Radiation monitor, and radiation detection method

Abstract

To provide a radiation monitor capable of precisely measuring even under being affection by radioactive contamination.SOLUTION: The radiation monitor includes: a detector that is placed adjacent to a flow path to detect radiation from radioactive materials contained in the liquid being detected in the flow path and output signals; and an energy-measuring device that measures the energy of radiation from the signal output from the detector. The radiation monitor further includes a background correction device that corrects background components based on the energy spectrum measured by the energy measuring device and calculates the concentration of radioactive material in the detected liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radiation monitor and a radiation detection method. [Background technology]

[0002] As a method for measuring radiation from radioactive materials contained in contaminated water, for example, a method using a liquid scintillator, an ionization chamber, a solid scintillator, etc. is known. Among these methods, a radiation monitor in which a sampling container is placed between two flat solid scintillators arranged opposite each other is known. As such a radiation monitor, for example, a technology has been proposed in which contaminated water (detection liquid) is passed through a sampling container, the solid scintillator is excited by radiation emitted from the detection liquid, and the generated photons are measured to monitor the concentration of the radioactive material (see, for example, Patent Document 1). This radiation monitor uses a large flat solid scintillator as a detector. Then, by closely contacting a large sampling container with a large flat detector, the contact area between the detector and the detection liquid is increased, thereby improving the sensitivity. This results in a radiation monitor with high sensitivity that can perform real-time measurement at all times. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-178336 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the radiation monitor described in Patent Document 1 has a large surface area of ​​the container in contact with the liquid to be detected, and is therefore subject to a large influence of contamination caused by radioactive substances adhering to the container surface. The radiation monitor described in Patent Document 1 cannot distinguish between signals from contamination caused by radioactive substances adhering to the container surface and signals from radioactive substances in the liquid to be detected. For this reason, when a container with a large surface area is contaminated, it is difficult to accurately measure the concentration of the radioactive substances. Thus, there is a demand for a radiation monitor and a radiation detection method that can perform accurate measurements even when the container is affected by contamination caused by radioactive substances adhering to the container surface.

[0005] In order to solve the above-mentioned problems, the present invention provides a radiation monitor and a radiation detection method that are capable of performing accurate measurements even when there is the influence of contamination by radioactive materials.

[0006] The above and other objects of the present invention and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0007] The radiation monitor of the present invention includes a detector disposed adjacent to the flow path for detecting radiation from a radioactive substance contained in a detection liquid in the flow path and outputting a signal, and an energy measuring device for measuring the energy of the radiation from the signal output from the detector. The radiation monitor further includes a background correction device for correcting background components based on the energy spectrum measured by the energy measuring device and calculating the concentration of the radioactive substance in the detection liquid.

[0008] The radiation detection method of the present invention also includes an energy spectrum measurement step of measuring the energy spectrum of the radiation detected by the detector using an energy measurement device, a background correction value calculation step of calculating a background correction value from the energy spectrum measured in the energy spectrum measurement step using a background correction device, and a background correction step of calculating the concentration of the radioactive material in the detected liquid from the background correction value calculated in the background correction value calculation step. Effect of the Invention

[0009] According to the present invention, it is possible to provide a radiation monitor and a radiation detection method that are capable of performing accurate measurements even when affected by contamination with radioactive materials.

[0010] Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a radiation monitor. [Diagram 2] 2 is an example of a signal energy spectrum and a background energy spectrum measured by a radiation monitor. [Diagram 3] FIG. 13 is a diagram for explaining a background correction processing method using the number of counts equal to or greater than an energy threshold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of a radiation monitor and a radiation detection method according to the present invention will be described with reference to the drawings. The following description shows a specific example of the contents of the present invention, and the present invention is not limited to these descriptions. Various changes and modifications can be made by those skilled in the art within the scope of the technical ideas disclosed in this specification. Furthermore, in all the drawings for explaining the present invention, parts having the same functions are given the same reference numerals, and repeated explanations thereof may be omitted.

[0013] [Radiation monitor] FIG. 1 shows a schematic diagram of a radiation monitor. The radiation monitor 100 shown in FIG. 1 includes a detector 20, an energy measuring device 30, and a background correction device 40. The detector 20 is installed adjacent to a flow path 10 through which a liquid to be detected flows. The radiation monitor 100 has the detector 20 arranged in at least one direction of the flow path 10. The radiation monitor 100 may have a plurality of detectors 20 arranged in two or more directions of the flow path 10. When a plurality of detectors 20 are arranged, it is preferable to have the same number of energy measuring devices 30 as the detectors 20. Furthermore, the radiation monitor 100 only needs to have at least one background correction device 40, regardless of the number of detectors 20.

[0014] The liquid to be detected contains a nuclide that generates radiation. The nuclide is not particularly limited, but is, for example, Sr-90 or Y-90. The generated radiation is not particularly limited, but includes particle rays such as α-rays, β-rays, and neutron rays, electromagnetic waves such as X-rays and γ-rays, and among them, α-rays and β-rays are preferable. The liquid to be detected contains the nuclide in a dissolved or dispersed state. The portion of the liquid to be detected excluding the nuclide is not particularly limited as long as it is liquid, but is, for example, aqueous solutions such as nuclear power plant treated water, seawater, and brackish water (brine water, etc.), but may be fresh water.

[0015] [Detector] The detector 20 is disposed adjacent to a flat surface that serves as a detection surface of the flow path 10 through which the detection liquid flows. The detector 20 detects radiation from the detection liquid in the flow path 10. The detector 20 also converts the detected radiation into an electrical signal and outputs it. The detector 20 includes a radiation light emitting unit 21 and a photoelectric converter 22. In the detector 20, the radiation light emitting unit 21 is disposed on the side adjacent to the flow channel 10, and the photoelectric converter 22 is disposed on the opposite side of the flow channel 10.

[0016] The radiation light emitting unit 21 includes a radiation light emitting material. The radiation light emitting material emits light in response to radiation incident from the liquid to be detected in the flow channel 10. The intensity of the emitted light from the radiation light emitting material changes depending on the amount of incident radiation. The radiation light emitting material is, for example, an inorganic scintillator or a plastic scintillator. The inorganic scintillator is, for example, composed of NaI(Tl), CsI(Tl), CsI(Na), LnBr3, ZnS(Ag), CsI, etc.

[0017] The photoelectric converter 22 is connected to the radiation light emitting unit 21 via a light guide (not shown) or the like. The photoelectric converter 22 converts the light from the radiation light emitting unit 21 into an electric signal. The photoelectric converter 22 is configured by, for example, a photomultiplier tube, an avalanche photodiode, or the like.

[0018] [Energy measuring device] The energy measuring device 30 is connected to the photoelectric converter 22 of the detector 20. The energy measuring device 30 is connected so as to be able to receive the electrical signal generated by the photoelectric converter 22. The energy measuring device 30 measures the energy of the radiation detected by the detector 20 based on the electrical signal output by the detector 20. The specific method of the energy measuring device 30 to measure the energy based on the signal obtained from the photoelectric converter 22 is not particularly limited, and a known technique can be appropriately selected depending on the type of computer used and the situation. For example, the energy measuring device 30 may hold the signal obtained from the photoelectric converter 22 as energy information for each detected radiation event. In addition, the energy measuring device 30 may hold the signal obtained from the photoelectric converter 22 as energy spectrum data indicating the count number of the photoelectric effect, as shown in FIG. 2.

[0019] [Background correction device] The background correction device 40 is connected so as to be able to communicate various signals with the energy measurement device 30. The background correction device 40 performs the following background correction process. The background correction device 40 takes in the energy information and the energy spectrum measured by the energy measuring device 30. Then, the background correction device 40 calculates the background components from the shape of the energy spectrum. Furthermore, the background correction device 40 calculates the concentration of the radioactive material in the detected liquid by correcting the background components for the measurement value of the energy measuring device 30.

[0020] The background correction device 40 includes a known arithmetic device. For example, the background correction device 40 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and a storage unit. The CPU reads out program codes of software related to various processes of background correction stored in a ROM (an example of a recording medium) and expands the codes in the RAM. The CPU then performs background correction processing according to the expanded programs. The storage unit includes a storage device such as a hard disk drive (HDD), and stores programs for the CPU to control each unit, an operating system (OS), programs for a controller, data, and the like. The background correction device 40 may include another arithmetic device such as a micro processing unit (MPU) as the arithmetic unit instead of the CPU.

[0021] [Flow path] The flow path 10 is, for example, in the form of a flat plate having a predetermined thickness, and has a space inside through which the detectable liquid flows. The detector 20 is disposed on the flat surface that is the detectable surface of the flow path 10. The detectable surface of the flow path 10 on which the detector 20 is disposed may have any shape to match the shape of the detector 20. The detection of radiation by the detector 20 may be performed in a state in which the detectable liquid is allowed to flow within the flow path 10, or in a state in which the flow of the detectable liquid is stopped and the detectable liquid is allowed to stagnate. For this reason, the flow path 10 may have a valve or the like for stagning the detectable liquid within the flow path 10.

[0022] The flow path 10 preferably has a thickness of the liquid to be detected (the thickness of the inside of the flow path 10) that is equal to or greater than the maximum range in water of the beta rays of the nuclide in the liquid to be detected. By making the thickness of the liquid to be detected greater than the maximum range in water of the beta rays to be measured, the flow path 10 is not affected by contamination of radioactive nuclides attached to the surface of the flow path 10 opposite to the surface in contact with the detector 20. Beta rays from the surface opposite the detector 20 cannot be distinguished from a beta ray source in water. Therefore, by making the thickness of the flow path 10 greater than the maximum range in water of the beta rays to be measured, the influence of contamination on the opposite surface can be eliminated. This allows for more accurate background correction in the radiation monitor 100.

[0023] For example, when the nuclide to be measured is Y-90, the maximum energy of β rays is 2.28 MeV, and the maximum range in water is about 11 mm. Therefore, the thickness of the flow path 10 needs to be 11 mm or more. However, if the thickness of the water is made thicker than necessary, the β rays will lose energy in the water before entering the detector 20. In this case, the detector 20 cannot measure the β rays, and the sensitivity of the radiation monitor 100 will decrease. Therefore, it is preferable that the thickness of the flow path 10 is approximately the same as the maximum range of the β rays of the nuclide in the liquid to be detected. It is also preferable to consider the energy loss due to the structural material when determining the inner thickness of the flow channel 10. For example, it is preferable to determine the inner thickness of the flow channel 10 by subtracting the water equivalent thickness of the structural material of the flow channel 10 from the maximum range of β rays.

[0024] [Radiation detection method] Next, a radiation detection method using the radiation monitor 100 will be described. First, in the detector 20, light emitted by incident radiation is converted into an electrical signal and output (photoelectric conversion step). Next, in the energy measuring device 30, the energy spectrum of the radiation is measured based on the electrical signal output by the detector 20 (energy spectrum measuring step). Next, in the background correction device 40, a background correction value is calculated from the energy spectrum measured in the energy spectrum measurement step (background correction value calculation step). Furthermore, in the background correction device 40, the concentration of the radioactive substance in the detection liquid is calculated from the background radioactivity correction value calculated in the background correction value calculation step (background correction step). Through the above steps, radiation is detected by the radiation monitor 100.

[0025] [Background correction process (1)] Next, there will be described the background correction process performed by the background correction device 40 of the radiation monitor 100. The background correction process performs the above-mentioned background correction value calculation process and background correction process.

[0026] The background correction device 40 performs background correction processing based on the change in the shape of the energy spectrum as described above. Figure 2 shows the energy spectrum measured by the energy measurement device 30. In the energy spectrum shown in Figure 2, the vertical axis represents the detected count number of photoelectric conversion, and the horizontal axis represents the energy amount of β rays.

[0027] FIG. 2 also shows a signal energy spectrum (signal curve) and a background energy spectrum (background curve). The signal curve is an energy spectrum obtained by detecting β-rays from β-ray emitting nuclides in the detection liquid in the flow channel 10. In other words, the signal curve is an energy spectrum of only the detection liquid, not including background components due to contamination. On the other hand, the background curve is an energy spectrum of β-rays from β-ray emitting nuclides attached to the surface of the flow channel 10. In other words, the background curve is an energy spectrum of only the background due to contamination, not including β-rays from the liquid to be detected. The signal curve and background curve shown in FIG. 2 are the results of a Monte Carlo simulation.

[0028] As shown in Figure 2, the background curve has an increased count at high energy compared to the signal curve. The reason why the background curve has an increased count more than the signal curve at high energy is considered as follows. The signal count is the β-rays generated in the liquid to be detected. Therefore, the β-rays necessarily reach the detector 20 via the structural material forming the flow channel 10 after interacting with water. On the other hand, the background count is β-rays generated from the surface of the structural material forming the flow channel 10. Therefore, these β-rays reach the detector 20 via the structural material forming the flow channel 10 without interacting with water. Therefore, the signal counts are detected at a lower energy than the background counts due to the interaction with water. As a result, the energy spectrum of the background curve has an increased number of high energy counts compared to the energy spectrum of the signal curve, as shown in Figure 2.

[0029] As described above, the signal curve and the background curve have different shapes of energy spectrum. Therefore, it is possible to estimate the increase in background count relative to the signal count from the shape of the energy spectrum. That is, in the radiation monitor 100, the amount of background count is estimated and subtracted or multiplied by a coefficient from the energy information and energy spectrum data measured by the energy measuring device 30. In this way, background correction processing is performed to calculate the net signal count. By performing these background correction processing, the radiation monitor 100 can calculate the net concentration of radioactive material in the flow path 10.

[0030] In order to carry out the above-mentioned background correction process, the energy spectrum of a signal that does not contain background components and the shape of the background energy spectrum are acquired in advance. The energy spectrum of the signal without background components is obtained, for example, from initial measurement data before contaminants adhere to the flow channel 10. The energy spectrum of the signal without background components may be measured in advance using various assumed radiation sources before starting measurement. The energy spectrum of the signal without background components may be obtained by simulation instead of actual measurement. The shape of the background energy spectrum may be stored based on actual measurements, or may be measured in advance using a radiation source that simulates a contamination source, or may be determined by simulation. Then, the difference in the shape of the energy spectrum between the acquired signal and the background is grasped, and the difference in the shape of the energy spectrum of a signal without background components during measurement is evaluated, allowing background correction processing to be performed.

[0031] In a specific background correction process, for example, a machine learning model is used to estimate the amount of background components, and the concentration of the radioactive substance in the detection liquid is calculated. For example, the background correction device 40 stores a machine learning model that is generated in advance by a learning device during the manufacturing stage of the radiation monitor 100. The learning device acquires a plurality of learning energy spectra with different background count amounts during machine learning. The learning device then acquires a spectral shape for each learning energy spectrum. Furthermore, the learning device performs machine learning using a data set in which the spectral shape of the learning energy spectrum is input and the background count amount included in the learning energy spectrum is output as teacher data. The machine learning algorithm used for machine learning is not particularly limited, and a machine learning algorithm is selected according to the shape of the energy spectrum. The learning device generates a machine learning model that estimates the background count amount from the shape of the energy spectrum as a learning result of the above machine learning. Furthermore, the learning device may evaluate the generated machine learning model by using a signal energy spectrum and a background energy spectrum stored in a database in advance, and an energy spectrum measured by the energy measuring device 30. The learning device may repeat the creation of a learning model using the above-mentioned machine learning algorithm and the evaluation of the created learning model until a desired accuracy is obtained.

[0032] The background correction device 40 stores the generated machine learning model in a storage unit. Then, the background correction device 40 performs a process of estimating the background component from the shape of the energy spectrum using the generated machine learning model. Furthermore, the background correction device 40 performs a background correction process of the energy spectrum using the background count amount acquired in the process of estimating the background component. In this way, the background correction device 40 can measure the net concentration of the radioactive material in the flow path 10 by removing the influence of the background component from the energy spectrum measured by the energy measurement device 30.

[0033] [Background correction process (2)] Next, a description will be given of another embodiment of the background correction process by the background correction device 40. In this embodiment, the background correction device 40 performs background correction process based on the ratio between the count of high-energy radiation equal to or higher than a specific energy threshold and the count of low-energy radiation below the threshold.

[0034] A method of background correction using counts equal to or greater than a specific energy threshold will be described with reference to Fig. 3. In Fig. 3, the horizontal axis indicates the ratio "N / Nall" of the total count Nall to the count N equal to or greater than a specific threshold. The vertical axis indicates the ratio K of background counts to signal counts in the total counts [background counts / signal counts]. In Figs. 2 and 3, the specific threshold is set to 1.5 MeV as an example.

[0035] Figure 3 shows the change in the ratio K [background counts / signal counts] when the ratio of counts above 1.5 MeV (N / Nall) to the total counts is changed from 0.1 to 0.15 in the energy spectra under various conditions. As shown in Figure 3, the background ratio to the signal increases as the N / Nall ratio increases. This is because, as explained in Figure 2 above, the detection energy of the background count is higher than that of the signal count.

[0036] That is, the background ratio K to the signal can be determined from the ratio of N to Nall as shown in Figure 3. Then, the signal count S can be calculated from the background ratio K to the signal using the following formula 1. S=Nall / (1+K) (Formula 1)

[0037] The relationship between "N / Nall" and the ratio K [background count number / signal count number] shown in the above-mentioned FIG. 3 is compiled into a database in advance and stored in the background correction device 40. For example, the database may use actual measurements using the energy spectrum measured by the energy measurement device 30 or energy spectra obtained by simulation. Then, the relationship between "N / Nall" and the ratio K when a predetermined threshold value is set can be obtained from the various acquired energy spectra.

[0038] In a specific background correction process, for example, the background correction device 40 applies the above (Equation 1) to the energy spectrum measured by the energy measurement device 30, thereby performing background correction. The background correction device 40 sets a predetermined threshold value for the energy spectrum measured by the energy measuring device 30. Then, the background correction device 40 obtains a ratio "N / Nall" between the count number Nall and the count number N equal to or greater than the predetermined threshold. Furthermore, the background correction device 40 reads out the relationship between "N / Nall" stored in the storage unit and the ratio K. Then, the background correction device 40 applies the above (Equation 1) to the energy information measured by the energy measuring device 30, thereby being able to measure the net concentration of radioactive material in the flow channel 10 excluding the influence of background components.

[0039] In radiation detection using the above-described radiation monitor 100, the background correction device 40 can constantly estimate and correct background components for the radiation dose obtained from the detector 20 installed in contact with the flow path 10. Therefore, the radiation monitor 100 can constantly monitor radiation in water with high accuracy. Furthermore, the radiation monitor 100 has a larger detector 20 to increase the contact area with the flow path 10, and can easily perform correction processing for the increasing background components even when contamination by radioactive materials adhering to the surface of the flow path 10 increases. Therefore, the radiation monitor 100 can achieve high sensitivity by increasing the area of ​​the detector 20. Therefore, the radiation monitor 100 can constantly monitor radiation in water with high accuracy and even higher sensitivity. Furthermore, the radiation monitor 100 can perform background correction processing relatively easily by counting the number of counts equal to or greater than a predetermined energy threshold. Therefore, the radiation monitor 100 can be used as an inexpensive underwater radiation monitor that can constantly monitor with high accuracy and high sensitivity.

[0040] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the configurations described. It is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to delete a part of the configuration of each embodiment, or to add or replace another configuration. [Explanation of symbols]

[0041] 10 flow path, 20 detector, 21 radiation emitting unit, 22 photoelectric converter, 30 energy measuring device, 40 background correction device, 100 radiation monitor

Claims

1. a detector disposed adjacent to the flow path, for detecting radiation from a radioactive substance contained in the liquid to be detected in the flow path and outputting a signal; an energy measuring device that measures the energy of the radiation from a signal output from the detector; and a background correction device that corrects background components based on the energy spectrum measured by the energy measurement device and calculates the concentration of the radioactive material in the detection liquid. Radiation monitor.

2. The background correction device acquires in advance a signal energy spectrum that does not include the background component and a background energy spectrum that includes only the background component.

2. The radiation monitor of claim 1.

3. The background correction device estimates the amount of the background component using a machine learning model and calculates the concentration of the radioactive substance in the detection liquid.

3. The radiation monitor of claim 2.

4. The background correction device corrects the background component from a ratio of the counts of high-energy radiation to the counts of low-energy radiation.

2. The radiation monitor of claim 1.

5. The thickness of the detection liquid in the flow path is equal to or greater than the range of beta rays of the nuclides contained in the detection liquid.

2. The radiation monitor of claim 1.

6. an energy spectrum measuring step of measuring an energy spectrum of the radiation detected by the detector with an energy measuring device; a background correction value calculation step of calculating a background correction value from the energy spectrum measured in the energy spectrum measurement step by a background correction device; and a background correction step of calculating a concentration of a radioactive substance in the detection liquid from the background correction value calculated in the background correction value calculation step. Radiation detection methods.

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