Beta ray measuring device

Abstract

To provide a beta ray measurement device that does not use Q gas mainly containing helium gas and uses a plastic scintillator as a beta ray detector, and similarly to a GM counter, can reduce a detection lower limit concentration by avoiding the influence of cosmic rays and environmental gamma rays.SOLUTION: A beta ray measurement device comprises: a sample measurement unit that has a first plastic scintillator for detecting beta rays emitted from a sample; a first detection unit that has a second plastic scintillator that detects the influence of cosmic rays; a first anticoincidence circuit for outputting corrected first counts obtained by excluding, from first counts detected by the first plastic scintillator, second counts simultaneously measured and detected by the second plastic scintillator; and an operation unit that calculates the concentration of total beta radioactivity emitted from the sample based on the corrected first counts.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a beta-ray measuring device using a plastic scintillator in beta-ray measurement for performing total beta radioactivity, beta-ray nuclide analysis, etc.

Background Art

[0002] In nuclear facilities such as nuclear power plants, it is necessary to measure the total beta radioactivity concentration of beta rays (β-rays) emitted from samples containing radioactive substances such as gas and treated water, or to measure the radioactivity concentration of beta-ray-emitting nuclides such as strontium 90 (hereinafter, Sr-90) and strontium 89 (hereinafter, Sr-89) contained in samples derived from spent fuel.

[0003] Total beta radioactivity concentration measurement measures the total amount of beta-ray-emitting nuclide concentrations contained in a sample without identifying nuclides such as Sr-90 and Sr-89. In total beta radioactivity concentration measurement, a method is known in which a beta-ray emitted from a radioactive nuclide in a sample is measured using a GM counter (Geiger-Mueller counter), and the total beta radioactivity concentration is determined based on the counting rate and the sample amount (for example, see Non-Patent Document 1 and Non-Patent Document 2).

[0004] Also, a method for obtaining the radioactivity concentration for each beta-ray-emitting nuclide of radioactive strontium such as Sr-90 and Sr-89, which are so-called pure beta nuclides that emit only beta rays, is known (for example, see Non-Patent Document 3). According to this method, first, a stable isotope of Sr to be measured is added to the sample water to make a measurement sample in the chemical form of carbonate precipitation, then the sample count is measured using a GM counter, then the sample is dissolved, and after adding yttrium 89 (Y-89), which is a stable isotope, to make an iron precipitation sample, the radioactivity concentration of Sr-90 and Sr-89 can be obtained by measuring the time change of the sample count of the iron precipitation sample using a GM counter.

[0005] In addition, a method is known for measuring total beta radioactivity concentration by using a plastic scintillator to measure the beta rays emitted from radionuclides in a sample, and determining the total beta radioactivity concentration based on the count rate and the amount of sample (see, for example, Non-Patent Document 4).

[0006] In addition, a method for determining the radioactivity concentration of each beta-ray emitting nuclide is known (see, for example, Non-Patent Document 5). This method involves adding stable isotopes of the nuclide to be measured, creating a measurement sample in chemical form with carbonate precipitate, and then using a measuring device that combines a GM counter tube with a thickness of about 5 mm and a plastic scintillator formed to a thickness of about 1 cm. With this method, the luminescence of the GM counter tube and the plastic scintillator is measured, and when the measurement by the GM counter tube and the luminescence of the plastic scintillator occur simultaneously, it is determined that it is due to beta rays from the sample, and the radioactivity concentration of each beta-ray emitting nuclide can be determined by beta-ray spectrometry using the plastic scintillator. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Guidelines for the Measurement of Radioactive Substances Released from Light Water Reactor Facilities for Power Generation (Nuclear Safety Commission, partially revised March 29, 2001) [Non-Patent Document 2] Method for Measuring Total Beta Radioactivity (Ministry of Education, Culture, Sports, Science and Technology, revised in 1976) https: / / www.kankyo-hoshano.go.jp / wp-content / uploads / 2020 / 11 / No1.pdf [Non-Patent Document 3] Method for Analyzing Radioactive Strontium (Ministry of Education, Culture, Sports, Science and Technology, revised in 2003) https: / / www.kankyo-hoshano.go.jp / wp-content / uploads / 2020 / 12 / No2.pdf [Non-Patent Document 4] Study on estimation methods for background counts of total environmental beta radioactivity using meteorological data (Annual Report of Tokyo Metropolitan Institute of Public Health, 66, 235-245, 2015) https: / / www.tmiph.metro.tokyo.lg.jp / files / archive / issue / kenkyunenpo / nenpou66 / 235-245.pdf [Non-Patent Document 5] Rapid determination of 89Sr and 90Sr in radioactive waste using Sr extraction disk and beta-ray spectrometer, Y. Kameo et al. JAEA Journal of Radioanalytical and Nuclear Chemistry p.71-78 2007 / 10 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the methods described in Non-Patent Documents 1, 2, and 3, a detector with a GM counter is used to detect beta rays from radioactive nuclides in a sample. In this case, the GM counter measures not only beta rays emitted from the sample but also noise from cosmic rays and natural gamma rays arriving from around the detector. To reduce background counts due to gamma-ray noise, another GM counter is placed in the detector as a guard detector. With this detector, the beta ray count from radioactive nuclides in the sample can be calculated based on the detection values ​​of the other GM counter.

[0009] The gas inside a GM counter tube is altered by radiation, affecting the measurement results. Therefore, GM counter tubes are configured to continuously circulate Quenching Gas (Q gas), which is helium (He) gas with added organic gas, during measurement. However, helium, which makes up about 98% of Q gas, has recently attracted attention as a strategic material, leading to soaring prices and difficulties in obtaining it.

[0010] According to the method described in Non-Patent Document 3, in order to increase the beta-ray detection sensitivity of the GM counter, it is necessary to continuously flow Q gas through the GM counter, which is a guard detector, similar to the methods described in Non-Patent Documents 1 and 2. Therefore, the method described in Non-Patent Document 3 presents the problem of difficulty in obtaining helium, similar to the methods described in Non-Patent Documents 1 and 2.

[0011] According to the method described in Non-Patent Literature 4, a plastic scintillator is used instead of a GM counter to detect beta rays from radioactive nuclides in a sample. Plastic scintillators have the property of being more sensitive to detecting cosmic rays and gamma rays from the vicinity of the detector compared to GM counters. Therefore, the method described in Non-Patent Literature 3 has the problem that the background count due to noise based on Compton light of the plastic scintillator, influenced by cosmic rays and gamma rays in the detector environment, is high, resulting in a higher detection limit for the total beta radioactivity concentration compared to the methods described in Non-Patent Literature 1 and Non-Patent Literature 2.

[0012] According to the method described in Non-Patent Document 5, beta rays from radionuclides in the sample are measured using a relatively thin GM counter tube and a thickly formed plastic scintillator. Similar to the method described in Non-Patent Document 4, this method suffers from high background counts due to the influence of cosmic rays and gamma rays in the detector environment, resulting in a higher detection limit for Sr-90 and Sr-89 radioactivity concentrations compared to the method described in Non-Patent Document 3.

[0013] For the reasons stated above, there is a need for a beta-ray measurement device that does not use the helium-based Q gas required when using conventional GM counters. Furthermore, when using plastic scintillators as an alternative to GM counters, there is a need for a low-background beta-ray measurement device that can ensure the same detection limits as when using GM counters alone or in combination with plastic scintillators.

[0014] The present invention aims to provide a beta-ray measuring device that does not use a helium-based Q gas, but instead uses a plastic scintillator as a beta-ray detector, and that, like a GM counter, can reduce the detection limit concentration due to the effects of cosmic rays and natural radiation (also known as environmental gamma rays). [Means for solving the problem]

[0015] One aspect of the present invention is a sample measurement unit having a first plastic scintillator for detecting beta rays emitted from a sample; a first detection unit having a second plastic scintillator for detecting the effects of cosmic rays; a first anti-simultaneous counting circuit that outputs a corrected first count obtained by excluding a second count detected by the second plastic scintillator that was measured simultaneously from a first count detected by the first plastic scintillator; and a calculation unit that calculates the total beta radioactivity concentration emitted from the sample based on the corrected first count. The main body reduces the effects of cosmic rays and environmental gamma rays, Equipped with The sample measurement unit is housed inside the main body, and the first detection unit is positioned above and outside the main body. This is a beta ray measuring device. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a low-background beta-ray measuring device that does not use a helium-based Q gas, uses a plastic scintillator as a beta-ray detector, and, like a GM counter, can suppress the detection limit concentration due to the influence of cosmic rays and environmental gamma rays. [Brief explanation of the drawing]

[0017] [Figure 1] This diagram schematically shows the configuration of a beta-ray measuring device according to an embodiment. [Figure 2] It is a diagram showing the configurations of the first detection unit and the second detection unit. [Figure 3] It is a diagram schematically showing the configuration of a beta-ray measuring device according to a comparative example. [Figure 4] It is a diagram schematically showing the configuration of a beta-ray measuring device according to a comparative example. [Figure 5] It is a diagram schematically showing the configuration of a beta-ray measuring device according to a modified example. [Figure 6] It is a diagram schematically showing the configuration of a beta-ray measuring device according to a comparative example. [Figure 7] It is a diagram schematically showing the configuration of a beta-ray measuring device according to a comparative example.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, a beta-ray measuring device according to an embodiment of the present invention will be described with reference to the drawings.

[0019] As shown in FIG. 1, the beta-ray measuring device 1 includes, for example, a detection unit 2 that measures the beta-rays of a sample S, and an arithmetic unit 20 connected to the detection unit 2. The beta-ray measuring device 1 is, for example, a device that measures the total beta radioactivity concentration of the sample S. The sample S is, for example, collected from gas, treated water, etc. and contains strontium (Sr), which is a radioactive nuclide that undergoes beta decay.

[0020] The detection unit 2 includes, for example, a main body unit C that houses a container K on which the sample S is placed. The main body unit C is formed, for example, by a shielding wall such as lead so as to reduce the influence of cosmic rays and environmental gamma rays. A housing space C1 for housing the container K is formed below the inside of the main body unit C. The housing space C1 is formed so that the container K can be inserted and removed from the side. Above the housing space C1, a sample measurement unit 3 that measures the beta-rays emitted from the sample is provided. The sample measurement unit 3 has a first plastic scintillator 4 (PLS-M) that detects beta-rays, and a first photomultiplier tube 5 (PMT-M) that detects the light emission of the first plastic scintillator 4.

[0021] The first plastic scintillator 4 is positioned above the location where the container K is placed. The first plastic scintillator 4 is made of a plastic plate containing a fluorescent material. The first plastic scintillator 4 is excited and emits light when beta rays emitted from the sample S in the container K pass through it. The first photomultiplier tube 5 is positioned above the first plastic scintillator 4.

[0022] The first photomultiplier tube 5 comprises a cathode and an anode, and a high voltage is applied between the two electrodes by a high-voltage power supply 28, which will be described later. The first photomultiplier tube 5 utilizes the photoelectric effect to generate and amplify photoelectrons based on the light emitted from the first plastic scintillator 4, and outputs the first count of beta rays emitted from the sample S as an electrical signal. The electrical signal is output to the first anti-simultaneous counting circuit 23, which will be described later.

[0023] The first plastic scintillator 4 measures not only beta rays emitted from the sample S but also cosmic rays (gamma rays) and natural radiation (gamma rays) arriving from space. In order to accurately measure the beta rays emitted from the sample S, the detection unit 2 is provided with a first detection unit 6 for detecting the effects of cosmic rays and a second detection unit 10 for detecting the effects of natural radiation. Above the sample measurement unit 3, for example, the first detection unit 6 for detecting the effects of cosmic rays is provided.

[0024] The first detection unit 6 includes a second plastic scintillator 7 (PLS-U) for detecting cosmic rays and a second photomultiplier tube 8 (PMT-U) for detecting the light emitted from the second plastic scintillator 7. The second plastic scintillator 7 is located above and outside the main body C. The second plastic scintillator 7 is formed from a plastic plate containing a fluorescent material. The second plastic scintillator 7 is excited and emits light when cosmic rays or natural radiation pass through it. The second photomultiplier tube 8 is located adjacent to the second plastic scintillator 7. The second photomultiplier tube 8 has a cathode and an anode, and a high voltage is applied between the two electrodes by a high-voltage power supply 28, which will be described later.

[0025] The second photomultiplier tube 8 utilizes the photoelectric effect to generate and amplify photoelectrons based on the light emitted from the second plastic scintillator 7, and outputs the second count, which is detected by cosmic rays, as an electrical signal. The electrical signal is output to the first anti-simultaneous counting circuit 23 and the second anti-simultaneous counting circuit 24, which will be described later.

[0026] The second plastic scintillator 7 is formed, for example, in a disc shape when viewed from above. The second plastic scintillator 7 is covered with a metal film 7B that shields beta rays emitted from the sample S. The second plastic scintillator 7 has a protruding portion 7A that extends horizontally in part. A second photomultiplier tube 8 is positioned on the upper part of the protruding portion 7A. The protruding portion 7A is covered with a metal film 7C, similar to the second plastic scintillator 7. The metal film 7C is made of a metal film that is thicker than the metal film 7B. The second photomultiplier tube 8 is covered with a metal film 8C. The metal film 8C may be made of a film material such as paper, as long as it can shield light. As a result, the first detection unit 6 can measure cosmic rays arriving from above the sample measurement unit 3.

[0027] Below the sample measurement unit 3, a second detection unit 10 is provided for detecting, for example, the effects of natural radiation. The second detection unit 10 includes a third plastic scintillator 11 (PLS-D) for detecting environmental gamma rays arriving from below, and a third photomultiplier tube 12 (PMT-D) for detecting the light emitted from the third plastic scintillator 11. The second detection unit 10 has the same configuration as the first detection unit 6. The third plastic scintillator 11 is located below and outside the main body unit C.

[0028] The third plastic scintillator 11 is formed from a plastic plate containing a fluorescent substance. The third plastic scintillator 11 is excited and emits light when environmental gamma rays pass through it. The third photomultiplier tube 12 is positioned adjacent to the third plastic scintillator 11. The third photomultiplier tube 12 has a cathode and an anode, and a high voltage is applied between the two electrodes by a high-voltage power supply 28, which will be described later.

[0029] The third photomultiplier tube 12 utilizes the photoelectric effect to generate and amplify photoelectrons based on the light emitted from the third plastic scintillator 11, and outputs the third count, which is detected by ambient gamma rays, as an electrical signal. The electrical signal is output to the second anti-simultaneous counting circuit 24, which will be described later.

[0030] The third plastic scintillator 11 is formed, for example, in the shape of a disc. The third plastic scintillator 11 is covered with a metal film 11B that shields against beta rays emitted from the sample S. The third plastic scintillator 11 has a protruding portion 11A that extends horizontally in part. A third photomultiplier tube 12 is positioned on the upper part of the protruding portion 11A. The protruding portion 11A is covered with a metal film 11C, similar to the third plastic scintillator 11. The metal film 11C is made of a metal film that is thicker than the metal film 11B. The third photomultiplier tube 12 is covered with a metal film 12C. The metal film 12C may be made of a film material such as paper, as long as it can shield against light. As a result, the second detection unit 10 can measure environmental gamma rays such as natural radiation arriving from below the sample measurement unit 3. In environments where natural radiation is shielded, the second detection unit 10 may not be provided.

[0031] Next, the configuration of the arithmetic unit 20 will be described. The arithmetic unit 20 includes, for example, a first anti-reciprocity counting circuit 23 and a second anti-reciprocity counting circuit 24 for detecting the count of beta rays emitted from the sample S, a calculation unit 25 for calculating the total beta radioactivity emitted from the sample S based on the output values ​​of the first anti-reciprocity counting circuit 23 and the second anti-reciprocity counting circuit 24, a high-voltage power supply 28 for inputting a high voltage to each photomultiplier tube, an input unit 26 for inputting information and operation details necessary for the calculation, a display unit 27 for displaying the calculation results, and a storage unit 29 for storing data necessary for the calculation.

[0032] The high-voltage power supply 28 is a power supply device that applies a high voltage (for example, about 500-1000V) DC current (for example, a maximum of about 10mA) to the first photomultiplier tube 5, the second photomultiplier tube 8, and the third photomultiplier tube 12.

[0033] The first counter-similarity counting circuit 23 measures a corrected first count obtained by excluding the cosmic ray count from the first count of the first plastic scintillator 4. The first count output from the first photomultiplier tube 5 includes not only the beta ray count emitted from the sample S but also the cosmic ray count that has passed through the main body C. The first counter-similarity counting circuit 23 outputs a corrected first count electrical signal, excluding the case where the electrical signal of the first count output from the first photomultiplier tube 5 and the electrical signal of the second count output from the second photomultiplier tube 8 are measured simultaneously. That is, the first counter-similarity counting circuit 23 outputs a first output value of the corrected first count obtained by excluding the second count of the second plastic scintillator 7, which was measured simultaneously, from the first count of the first plastic scintillator 4.

[0034] The second reciprocal counting circuit 24 measures a corrected count obtained by excluding the environmental gamma ray count from the first corrected count of the first reciprocal counting circuit 23. The first corrected count output from the first reciprocal counting circuit 23 includes not only the beta ray count emitted from the sample S but also the environmental gamma ray count that has passed through the main body C. The second reciprocal counting circuit 24 outputs an electrical signal of a corrected count, excluding the case where the electrical signal of the third count output from the third photomultiplier tube 12 and the electrical signal of the corrected first count output from the first reciprocal counting circuit 23 are measured simultaneously. That is, the second reciprocal counting circuit 24 outputs a second output value of the corrected count obtained by excluding the third count of the third plastic scintillator 11 that was measured simultaneously from the first corrected count of the first plastic scintillator 4. The first anti-simultaneous counting circuit 23 and the second anti-simultaneous counting circuit 24 subtract the cosmic ray count and the environmental gamma ray count included in the first count to measure the beta ray count emitted from the sample S.

[0035] The calculation unit 25 calculates the total beta radioactivity emitted from the sample S based on the second output value of the second anti-simultaneous counting circuit 24. The calculation unit 25 is realized, for example, by a processor such as a CPU executing a program (software) stored in the memory unit 29. Some or all of the functions of these components may be realized by hardware (including circuitry) such as LSIs, ASICs, FPGAs, and GPUs, or by the cooperation of software and hardware. The program may be stored in advance in a storage device such as an HDD or flash memory, or it may be stored in a removable storage medium such as a DVD or CD-ROM and installed when the storage medium is inserted into a drive device.

[0036] The memory unit 29 stores programs and various data necessary for calculations performed by the arithmetic unit 25. The memory unit 29 is a storage device equipped with a storage medium such as RAM, ROM, HDD, or flash memory.

[0037] The display unit 27 is a display device that outputs the calculation results of the calculation unit 25. The display unit 27 is a display device such as a liquid crystal display or an organic EL display. The display unit 27 may be configured separately as a personal computer, tablet terminal, smartphone, etc.

[0038] Next, the beta ray measurement method in the beta ray measurement device 1 will be described.

[0039] The beta rays emitted from sample S are the sum of the beta rays emitted from multiple nuclides contained in sample S derived from spent fuel, such as Sr-90, Sr-89, and yttrium-90 (Y-90) produced from Sr-90 (total beta radioactivity concentration). Sample S has been pre-scavenged, for example, to remove Y-90. The container K on which sample S is placed is housed in the containment space C1 of the main body C. The sample measurement unit 3 detects the beta rays emitted from sample S and outputs an electrical signal for the first count to the first reciprocal counting circuit 23. At this time, the first detection unit 6 detects cosmic rays and outputs an electrical signal for the second count to the first reciprocal counting circuit 23. In addition, the second detection unit 10 detects environmental gamma rays and outputs an electrical signal for the third count to the second reciprocal counting circuit 24.

[0040] The first counter-simultaneous counting circuit 23 outputs an electrical signal of a corrected first count to the second counter-simultaneous counting circuit 24, which excludes the second count detected simultaneously with the first count from the first count, based on the electrical signals of the first count and the second count. The second counter-simultaneous counting circuit 24 outputs an electrical signal of a corrected count to the calculation unit 25, which excludes the third count detected simultaneously with the first corrected count from the first corrected count, based on the electrical signals of the corrected first count and the third count. The calculation unit 25 calculates the count of the sample S based on the electrical signals of the corrected counts and calculates the total beta radioactivity concentration emitted from the sample S based on the calculation results.

[0041] The calculation unit 25 outputs the calculation result to the display unit 27. If the second detection unit 10 is not provided, the calculation unit 25 may calculate the count of the sample S based on the corrected first count electrical signal output from the first anti-simultaneous counting circuit 23, and calculate the total beta radioactivity concentration emitted from the sample S based on the calculation result.

[0042] The following describes a beta-ray measuring device using a conventional GM counter tube as a comparative example. In the following description, the same names and reference numerals will be used for components identical to those in the above embodiment, and redundant explanations will be omitted as appropriate.

[0043] As shown in Figure 3, the beta-ray measuring device 100 according to the comparative example includes a first GM counter 304 for detecting beta rays emitted from the sample S and a second GM counter 303 for detecting cosmic rays. The output values ​​of the first GM counter 304 and the second GM counter 303 are output to the anti-simultaneous counting circuit 22. The calculation unit 25 calculates the total beta radioactivity concentration of the sample S based on the output values ​​of the anti-simultaneous counting circuit 22.

[0044] Upstream of the first GM counter tube 304 and the second GM counter tube 303, a Q gas cylinder 301 filled with Q gas is connected via a supply channel 302. Downstream of the first GM counter tube 304 and the second GM counter tube 303, an exhaust channel 306 is connected to exhaust the Q gas that has flowed through the first GM counter tube 304 and the second GM counter tube 303. In the comparative example, the beta ray measuring device 100, with the above configuration, requires that Q gas always flow through the first GM counter tube 304 and the second GM counter tube 303 when measuring the sample S, which may increase the cost of measurement.

[0045] As shown in Figure 4, the beta-ray measuring device 101 according to the comparative example includes a sample measuring unit 3 that detects beta rays emitted from a sample S. The sample measuring unit 3 includes a first plastic scintillator 4 and a first photomultiplier tube 5. The output value of the sample measuring unit 3 is output to a counting circuit 200. The calculation unit 25 calculates the total beta radioactivity concentration of the sample S based on the output value of the counting circuit 200. When measuring beta rays emitted from a sample S based on the first plastic scintillator 4 without using a GM counter, as in the beta-ray measuring device 101 according to the comparative example, the sensitivity of the first plastic scintillator 4 to gamma rays is higher than that of a GM counter, so the first plastic scintillator 4 also detects cosmic rays and environmental gamma rays.

[0046] The beta-ray measuring device 101 in the comparative example is not equipped with a detection unit for detecting cosmic rays or environmental gamma rays. As a result, the background of the first plastic scintillator 4 increases, which may lead to an inaccurate total beta radioactivity concentration and an increase in the detection limit of the total beta radioactivity concentration.

[0047] As described above, the beta-ray measuring device 1 can detect cosmic rays using the second plastic scintillator 7 provided in the first detection unit 6, and detect environmental gamma rays using the third plastic scintillator 11 provided in the second detection unit 10, thereby excluding the influence of cosmic rays and environmental gamma rays from the detection value of the first plastic scintillator 4 provided in the sample measuring unit 3. The beta-ray measuring device 1 can suppress the background increase of the first plastic scintillator 4 for detecting beta rays emitted from the sample S, and can reduce the detection limit concentration of the total beta radioactivity.

[0048] According to the beta-ray measuring device 1, by using a plastic scintillator, it is possible to perform measurements at a lower cost compared to existing beta-ray measuring devices that have a GM counter, as it does not require the use of Q gas. According to the beta-ray measuring device 1, by using a plastic scintillator, the influence of cosmic rays and environmental gamma rays is reduced, and it is possible to detect only the beta rays emitted from the sample S, and it is possible to measure relatively low concentrations of total beta radioactivity. Furthermore, according to the beta-ray measuring device 1, since cosmic rays and environmental gamma rays can be detected with high sensitivity by the first detection unit 6 and the second detection unit 10, the shielding capability of the main body unit C can be simplified. According to the beta-ray measuring device 1, for example, the main body unit C may be formed of a metal film that does not allow beta rays emitted from the sample S to leak to the outside.

[0049] [Differentiation] The following describes a modified beta-ray measuring device. In the following description, the same names and reference numerals will be used for components identical to those in the above embodiment, and redundant explanations will be omitted as appropriate.

[0050] The modified beta-ray measuring device 1A shown in Figure 5 is configured to measure the spectrum of beta rays emitted from a sample S1. The beta-ray measuring device 1A includes a multi-channel analyzer 30 (MCA) that receives the output value output from the second anti-simultaneous counting circuit 24 and analyzes the spectrum of beta rays emitted from the sample S. The sample S1 is, for example, a sample S containing radioactive material from which only beta-ray nuclides such as strontium have been isolated. Below the sample S1, a raised base is provided to bring the sample S1 closer to the sample measuring unit 3A.

[0051] The beta-ray measuring device 1A comprises a sample measuring unit 3A which includes a first plastic scintillator 4, a fourth plastic scintillator 4A positioned below the first plastic scintillator 4, and a first photomultiplier tube 5. The fourth plastic scintillator 4A is formed from, for example, a thinner, plate-shaped plastic material compared to the first plastic scintillator 4. The fourth plastic scintillator 4A is formed to have a longer emission time when beta rays are transmitted compared to the first plastic scintillator 4. As a result, the first photomultiplier tube 5 can detect the rise time distribution spectrum of beta ray counts emitted from different beta-ray nuclides.

[0052] The first counter-simultaneous counting circuit 23 outputs an electrical signal of the corrected first count to the second counter-simultaneous counting circuit 24, as described above. The second counter-simultaneous counting circuit 24 outputs an electrical signal of the corrected count to the multi-channel analyzer 30, based on the electrical signal of the corrected first count and the electrical signal of the third count, as described above.

[0053] The multichannel analyzer 30 performs beta-ray spectrometry of beta rays emitted from sample S1 based on the electrical signals output from the second anti-simultaneous counting circuit 24, specifically the electrical signals output from the first photomultiplier tube 5 based on the emission of the first plastic scintillator 4 and the fourth plastic scintillator 4A, with background effects removed. The multichannel analyzer 30 analyzes the energy spectrum of beta rays emitted from different beta-ray nuclides contained in sample S1, such as Sr-89, Sr-90, and Y-90.

[0054] The multi-channel analyzer 30 has multiple channels corresponding to the energy spectrum of beta rays. The multi-channel analyzer 30 outputs the rise time distribution spectrum of the beta ray count emitted from the beta ray nuclide contained in the sample S1 for each channel. The multi-channel analyzer 30 amplifies the electrical signal of the output value output from the second anti-simultaneous counting circuit 24, distributes the maximum value of the electrical signal to the corresponding channel, and outputs an output value based on the electrical signal from each channel.

[0055] The calculation unit 25 individually calculates the energy spectrum of beta rays contained in the sample S1 based on the output values ​​output from each channel of the multi-channel analyzer 30. The calculation unit 25 displays the calculation results on the display unit 27.

[0056] Below, as a comparative example, a beta-ray measuring device for analyzing the energy spectrum of beta rays using a conventional GM counter will be described. In the following description, the same names and reference numerals will be used for components identical to those in the above embodiment, and redundant explanations will be omitted as appropriate.

[0057] As shown in Figure 6, the beta-ray measuring device 102 according to the comparative example is provided with a third GM counter 305 for detecting beta rays from sample S1 between the sample measuring unit 3 and sample S1. The third GM counter tube 305 corresponds to the fourth plastic scintillator 4A of the beta-ray measuring device 1A. The beta-ray measuring device 102 includes a synchronization circuit 201 that outputs the simultaneous count of the signals detected by the sample measuring unit 3 and the third GM counter tube 305.

[0058] The beta-ray measuring device 102 includes a multi-channel analyzer 30 that receives output values ​​from the synchronization circuit 201 and analyzes the spectrum of beta rays emitted from the sample S1. The calculation unit 25 individually calculates the energy spectrum of beta rays contained in the sample S1 based on the output values ​​from each channel of the multi-channel analyzer 30.

[0059] Upstream of the third GM counter tube 305, a Q gas cylinder 301 filled with Q gas is connected via a supply channel 302. Downstream of the third GM counter tube 305, an exhaust channel 306 is connected to exhaust the Q gas that has flowed through the third GM counter tube 305. In the comparative example, the beta ray measuring device 102, with the above configuration, requires that Q gas always flow through the third GM counter tube 305 when measuring the sample S, which may increase the cost of measurement.

[0060] As shown in Figure 7, the beta-ray measuring device 103 according to the comparative example is provided with a sample measuring unit 3A and a detection unit 10D for detecting the effects of cosmic rays and natural radiation. The detection unit 10D is located below the sample measuring unit 3A. The detection unit 10A has a plastic scintillator 11D for detecting cosmic rays and environmental gamma rays, and a photomultiplier tube 12D for detecting the light emitted from the plastic scintillator 11D.

[0061] The anti-simultaneous counting circuit 202 outputs an electrical count signal to the multi-channel analyzer 30 that excludes the simultaneous counts detected by the sample measurement unit 3A and the detection unit 10D. The calculation unit 25 individually calculates the energy spectrum of beta rays contained in the sample S1 based on the output values ​​output from each channel of the multi-channel analyzer 30. In the comparative example, the beta-ray measurement device 103 has one detection unit 10D located below for detecting cosmic rays and environmental gamma rays. In the beta-ray measurement device 103, since the first detection unit 6 is not located above compared to the beta-ray measurement device 1A, the background of the first plastic scintillator 4 may increase due to the detection of noise based on cosmic rays arriving from above, and the lower limit of beta ray detection may increase.

[0062] As described above, the modified beta-ray measuring device 1A is equipped with a multi-channel analyzer 30, which allows for the measurement of the beta-ray spectrum emitted from the sample S1. With the beta-ray measuring device 1A, during beta-ray spectrum measurement, cosmic rays can be detected using the second plastic scintillator 7 provided in the first detection unit 6, and environmental gamma rays can be detected using the third plastic scintillator 11 provided in the second detection unit 10. This allows for the exclusion of the influence of cosmic rays and environmental gamma rays from the detection values ​​of the first plastic scintillator 4 and the fourth plastic scintillator 4A provided in the sample measuring unit 3A for detecting beta rays emitted from the sample S1.

[0063] The beta-ray measuring device 1A can suppress the background increase of the first plastic scintillator 4 and the fourth plastic scintillator 4A for detecting beta rays emitted from the sample S1, thereby reducing the detection limit concentration for beta-ray spectral measurement.

[0064] According to the beta-ray measurement device 1A, by using a plastic scintillator, it is possible to perform measurements at a lower cost compared to existing beta-ray measurement devices that have a GM counter, as it does not require the use of Q gas. According to the beta-ray measurement device 1A, by using a plastic scintillator, the influence of cosmic rays and environmental gamma rays is reduced, making it possible to detect only the beta rays emitted from the sample S1, and to measure the spectrum of relatively low concentrations of beta rays.

[0065] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. For example, the components shown in beta-ray measuring device 1 and beta-ray measuring device 1A according to a modified example may be substituted for each other or added to each other. [Explanation of Symbols]

[0066] 1. 1A Beta Ray Measurement Device 2 Detection unit 3, 3A Sample Measurement Section 4. First Plastic Scintillator 4A Fourth Plastic Scintillator 6. First detection unit 7. Second Plastic Scintillator 7B, 7C, 8C metal film 10 Second detection unit 11. Third Plastic Scintillator 11B, 11C, 12C metal film 23. First Anti-Simultaneous Clock Circuit 24. Second Anti-Simultaneous Clock Circuit 25 Arithmetic section 30 Multi-channel analyzer

Claims

1. A sample measurement unit having a first plastic scintillator for detecting beta rays emitted from a sample, A first detection unit having a second plastic scintillator for detecting the effects of cosmic rays, A first counter-simultaneous counting circuit outputs a corrected first count obtained by excluding the second count detected by the second plastic scintillator, which was measured simultaneously, from the first count detected by the first plastic scintillator, and A calculation unit that calculates the total beta radioactivity concentration emitted from the sample based on the first corrected count, The system comprises a main body that reduces the effects of cosmic rays and environmental gamma rays, The sample measurement unit is housed inside the main body. The first detection unit is a beta ray measuring device positioned above and outside the main body.

2. A second detection unit having a third plastic scintillator for detecting the effects of environmental gamma rays, The circuit comprises a second anti-simultaneous counting circuit that outputs a corrected count obtained by excluding the third count detected by the third plastic scintillator, which was measured simultaneously, from the first corrected count, The calculation unit calculates the total beta radioactivity concentration emitted from the sample based on the correction coefficient. The beta ray measuring device according to claim 1.

3. A fourth plastic scintillator is provided in the first detection unit and has different light emission characteristics from the first plastic scintillator with respect to beta rays, The system includes a multichannel analyzer that analyzes the spectrum of beta rays emitted from the sample based on the correction count detected by the first plastic scintillator and the fourth plastic scintillator, The calculation unit calculates the spectrum based on the analysis results of the multichannel analyzer. The beta ray measuring device according to claim 2.

4. The third plastic scintillator is covered with a metal film that shields the beta rays. The beta ray measuring device according to claim 3.

5. The second plastic scintillator is covered with a metal film that shields the beta rays. A beta ray measuring device according to any one of claims 1 to 4.

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