JP2015184188A - γ-RAY ENERGY SPECTRUM MEASURING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a γ-ray energy spectrum measuring method in which a detector is mounted in a moving body such as a vehicle, moves at a desired speed, and measures γ-ray energy on surfaces of a plurality of measurement blocks.SOLUTION: The γ-ray energy spectrum measuring method includes the steps of: installing a γ-ray detector; extracting energy information of a γ ray entering the γ-ray detector from the output from the γ-ray detector; acquiring current position information and current time information corresponding to the time when the γ ray enters the γ-ray detector; and storing the energy information of the γ ray, the current position information, and the current time information in association with each other.

Description

  The present invention relates to a method for measuring an energy spectrum of γ rays while moving, for example, mounted on a moving body.

  When a nuclear disaster such as a large-scale radioactive material leakage accident occurred at the Fukushima Daiichi Nuclear Power Station, the leaked radioactive material has a wide area with a radius of tens to hundreds of kilometers (or more). To spread. When such a nuclear disaster occurs, creating a map showing the distribution of air dose (hereinafter referred to as radiation dose rate map) is to estimate where and how much diffused radioactive material is distributed, and It is important to manage the exposure of residents and estimate the diffusion status of radioactive materials. Define evacuation areas and indoor evacuation areas for residents, and establish various restricted areas to prevent residents from unnecessary exposure. Useful for. The creation of a radiation dose rate map is also very important in planning decontamination plans and environmental restoration plans for damaged areas.

  The air dose rate (or radiation dose rate) is the radiation dose per unit time of the target space. When the amount of radiation is measured by the amount of energy absorbed by the substance (absorbed dose), the air dose rate is expressed in Gy / h (gray / hour) using Gy (gray) which is the unit of absorbed dose. Is done. Alternatively, when the amount of radiation is measured by the magnitude of the biological effect (dose equivalent) due to the effects of exposure to the living body, the air dose rate is calculated using Sv (sievert), which is a unit of dose equivalent. It is expressed in h (sievert / hour). The dose equivalent is obtained by multiplying the absorbed dose by a coefficient corresponding to the influence on the living body. By monitoring the air dose rate, it is possible to quickly detect the leakage of radioactive materials, and to issue appropriate instructions such as evacuation recommendations to neighboring residents as necessary.

  Therefore, the present inventors easily set the radiation dose rate (gamma ray air dose rate, etc.) in order to grasp the environmental pollution situation after the radioactive material leakage accident that occurred at the Fukushima Daiichi Nuclear Power Station, In addition, as a radiation dose rate map data collection system suitable for long-term measurement, a KURAMA system (Kyoto University Radiation Mapping system) was developed (see Patent Document 1). Furthermore, as shown in Patent Document 2, the KURAMA system has been improved as a radiation dose rate map data collection system that can easily and accurately collect radiation dose rate map data even by a user who is not familiar with radiation measurement. The KURAMA-II system has also been developed.

  As will be described later, the KURAMA-II system has already been tested for practical use in Fukushima Prefecture and the like. For example, in Fukushima City and Koriyama City, some route buses that regularly circulate a predetermined route are equipped with the KURAMA-II system and measure the air dose rate on the route bus route. It is used for.

JP 2013-032926 A JP2013-134105A

  The KURAMA-II system can not only measure the air dose rate of γ rays, but also can measure the energy spectrum as described later. Here, conventionally, when measuring the energy spectrum of γ-rays at a certain point, a γ-ray detector is installed at that point, and it takes several minutes to several hours until the count reaches a sufficient statistic. It was common to continue the measurement. In this case, it is necessary to repeat the installation of the detector → measurement → movement → installation of the detector → measurement → movement in order to set a plurality of measurement sections and perform planar measurement across these plurality of measurement sections. was there. Even when mounted on a moving body such as a car, as in the KURAMA-II system, it is necessary to move at a slow speed so that sufficient statistics can be obtained in the target measurement section. It was. However, it was difficult to carry out such a measurement in consideration of general traffic.

  An object of the present invention is to provide a γ-ray energy measurement method that can be mounted on a moving body such as a car and can measure γ-ray energy across a plurality of measurement sections while moving at a desired speed. It is to be.

According to an aspect of the present invention, a method for measuring the energy spectrum of γ-rays, comprising:
installing a gamma ray detector;
Extracting energy information of γ rays incident on the γ ray detector from the output from the γ ray detector;
Obtaining current position information and current time information corresponding to the time when the γ-rays are incident on the γ-ray detector;
Storing the γ-ray energy information, the current position information, and the time information in association with each other;
A method for measuring γ-ray energy spectrum is provided.

  According to the γ-ray energy spectrum measurement method of the present invention, for example, by mounting a γ-ray detector on a moving body, the energy spectrum of γ-rays in a desired measurement section can be measured while moving. And the energy spectrum of the gamma ray regarding a desired point and / or desired time can be reconfigure | reconstructed after a measurement or during a measurement.

  According to the present invention, it is possible to measure γ-ray energy across a plurality of measurement sections while being mounted on a moving body such as a car and moving at a desired speed.

FIG. 1 is a schematic diagram of the KURAMA system 1. FIG. 2 is a schematic diagram of the NaI scintillation detector 10. FIG. 3 is an example of an air dose rate map in which markers color-coded according to the size of the air dose rate are displayed on a three-dimensional map. FIG. 4 is an example of an air dose rate map in which markers color-coded according to the size of the air dose rate are displayed on a two-dimensional map. FIG. 5 is a schematic diagram of the KURAMA-II system. FIG. 6 is a schematic diagram of a CsI scintillation detector. FIG. 7 shows an example of a pulse height spectrum. FIG. 8 is a diagram showing a mesh applied to Fukushima city in the demonstration experiment. FIG. 9 is an energy spectrum of the reconstructed Fukushima station square (mesh indicated by the balloon in FIG. 8). FIG. 10 is a ⁴⁰ K decay scheme. FIG. 11 is a decay scheme of ¹³⁴ Cs. FIG. 12 is a decay scheme of ¹³⁷ Cs.

  As described above, prior to the development of the γ-ray energy spectrum measurement system according to the present embodiment, the present inventor has developed a radiation dose rate map data collection system called the KURAMA system and an improved version thereof, the KURAMA-II system. did. Here, KURAMA is an abbreviation for “Kyoto University Radiation Mapping” and is a system for producing an air dose rate map developed at Kyoto University with the present inventor at the center.

The γ-ray energy spectrum measurement system according to this embodiment is an improvement of the KURAMA-II system. Therefore, before describing the γ-ray energy spectrum measurement system according to the present embodiment, first, the KURAMA system 1 (radiation dose rate map data collection system) developed mainly by the present inventor and its improved version. The KURAMA-II system 100 will be described.
<Outline of KURAMA system 1>

  As shown in FIG. 1, the KURAMA system 1 uses a NaI scintillation detector 10 as a radiation measuring device for measuring an air dose rate, and a GPS that acquires information on the current position using a global positioning system (GPS system). A unit 20 (position information acquisition mechanism), a data processing system 30 for processing data (dose rate data and position data) acquired by the NaI scintillation detector 10 and the GPS unit 20, and an analog output from the NaI scintillation detector 10 Are mainly provided with an interface unit 40 for A / D converting the data into the data processing system 30 and a data transmission unit 50 for transmitting data processed by the data processing system 30 to a server 90 described later.

  As shown in FIG. 2, the NaI scintillation detector 10 includes a NaI crystal 11 doped with thallium (Tl) as an emission center and a photomultiplier tube (not shown) optically connected to the NaI crystal 11. A main body in which a cylindrical measuring unit 12 disposed inside and a high-voltage power source for applying a predetermined voltage to the photomultiplier tube and an electronic circuit for shaping an output signal from the photomultiplier tube and classifying the wave height are arranged And a cable 14 that electrically connects the measurement unit 12 and the main body unit 13. The main body 13 includes a meter 13a for displaying a measured dose of radiation (γ-rays or X-rays) per unit time (hereinafter referred to as an air dose rate), and a range switch for switching a measurement range of the NaI scintillation detector 10 13b, and an output unit 13c for outputting an analog voltage signal corresponding to the measured air dose rate.

  Here, when radiation such as γ-rays or X-rays is incident on the inside of the NaI crystal 11, high-energy electrons may be emitted due to the interaction between the atoms constituting the NaI crystal 11 and the radiation. The emitted high-energy electrons lose energy while exciting surrounding atoms, but scintillation light is emitted from the excited surrounding atoms. In other words, the kinetic energy of the emitted high-energy electrons is converted into scintillation light. The amount of this scintillation light depends on the magnitude of the kinetic energy of the emitted electrons, and the magnitude of the kinetic energy of the emitted electrons depends on the magnitude of the interaction between the atoms constituting the NaI crystal 11 and the radiation. Dependent. Thus, by measuring the amount of scintillation light emitted from the NaI crystal 11, the magnitude of energy lost inside the crystal due to the interaction of radiation such as γ rays and X-rays with atoms constituting the NaI crystal 11. Can be requested. Specifically, the amount of scintillation light emitted from the NaI crystal 11 is measured by a photomultiplier tube (not shown) optically connected to the NaI crystal 11. The output signal from the photomultiplier tube is signal-processed by an electronic circuit disposed in the main body 13 to obtain the air dose rate. The measured air dose rate is displayed on the meter 13a, and an analog voltage signal (for example, 0 to 10 mV) corresponding to the magnitude of the air dose rate is output from the output unit 13c.

  The interface unit 40 mainly includes an operational amplifier 41 that amplifies the analog voltage signal output from the output unit 13c, and an AD converter 42 that converts the analog voltage signal amplified by the operational amplifier 41 into a digital signal. The operational amplifier 41 amplifies a low voltage analog voltage signal of, for example, 0 to 10 mV to an analog voltage signal of 0 to 10 V.

  A digital signal (hereinafter, referred to as an air dose rate signal) that is AD-converted by the AD converter 42 of the interface unit 40 and that includes information on the current position and an output signal (hereinafter referred to as a GPS signal) that includes information on the current position. , Referred to as a GPS output signal) is input to the data processing system 30. The data processing system 30 extracts information on the current position (measurement position data) from the air dose rate signal and the GPS output signal, and extracts air dose rate data at the position. Then, air dose rate map data (radiation dose rate map data) is created by associating measurement position data (for example, latitude information and longitude information) with air dose rate data, and this is recorded in a text file. In this text file, air dose rate map data (that is, measurement position data and air dose rate data at that position) is additionally updated at intervals of 1 to 10 seconds.

  The text file in which the air dose rate map data is sequentially described is transmitted to the server 90 by the data transmission unit 50. Files placed on the server 90 can also be shared with other users.

  As described above, since the measurement position data and the air dose rate data associated therewith are described in the text file, the air dose rate map can be created using this data. Specifically, for example, a white map may be prepared, and markers (for example, dots, etc.) color-coded according to the magnitude of the air dose rate may be displayed at locations corresponding to the measurement positions on the white map. Alternatively, a contour map may be created.

Further, the measurement position data and the air dose rate data can be combined with electronic map data (for example, Google Earth (registered trademark) of Google). In this case, using the Google Earth (registered trademark) as described above, the air dose rate map in which the markers color-coded according to the size of the air dose rate are displayed on the three-dimensional map (see FIG. 3). ) And an air dose rate map (see FIG. 4) in which markers colored by the size of the air dose rate are displayed on a two-dimensional map can be formed. .
<Outline of KURAMA-II System 100>

  Furthermore, led by the present inventor, the above-described KURAMA system 1 has been improved not only to collect air dose rate data but also to be able to simultaneously measure γ-ray energy, and the following KURAMA-II A system 100 was developed.

  Hereinafter, the KURAMA-II system 100 will be described with reference to FIG. Note that the difference from the above-described KURAMA system 1 will be described, and the same components are denoted by the same reference numerals and description thereof will be omitted.

  As shown in FIG. 5, the KURAMA-II system 100 includes a CsI scintillation detector 110, a GPS unit 20, a data processing system 30, an interface unit 140, a data transmission unit 50, and a controller 160. As will be described later, the interface unit 140 is realized by a Compact RIO system of National Instrument. In the KURAMA system 1 described above, the data processing system 30 is realized by a program that is activated on a lightweight, small notebook personal computer called a netbook. The KURAMA-II system 100 is realized by a program that is activated in a small PC module mounted on the Compact RIO system that constitutes the interface unit 140. The GPS unit 20 and the data transmission unit 50 are also small modules that are attached to the PC module via a USB or the like. The controller 160 is also realized by the same PC module. That is, the KURAMA-II system 100 substantially includes the Compact RIO system, the CsI scintillation detector 110, the GPS unit 20, the data transmission unit 50, and the like that constitute the interface unit 140, the data processing system 30, the controller 160, and the like. And a small module. These devices (units) can be arranged in the same housing. Therefore, compared with the KURAMA system 1, the portability is remarkably excellent, and the user hardly needs to perform connection work of each unit, so that occurrence of troubles such as erroneous connection can be suppressed.

  In the KURAMA-II system 100, a CsI scintillation detector 110 is employed instead of the NaI scintillation detector 10. The reason is as follows. In general, it is known that the interaction between a substance and γ rays increases as the atomic number of the element constituting the substance increases. Here, the atomic number of Na is 11, whereas the atomic number of Cs is 55. Therefore, when comparing the NaI scintillation detector and the CsI scintillation detector, the CsI scintillation detector is more γ-rayed. It can be said that the sensitivity to is high. Therefore, in the KURAMA-II system 100, by adopting the CsI scintillation detector 110 in place of the NaI scintillation detector 10, the entire system is smaller and lighter than the KURAMA system 1 while maintaining the sensitivity to γ rays. I was able to.

  As shown in FIG. 6, the CsI scintillation detector 110 includes a CsI crystal 111, a photomultiplier tube optically connected to the CsI crystal 111, and a light receiving element 112 such as an MPPC (Multi-Pixel Photon Counter). And a pulse signal output unit 113 for outputting a pulse signal output from the light receiving element 112. In the KURAMA-II system 100, MMPC is adopted as the light receiving element 112. MMPC is a small-sized optical semiconductor element that can be used at room temperature, including multiple Geiger mode APD (avalanche photodiode) pixels. It can be operated at a lower voltage than a photomultiplier tube, and the influence of a magnetic field can be reduced. It has excellent characteristics that it is difficult to receive.

  The interface unit 140 includes an amplifier (pulse shaping amplifier) 141 that amplifies the pulse signal output from the pulse signal output unit 113, and an AD converter that converts the output signal (analog signal) of the amplifier 141 into a digital signal (digital value). 142, FPGA 143, and CPU 144. Note that FPGA 143 is an abbreviation for Field Programmable Gate Array, and is an integrated circuit that can be configured by a purchaser or designer after manufacturing. In the KURAMA-II system 100, a Compact RIO system manufactured by National Instrument is adopted as the interface unit 140. The above-described amplifier 141, AD converter 142, FPGA 143, and CPU 144 are mounted as modules mounted in the Compact RIO system. As described above, the CPU 144 is realized by a PC module mounted in the Compact RIO system, and this PC module also serves as the data processing system 30 and the controller 160. Here, the Compact RIO system is a reconfigurable built-in control and acquisition system, and a program for directly controlling each module using the above-described LabVIEW (registered trademark) can be easily created. Further, in the KURAMA-II system 100, by using the FPGA 143, based on the digital signal output from the AD converter 142, the peak height discrimination of the pulse and the noise level discrimination are performed by software. Realized. Information on the peak height of the pulse obtained by the FPGA 143 is sent to the CPU 144, and the CPU 144 creates a pulse wave height spectrum as shown in FIG.

The horizontal channel (CH) of the pulse height spectrum shown in FIG. 7 represents the pulse height, and the vertical axis represents the count number of each CH. Here, the pulse height of the pulse signal output from the pulse signal output unit 113 is proportional to the energy of γ rays lost in the CsI crystal 111. That is, the pulse wave height spectrum shown in FIG. 7 corresponds to the energy spectrum of γ rays. The pulse height spectrum shown in FIG. 7 was measured using a standard source of ¹³⁷ Cs, and a peak seen at a position of about 80 CH is a photoelectric peak of 661.7 keV γ-ray (see FIG. 12). Corresponding to The photoelectric peak is a peak corresponding to a pulse generated when high energy electrons generated by the photoelectric effect lose all energy in the CsI crystal 111. Here, the photoelectric effect refers to the γ-rays disappeared from the atoms instead of the γ-rays disappearing because the total energy of the γ-rays is given to the atoms through the interaction between the atoms constituting the CsI crystal 111 and the γ-rays. A phenomenon in which high-energy electrons with almost the same kinetic energy as the energy of are emitted. In other words, the peak at the position of about 80 CH in FIG. 7 is due to a pulse generated when the total energy of 661.7 keV γ rays emitted from the standard source of ¹³⁷ Cs is lost in the CsI crystal 111. It is a peak.

As described above, the KURAMA-II system 100 is configured not only to measure the air dose rate but also to measure the pulse height spectrum of the output pulse signal from the CsI scintillation detector 110. The energy measurement can be performed simultaneously.
<Improvement of KURAMA-II system 100>

  As described above, in the KURAMA-II system 100, gamma ray energy measurement could be performed, but the obtained energy spectrum is an energy spectrum measured over the entire measurement time, and a plurality of desired measurement sections. As for (hereinafter, also referred to as mesh), the energy spectrum for each mesh could not be obtained. Therefore, in order to enable the KURAMA-II system 100 to perform γ-ray energy measurement across a plurality of measurement sections while moving the KURAMA-II system 100 at a desired speed, the following is described. Improvements were made and the KURAMA-II system 100A was developed.

  Here, in the KURAMA-II system 100 before improvement, the pulse signal output from the pulse signal output unit 113 of the CsI scintillation detector 110 is amplified and shaped by the amplifier 141 and converted into a digital signal by the AD converter 142. Is done. As a result, pulse height data of the pulse peak height (hereinafter referred to as pulse height data) is output from the AD converter 142. Here, the pulse height of the pulse signal output from the pulse signal output unit 113 is proportional to the energy of γ rays lost in the CsI crystal 111. That is, the pulse wave height data includes energy information of γ rays incident on the CsI scintillation detector 110, and the pulse height of the pulse signal output from the pulse signal output unit 113 and the γ rays lost in the CsI crystal 111. By preparing a calibration curve with the energy of γ, it is possible to obtain γ-ray energy information from pulse height data. Utilizing this fact, in the KURAMA-II system 100, based on the digital signal output from the AD converter 142, the pulse height discrimination of the pulse peak height and the noise level discrimination are performed by software based on the FPGA 143. The information on the peak height of the obtained pulse was sent to the CPU 144, and a pulse wave height spectrum as shown in FIG. 7 was produced.

  On the other hand, in the improved KURAMA-II system (hereinafter referred to as KURAMA-II system 100A) according to this embodiment, not only the above-described pulse wave height spectrum but also an AD converter is produced. Each time the pulse wave height data is output from 142, the pulse wave height data, the measurement position data extracted from the GPS output signal at that time, and the time data are associated with each other to create energy spectrum mapping data. Here, the KURAMA-II system 100A modifies the data processing system 30 of the KURAMA-II system 100 so that the measurement position data and the time data can be added to the pulse height data collected at a measurement interval of about 3 to 5 seconds. I have to. The KURAMA-II system 100A thus improved is configured to transmit the obtained energy spectrum mapping data to a predetermined server via a network at a predetermined time interval. Then, after the measurement (or during the measurement), the energy spectrum mapping data accumulated in the server is sorted by the measurement position data and / or time data, thereby building an energy spectrum at a desired position and / or time. It has become possible.

  The improved KURAMA-II system 100A is installed in a route bus that runs in the center of Fukushima city, and energy spectrum mapping data is acquired for 11 days from April 20th to April 30th, 2013. A demonstration experiment was conducted. And the energy spectrum was reconfigure | reconstructed for every mesh (refer FIG. 8) which divided | segmented the center part of Fukushima city by 1 km mesh from the acquired energy spectrum mapping data. In this demonstration experiment, the energy spectrum mapping data acquired by the KURAMA-II system 100A was accumulated in the SQL database, sqlite, with the addition of spatialite for expanding the function of geographic information processing. The accumulated data was extracted for each third area section (corresponding to about 1 km section) of the Ministry of Internal Affairs and Communications, and an energy spectrum was constructed.

  Here, the installation position of the KURAMA-II system 100A in the route bus is determined to be the rear rear seat center line side in the vehicle. Although a verification experiment was performed using a plurality of KURAMA-II systems 100A mounted on a plurality of route buses, since all the KURAMA-II systems 100A are installed at substantially the same position in the route buses, the above measurement is performed. It can be said that almost the same measurement conditions are maintained over the period. Thereby, energy spectrum mapping data obtained from a plurality of KURAMA-II systems 100A can be integrated.

In the mesh (see Fig. 8) in the center of Fukushima City, accumulated data of about 11 hours is obtained between April 20th and April 30th 2013, and the energy spectrum shown in Fig. 9 is reconstructed. I was able to. In the energy spectrum shown in FIG. 9, peaks derived from ¹³⁷ Cs, ¹³⁴ Cs, and ⁴⁰ K gamma rays can be discriminated, and the abundance ratio of natural nuclides and accident-derived nuclides in this region can be estimated. I understood. As shown in FIG. 10, γ-rays having an energy of 1460.8 keV are emitted from ⁴⁰ K with a probability of 10.7 per 100 decays. Further, as shown in FIG. 11, γ-rays with an energy of 795.8 keV are emitted from ¹³⁴ Cs with a probability of 85.4 per 100 decays, and γ-rays with an energy of 604.7 keV are 97.97 per 100 decays. It is emitted with a probability of 6 times, and gamma rays with an energy of 1365.2 keV are emitted with a probability of 3.04 times per 100 decays. Further, as shown in FIG. 12, ¹³⁷ Cs emits γ-rays having an energy of 661.7 keV with a probability of 85.1 times per 100 decays.

  As described above, in the demonstration experiment, it was found that the energy spectrum in the mesh can be reconstructed by extracting the data corresponding to the specific mesh from the obtained energy spectrum mapping data. Furthermore, the energy spectrum mapping data includes not only measurement position data but also time data. Therefore, it is possible to reconstruct the energy spectrum measured at a specific time by sorting using time data. Alternatively, it is possible to reconstruct an energy spectrum measured with a specific mesh at a specific time by sorting using both time data and measurement position data. For example, an energy spectrum in a specific mesh can be created every day. In this case, the fluctuation of the energy spectrum in the mesh every day can be examined.

  As described above, by adding the measurement position data and time data to the pulse height data as energy spectrum mapping data, the energy spectrum at a desired time and / or location can be reconstructed. Thus, for example, when the KURAMA-II system 100A is mounted on a mobile that periodically circulates a predetermined route, for example, when the KURAMA-II system 100A is mounted on a route bus, various times can be selected depending on the purpose. The energy spectrum in the measurement compartment can be freely reconstructed.

  In addition, when the energy spectrum is measured at each measurement point for each mesh as in the conventional method and the measurement is repeated after moving to the next measurement point after acquiring the energy spectrum, It was necessary to occupy the equipment. In this case, since the measurement is limited to the measurement at the representative point in the mesh, if the selection of the representative point is wrong, there is a possibility that the data may not be suitable as the representative value of the mesh range. On the other hand, when the KURAMA-II system 100A according to the present embodiment is used, measurement can be performed while moving in the mesh. Therefore, it is possible to use measurement data at a plurality of points in the mesh, and it is considered that data close to average characteristics in the mesh can be obtained.

  In addition, for example, when the KURAMA-II system 100A is mounted on a route bus and measurement is performed along the route of the route bus, the γ dose may fluctuate rapidly at a certain point. For example, an actual example is that a patient who has been administered a radiopharmaceutical to perform positron emission tomography (PET diagnosis) returns home using a route bus. In this case, the γ-ray dose inside the route bus increases rapidly from when the patient who received the radiopharmaceutical gets on the route bus equipped with the KURAMA-II system 100A until it gets off the route bus. Become.

  Even in such a case, when the KURAMA-II system 100A according to the present embodiment is used, a change in the energy spectrum for each desired time can be followed. As a result, it is possible to remove data in a section in which the γ dose increases rapidly, and to remove the influence of γ rays emitted from a patient who has been administered a radiopharmaceutical. As described above, when the KURAMA-II system 100A according to the present embodiment is used, if any change occurs in the energy spectrum, the energy spectrum for each desired time or each desired measurement section is obtained. It can be configured to track changes in the energy spectrum. As a result, it is easy to determine the cause of the abnormality, and if necessary, the data of the period (or measurement section) in which the abnormality has occurred can be removed, and the measurement data can be effectively used without wasting it. Can be used. Alternatively, when the decontamination work is performed, it becomes easy to compare the energy spectra before and after the decontamination work in the section where the decontamination work is performed, and the decontamination effect can be easily verified. In addition, when a new hot spot (point where the air dose rate is high) is generated, it is easy to find out when and where the hot spot has occurred.

  In the above description, the NaI scintillation detector 10 or the CsI scintillation detector 110 has been described as an example of the radiation measuring instrument for measuring the air dose rate. However, the present invention is not limited to such a configuration, and any radiation measuring instrument can be used as long as the energy spectrum of γ rays can be measured. For example, not only solid scintillation detectors such as NaI scintillation detectors and CsI scintillation detectors, but also semiconductor detectors such as Ge detectors can be used. Here, a semiconductor detector such as a Ge detector has an advantage that sensitivity to γ rays is high to some extent and energy resolution is also high. However, it is difficult to handle, for example, it is necessary to continue cooling with liquid nitrogen during measurement, or a very complicated electronic circuit is required to extract and process the signal from the detector. On the other hand, the solid scintillation detector is easy to handle and is preferable as a radiation measuring instrument used in the present invention.

  In the above description, the interface unit 140 amplifies the pulse signal output from the pulse signal output unit 113 (pulse shaping amplifier) 141, and the output signal (analog signal) of the amplifier 141 is a digital signal (digital value). The AD converter 142, the FPGA 143, and the CPU 144 for converting the signal into the analog R / A converter, and the amplifier 141, the AD converter 142, the FPGA 143, and the CPU 144 are mounted as modules mounted in the Compact RIO system. The present invention is not limited to this, and can have any configuration as necessary. For example, when an amplifier and an ADC are incorporated in the CsI scintillation detector, a digital signal converted by the ADC is output from the CsI scintillation detector. In such a configuration, the interface unit 140 may be configured to generate energy spectrum mapping data based on a digital signal output from the CsI scintillation detector. For example, C12137 manufactured by Hamamatsu Photoelectronics Co., Ltd. is configured such that an amplifier and an ADC are incorporated in a CsI scintillation detector, and an output signal of the ADC is output via USB. It is also possible to employ such a detector.

  In the above description, an embedded PC module mounted on the Compact RIO system is used as the data processing system 30, and the data processing system 30 and other devices (for example, the data transmission unit 50 and the GPS unit 20) are data. It was provided as a device independent of the processing system 30. However, the present invention is not limited to this, and in order to further reduce the size and weight of the KURAMA-II system 100A, some or all of the constituent parts constituting the KURAMA-II system 100A may be integrally formed. Good. For example, a module in which the GPS unit 20 and the data transmission unit 50 are incorporated may be produced and incorporated in a Compact RIO system that constitutes the interface unit 140 and the like. In the above description, the data processing system 30, the CPU 144, and the controller 160 are realized by one PC module mounted on the Compact RIO system. However, the present invention is not necessarily limited to such a configuration. . For example, the controller 160, the CPU 144, and the data processing system 30 may be realized by independent PC modules. In addition, a compact computer including a CPU is also mounted on the chassis of the Compact RIO system in which a module is inserted and removed, and each module is controlled by a small computer included in the chassis without necessarily using a PC module. Is possible. A part or all of the controller 160, the CPU 144, and the data processing system 30 described above can be realized by a small computer included in the chassis. In the above description, the measured energy spectrum mapping data is transmitted to a predetermined server such as an SQL database via the network. However, the present invention is not limited to such a configuration. For example, the measured energy spectrum mapping data may be stored in a memory means (semiconductor memory, HDD, or the like) included in the computer constituting the controller 160, and is included in a computer different from the computer constituting the controller 160. It may be stored in a memory means.

  Further, in the above description, the interface unit 140 and the CsI scintillation detector 110 are arranged inside one housing, but the present invention is not necessarily limited to such a configuration, and these are independent. It may be provided. In addition, the interface unit 140, the data processing system 30, and the controller 160 of the present invention do not necessarily need to adopt a Compact RIO system manufactured by National Instrument, and may adopt any system as necessary.

  As another use of the KURAMA-II system 100A according to the present embodiment, application to agriculture can be considered. Along with radioactive material leakage accidents that occurred at the Fukushima Daiichi Nuclear Power Station, shipments of agricultural products have been suspended due to the contamination of radioactive materials often exceeding the standard value. This is because radioactive cesium in the soil migrates to the edible part of the crop, and suppressing this migration is an extremely important issue for providing safe food. It has been found that the amount of radioactive cesium migrating to the edible part of the crop does not necessarily depend solely on the amount of cesium in the soil. For example, in rice and the like, it is known that the amount of radioactive cesium transferred to the edible part depends not only on the cesium concentration in the soil but also on the potassium concentration, and the radioactive cesium concentration in the soil, and It is required to accurately measure both potassium concentrations. However, in the past, it was necessary to obtain a soil sample and check the concentration of radioactive cesium contained in the soil and the concentration of potassium in the soil. It was difficult to do.

On the other hand, the KURAMA-II system 100A according to the present embodiment can be configured to be driven by a battery as a configuration for walking, and can also use high-precision DGPS (differential GPS) as GPS. . The KURAMA-II system 100A configured for walking is light in weight and excellent in portability, and can be measured while walking on the farmland on a person's back. Alternatively, it can be mounted on an agricultural machine such as a field cultivator. At this time, by using DGPS, it is possible to measure a change in position accompanying a low-speed movement such as walking with sufficient resolution. By using such a KURAMA-II system 100A configured for walking, it is possible to easily grasp the distribution state of radioactive cesium in farmland. Here, potassium contains about 30 Bq of natural radioisotope potassium ⁴⁰ K per gram. It is known that ⁴⁰ K captures orbital electrons and decays to ⁴⁰ Ar with a probability of 10.7 times per 100 decays (see FIG. 10). ^{When 40} K decays to ⁴⁰ Ar, 1460.9 keV γ-rays are emitted, so the concentration of ⁴⁰ K in the soil (and hence the potassium concentration in the soil) can be measured from the amount of γ-rays. it can. Therefore, in the farmland sprayed with potassium, by measuring the energy spectrum of γ rays using the KURAMA-II system 100A configured for walking as described above, not only the distribution of radioactive cesium in the farmland, The distribution situation of potassium can also be grasped at the same time. In other words, it is possible to grasp the situation of the ratio of potassium and cesium in the farmland. If decontamination and additional fertilization of potassium are performed based on these, it can greatly contribute to reducing the migration of radioactive cesium to crops.

1 KURAMA system 10 NaI scintillation detector 20 GPS unit 30 data processing system 40 interface unit 100 KURAMA-II system 100A improved KURAMA-II system 110 CsI scintillation detector 140 interface unit

Claims (4)

A method for measuring the energy spectrum of gamma rays,
installing a gamma ray detector;
Extracting energy information of γ rays incident on the γ ray detector from the output from the γ ray detector;
Obtaining current position information and current time information corresponding to the time when the γ-rays are incident on the γ-ray detector;
Storing the γ-ray energy information, the current position information, and the time information in association with each other;
A gamma ray energy spectrum measurement method comprising: The γ-ray detector is mounted on a moving body,
The extraction of the energy information of the γ-ray and the acquisition of the current position information and the current position information are performed while the moving body is moving. The gamma ray energy spectrum measuring method as described.   The γ-ray energy spectrum measurement method according to claim 1, wherein the γ-ray detector is a CsI scintillation detector. The energy spectrum measurement method according to claim 1, wherein the current position information is acquired using a differential GPS.

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