Radiation measuring device

Abstract

To provide a radiation measuring device that can improve the accuracy of calibration and analysis.SOLUTION: A radiation measuring device 10 comprises a radiation detector 11, a processor 12, and an analyzer 13. The radiation detector 11 outputs a pulse signal according to the energy of radiation. The processor 12 generates pulse-height distribution data (energy spectrum) having a count associated with each of a plurality of channels on the basis of the pulse signal. The analyzer 13 acquires the maximum energy of radiation on the basis of the energy spectrum. When the count reaches a threshold count in at least one predetermined channel of the plurality of channels in the energy spectrum generated by the processor 12, during measurement of radiation performed by the radiation detector 11, the analyzer 13 terminates the measurement of radiation performed by the radiation detector 11.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a radioactivity measuring device.

Background Art

[0002] Conventionally, for example, based on a photoelectric peak or a Compton edge in the energy spectrum of radiation emitted from a calibration radiation source and a reference energy value stored in advance, the applied voltage of a radiation detector, the gain of an amplifier, etc. are automatically adjusted (calibrated). There is known a radioactivity measuring device (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the case of radiation having a continuous spectrum such as beta rays, it is difficult to detect an appropriate peak or the like in the energy spectrum. For example, by detecting the maximum energy corresponding to the end position of the energy spectrum, a method of calibrating the device and analyzing a sample is known. However, the count value near the end position of the energy spectrum decreases as the energy increases, and the statistical error increases. For example, when the number of radiations to be measured is small, the maximum energy detected from the energy spectrum after removing the background component changes to a value lower than the original value, etc., and there is a possibility that the accuracy of device calibration and sample analysis cannot be improved. In addition, since the number of radiations measured during calibration using a standard radiation source is proportional to the intensity of the standard radiation source and the measurement time, for example, even if the measurement time is constant, due to the attenuation of the radiation source intensity over time, the detected maximum energy may change.

[0005] An object of the present invention is to provide a radioactivity measurement device capable of improving the accuracy of calibration and analysis.

Means for Solving the Problems

[0006] In order to solve the above problems and achieve the above object, the present invention adopts the following aspects. (1): A radioactivity measurement device (10) according to an aspect of the present invention includes a radiation detector (11) that outputs a pulse signal corresponding to the energy of radiation, and a processing unit (12) that generates pulse height distribution data having counts associated with each of a plurality of channels based on the pulse height value of the pulse signal, and an arithmetic unit (13) that obtains the maximum energy of the radiation based on the pulse height distribution data, and a control unit (13) that ends the measurement of the radiation by the radiation detector when the count at at least one predetermined channel among the plurality of channels in the pulse height distribution data generated by the processing unit reaches a predetermined count during the measurement of the radiation by the radiation detector.

[0007] (2): In the radioactivity measurement device according to (1) above, the control unit may end the measurement of the radiation by the radiation detector when the counts at each of a plurality of predetermined channels among the plurality of channels reach the predetermined count or more.

[0008] (3): In the radioactivity measurement device according to (1) above, the control unit may end the measurement of the radiation by the radiation detector when the integrated count in a predetermined channel region among the plurality of channels reaches a predetermined integrated count.

[0009] (4): In the radioactivity measurement device according to (1) above, the arithmetic unit may obtain data indicating the correspondence between the maximum energy and the measurement time of the radiation by the radiation detector or the count at at least one predetermined channel among the plurality of channels, and estimate the maximum energy based on the data.

[0010] (5): In the radioactive measurement device according to any one of (1) to (4) above, the radiation detector may include a scintillator that emits scintillation light according to the energy of the radiation, and a photodetector that outputs the pulse signal according to the scintillation light.

Effect of the Invention

[0011] According to (1) above, by providing a control unit that enables acquisition of pulse height distribution data in which the count in at least one predetermined channel becomes a predetermined count, it is possible to suppress a change in the maximum energy of the radiation acquired from the pulse height distribution data. For example, by making the maximum energy of the radiation acquired from the pulse height distribution data of the same nuclide be substantially the same regardless of the measurement time, the state of the sample, etc., the accuracy of calibration and analysis can be improved.

[0012] In the case of (2) above, by providing a control unit that enables acquisition of pulse height distribution data in which the count in each of a plurality of predetermined channels among the plurality of channels becomes a predetermined count or more, it is possible to reduce the statistical error of the maximum energy of the radiation acquired from the pulse height distribution data. In the case of (3) above, by providing a control unit that enables acquisition of pulse height distribution data in which the integrated count in a predetermined channel region among the plurality of channels becomes a predetermined integrated count, it is possible to reduce the statistical error of the maximum energy of the radiation acquired from the pulse height distribution data.

[0013] In the case of (4) above, by providing an arithmetic unit that estimates the maximum energy based on data indicating the correspondence between the maximum energy and the measurement time or the count in at least one predetermined channel, the efficiency of calibration and analysis can be improved. For example, by using the data of the correspondence relationship acquired in advance, even when the measurement time or the count at the time of acquiring the maximum energy by a later measurement is relatively small, it is possible to estimate a highly accurate maximum energy corresponding to a larger arbitrary measurement time or count.

[0014] In the case of (5) above, even when detecting the maximum energy of radiation using a radiation detector composed of a combination of a scintillator and a photodetector, the accuracy of calibration and analysis can be improved.

Brief Description of the Drawings

[0015]

Figure 1

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Modes for Carrying Out the Invention

[0016] Hereinafter, a radioactivity measurement device according to an embodiment of the present invention will be described with reference to the accompanying drawings. The radioactivity measurement device of the embodiment measures the radioactivity of a sample that emits radiation such as beta rays. FIG. 1 is a block diagram showing the functional configuration of a radioactivity measurement device 10 according to the embodiment. FIG. 2 is a cross-sectional view showing the configuration of a radiation detector 11 according to the embodiment. As shown in FIG. 1, the radioactivity measurement device 10 of the embodiment includes, for example, a radiation detector 11, a processing device 12, and an analysis device 13.

[0017] The radiation detector 11 is, for example, a phoswich detector including two different optically coupled scintillators. As shown in FIG. 2, the radiation detector 11 includes, for example, a first scintillator 21, a second scintillator 22, a photodetector 23, a shield 24, and a guard detector 25.

[0018] The first scintillator 21 and the second scintillator 22 are, for example, plastic scintillators having different mutual thicknesses, decay times of scintillation light, and the like. For example, the first scintillator 21 is disposed so as to contact the incident window of the photodetector 23, and the second scintillator 22 is disposed so as to be laminated on the first scintillator 21 in the thickness direction. The photodetector 23 is, for example, a head-on type photomultiplier tube. The photodetector 23 outputs a signal of a current value corresponding to the scintillation light for each event in which the scintillation light is emitted by each of the scintillators 21 and 22. The signal output from the photodetector 23 is a pulse signal having a pulse height value corresponding to the energy of the radiation detected by the radiation detector 11.

[0019] The outer shape of the shield 24 is, for example, a box shape surrounding the sensitive part of the radiation detector 11 and the sample S. The sensitive part of the radiation detector 11 is, for example, each of the scintillators 21 and 22 and the head of the photodetector 23. The sample S is disposed, for example, at a predetermined position appropriately separated from the sensitive part of the radiation detector 11. The shield 24 is formed of a material that shields radiation, such as lead or tungsten.

[0020] The guard detector 25 is, for example, a scintillation detector. The scintillation detector includes, for example, a scintillator such as a plastic scintillator and a photodetector such as a photomultiplier tube. The guard detector 25 is disposed, for example, on the rear side of the shield 24 as viewed from each of the scintillators 21 and 22 and the photodetector 23. The guard detector 25 detects radiation other than the radiation emitted from the sample S to be measured (for example, background radiation).

[0021] The processing device 12 is housed, for example, together with the radiation detector 11 in a predetermined housing. The processing device 12 includes, for example, a signal processing unit, a control unit, and an input / output unit. The signal processing unit processes the signal output from the radiation detector 11. For example, for each event in which a pulse signal is output from the radiation detector 11, the signal processing unit performs processes such as conversion from an analog signal to a digital signal, removal of events detected by the guard detector 25, and generation of an energy spectrum of radiation. The signal processing unit generates pulse height distribution data having counts associated with each of a plurality of channels based on the pulse signal corresponding to the energy of the radiation. The signal processing unit generates an energy spectrum of the radiation by associating the pulse height value and the energy of the pulse height distribution data. The control unit controls, for example, the measurement by the radiation detector 11, the operation of attached devices such as the sample changer, and the operation of the signal processing unit. The input / output unit is, for example, a touch panel or the like. The input / output unit receives various input operations of the operator and displays various information such as the energy spectrum generated by the signal processing unit.

[0022] The analysis device 13 is an information processing device such as a personal computer, a smartphone, or a tablet terminal. The analysis device 13 is connected to the processing device 12, for example, from outside the predetermined housing in which the radiation detector 11 and the processing device 12 are housed. The analysis device 13 includes, for example, an arithmetic unit, a control unit, and an input / output unit. The arithmetic unit performs processes such as calibration and inspection of the radiation detector 11 and the processing device 12, spectrum analysis, and nuclide analysis, for example, based on the energy spectrum of the radiation generated by the processing device 12. The control unit controls the operation of the arithmetic unit, for example, in addition to the same control as the control unit of the processing device 12. The input / output unit is, for example, a keyboard, a display, a touch panel, or the like. The input / output unit receives various input operations from the operator and displays various information such as the energy spectrum and analysis results generated by the processing device 12.

[0023] A part of each of the processing device 12 and the analysis device 13 includes a software functional unit that functions when a predetermined program is executed by a processor such as a CPU (Central Processing Unit). The software functional unit is an ECU (Electronic Control Unit) that includes a processor such as a CPU, a ROM (Read Only Memory) that stores a program, a RAM (Random Access Memory) that temporarily stores data, and an electronic circuit such as a timer. Note that a part of each of the processing device 12 and the analysis device 13 may include an integrated circuit such as an LSI (Large Scale Integration).

[0024] The operation of the radiation measuring device 10 according to the embodiment will be described below. FIG. 3 is a flowchart showing the measurement operation during calibration and inspection of the radiation measuring device 10 according to the embodiment. The calibration and inspection of the radiation measuring device 10 are, for example, 90 Sr and 137 performed based on the energy spectrum generated by measuring beta rays emitted from a standard radiation source of a predetermined nuclide such as Cs. As shown in FIG. 3, first, the analysis device 13 acquires a target channel that is preset for the energy spectrum corresponding to a predetermined standard radiation source (step S01). The target channel is, for example, a plurality of predetermined channels on the low-energy side of the energy spectrum. The plurality of channels is at least three channels, such as three to five channels, for example.

[0025] Next, the analyzer 13 acquires a threshold count set in advance for the target channel (step S02). The threshold count is, for example, about 2,500 counts for each of the plurality of target channels. Next, the analyzer 13 starts measuring the radiation (beta rays) with the radiation detector 11 for a predetermined standard radiation source (step S03). The processing device 12 generates an energy spectrum of the radiation according to the signal output from the radiation detector 11.

[0026] Next, the analyzer 13 determines whether or not the count of each target channel in the energy spectrum updated for each event by the processing device 12 has reached the threshold count (step S04). If the determination result is "NO", the analyzer 13 repeatedly executes the determination process of step S04. On the other hand, if the determination result is "YES", the analyzer 13 proceeds to step S05. Next, the analyzer 13 ends the measurement of the radiation by the radiation detector 11 (step S05). Then, the analyzer 13 proceeds to the end of the process.

[0027] FIG. 4 is a flowchart showing the maximum energy calculation operation of the radioactivity measurement device 10 according to the embodiment. FIG. 5 is a diagram showing an example of the operation of calculating the count sum shown in FIG. 4. The analyzer 13 calculates the maximum energy from the energy spectrum of the radiation (beta rays) generated by the processing device 12 in processes such as calibration, inspection, spectrum analysis, and nuclide analysis of the radioactivity measurement device 10. As shown in FIG. 4, first, the analyzer 13 acquires a predetermined channel n as an initial estimated value of the end channel m corresponding to the maximum energy of the energy spectrum using arbitrary natural numbers m and n (step S11). The predetermined channel n is, for example, a channel where radiation counts exist around the end channel m. The predetermined channel n is, for example, a channel preset for the energy spectrum corresponding to a predetermined standard radiation source or a channel input from an operator based on the energy spectrum generated by the processing device 12.

[0028] Next, the analysis device 13 calculates the total count for a predetermined number k of channels m, (m-1), ..., (m-(k-2)), (m-(k-1)) consecutively going back to the low energy side, including the terminal channel m, i.e., the count sum Sg, which is the integrated number of counts C for each channel (step S12).

[0029] Next, the analysis device 13 determines whether or not a value (Sg / k) obtained by dividing the count sum Sg as the dividend and a predetermined number k as the divisor is less than 1 (step S13). If the result of this determination is "NO", the analysis device 13 advances the process to step S14. On the other hand, if the result of this determination is "YES", that is, if the average count is no longer being obtained, the analysis device 13 determines that the terminal channel m at this point is the channel corresponding to the maximum energy, and advances the process to the end. Furthermore, the analysis device 13 adds 1 to the termination channel m at this point to obtain a channel (m+1), which is set as a new termination channel m (step S14).Then, the analysis device 13 returns the process to step S12.

[0030] For example, as shown in FIG. 4, when a specific channel n is first set as a termination channel m, the count sum Sg is the integrated value of a specific number k of consecutive counts C from the count C(n) of the specific channel n to the count C(n-k+1) of channel (n-k+1). Next, if the division value (Sg / k) of the count sum Sg is 1 or more, the channel (n+1) obtained by adding 1 to the specified channel n is set as the terminal channel m. In other words, the terminal channel m is updated to the channel on the higher energy side by one channel. In this case, the count sum Sg is the integrated value of the consecutive counts C of a specified number k from the count C(n+1) of channel (n+1) to the count C(n-k+2) of channel (n-k+2). As described above, the terminal channel m is sequentially shifted by one channel toward the higher energy side until the division value (Sg / k) of the count sum Sg becomes less than 1.

[0031] FIG. 6 is a graph showing an example of the correspondence between the channel Ch of the maximum energy used in the maximum energy estimation operation of the radioactivity measurement device 10 according to the embodiment and the measurement time (or total count). For example, the analyzer 13 acquires data showing the correspondence between the channel of the maximum energy (maximum energy Ch) calculated from the energy spectrum and the total count in a predetermined region such as the measurement time or the entire energy spectrum by performing measurement of radiation (beta rays) on a predetermined standard radiation source in advance. The analyzer 13 acquires data of a predetermined function that can be applied (fitted) to the correspondence between the channel of the maximum energy and the measurement time or the total count, for example. For example, at the time of calibration and inspection of the radioactivity measurement device 10 that is performed at an appropriate timing later, the analyzer 13 uses the data of the maximum energy obtained under the conditions of an appropriate measurement time or an appropriate total count for the standard radiation source and the data of the predetermined function acquired in advance to estimate the maximum energy obtained at an arbitrary measurement time or an arbitrary total count.

[0032] For example, as shown in FIG. 6, the analyzer 13 fits the correspondence between a plurality of different measurement times or total counts obtained by measurement on the standard radiation source in advance and the maximum energy Ch with a predetermined function F. By using the data of the predetermined function F acquired in advance, the analyzer 13 can estimate the maximum energy corresponding to a larger arbitrary measurement time or total count even when the measurement time or total count at the time of calculating the maximum energy by a later measurement is relatively small.

[0033] As described above, according to the radioactive ray measuring apparatus 10 of the embodiment, by including the analyzer 13 configured to obtain an energy spectrum in which the count in the target channel becomes the threshold count, it is possible to suppress a change in the maximum energy of the radiation obtained from the energy spectrum. For example, regardless of the measurement time, the state of the standard radiation source, etc., the maximum energy of the radiation obtained from the energy spectrum of the same nuclide becomes substantially the same, thereby improving the accuracy of calibration and analysis. For example, by increasing the threshold count, it is possible to reduce the statistical error of the maximum energy of the radiation obtained from the energy spectrum.

[0034] By including the analyzer 13 configured to estimate the maximum energy based on the data indicating the correspondence between the channel of the maximum energy and the measurement time or the total count, the efficiency of calibration and analysis can be improved. For example, by using the previously acquired correspondence data, even when the measurement time or the total count for obtaining the maximum energy by a later measurement is relatively small, it is possible to estimate a highly accurate maximum energy corresponding to a larger arbitrary measurement time or total count.

[0035] (Modification example) Hereinafter, a modification example of the embodiment will be described. For the same parts as those in the above-described embodiment, the same reference numerals are given and the description will be omitted or simplified. In the above-described embodiment, as shown in FIG. 3, it is determined whether or not the count of each target channel has reached the threshold count, but the present invention is not limited to this. For example, it may be determined whether or not the total count (total count) in a predetermined region in the energy spectrum has reached the threshold count. FIG. 7 is a flowchart showing the measurement operation at the time of calibration and inspection of the radioactive ray measuring apparatus 10 according to the modification example of the embodiment. As shown in FIG. 7, first, the analyzer 13 acquires a target region preset for the energy spectrum corresponding to a predetermined standard radiation source (step S21). The target region is, for example, a predetermined region such as the entire region of the energy spectrum.

[0036] Next, the analyzer 13 acquires a threshold count set in advance for the region of interest (step S22). The threshold count is, for example, about 1 million counts for the entire region. Next, the analyzer 13 starts measuring radiation (beta rays) with the radiation detector 11 for a predetermined standard radiation source (step S23). The processing device 12 generates an energy spectrum of the radiation according to the signal output from the radiation detector 11.

[0037] Next, the analyzer 13 determines whether or not the total count (total count) of the region of interest in the energy spectrum, which is updated by the processing device 12 at any time, has reached the threshold count (step S24). If the determination result is "NO", the analyzer 13 repeatedly executes the determination process of step S24. On the other hand, if the determination result is "YES", the analyzer 13 proceeds to step S25. Next, the analyzer 13 ends the measurement of radiation by the radiation detector 11 (step S25). Then, the analyzer 13 proceeds to the end of the process.

[0038] In the above-described embodiment, the radiation detector 11 is assumed to be a phoswich detector, but it is not limited thereto. For example, the radiation detector 11 may be another radiation detector such as another scintillation detector or semiconductor detector.

[0039] In the above-described embodiment, the radioactivity measurement device 10 is assumed to include the analyzer 13 connected to the processing device 12, but it is not limited thereto. For example, by additionally providing the processing device 12 with the same function as the analyzer 13, the analyzer 13 may be omitted.

[0040] In the above-described embodiment, the analyzer 13 is assumed to acquire data indicating the correspondence between the channel of the maximum energy calculated from the energy spectrum and the total count in a predetermined region such as the measurement time or the entire energy spectrum. However, the present invention is not limited to this. For example, the analyzer 13 may acquire data indicating the correspondence between the channel of the maximum energy and the count at at least one predetermined channel of the measurement time or the energy spectrum.

[0041] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0042] 10... Radioactivity measurement device, 11... Radiation detector, 12... Processing device (processing unit), 13... Analyzer (calculation unit, control unit), 21... First scintillator, 22... Second scintillator, 23... Photodetector, 24... Shield, 25... Guard detector.

Claims

1. A radiation detector that outputs a pulse signal according to the energy of radiation, a processing unit that generates pulse height distribution data having counts associated with each of a plurality of channels based on the pulse height values of the pulse signals, a calculation unit that obtains the maximum energy of the radiation based on the pulse height distribution data, and a control unit that ends the measurement of the radiation by the radiation detector when the count at at least one predetermined channel among the plurality of channels in the pulse height distribution data generated by the processing unit reaches a predetermined count during the measurement of the radiation by the radiation detector. The radioactive substance measuring device is provided with: A radioactive substance measuring device.

2. The control unit: ends the measurement of the radiation by the radiation detector when the counts at each of a plurality of predetermined channels among the plurality of channels reach the predetermined count or more. The radioactive substance measuring device according to Claim 1.

3. The control unit: ends the measurement of the radiation by the radiation detector when the integrated count in a predetermined channel region among the plurality of channels reaches a predetermined integrated count. The radioactive substance measuring device according to Claim 1.

4. The calculation unit: obtains data indicating the correspondence between the maximum energy and the measurement time of the radiation by the radiation detector or the count at at least one predetermined channel among the plurality of channels, and estimates the maximum energy based on the data. The radioactive substance measuring device according to Claim 1.

5. The radiation detector: includes a scintillator that emits scintillation light according to the energy of the radiation, and a photodetector that outputs the pulse signal according to the scintillation light. The radioactive substance measuring device is provided with: The radioactive substance measuring device according to any one of Claims 1 to 4.

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