Radiation measuring device

Abstract

Provided is a radiation measuring device comprising: a gas scintillator; at least two optical sensors that generate pulse signals in response to the reception of scintillation light; and a detection unit that detects the generation of radiation on the basis of the pulse signals generated by each of the optical sensors, wherein the detection unit excludes a calculation result less than a prescribed threshold, from calculation results for the pulse signals generated by the optical sensors during a prescribed time period in a state in which an object to be measured for the radiation is present in the gas scintillator, and the detection unit thereby detects the radiation generated by the object to be measured, and the threshold value is determined through calculations for the pulse signals generated by the optical sensors during a prescribed time period in a state in which the object to be measured for the radiation is not present in the gas scintillator.

Description

Radiation measuring device

[0001] The present disclosure relates to a radiation measurement device.

[0002] A technology has been disclosed relating to a radiation detector that utilizes the phenomenon of gas scintillation caused by radiation.

[0003] Japanese Patent Laid-Open Publication No. 6-130153 discloses a technology aimed at providing a scintillation detector for monitoring radioactive gases that can measure low-energy radiation down to low concentrations by using a gas container in the shape of a short cylinder and arranging scintillators on both end faces of the container at an interval that takes into account the range of radiation.

[0004] Japanese Patent Laid-Open Publication No. 9-80160 discloses a technology aimed at providing a reactor power measurement device that is highly accurate, stable, and radiation-resistant, using a simple power measurement device that utilizes the luminescence phenomenon of a gas scintillation radiation detector.

[0005] Japanese Patent Application Laid-Open Publication No. 2004-20249 discloses a technology aimed at providing a radiation detection device using a gas ionization chamber that has a wide measurement dynamic range and a low alpha ray background, by including an electrode support portion that is electrically insulated from a conductive container containing a detection gas and that airtightly penetrates the conductive container and is disposed within the conductive container; an electrode end portion that is located at the tip of the electrode support portion and covers the tip of the electrode support portion while being insulated from the electrode support portion; and an ionization current measurement circuit connected to the electrode support portion and the electrode end portion.

[0006] Japanese Patent Laid-Open Publication No. 8-338876 discloses a technology aimed at providing a particle measuring instrument capable of measuring the distribution of neutrons near a reactor in a nuclear power plant with a single measuring instrument, by comprising an emission transmitting means that emits light when ionizing radiation is incident on it and transmits this light, a light receiving means that receives the light via a plurality of different transmission paths, and a signal processing means that processes an output signal from the light receiving means.

[0007] There is a demand for radiation measurement devices that can measure even alpha rays with high accuracy. For example, radiation detectors for underground experiments must be large and contain as few impurities as possible. Even minute amounts of radioactive contamination on the surface of materials can be a major problem in underground experiments. Specifically, if the sample surface is contaminated in a full-scale test using a high-purity germanium semiconductor gamma-ray detector, there is a possibility that the radiation will be underestimated. Therefore, there is a demand for radiation measurement devices that can measure even minute amounts of radiation with high accuracy.

[0008] Furthermore, for example, solder materials used to join semiconductor elements to substrates contain minute amounts of radioactive material, which emits alpha rays. The emitted alpha rays can adversely affect the operation of semiconductor elements. As semiconductor elements become increasingly miniaturized, their radiation resistance weakens. Therefore, there is a demand for materials that emit extremely little alpha rays (ultra-low alpha materials), as well as radiation measurement devices that can measure even minute amounts of alpha rays with high accuracy.

[0009] The present disclosure has been made in consideration of the above points, and aims to provide a radiation measurement device that uses gas scintillation and is capable of measuring even trace amounts of radiation with high accuracy.

[0010] According to an aspect of the present disclosure, there is provided a radiation measurement device comprising: a gas scintillator that emits scintillation light due to the interaction between gas molecules and radiation; at least two optical sensors that generate pulse signals in response to receiving the scintillation light; and a detection unit that detects the generation of the radiation based on the pulse signals generated by each of the optical sensors, wherein the detection unit detects the radiation generated by the measurement object by excluding calculation results that are less than a predetermined threshold from calculation results for the pulse signals generated by the optical sensors during a predetermined period in a state in which the measurement object for the radiation is present in the gas scintillator, and the threshold is a value determined by calculation for the pulse signals generated by the optical sensors during a predetermined period in a state in which the measurement object for the radiation is not present in the gas scintillator.

[0011] The detection unit may perform an operation on the pulse signal by calculating a first integral value by integrating the voltage value during a period in which the pulse signal is generated and a second integral value by integrating the voltage value during a period in which the pulse signal is attenuated, and detect the radiation generated by the object to be measured using a ratio between the first integral value and the second integral value.

[0012] The gas may be an inert gas.

[0013] The inert gas may be carbon tetrafluoride, argon, neon, or xenon.

[0014] The gas in the gas scintillator may have a pressure of 0.1 atmospheres to 1.2 atmospheres.

[0015] The gas scintillator may be housed in a cylindrical container.

[0016] The at least two optical sensors may be provided in a container that houses the gas scintillator.

[0017] According to the present disclosure, it is possible to provide a radiation measurement device that uses gas scintillation and is capable of measuring even trace amounts of radiation with high accuracy.

[0018] 2B is a diagram showing a schematic configuration of a radiation measurement device according to an embodiment of the disclosed technology. FIG. 2C is a diagram showing an example of a result of light detection by a photomultiplier tube. FIG. 2D is a diagram showing an example of a result of light detection by a photomultiplier tube. FIG. 2E is a diagram showing an example of measurement results of the number of photoelectrons and the number of counts, both in a state where a measurement object 55 is present in a housing and in a state where it is not present. FIG. 2F is a diagram showing a correspondence relationship between the result of light detection by the photomultiplier tube of FIG. 2A and the radiation present in the housing. FIG. 2G is a diagram showing a correspondence relationship between the result of light detection by the photomultiplier tube of FIG. 2B and the radiation present in the housing. FIG. 2H is a diagram showing an example of a voltage waveform output by a photomultiplier tube. FIG. 2I is a graph showing the relationship between "Slow" and "Total". FIG. 2J is a graph showing the relationship between "Slow" and "Total". FIG. 2J is a diagram explaining an example of setting a threshold for event selection. FIG. 2I is a graph showing the relationship between "Slow" and "Total". 1 is a graph showing the relationship between "Slow" and "Total". FIG. 2 is a graph showing the relationship between "Slow" and "Total". FIG. 3 is a graph showing the relationship between "Slow" and "Total". FIG. 4 is a graph showing the relationship between "Slow" and "Total". FIG. 5 is a graph showing the relationship between "Slow" and "Total". FIG. 6 is a graph showing the relationship between "Slow" and "Total". FIG. 7 is a graph showing the relationship between "Slow" and "Total". FIG. 8 is a graph showing the relationship between "Slow" and "Total". FIG. 9 is a graph showing the relationship between the number of photoelectrons and the count number before and after event selection. FIG. 10 is a graph showing the relationship between the number of photoelectrons and the count number before and after event selection.

[0019] Before describing the embodiments of the present disclosure, the background to the embodiments of the present disclosure will be described.

[0020] One type of detector for detecting alpha rays is a detector that uses a TPC (time projection chamber). A TPC is a detector that three-dimensionally reconstructs the tracks of charged particles that have passed through a sensitive region filled with rare gas. Specifically, a TPC transports electrons that are generated when alpha rays pass through an electrostatic field to a micropixel chamber (μ-PIC), records the two-dimensional hit position and time, and converts the time into a z-coordinate to reconstruct the three-dimensional track. A TPC using a μ-PIC can achieve up to 10 －３ a / cm ２ It is a high-precision alpha-ray imaging detector with a detection limit of 1000 kJ / h.

[0021] Although the TPC alone can construct the three-dimensional track of a charged particle, it cannot grasp the z coordinate of the position where alpha rays are generated. This is because radon is a radioactive substance that occurs everywhere in nature, and the z coordinate of the position where alpha rays are generated from a radiation source is constant, but the alpha rays originating from radon are uniformly present inside the TPC container.

[0022] On the other hand, as mentioned above, there has been disclosed a technology relating to a radiation detector that utilizes the phenomenon of gas luminescence due to radiation (gas scintillation).

[0023] As mentioned above, there is a demand for a radiation measuring device that can measure even alpha rays with high accuracy. For example, solder materials used to join semiconductor elements to substrates contain trace amounts of radioactive material, which emits alpha rays. The emitted alpha rays can adversely affect the operation of semiconductor elements. As semiconductor elements become increasingly miniaturized, the radiation resistance of semiconductor elements becomes weaker. Therefore, there is a demand for ultra-low alpha materials that emit extremely little alpha rays, as well as for a radiation measuring device that can measure even trace amounts of alpha rays with high accuracy.

[0024] If gas scintillation can distinguish between alpha rays emitted from the object being measured and alpha rays emitted from radon, then it is thought that by combining it with TPC, even trace amounts of alpha rays can be measured with high accuracy.

[0025] The present inventors have conducted extensive research into a radiation measuring device that can measure even minute amounts of alpha rays with high accuracy using gas scintillation, and as a result, as will be explained below, have devised a radiation measuring device that can measure even minute amounts of alpha rays with high accuracy by detecting the generation of radiation based on a pulse signal generated in response to the reception of scintillation light.

[0026] Next, an example of an embodiment of the present disclosure will be described with reference to the drawings. Note that the same reference numerals are used to designate the same or equivalent components and parts in each drawing. Furthermore, the dimensional proportions of the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0027] 1 is a diagram showing a schematic configuration of a radiation measurement apparatus according to this embodiment. The radiation measurement apparatus 1 shown in FIG. 1 includes a vacuum pump 10, a CF ４ The device includes a gas cylinder 20, a pressure measuring device 30, valves 40A and 40B, a housing 50, photomultiplier tubes (PMTs) 60A and 60B, a memory unit 70, and a detection unit 100.

[0028] The vacuum pump 10 is a pump for discharging gas from the housing 50, and a valve 40A prevents the gas discharged from the housing 50 from flowing back. The pressure measuring device 30 measures the air pressure inside the housing 50. For example, a diaphragm vacuum gauge that detects displacement as capacitance is used as the pressure measuring device 30. By checking the air pressure measured by the pressure measuring device 30, it is possible to determine whether a vacuum state has been created inside the housing 50.

[0029] CF ４ The gas cylinder 20 is filled with CF ４ In this embodiment, CF4 gas is supplied to the housing 50. ４ The atmospheric pressure is set to any pressure between 0.1 and 1.2 atmospheres.

[0030] The housing 50 accommodates a radiation measurement target 55. In this embodiment, the housing 50 has a cylindrical shape with an inner diameter of 4 cm and a length of 10 cm, but the present disclosure is not limited to this example. In this embodiment, the radiation measurement target 55 is a copper plate to which a naturally occurring radioactive substance, for example, a polonium-210 radioisotope, is attached. This copper plate with the polonium-210 radioisotope attached to its surface generates monochromatic alpha rays of 5.3 MeV.

[0031] The housing 50 also contains a CF ４ CF supplied from gas cylinder 20 ４ Gas is filled. CF ４ The gas is an example of an inert gas of the present disclosure, and is CF ４ The interaction between the gas molecules and the radiation causes the emission of scintillation light. The emitted scintillation light passes through quartz windows 52A and 52B and sheet resistors 53A and 53B to reach photomultiplier tubes 60A and 60B. The reason for using quartz windows 52A and 52B is to reduce radiation other than alpha rays from the measurement object 55, which becomes background noise, as will be described later.

[0032] In this embodiment, the housing 50 is ４ Although the housing 50 is filled with a gas, the present disclosure is not limited to such an example. The gas filled in the housing 50 may be an inert gas such as argon gas, neon gas, or xenon gas.

[0033] The photomultiplier tubes 60A and 60B are an example of an optical sensor of the present disclosure, and are particularly suitable for detecting weak light. The photomultiplier tubes 60A and 60B include photocathodes 61A and 61B, respectively. The photocathodes 61A and 61B are electrodes that convert scintillation light generated within the housing 50 into electrons. The photomultiplier tubes 60A and 60B amplify the electrons converted by the photocathodes 61A and 61B, and output them as pulse signals.

[0034] The storage unit 70 stores pulse signals generated by the photomultiplier tubes 60A and 60B during a predetermined period (for example, one to several days) while the radiation measurement target 55 is present inside the housing 50.

[0035] The detection unit 100 detects radiation generated by the measurement object 55 based on the pulse signals output by the photomultiplier tubes 60A, 60B. Specifically, the detection unit 100 detects radiation generated by the measurement object 55 by excluding calculation results for the pulse signals stored in the storage unit 70 that are less than a predetermined threshold. Here, the predetermined threshold is a value determined by calculation for pulse signals generated by the photomultiplier tubes 60A, 60B during a predetermined period when the measurement object 55 is not present within the housing 50. A method for setting the threshold will be described in detail later.

[0036] The detection unit 100 calculates a first integral value by integrating the voltage value during the period in which the pulse signal is generated and a second integral value by integrating the voltage value during the period in which the pulse signal is attenuated, as calculations for the pulse signals output from the photomultiplier tubes 60A and 60B. The detection unit 100 then detects radiation generated by the measurement object 55 using the ratio between the first integral value and the second integral value.

[0037] The detection unit 100 can be realized by an information processing device such as a personal computer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a storage, and the like.

[0038] The principle by which radiation generated by the measurement object 55 can be measured using the configuration of the radiation measurement device 1 shown in FIG. 1 will be described.

[0039] First, CF ４ This shows that the gas is emitting light in response to radiation. Figures 2A and 2B are diagrams showing examples of the results of light detection by photomultiplier tubes 60A and 60B. Figure 2A shows the detection result when a measurement object 55 is present in housing 50, and Figure 2B shows the detection result when a measurement object 55 is not present in housing 50. In the graphs of Figures 2A and 2B, the horizontal axis shows the amount of light detected by photomultiplier tube 60A, and the vertical axis shows the amount of light detected by photomultiplier tube 60B.

[0040] As shown in Figure 2A, when the measurement object 55 is present in the housing 50, the photomultiplier tubes 60A and 60B detect a total of about 80 p.e. (photoelectrons) of photoelectrons. ４ It can be seen that the gas emits light in response to radiation.

[0041] 2B, photomultiplier tubes 60A and 60B detect light even when no measurement object 55 is present inside housing 50. This is thought to be due to various reasons, as will be described later, whereby radiation reaches inside housing 50. Therefore, if only α-rays emitted by measurement object 55 can be detected, radiation emitted by measurement object 55 can be detected with high accuracy.

[0042] 3 is a diagram showing an example of measurement results of the number of photoelectrons and the number of counts in both a state where the measurement object 55 is present in the housing 50 and a state where it is not present. The graph in FIG. 3 is a graph of the graph shown in FIG. 2, in which the horizontal axis represents the number of photoelectrons measured by the photomultiplier tubes 60A and 60B, and the vertical axis represents the number of photoelectron counts per unit time. ４ The gas pressure is set to 1.2 atmospheres.

[0043] In the graph of Figure 3, the histogram without a pattern on the background represents the state where the measurement object 55 is present in the housing 50, and the histogram with a pattern on the background represents the state where the measurement object 55 is not present in the housing 50. The tendency of the light amount when the measurement object 55 is present and when it is not present in the housing 50 is due to the CF ４ It has been found through experiments by the present inventors that the CF in the housing 50 does not change significantly depending on the gas pressure. ４ The change in gas pressure causes the CF ４ It is not expected to affect the luminescence tendency of the gas.

[0044] Next, CF due to the interaction with radiation ４ The detection sensitivity of radiation using gas emission is determined.

[0045] In the graph shown in Figure 3, the radiation detection sensitivity was calculated by setting the event integral region between 40 p.e. and 120 p.e. The measurement time was 36,000 [sec], and the conversion coefficient was 0.7 [cps] / [alpha / sec]. The background count was 426. The alpha-ray emission frequency, calculated by dividing the count number by the measurement time and the conversion coefficient, was 1.18 x 10 －２ It was a / s.

[0046] By using the area S of the measurement object 55, it is possible to determine the lower limit of the α-ray emission frequency per unit area of ​​the measurement object 55. When the area S of the measurement object 55 is 12.5 cm ２ When the measurement time is 10 hours, the lower limit of the α-ray emission frequency of the measurement object 55 is 4.5 a / cm ２ / h.

[0047] That is, even if the area of ​​the measurement object 55 is small and the measurement time is set to about 10 hours, －０ I was able to get a level of sensitivity.

[0048] In this way, CF ４ It was found that the gas emitted light, and CF ４ It was found that a certain degree of sensitivity can be obtained simply by using the phenomenon of gas emission. As described above, even when the measurement object 55 is not present in the housing 50, a certain degree of radiation is detected. Therefore, if the radiation detected when the measurement object 55 is not present in the housing 50 is treated as background noise and this background noise is removed, the radiation measuring device 1 can detect only the alpha rays generated by the measurement object 55 at 10 －１ It is believed that it can be detected with the following level of sensitivity.

[0049] Here, the following are possible types of radiation present in the housing 50: (a) α-rays generated by the measurement object 55; (b) CF ４ (c) Alpha rays from the wall of the housing 50 (d) Environmental gamma rays (from concrete and air) (e) Gamma rays inside the housing 50 (f) Cosmic ray muons

[0050] Of these (a) to (f), it is difficult to distinguish between (a) to (c). Therefore, it is advisable to remove α rays originating from (b) and (c) by cleaning the housing 50 by electrolytic polishing or by adsorbing and removing residual radon with activated carbon. In addition, since the use of a glass window may affect the measurement due to RI (Radio Isotope) impurities, in this embodiment, a CF ４ Quartz windows 52A, 52B are used to detect gas emissions with photomultiplier tubes 60A, 60B.

[0051] Regarding (d) and (e), the following cases are possible: １ ), (e １ ) γ-rays are CF ４ interacts with electrons in the gas (d ２ ), (e ２ ) gamma rays interact with the quartz windows 52A, 52B

[0052] 4A and 4B are diagrams showing the correspondence between the results of light detection by the photomultiplier tubes 60A and 60B in FIG. 2 and the radiation present in the housing 50 described above. ２ ), (e ２ ) are considered to be near the x-axis and y-axis, respectively. ２ ), (e ２ ) is easy to eliminate. １ ), (e １ It is reasonable to consider that events (a), (b), and (c) exist at positions away from the x-axis and y-axis.

[0053] Here, the radiation measuring device 1 according to this embodiment is particularly １ ), (e １ To distinguish between events (a), (b), and (c), pulse shape discrimination (PSD) was employed.

[0054] 5 is a diagram showing an example of a voltage waveform output by the photomultiplier tubes 60A and 60B. In the graph of FIG. 5, the horizontal axis represents time (nanoseconds) and the vertical axis represents voltage (mV). In the graph of FIG. 5, "Total" represents the time t ｒFrom time t ｒ +τ ２ time to (i.e., τ ２ ) and is an example of the first integral value of the present disclosure. ｒ +τ １ From time t ｒ +τ ２ time to (i.e., τ ２ -τ １ ) and is an example of the second integral value of the present disclosure.

[0055] "Total" and "Slow" can be expressed by the following formula: "Total" is the CF ４ It corresponds to the total amount of light emitted by the gas in one emission. １ and τ ２ is CF ４ The value is adjusted so that alpha rays can be identified from the gas's light emission.

[0056]

[0057]

[0058] 6A and 6B are graphs showing the relationship between "Slow" and "Total" calculated by the above formula. In the graphs of FIGS. 6A and 6B, the horizontal axis is "Total" and the vertical axis is "Slow / Total". FIG. 6A is a graph when the measurement object 55 is present in the housing 50, and FIG. 6B is a graph when the measurement object 55 is not present in the housing 50. Note that in FIGS. 6A and 6B, CF ４ The graph shows the case where the gas pressure is 1.2 atmospheres.

[0059] 6A and 6B, a difference can be seen in the distribution between when the measurement object 55 is present in the housing 50 and when the measurement object 55 is not present in the housing 50. If a threshold value for event selection is set and events present below the threshold are removed as background noise in the detection unit 100, the radiation measurement device 1 can extract only events caused by α rays emitted by the measurement object 55.

[0060] An example of setting the threshold value for event selection will now be described with reference to Fig. 7. An example of setting the threshold value for event selection is shown in Fig. 7.

[0061] First, the two-dimensional histogram is thinly sliced ​​vertically and projected onto a one-dimensional histogram. Next, from the distribution at a certain Total value, a threshold x is determined such that the number of events integrated from Slow / Total = 0 to x is 99.5% or more of the total (corresponding to 2σ). Next, thresholds are determined similarly for all Total values ​​and plotted on the two-dimensional histogram. Note that this threshold is not necessarily constant because it varies depending on the setup conditions of the radiation measurement device 1, such as the type of gas used for radiation detection, pressure, temperature, and humidity, and is therefore determined after each measurement.

[0062] 8A to 14B show different CFs. ４ 8A and 8B are graphs showing the relationship between "Slow" and "Total" in gas pressure. ４ The graphs show the case where the gas pressure is 1.0 atmosphere. ４ The graphs show the case where the gas pressure is 0.8 atmospheres. ４ The graphs show the case where the gas pressure is 0.6 atmospheres. ４ The graphs show the case where the gas pressure is 0.4 atmospheres. ４ The graphs show the case where the gas pressure is 0.3 atmospheres. ４ The graphs show the case where the gas pressure is 0.2 atmospheres. ４ The graph shows the case where the gas pressure is 0.1 atmospheres.

[0063] As shown in Figures 8A to 14B, CF ４ It can be seen that even if the gas pressure changes, events can be selected by setting a threshold value. Therefore, the radiation measurement device 1 according to this embodiment can extract only events caused by α rays generated by the measurement target 55 by selecting events by setting a threshold value.

[0064] The effect of event selection by setting a threshold using a PSD will be explained. Figures 15A and 15B are graphs showing the relationship between the number of photoelectrons and the count number before and after event selection. Figure 15A shows an example of the relationship when a measurement object 55 is present in the housing 50, and Figure 15B shows an example of the relationship when a measurement object 55 is not present in the housing 50.

[0065] 15A and 15B, calculations were performed with the event integration region between 40 p.e. and 120 p.e., and the background count was 21 counts. By using the area S of the measurement object 55, the area S of the measurement object 55 was set to 12.5 cm ２ When the measurement time is set to 10 hours, the lower limit of the α-ray emission frequency of the measurement object 55 is 2.4 × 10 －１ a / cm ２ / h.

[0066] Therefore, as a result of selecting events by setting a threshold using PSD, even if the area of ​​the measurement target 55 is small and the measurement time is set to about 10 hours, －１ I was able to get a level of sensitivity.

[0067] The area S of the measurement object 55 is 12.5 cm ２ In this case, the lower limit of the alpha ray emission frequency per unit area is 10 －１ Therefore, by increasing the area of ​​the measurement target 55, －２ If the measurement target 55 is made of a flexible material and can be curved and positioned so as to fit closely to the inside of the housing 50, the lower limit of the α-ray emission frequency per unit area of ​​the measurement target 55 is, by simple calculation, 2.5×10 －２ a / cm / h.

[0068] As described above, the radiation measurement device 1 according to this embodiment is ４ The housing 50 is filled with gas, and the radiation and CF generated by the measurement object 55 are ４ By detecting the light emitted by the reaction with gas molecules, the radiation generated by the measurement object 55 inside the housing 50 can be detected with high accuracy.

[0069] It should be noted that the CF in the housing 50 may be ４ The purity of the gas may decrease, and the accuracy of measuring radiation may decrease. ４ CF in the housing 50 to pass the gas through the activated carbon filter and return it to the housing 50. ４ The gas may be circulated.

[0070] Although the embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modifications or alterations within the scope of the technical idea described in the claims, and it is understood that these modifications or alterations also naturally fall within the technical scope of the present disclosure.

[0071] Furthermore, the effects described in the above embodiments are explanatory or exemplary and are not limited to those described in the above embodiments. In other words, the technology according to the present disclosure may achieve other effects that are obvious to a person skilled in the art of the present disclosure from the description in the above embodiments, in addition to or instead of the effects described in the above embodiments.

[0072] The disclosure of Japanese Patent Application No. 2022-135318, filed on August 26, 2022, is incorporated herein by reference in its entirety.

[0073] 1 Radiation measuring device 10 Vacuum pump 20 CF ４ Gas cylinder 30: Pressure measuring device 40A, 40B: Valve 50: Housing 60A, 60B: Photomultiplier tube 70: Memory unit 100: Detector

Claims

1. A gas scintillator that emits scintillation light due to the interaction between gas molecules and radiation, At least two optical sensors that generate a pulse signal in response to receiving the scintillation light, A detection unit that detects the occurrence of the radiation based on the pulse signals generated by each of the optical sensors, comprising The detection unit obtains a first integral value by integrating the voltage value during the period when the pulse signal is generated and a second integral value by integrating the voltage value during the period when the pulse signal decays, as operation results for the pulse signals generated by the optical sensors during a predetermined period in a state where the measurement target of the radiation exists in the gas scintillator, and excludes operation results less than a predetermined threshold value, thereby detecting the radiation generated by the measurement target. The threshold value is a value determined by an operation on the pulse signals generated by the optical sensors during a predetermined period in a state where the measurement target of the radiation does not exist in the gas scintillator, and is a value calculated from a two-dimensional histogram generated using the first integral value and the ratio of the first integral value to the second integral value. A radiation measurement device.

2. The detection unit calculates a first integral value by integrating the voltage value during the period when the pulse signal is generated and a second integral value by integrating the voltage value during the period when the pulse signal decays as operations on the pulse signal, and detects the radiation generated by the measurement target using the ratio of the first integral value to the second integral value. The radiation measurement device according to Claim 1.

3. The gas is an inert gas. The radiation measurement device according to Claim 1.

4. The inert gas is carbon tetrafluoride, argon, neon, or xenon. The radiation measurement device according to Claim 3.

5. The gas pressure of the gas in the gas scintillator is 0.1 atm to 1.2 atm. The radiation measurement device according to Claim 1.

6. The radiation measuring device according to claim 1, wherein the container that houses the gas scintillator is cylindrical.

7. The radiation measuring device according to claim 6, wherein the at least two optical sensors are provided on the bottom surface of the container that houses the gas scintillator.

8. The radiation measuring device according to claim 1, wherein the threshold value is a value of the ratio between the first integrated value and the second integrated value when the ratio between the first integrated value and the second integrated value in a one-dimensional histogram generated by slicing the two-dimensional histogram in the direction of the first integrated value counts the number of events in the one-dimensional histogram and the number of events reaches a predetermined value.

9. The radiation measuring device according to claim 8, wherein the predetermined value is a value corresponding to 2σ of the total value of the events.