104, 105, 106, 107 are arranged side by side in a row. The unit 101 is a mounting table on which the storage container 200 before inspection is placed in a state where each circular surface is used as an upper and lower surface and a cylindrical surface is used as a side surface.

The unit 102 is the radioactivity measuring device of the present embodiment, and is also referred to as a radioactivity measuring unit. The radioactivity measuring unit 102 measures the surface contamination (Bq / cm ² ) of the storage container 200 and inspects the appearance. The surface contamination is measured on the surface of the storage container 200 by moving the storage container 200 upright and rotating and moving it up and down along the measuring portions on the upper surface, the lower surface, and the side surface of the storage container 200. Determine contamination by radioactivity. The visual inspection is performed at the same time as the measurement of surface contamination, and the upper surface, lower surface, and side surface of the storage container 200 are imaged using a camera while rotating and moving up and down with the storage container 200 upright, and based on this image. Inspect the appearance of the storage container 200. The detailed configuration of the radioactivity measurement unit 102 will be described later.

The unit 103 is a radiation dose measuring device, and is also referred to as a radiation dose measuring unit. The radiation dose measuring unit 103 measures the dose equivalent rate (mSv / h) in the storage container 200 and also measures the radioactivity concentration. The dose equivalent rate is measured by measuring the dose equivalent rate on the upper surface, the lower surface, and the side surface of the storage container 200 by radioactivity (γ-rays) while rotating and moving the storage container 200 upright. The radioactivity concentration is measured based on the radioactivity (γ-ray) that measures the dose equivalent rate. The radiation dose measuring unit 103 also measures the weight of the storage container 200.

The unit 104 attaches a label to the storage container 200 if it passes according to the measurement results of the radioactivity measurement unit 102 and the radiation dose measurement unit 103. For example, when the inspection facility 100 of the present embodiment transports the storage container 200 containing radioactive waste from a nuclear power plant to an external disposal site, a label with a manageable number is attached to the storage container 200.

The unit 105 is a shipping container arrangement unit. The transport container is for mounting a plurality (for example, eight) of storage containers 200 that have passed through the units 102, 103, and 104 together, transporting them from the inspection equipment 100 by a forklift, and transporting them by ship.

The units 106 and 107 are mounting tables, respectively, and the storage containers 200 after the inspection for being put in the transport container of the unit 105 are separately mounted according to the above classification.

The inter-unit transfer mechanism 110 transfers the storage container 200 to each unit 101, 102, 103, 104, 105, 106, 107. The inter-unit transfer mechanism 110 includes rails 110A along the rows of units 101, 102, 103, 104, 105, 106, and 107 arranged in a row, and a moving platform 110B that can move along the rails 110A. A handling device 110C provided on the mobile table 110B for moving the hand 110Ca for gripping the storage container 200 closer to or further from each unit 101, 102, 103, 104, 105, 106, 107.

Hereinafter, the radioactivity measuring unit 102, which is the radioactivity measuring device of the present embodiment, will be described. FIG. 2 is a block diagram of the radioactivity measuring device according to the present embodiment. FIG. 3 is a schematic configuration diagram showing a radioactivity detection unit and a signal processing unit of the radioactivity measuring device according to the present embodiment. FIG. 4 is a side view of the radioactivity detection unit of the radioactivity measuring device according to the present embodiment. FIG. 5 is a front view of the radioactivity detection unit of the radioactivity measuring device according to the present embodiment. FIG. 6 is an enlarged cross-sectional view of the radioactivity detection unit of the radioactivity measuring device according to the present embodiment (enlarged cross-sectional view taken along the line AA in FIG. 4). FIG. 7 is a diagram showing the relationship between the γ-ray sensitivity and the β-ray detection efficiency depending on the thickness of the plastic scintillator of the β-ray detection unit in the radioactivity detection unit of the radioactivity measuring device according to the present embodiment. FIG. 8 is a diagram showing the relationship between the thickness of the inorganic scintillator of the γ-ray detection unit and the γ-ray sensitivity in the radioactivity detection unit of the radioactivity measuring device according to the present embodiment. FIG. 9 is a block diagram showing a signal processing unit of the radioactivity measuring device according to the present embodiment.

As shown in FIG. 2, the radioactivity measurement unit 102 includes a rotation mechanism 2, a radioactivity detection unit 3, a signal processing unit 4, a data acquisition unit 5, a storage unit 6, and a drive unit 7. ..

The rotation mechanism 2 places the storage container 200 in an upright state, and rotates the storage container 200 around the axis S, which is the center of the cylindrical shape. The rotation mechanism 2 is configured to include, for example, a rotary table rotatably provided around the axis S on which the storage container 200 is placed in an upright position, and a drive motor for rotationally driving the rotary table. ing.

The radioactivity detection unit 3 detects radioactivity emitted from dirt and the like adhering to the side surface 200a, the upper surface 200b, and the lower surface 200c, which are the surfaces of the storage container 200. The radioactivity detection unit 3 includes a side surface detection unit 3A for the side surface 200a of the storage container 200, a top surface detection unit 3B for the top surface 200b of the storage container 200, and a bottom surface detection unit 3C for the bottom surface 200c of the storage container 200. .. Each of the detection units 3A, 3B, and 3C, which is the radioactivity detection unit 3, is provided so as to be relatively movable along the surface of the storage container 200 by rotating the storage container 200 by the rotation mechanism 2. Details of each of the detection units 3A, 3B, and 3C, which are the radioactivity detection units 3, will be described later.

The signal processing unit 4 is provided corresponding to each of the detection units 3A, 3B, and 3C, which are the radioactivity detection units 3. That is, the signal processing unit 4 processes the signals of the side signal processing unit 4A for processing the signal of the side surface detection unit 3A for the side surface 200a of the storage container 200 and the signal of the top surface detection unit 3B for the top surface 200b of the storage container 200. The upper surface signal processing unit 4B and the lower surface signal processing unit 4C for processing the signal of the lower surface detection unit 3C for the lower surface 200c of the storage container 200 are included. The signal processing unit 4 (4A, 4B, 4C) processes the radioactivity detection signal by the radioactivity detection unit 3 (3A, 3B, 3C). Details of the signal processing of the signal processing unit 4 (4A, 4B, 4C) will be described later.

The data collection unit 5 collects the output signal output from the signal processing unit 4 (4A, 4B, 4C) as a count value.

The storage unit 6 stores the count value collected by the data collection unit 5.

The drive unit 7 drives the rotation mechanism 2 and the radioactivity detection unit 3 (3A, 3B, 3C).

The data acquisition unit 5, the storage unit 6, and the drive unit 7 are configured as a control unit 8. The control unit 8 includes a microprocessor such as a CPU (Central Processing Unit), and based on the measurement method stored in the storage unit 6, the rotation mechanism 2 by the drive unit 7 and the radioactivity detection unit 3 (3A, 3B, 3C) drive is controlled.

Therefore, the radioactivity measurement unit 102, which is the radioactivity measurement device of the present embodiment, drives (powers) the rotation mechanism 2 and the radioactivity detection unit 3 (3A, 3B, 3C) by the drive unit 7, and the radioactivity detection unit 102. The detection signal by 3 (3A, 3B, 3C) is processed by the signal processing unit 4 (4A, 4B, 4C), and the output signal output from the signal processing unit 4 (4A, 4B, 4C) is processed by the data acquisition unit 5. Collect and store in storage unit 6.

Hereinafter, the details of the radioactivity detection unit 3 (3A, 3B, 3C) and the signal processing unit 4 (4A, 4B, 4C) will be described. As shown in FIG. 3, the radioactivity detection unit 3 (3A, 3B, 3C) has a β-ray detection unit 31, a γ-ray detection unit 32, and a support unit 33.

The β-ray detection unit 31 mainly detects β-rays. As shown in FIGS. 3 to 6, the β-ray detection unit 31 includes a plastic scintillator (PLS) 31a, a light guide 31b, and a photomultiplier tube 31c.

The plastic scintillator 31a is formed in a long plate shape so as to form a detection side surface arranged toward the surface (side surface 200a, upper surface 200b, lower surface 200c) of the storage container 200. The thickness T1 of the plastic scintillator 31a is set to 0.1 mm or less. As shown in FIG. 7, from the relationship between the γ-ray sensitivity of the plastic scintillator 31a and the β-ray detection efficiency, it is desirable that the thickness T1 of the plastic scintillator 31a is 0.1 mm or less mainly for detecting β-rays. In the present embodiment, it is preferably 0.1 mm from the viewpoint of manufacturing.

The light guide 31b guides the light emitted by the plastic scintillator 31a by detecting radioactivity to the photomultiplier tube 31c and condenses it. The light guide 31b is laminated and arranged along the light emitting side surface opposite to the detection side surface facing the surface of the storage container 200 of the plastic scintillator 31a so as to be aligned with the long plate shape of the plastic scintillator 31a. Further, both ends of the light guide 31b in the length direction are formed so as to protrude longer than the length direction of the plastic scintillator 31a.

The photomultiplier tube 31c converts the light energy of the plastic scintillator 31a guided by the light guide 31b into electrical energy and outputs it. The photomultiplier tube 31c is connected to both ends of the light guide 31b in the length direction.

The γ-ray detection unit 32 mainly detects γ-rays. As shown in FIGS. 3 to 6, the γ-ray detection unit 32 includes an inorganic scintillator (GSO: Ce-added Gd ₂ SiO ₅ (gadolinium silicate), LSO (lutetium silicate), LaBr ₃ (lanthanum bromide), and YAP. (Yttrium orthoaluminate)) 32a, a light guide 32b, and a photomultiplier tube 32c.

The inorganic scintillator 32a is formed in a plate shape so as to form a detection side surface arranged toward the surface (side surface 200a, upper surface 200b, lower surface 200c) of the storage container 200. The inorganic scintillator 32a is formed in a long plate shape having the same length as the light guide 31b in the β-ray detection unit 31, and is laminated and arranged on the light guide 31b side. GSO, which is an inorganic scintillator 32a, has a high stopping power (high density) against γ-rays, a short decay time after light emission at a high count rate, and a high light yield (large light emission amount). , Desirable for handling high doses of gamma rays. Further, the thickness T2 of the inorganic scintillator 32a is set to 20 mm or more. As shown in FIG. 8, from the relationship between the thickness T2 of the inorganic scintillator 32a and the γ-ray sensitivity (Monte Carlo analysis result), setting the thickness T2 of the inorganic scintillator 32a to 20 mm or more is mainly for detecting γ-rays. In this embodiment, it is preferably 20 mm.

The light guide 32b guides the light emitted by the inorganic scintillator 32a by detecting radioactivity to the photomultiplier tube 32c and condenses it. The light guides 32b are provided at both ends of the inorganic scintillator 32a in the length direction and are continuously provided in the length direction.

The photomultiplier tube 32c converts the light energy of the inorganic scintillator 32a guided by the light guide 32b into electrical energy and outputs it. The photomultiplier tube 32c is connected to each end of the light guide 32b continuously provided in the length direction of the inorganic scintillator 32a.

The support unit 33 supports the β-ray detection unit 31 and the γ-ray detection unit 32. As shown in FIGS. 4 to 6, the support portion 33 has a base portion 33A, a pedestal 33B, a protective cover 33C, an inclined portion 33D, and a shielding cover 33E.

The base 33A is for supporting the entire radioactivity detection unit 3 (3A, 3B, 3C), and is formed of, for example, a metal material so as to have a rigid structure.

The pedestal 33B is fixed to the base 33A and is for fixing the β-ray detection unit 31 and the γ-ray detection unit 32. The pedestal 33B is not easily deformed and is formed of a resin material as a rectangular block. In the pedestal 33B, the inorganic scintillator 32a of the γ-ray detection unit 32 is arranged on the support surface 33Ba on the side facing the surface of the storage container 200 to be measured. Further, a light guide 31b of the β-ray detection unit 31 and a plastic scintillator 31a are arranged on the side of the γ-ray detection unit 32 facing the surface of the storage container 200 of the inorganic scintillator 32a.

The protective cover 33C is attached to the pedestal 33B and is provided so as to cover the light guide 31b and the plastic scintillator 31a of the β-ray detection unit 31 and the inorganic scintillator 32a of the γ-ray detection unit 32. The protective cover 33C is formed with an incident window 33Ca opened in a slit shape so as to expose the detection side surface of the β-ray detection unit 31 on the side facing the surface of the storage container 200 of the plastic scintillator 31a.

The inclined portions 33D are provided on both sides of the pedestal 33B in the length direction in which the light guide 31b and the plastic scintillator 31a of the β-ray detection unit 31 and the inorganic scintillator 32a of the γ-ray detection unit 32 extend. It is attached to the base 33A. The inclined portion 33D has an inclined surface 33Da that inclines from the pedestal 33B toward the base 33A in the above-mentioned length direction. A photomultiplier tube 32c of the γ-ray detection unit 32 and a photomultiplier tube 31c of the β-ray detection unit 31 are attached to the inclined surface 33Da. That is, the photomultiplier tubes 31c and 32c are arranged so as to be inclined from the pedestal 33B toward the base 33A along the inclined surface 33Da. Therefore, the light guide 32b of the γ-ray detection unit 32 and the light guide 31b of the β-ray detection unit 31 (the portion protruding longer than the length direction of the plastic scintillator 31a) are inspected for the plastic scintillator 31a of the β-ray detection unit 31. It is formed so as to be curved so as to be away from the surface of the storage container 200 to be measured rather than the side surface.

The shielding cover 33E is formed of a radioactivity shielding member and is provided so as to cover the periphery of the photomultiplier tube 31c of the β-ray detection unit 31 and the photomultiplier tube 32c of the γ-ray detection unit 32. That is, the shielding cover 33E shields the radioactivity in each of the photomultiplier tubes 31c and 32c.

The radioactivity detection unit 3 (3A, 3B, 3C) configured in this way directs the inspection side surface of the plastic scintillator 31a of the β-ray detection unit 31 toward the surface of the storage container 200 to be measured, and from the surface thereof. Arranged at a predetermined interval D apart. The predetermined interval D is, for example, about 19 mm. In the radioactivity detection unit 3, the side surface detection unit 3A is vertically arranged so as to correspond to the vertical dimension of the side surface 200a of the storage container 200 so as to be vertically aligned in the length direction. The side surface detection unit 3A may be formed continuously in the upper and lower portions, but may be formed in two or more upper and lower portions. For example, when the storage container 200 is a drum can, protrusions continuous in the circumferential direction are formed at two positions above and below the side surface 200a, but the side surface detection unit 3A is formed by being divided at the positions of the protrusions. , Placed avoiding protrusions. Further, in the radioactivity detection unit 3, the upper surface detection unit 3B is arranged in a longitudinal shape with the length direction aligned in the radial direction so as to correspond to the diameter dimension of the upper surface 200b of the storage container 200. The upper surface detection unit 3B may be arranged along the entire radial direction, but may be arranged along a radius. Further, in the radioactivity detection unit 3, the lower surface detection unit 3C is arranged in a longitudinal direction with the length direction aligned in the radial direction so as to correspond to the diameter dimension of the lower surface 200c of the storage container 200. The lower surface detection unit 3C may be arranged along the entire radial direction, but may be arranged along a radial portion.

The signal processing unit 4 (4A, 4B, 4C) is connected to each photomultiplier tube 31c of the β-ray detection unit 31 and each photomultiplier tube 32c of the γ-ray detection unit 32, and is also connected to the above-mentioned data collection unit. It is connected to 5. The signal processing unit 4 (4A, 4B, 4C) inputs a detection signal for each predetermined pulse from each photomultiplier tube 31c of the β-ray detection unit 31 and each photomultiplier tube 32c of the γ-ray detection unit 32. Further, in the signal processing unit 4 (4A, 4B, 4C), the pulse width for inputting a detection signal from each photomultiplier tube 31c and each photomultiplier tube 32c is set to, for example, a nanosecond level.

As shown in FIG. 9, the signal processing unit 4 (4A, 4B, 4C) inputs the AND circuit A1 to which the output from each photoelectron multiplying tube 31c is input and the output from each optoelectronic multiplying tube 32c. It has an AND circuit A2, a NAND circuit N1 to which the outputs from the AND circuits A1 and the AND circuit A2 are input, and an AND circuit A3 to which the outputs from the AND circuit A1 and the NAND circuit N1 are input. The AND circuit A1 has a high output only when there is an input from both the photomultiplier tubes 31c, while the output is low when there is no input from both the photomultiplier tubes 31c. The AND circuit A2 has a high output only when there is an input from both the photomultiplier tubes 32c, while the output is low when there is no input from both the photomultiplier tubes 32c. The NAND circuit N1 has a high output only when there is no high input from the AND circuit A2 and a high input from the AND circuit A1 or vice versa, while the output is low in other cases. Become. The AND circuit A3 has a high output only when there is a high input from the NAND circuit N1 and a high input from the AND circuit A1, while the output is low in other cases. That is, the signal processing unit 4 (4A, 4B, 4C) counts when the detection signal is input only from both the photomultiplier tubes 31c and outputs the data to the data collection unit 5. Therefore, the signal processing unit 4 (4A, 4B, 4C) counts and outputs to the data acquisition unit 5 when only β rays are detected at predetermined pulses, and does not count when γ rays are detected. ..

As described above, the radioactivity measuring device of the present embodiment measures the radioactive contamination on the surface of the storage container 200 to be measured, and is provided so as to be relatively movable along the surface of the storage container 200. The radioactivity detection unit 3 (3A, 3B, 3C) that detects the radioactivity and the signal processing unit 4 (4A, 4B, 4C) that processes the detection signal detected by the radioactivity detection unit 3 (3A, 3B, 3C). ) And. Then, the radioactivity detection unit 3 (3A, 3B, 3C) arranges the β-ray detection unit 31 that mainly detects β-rays along the surface of the storage container 200, and the γ-rays that mainly detect γ-rays. The detection unit 32 is laminated and arranged on the side of the β-ray detection unit 31 away from the storage container 200. Further, the signal processing unit 4 (4A, 4B, 4C) inputs a detection signal from the radioactivity detection unit 3 (3A, 3B, 3C) for each predetermined pulse, and inputs a detection signal only from the β-ray detection unit 31. Count if.

According to this radioactivity measuring device, when γ-rays are detected by the γ-ray detection unit 32, an inverse coincidence counting method capable of recognizing the detection pulse of the β-ray detection unit 31 as γ-rays and excluding them is provided. It is applied. Therefore, the influence of γ-rays can be minimized, and only β-rays can be detected. As a result, β-rays can be measured accurately without causing an error in the measured value due to the influence of γ-rays.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detection unit 3 (3A, 3B, 3C), the β-ray detection unit 31 includes a plastic scintillator 31a, and the γ-ray detection unit 32 is configured. It is desirable to have an inorganic scintillator 32a having a higher density than the plastic scintillator 31a.

According to this radioactivity measuring device, the plastic scintillator 31a of the β-ray detection unit 31 has a high β-ray detection sensitivity, and the inorganic scintillator 32a of the γ-ray detection unit 32 has a high γ-ray detection sensitivity. It is possible to obtain a remarkable effect of excluding the above and detecting only β rays.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detecting unit 3 (3A, 3B, 3C), the β-ray detecting unit 31 is configured to have a plastic scintillator 31a having a thickness of 0.1 mm or less. It is desirable that the γ-ray detection unit 32 has an inorganic scintillator 32a having a thickness of 20 mm or more and a higher density than the plastic scintillator 31a.

According to this radioactivity measuring device, the sensitivity to γ-rays can be lowered by setting the thickness of the plastic scintillator 31a in the β-ray detection unit 31 to 0.1 mm or less. Further, by setting the thickness of the inorganic scintillator 32a in the γ-ray detection unit 32 to 20 mm or more, the sensitivity of γ-rays can be improved. As a result, the β-ray detection unit 31 suppresses the detection of γ-rays, while the γ-ray detection unit 32 detects more γ-rays, thereby excluding γ-rays and detecting only β-rays. Can be remarkably obtained.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detection unit 3 (3A, 3B, 3C), the inorganic scintillator 32a of the γ-ray detection unit 32 is a GSO (gadolinium silicate) or LSO having a short emission decay time. It is desirable to use any of (lutetium silicate), LaBr ₃ (lanthanum bromide) and YAP (yttrium orthoaluminate).

According to this radioactivity measuring device, the inorganic scintillator 32a, which is gadolinium silicate, has a high stopping power (high density) against γ-rays, has a short decay time after light emission at a high count rate, and has a light yield. Since the rate is high (the amount of light emitted is large), it is possible to cope with high-dose γ-rays. As a result, by detecting more γ-rays in the γ-ray detection unit 32, the effect of excluding γ-rays can be remarkably obtained.

Further, in the radioactivity measuring device of the present embodiment, the radioactivity detection unit 3 (3A, 3B, 3C) has a protective cover 33C that covers the plastic scintillator 31a in the β-ray detection unit 31, and the protective cover 33C. It is desirable that a slit-shaped incident window 33Ca that exposes the detection side surface to be the measurement target side of the plastic scintillator 31a is formed in the plastic scintillator 31a.

^{According to this radioactivity measuring device, the radioactivity (Bq / cm 2} ) is quantified by protecting the plastic scintillator 31a with the protective cover 33C and limiting the radioactivity incident on the plastic scintillator 31a with the incident window 33Ca. Can be standardized.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detection unit 3 (3A, 3B, 3C), the β-ray detection unit 31 is from the long plate-shaped plastic scintillator 31a and the storage container 200 of the plastic scintillator 31a. It has a long plate-shaped light guide 31b laminated on the distant side and a photomultiplier tube 31c connected to both ends in the length direction of the light guide 31b, and has a signal processing unit 4 (4A, 4B, 4C). ) Is preferably counted when a signal is output from each photomultiplier tube 31c, and not counted when a signal is output from only one of the photomultiplier tubes 31c.

When the plastic scintillator 31a detects radioactivity and emits light, each photomultiplier tube 31c of the β-ray detection unit 31 inputs the light energy guided to both ends of the light guide 31b and outputs a signal. When a signal is output from only one of the photomultiplier tubes 31c, the plastic scintillator 31a does not detect the radioactivity and does not count as being affected by γ-rays. As a result, the influence of γ-rays can be reduced.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detection unit 3 (3A, 3B, 3C), the light guide 31b is formed so that the end portion in the length direction protrudes longer than the plastic scintillator 31a. Moreover, it is desirable that the storage container 200 is curved so as to be separated from the storage container 200.

The β-ray detection unit 31 preferably has the thickness of the plastic scintillator 31a as thin as possible in order to reduce the sensitivity to γ-rays, and is provided at both ends of the light guide 31b laminated on the plastic scintillator 31a in the length direction. Each photomultiplier tube 31c may be located closer to the storage container 200 than the inspection side of the plastic scintillator 31a. Therefore, the end of the light guide 31b in the length direction is formed so as to protrude longer than the plastic scintillator 31a, and is curved so as to be separated from the storage container 200, so that each photomultiplier tube 31c is provided in the storage container 200. It is possible to prevent the situation of contacting with.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detection unit 3 (3A, 3B, 3C), a shield formed by a radioactivity shielding member at a position facing the storage container 200 side of each photomultiplier tube 31c. It is desirable that the cover 33E is provided.

According to this radioactivity measuring device, by providing the shielding cover 33E, it is possible to prevent each photomultiplier tube 31c from being affected by γ-rays. As a result, the influence of γ-rays can be reduced.

Further, in the radioactivity measuring device of the present embodiment, in the radioactivity detection unit 3 (3A, 3B, 3C), the γ-ray detection unit 32 is arranged at both ends of the long plate-shaped inorganic scintillator 32a and the inorganic scintillator 32a. It has a light guide 32b and a photomultiplier tube 32c connected to each end of the light guide 32b, and the signal processing unit 4 (4A, 4B, 4C) has each photomultiplier tube of the γ-ray detection unit 32. It is desirable to count when the signal is output from both the tubes 32c and not to count when the signal is output from only one of the photomultiplier tubes 32c.

When the inorganic scintillator 32a detects radioactivity and emits light, each photomultiplier tube 32c of the γ-ray detection unit 32 inputs the light energy guided to both ends of the light guide 32b and outputs a signal. When a signal is output from only one of the photomultiplier tubes 32c, the inorganic scintillator 32a does not detect the radioactivity and does not count as being affected by γ-rays. As a result, the influence of γ-rays can be reduced.

Further, in the radioactivity measuring device of the present embodiment, the storage container 200 is formed in a cylindrical shape, and while being rotated around the vertical axis S in an upright state, it is placed on the side surface 200a, the upper surface 200b, and the lower surface 200c. The radioactivity detection unit 3 is configured to measure the radioactivity along the radioactivity detection unit 3, and the radioactivity detection unit 3 is a side surface detection unit arranged in a longitudinal shape so as to correspond to the vertical dimension of the side surface 200a of the storage container 200. 3A, the top surface detection unit 3B arranged longitudinally so as to correspond to the diameter dimension of the upper surface 200b of the storage container 200, and the top surface detection unit 3B arranged longitudinally so as to correspond to the diameter dimension of the lower surface 200c of the storage container 200. It is desirable to use the bottom surface detection unit 3C.

According to this radioactivity measuring device, the radioactivity on the surface of the storage container 200 can be measured in one rotation of the storage container 200, so that the measurement time can be shortened.

2 Rotation mechanism 3 Radioactivity detection unit 3A Side detection unit 3B Top surface detection unit 3C Bottom surface detection unit 31 β-ray detection unit 31a Plastic scintillator 31b Light guide 31c Photomultiplier tube 32 γ-ray detection unit 32a Inorganic scintillator 32b Light guide 32c Photomultiplier tube 33 Support 33A Base 33B Pedestal 33Ba Support surface 33C Protective cover 33Ca Incident window 33D Inclined part 33Da Inclined surface 33E Shielding cover 4 Signal processing unit 4A Side signal processing unit 4B Top surface signal processing unit 4C Bottom signal Processing unit 5 Data collection unit 6 Storage unit 7 Drive unit 8 Control unit 200 Storage container (measurement target)
200a Side surface 200b Top surface 200c Bottom surface A1 AND circuit A2 AND circuit A3 AND circuit N1 NAND circuit

Claims (8)

A radioactivity measuring device that measures radioactive contamination on the surface of the object to be measured.
A radioactivity detection unit that is provided so as to be relatively movable along the surface of the measurement target and detects radioactivity,
A signal processing unit that processes the detection signal detected by the radioactivity detection unit, and
Equipped with
The radioactivity detection unit is configured to have a plastic scintillator, and a β-ray detection unit that mainly detects β-rays is arranged along the surface of the measurement target, and is an inorganic scintillator having a higher density than the plastic scintillator. The γ-ray detection unit that mainly detects γ-rays is stacked and arranged on the side of the β-ray detection unit away from the measurement target, and the signal processing unit is configured for each predetermined pulse. In a radioactivity measuring device that counts when a detection signal is input from the radioactivity detection unit and a detection signal is input only from the β-ray detection unit.
The β-ray detection unit has a long plate-shaped plastic scintillator and a long plate-shaped light guide laminated on a side of the plastic scintillator away from the measurement target side.
The light guide is a radioactivity measuring device having an end portion in the length direction protruding longer than the plastic scintillator and curved so as to be away from the measurement target side. The β-ray detection unit has photomultiplier tubes connected to both ends in the length direction of the light guide.
The first aspect of claim 1, wherein the signal processing unit counts when a signal is output from each of the photomultiplier tubes, and does not count when a signal is output from only one of the photomultiplier tubes. Radioactivity measuring device. In the radioactivity detection unit, the β-ray detection unit is configured to have a plastic scintillator having a thickness of 0.1 mm or less, and the γ-ray detection unit has an inorganic scintillator having a thickness of 20 mm or more. The radioactivity measuring device according to claim 1 or 2, which is configured. In the radioactivity detection unit, the inorganic scintillator of the γ-ray detection unit is any one of GSO (gadolinium silicate), LSO (lutetium silicate), LaBr ₃ (lanthanum bromide), and YAP (yttrium orthoaluminate). The radioactivity measuring apparatus according to any one of claims 1 to 3. The radioactivity detection unit has a protective cover that covers the plastic scintillator in the β-ray detection unit, and the protective cover has a slit-shaped incident window that exposes the detection side surface of the plastic scintillator to be the measurement target side. The radioactivity measuring device according to any one of claims 1 to 4, which is formed. The β-ray detection unit has photomultiplier tubes connected to both ends in the length direction of the light guide, and is formed of a radioactivity shielding member at a position facing the measurement target side of each photomultiplier tube. The radioactivity measuring apparatus according to any one of claims 1 to 5, which is provided with a shield cover. In the radioactivity detection unit, the γ-ray detection unit includes a long plate-shaped inorganic scintillator, light guides arranged at both ends of the inorganic scintillator, and a photomultiplier tube connected to each end of the light guide. And have
The signal processing unit counts when a signal is output from each of the photomultiplier tubes of the γ-ray detection unit, and does not count when a signal is output from only one of the photomultiplier tubes. Item 6. The radioactivity measuring device according to any one of Items 1 to 6. The measurement target is formed in a cylindrical shape, and while being rotated around a vertical axis in an upright state, the radioactivity detection unit is aligned along the side surface, the upper surface, and the lower surface thereof to measure the radioactivity. Configured,
The radioactivity detection unit has a side surface detection unit that is vertically arranged so as to correspond to the vertical dimension of the side surface of the measurement target and a longitudinal detection unit that corresponds to the diameter dimension of the upper surface of the measurement target. The one according to any one of claims 1 to 7 , wherein the top surface detection unit arranged and the bottom surface detection unit arranged longitudinally so as to correspond to the radial dimension of the lower surface of the measurement target are used. Radioactivity measuring device.

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