JP3153484B2 - Environmental radiation monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environmental radiation monitor used for monitoring environmental radiation, and more particularly to a technique for energy calibration in an environmental radiation monitor.

[0002]

2. Description of the Related Art In a radiation handling facility such as a nuclear power plant, environmental radiation is monitored (monitored) around the facility to protect the public from radiation. For such monitoring, a measuring device called an environmental radiation monitor is installed around the facility.

One type of environmental radiation monitor is NaI.
(Tl) Radiation (γ
There are devices that detect and continuously measure and record the dose rate and dose equivalent rate. This apparatus calculates a dose rate and the like by sequentially adding radiations after weighting them according to their energies and then adding them. More specifically, in this device, the light emission of the scintillator due to the incidence of radiation is converted into an electrical detection pulse by a photomultiplier tube, and the detection pulse is weighted according to the wave height and counted. This is based on the fact that the wave height of the detection pulse corresponds to the energy of the incident radiation.

In such an environmental radiation monitor, the measurement result is obtained by weighting the incident radiation according to the energy. Therefore, in order to obtain a correct measurement result, the energy of the incident radiation must be correctly detected, that is, the incident radiation must be detected. It is necessary to obtain a detection pulse correctly corresponding to the energy.

However, the NaI (Tl) scintillator has a luminescence characteristic that varies with temperature. Therefore, even when the same radiation (radiation having the same radiation type and energy) is incident, the amount of luminescence varies depending on the temperature of the scintillator. The pulse height of the pulse also differs. The characteristics of the photomultiplier also slightly change depending on the temperature. As a result,
In an environmental radiation monitor, an error occurs in energy evaluation of incident radiation due to a change in the temperature of the environment, and as a result, an error may occur in a measurement result such as a dose rate. For this reason, in a conventional environmental radiation monitor, for example, a gain of the preamplifier circuit is adjusted according to the temperature by providing a temperature sensor such as a thermistor in a preamplifier circuit connected to the subsequent stage of the photomultiplier tube. , Thereby performing energy calibration. The error in the energy evaluation due to the temperature is a problem that occurs not only in a detector using a NaI (Tl) scintillator but also in a detector using another scintillator, a semiconductor detector, or the like.

In this conventional method, energy calibration is performed based on the changing characteristics of the thermistor.
(Tl) It is actually difficult to obtain a thermistor capable of completely compensating for the temperature characteristics of the scintillator and the photomultiplier tube, and the accuracy of calibration is limited. Further, NaI (T
l) The temperature characteristics of the scintillator slightly change due to aging, but it has conventionally been difficult to improve deterioration of the calibration accuracy due to such aging.

Accordingly, the present applicant has filed a Japanese Patent Application No. Hei 8-1250.
No. 91 proposed a new energy calibration method instead of the conventional method. In this method, an energy spectrum of environmental radiation is obtained in parallel with a normal monitoring process, and energy calibration is performed based on this spectrum. Specifically, from the energy spectrum, ⁴⁰ K (potassium 4) which is a natural radionuclide relatively abundant in the environment
0) and ²⁰⁸ Tl (thallium 208) are detected, and the gain of the circuit system (that is, the gain of the amplifier, the voltage applied to the photomultiplier, etc.) is adjusted so that this peak always comes to the correct channel. In this method, for example, since the gain of the circuit system is adjusted at predetermined time intervals in parallel with the normal measurement processing, high-precision energy calibration can be performed for both temperature change and aging change.

[0008]

However, with this new calibration method, there is a possibility that erroneous energy calibration may be performed when an abnormality such as leakage of an artificial radionuclide from a facility occurs. That is, in the above-mentioned new method, when an artificial radionuclide peak appears in the energy spectrum in the vicinity of the photoelectric peak of ⁴⁰ K or ²⁰⁸ Tl used as a calibration standard, the peak of the artificial radionuclide is mistakenly added to the peak. The gain may be adjusted based on the gain, and as a result, the error may be rather increased.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and in an environmental radiation monitor that performs energy calibration based on an energy spectrum, prevents erroneous energy calibration when the radiation state of the environment is abnormal. The purpose is to do.

[0010]

In order to achieve the above-mentioned object, an environmental radiation monitor according to the present invention comprises: a wave height analyzing means for wave height analyzing a detection pulse output from a radiation detector to obtain an energy spectrum; Spectrum-based calibration means for performing energy calibration based on a peak related to a predetermined natural radionuclide in the determined energy spectrum, and abnormality determination means for determining whether the state of environmental radiation is normal or abnormal based on environmental radiation measurement results, A calibration control unit that stops the energy calibration process by the spectrum use calibration unit when it is determined that the radiation is abnormal.

In this calibration, the radiation detector is a detector that detects radiation and outputs an electrical detection pulse, such as a probe including a scintillator and a photomultiplier, a semiconductor detector, and the like.

In this configuration, the abnormality determining means determines whether the radiation state of the environment is normal or abnormal based on the measurement result of the environmental radiation, that is, the environmental radiation dose and the energy spectrum. And, as a result of this determination, when the radiation state of the environment is determined to be abnormal, by stopping the energy calibration process based on the peak of the predetermined natural radionuclide in the energy spectrum, erroneous energy due to the influence of the artificial radionuclide Calibration can be prevented.

Further, the environmental radiation monitor according to the present invention comprises:
Pulse height analysis means for obtaining an energy spectrum by performing a pulse height analysis on a detection pulse output from a radiation detector, spectrum-based calibration means for performing energy calibration based on a peak relating to a predetermined natural radionuclide in the obtained energy spectrum, and radiation detection. Temperature detecting means for detecting the temperature of the detector, a temperature calibration table in which a calibration coefficient corresponding to each temperature is set, and a calibration coefficient corresponding to the temperature of the radiation detector are searched from the temperature calibration table, and this calibration coefficient is Temperature-based calibration means for performing energy calibration using
Abnormality determining means for determining whether the state of environmental radiation is normal or abnormal based on the measurement result of environmental radiation, and when it is determined to be normal, make the spectrum use calibrating means perform energy calibration, and when it is determined to be abnormal Is characterized by having calibration control means for causing the temperature utilization calibration means to perform energy calibration.

In this configuration, as means for energy calibration, in addition to spectrum-based calibration means for performing energy calibration based on a predetermined peak of the energy spectrum, temperature-based calibration for performing energy calibration according to the temperature of the radiation detector. Having means. Here, the temperature-using calibration unit reads a calibration coefficient corresponding to the temperature of the radiation detector from the temperature calibration table, and performs energy calibration using the calibration coefficient. Specifically, the calibration is performed by a method such as changing the gain of the amplifier according to the calibration coefficient. The spectrum-based calibration means may perform erroneous calibration when the radiation condition of the environment becomes abnormal, such as leakage of artificial radionuclides from facilities, instead of being able to perform high-precision calibration. . Temperature utilization calibration means
Although the accuracy of the calibration is lower than that of the spectrum-based calibration means, no malfunction occurs even when the radiation condition of the environment is abnormal. Therefore, in this configuration, the abnormality determination means determines whether the radiation state of the environment is normal or abnormal, and if it is normal, performs highly accurate energy calibration using the energy spectrum. Then, the calibration based on the energy spectrum is stopped, and the energy calibration is performed based on the temperature of the radiation detector. According to this configuration,
If the radiation condition of the environment is normal, high-precision energy calibration can be performed by the spectrum-based calibration means.If the radiation condition of the environment becomes abnormal, the accuracy will be slightly reduced, but the radiation condition of the environment will be affected. Since energy calibration is performed by the temperature-based calibration means that is not performed, erroneous calibration processing that widens the error is not performed.

In a preferred aspect of the present invention, when energy calibration is performed by the spectrum-based calibration means, a calibration coefficient in the calibration is obtained, and the temperature calibration is performed based on the calibration coefficient and the temperature detected by the temperature detection means. A table updating means for updating the setting contents of the table is provided.

For this reason, in the present configuration, when the radiation condition of the environment is normal, every time energy calibration is performed by the spectrum utilization calibration means, a calibration coefficient in the calibration process is obtained, and the temperature of the radiation detector at that time is obtained. Is obtained from the temperature detecting means, and the temperature calibration table is updated with the obtained information on the calibration coefficient and the temperature. According to this configuration, the temperature calibration table can be updated according to the temporal change of the temperature characteristic of the radiation detector, and the accuracy of energy calibration based on temperature can be maintained.

In another aspect of the present invention, the abnormality judging means makes an abnormality judgment based on a judgment criterion in consideration of a condition relating to a concentration change of radon and thoron in the atmosphere.

[0018] Generally, natural variations in the radiation state of the environment is caused by density variation of radon ⁽²²² Rn) and thoron ⁽²²⁰ Rn) which is a natural radioactive nuclides mainly present in the atmosphere. Therefore, in the present configuration, by performing the abnormality determination based on the determination criterion including the condition of the concentration change of radon and thoron, it is possible to perform a more precise abnormality determination in consideration of the natural fluctuation of the environmental radiation.

In another aspect of the present invention, the abnormality determining means has a plurality of determination criteria corresponding to each weather condition, and performs an abnormality determination using the determination criteria corresponding to the weather condition. Since the ratio of the concentration change of radon and thoron in the atmosphere changes depending on weather conditions such as fine weather and rainfall, in this configuration, the criteria for abnormality determination are set separately for each weather condition, and By properly using these determination conditions, more detailed abnormality determination can be performed.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an environmental radiation monitor according to the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram showing the overall configuration of an environmental radiation monitor according to the present invention.

The environmental radiation monitor shown in FIG. 1 is mainly intended for monitoring gamma rays in the environment.
A NaI (Tl) scintillator 12 having good sensitivity to γ-rays is provided as a detector. The NaI (Tl) scintillator 12 emits light in an amount corresponding to the energy that the incident radiation has lost inside the scintillator. A high bias voltage is applied to the photomultiplier tube 14 from a high voltage power supply (HV) 16, and the light emission of the NaI (Tl) scintillator 12 is converted into an electrical detection pulse having a wave height corresponding to the light emission amount. Convert and output. This detection pulse is applied to the preamplifier 1 provided near the photomultiplier tube 14.
At 8 the pulse is converted to a low impedance pulse. The NaI (Tl) scintillator 12, the photomultiplier tube 14, and the preamplifier 18 constitute a main part of the probe unit 10.

The detection pulse output from the preamplifier 18 is proportionally amplified by the main amplifier 20. In the present embodiment, the main amplifier 20 is a variable gain amplifier. The detection pulse amplified by the main amplifier 20 is converted into a digital signal corresponding to the pulse height by the pulse height analyzer 22. This wave height analyzer 22 is, for example, an A / D (analog
A digital) conversion circuit can also be used. The digital signal output from the wave height analyzer 22 is input to a DSP (Digital Signal Processor) 24. DSP2
4 is provided with a conversion table for converting the wave height of the detection pulse (that is, the energy of the incident radiation) into a predetermined unit such as a dose, and converts the digital signal input from the wave height analyzer 22 into a predetermined value by the conversion table. Convert to unit and output. The dose calculator 26 tallies the outputs of the DSP 24 and calculates values such as a dose rate and a dose equivalent rate. Then, the calculation result is recorded / stored in a predetermined recording medium by the output unit 28 or displayed and output on a display device.

The above is the configuration of the part relating to the dose monitoring of the environmental radiation monitor of the present embodiment. Next, a part related to energy calibration will be described.

In this embodiment, there are two systems for energy calibration, one using the energy spectrum of environmental radiation and the other using the temperature detection result of the probe unit 10. The calibration process based on the energy spectrum is realized by the spectrum memory 30, the spectrum utilization calibration processing unit 32, and the reference value memory 34. The calibration process based on the temperature is performed by the temperature sensor 40, the A / D converter 42, and the temperature utilization calibration processing unit. 44 and temperature calibration table 4
6 is realized. In the present embodiment, the two systems of energy calibration means are switched and controlled by the calibration control unit 52, and an appropriate calibration means is always operated. In the present embodiment, a correct measurement result is obtained by performing such an energy calibration process every predetermined time.

First, the calibration process based on the energy spectrum will be described. The spectrum memory 30 has a plurality of channels corresponding to each wave height (ie, radiation energy). Each time a digital signal is input from the wave height analyzer 22, the spectrum memory 30 adds a count to a channel corresponding to the wave height indicated by the digital signal. By continuing this process for a predetermined time, a peak height distribution of the environmental radiation, that is, an energy spectrum is formed in the spectrum memory 30. Here, the predetermined time for the formation of the energy spectrum is preferably about 10 to 20 minutes according to the experiment of the inventor. FIG. 2 shows an example of the energy spectrum thus formed. When the radiation state of the environment is normal, that is, when there is no leakage of the artificial radionuclide from the facility, as shown in FIG. 2, the energy spectrum of the environmental radiation shows the natural abundance which is relatively abundant in the environment. Photoelectric peaks (total absorption peaks) corresponding to radionuclides of ⁴⁰ K and ²⁰⁸ Tl are observed. Incidentally, the energy of the photopeak at ⁴⁰ K is 1.46 MeV, and the energy of the photopeak at ²⁰⁸ Tl is 2.6 MeV.

The spectrum use calibration processing unit 32 uses the energy spectrum stored in the spectrum memory 30
Energy calibration is performed by detecting a photoelectric peak of ⁴⁰ K or ²⁰⁸ Tl and adjusting the gain of the main amplifier 20 so that the photoelectric peak comes to the correct channel (ie, energy). The specific processing procedure for this energy calibration may be the same as that described in the aforementioned Japanese Patent Application No. 8-125091. In brief, the spectrum-based calibration processing unit 32 determines a predetermined search range (for example, a predetermined range) of the energy spectrum obtained from the spectrum memory 30.
^{In the} case of 40K, a point at which the count value becomes maximum in the range of a predetermined number of channels near 1.46 MeV) is determined as a peak, and the channel of this peak is determined. Reference value memory 3
In 4, a correct energy value of a photoelectric peak of ⁴⁰ K or ²⁰⁸ Tl or a channel value corresponding to this energy value is registered as a reference value. Spectrum-based calibration processing unit 32
Compares the channel value of the peak detected from the energy spectrum with the reference value read from the reference value memory 34. If the two do not match, the main amplifier is adjusted so that the peak comes to the correct channel (that is, the reference value). Adjust the gain command signal to 20. As a result, the main amplifier 20
, A detection pulse having a wave height corresponding to the energy of the incident radiation is output, and energy calibration is realized.

Next, the calibration process based on the temperature will be described. In this embodiment, the probe unit 10 is provided with a temperature sensor 40, and a temperature signal output from the temperature sensor 40 is converted into an A / D converter 42. Is converted into digital data and input to the temperature use calibration processing unit 44. In the temperature calibration table 46, calibration coefficients corresponding to each temperature are set as shown in FIG. In the example of FIG. 3, when the appropriate gain of the main amplifier 20 at the reference temperature (20 ° C.) is defined as a unit (that is, 1.0), the relative value of the appropriate gain at each temperature is used as the calibration coefficient. This temperature calibration table 46 is constructed on a rewritable medium.
The temperature calibration table 46 is shipped after the value is set at the factory according to the inspection, and thereafter, the setting content is updated as the user uses it. The details of the table updating process will be described later. The temperature use calibration processing unit 44 reads a calibration coefficient corresponding to the temperature detected by the temperature sensor 40 from the temperature calibration table 46, and adjusts the gain of the main amplifier 20 according to the calibration coefficient. By the above-described calibration processing, the detection pulse output from the main amplifier 20 has a wave height that properly corresponds to the energy of the incident radiation.

Next, a description will be given of the procedure of selectively using these two types of energy calibrating means and controlling the switching thereof. In the present embodiment, it is determined whether the radiation state of the environment is normal or abnormal, and the energy calibration means is switched and operated according to the result of the determination. That is, the abnormality determination unit 50
Analyzes the dose rate, the energy spectrum, and the like, determines whether the radiation state of the environment is normal or abnormal, and operates the spectrum-based calibration processing unit 32 if the radiation state is normal; To work. Memory 54
Stores reference values and past data used in the determination process in the abnormality determination unit 50.

The table updating unit 60 updates the setting contents of the temperature calibration table 46 by using the result of the energy calibration process performed repeatedly. This table update process
This is performed based on the result of the calibration process of the spectrum-based calibration processing unit 32 when the radiation state of the environment is normal. That is, the spectrum-based calibration processing unit 32 converts the gain of the main amplifier 20 adjusted in the energy calibration process into a calibration coefficient, and notifies the table updating unit 60 of this. The table updating unit 60 receives the calibration coefficient from the spectrum use calibration processing unit 32, receives the temperature of the probe unit 10 at that time from the temperature sensor 40, and sets the value of the calibration coefficient in the column corresponding to the temperature in the temperature calibration table 46. To
The calibration coefficient received from the spectrum use calibration processing unit 32 is rewritten. Through such processing, the temperature calibration table 46 is updated every time the spectrum use calibration processing unit 32 performs the calibration processing. In the present embodiment, since the setting contents of the temperature calibration table 46 can be updated with time, the energy calibration processing based on temperature can also follow the time-dependent change of the characteristics of the detector and the like. Calibration can be performed with good accuracy.

FIG. 4 is a flowchart showing the procedure of the switching control of the energy calibration means. Less than,
This procedure will be described in more detail with reference to FIGS.

In the present embodiment, a process for energy calibration is executed in parallel with a normal monitoring process such as measurement of a dose rate. In the energy calibration process, first,
The measurement of the energy spectrum (S10) is performed. That is, the analysis results of the pulse height analyzer 22 are sequentially accumulated in the spectrum memory 30, and an energy spectrum is formed in the spectrum memory 30 by accumulation for a predetermined period of time (for example, 10 to 20 minutes). In parallel with this, the DSP 24, based on the analysis result of the pulse height analyzer 22,
The dose calculation unit 26 performs a dose evaluation, that is, a calculation process of a dose rate or the like (S12). The process of S12 is
This is performed as a process for normal monitoring. This dose evaluation may be performed based on the energy spectrum. Hereinafter, data such as the dose rate for dose evaluation is referred to as dose data.

When the measurement of the energy spectrum is completed, the abnormality judging section 50 starts the judgment processing for the radiation state of the environment. First, the abnormality determination unit 50 receives the calculation result of the dose data from the dose calculation unit 26, and determines whether the environmental dose data is within the range of the statistical fluctuation (S14).
Whether the value is within the range of the statistical fluctuation is determined based on the average and standard deviation of the past normal dose data stored in the memory 54, and a threshold value indicating the statistical fluctuation range is set. It is determined by comparing with a value. The result of this determination is passed to the calibration control unit 52. If it is determined that the radiation state is within the range of the statistical fluctuation, the radiation state of the environment is normal, and the calibration control unit 52 operates the spectrum use calibration processing unit 32 to perform the energy calibration (S1).
6). When the energy calibration by the spectrum use calibration processing unit 32 is completed, the calibration control unit 52 operates the table updating unit 60 to update the temperature calibration table 46 (S18).

If the determination in S14 is not within the range of the statistical fluctuation, it is next determined whether or not the state fluctuation of the environmental radiation exceeding the statistical fluctuation range is a fluctuation in the natural world (S14).
20). The main cause of natural variations in the radiation condition, because the concentration fluctuation of their daughters and radon in the air ⁽²²² Rn) and thoron ⁽²²⁰ Rn), in S20, are representative daughter radon-Tron ²¹⁴ Bi (bismuth 214)
The determination is made by focusing on the photoelectric peaks (1.764 MeV and 609 keV). That is, the abnormality determination unit 50 calculates the sum of the count values in a range of a predetermined channel before and after 1.764 MeV in the energy spectrum, and 609 k
The sum of the count values in the range of the predetermined channels before and after eV is obtained, and these are compared with the respective values at the time of the previous calibration processing. The values at the time of the previous calibration processing are stored in the memory 54 together with the time of the previous calibration processing. The determination is made, for example, based on whether or not the rate of increase of the count value of the both channel ranges with respect to the previous value is within the range of the rate of increase of the Radon-Tron component in nature, which is empirically known. If the rate of increase of one of the channel ranges exceeds the range of the natural rate of increase, it is determined that there is no fluctuation in the natural world.
The increase rate can be obtained from the difference between the count numbers and the time difference between the previous calibration process and the current time. In addition to this determination, it is possible to make a more detailed determination by checking whether the rate of increase of the count value in both channel ranges is about the same. In other words, in the case of a natural increase in Radon / Tron, the rate of increase in the count value in both channel ranges is about the same, so that the difference between the rate of increase in both channels is compared with a predetermined threshold value. Can be determined not to be a change in the natural world.

If it is determined in step S20 that there is no change in the natural world, the radiation state of the current environment can be determined to be abnormal, so the calibration control unit 52 operates the temperature use calibration processing unit 44 to operate the temperature utilization calibration processing unit 44. A calibration process based on the temperature is performed (S28). At this time, the temperature utilization calibration processing unit 44
Performs a calibration process based on the temperature calibration table 46 which is updated momentarily in the process of S18.

On the other hand, if it is determined in S20 that the change is in the natural world, the abnormality determination unit 50 further determines whether the weather condition of the environment is raining or clear (S22). That is, the abnormality determination unit 50 determines the current weather condition based on weather information data received from a rain gauge attached to the environmental radiation monitor or a weather observation device in the facility. As a result of this determination, when it is determined that the weather is clear (or cloudy), it is determined whether the current dose data used in the determination of S14 is within the fluctuation range of fine weather as viewed from the average of the past dose data. Is determined (S2
4). Experience has shown that the range of fluctuations in the dose of environmental radiation caused by radon and thoron in the atmosphere when the weather is clear is 1-2 nGy.
/ H (nano gray per hour). Therefore, in this step, the threshold value is determined by adding the maximum value of the statistical variation and the maximum value of the variation due to the radon thoron (for example, 2 nGy / h) to the past average of the dose data, It is determined whether the threshold is exceeded. If the current dose data exceeds the threshold value, it means that the radiation of the current environment has increased beyond the natural fluctuation range, and the radiation state of the environment is determined to be abnormal. Therefore, in this case, an energy calibration process based on the temperature is performed in S28. If it is determined in S24 that the value is equal to or less than the threshold value, that is, if it is within the fluctuation range in fine weather, the state of the environmental radiation is within the range of natural fluctuation, and it can be determined that it is normal. Therefore, in this case, the process proceeds to S16, where the energy calibration process based on the energy spectrum is performed, and the temperature calibration table 46 is updated.

If it is determined in S22 that rain is occurring, it is determined whether or not the current dose data is within the range of variation during rain as seen from the average of past dose data (S26). . It has been empirically known that the range of dose variation due to radon thoron during rainfall is 5 to 6 nGy / h. Therefore, in this step, the threshold value is determined by adding the maximum value of the statistical variation and the maximum value of the variation due to the radon thoron (for example, 2 nGy / h) to the past average of the dose data, It is determined whether the threshold is exceeded. If the result of the determination indicates that the dose data exceeds the threshold value, an energy calibration process based on the temperature is performed (S28), and if the dose data does not exceed the threshold value, a calibration process based on the energy spectrum (S1).
6) and update processing of the temperature calibration table (S18).

The flow of the energy calibration process according to the present embodiment has been described above. In this embodiment, an accurate measurement result can be always obtained by repeating such a process after a predetermined time interval.

In this embodiment, the dose calculation unit 2
6. The spectrum-based calibration processing unit 32, the temperature-based calibration processing unit 44, the abnormality determination unit 50, the calibration control unit 52, and the table updating unit 60 can be implemented by software, for example. That is, each of these units can be realized by causing a CPU to execute a program describing each function. Of course, each of these units may be constructed as a hardware circuit.

As described above, according to the present embodiment, energy calibration can be performed by selecting an appropriate calibration means in accordance with the state of environmental radiation, so that erroneous energy calibration due to the influence of artificial radionuclides can be performed. In addition to the above, it is possible to perform the energy calibration process based on the temperature even at the time of abnormality.

In the above-described embodiment, the energy calibration is performed by adjusting the gain of the main amplifier 20. However, the present invention is not limited to this. For example, the gain of the preamplifier 18 may be adjusted or the high-voltage power supply 16 applied to the photomultiplier 14 may be adjusted. Calibration may be performed by voltage adjustment or the like.

In the above embodiment, when the radiation state of the environment is abnormal, the energy calibration based on the temperature is performed. However, when the radiation state of the environment is abnormal, the energy calibration process simply based on the energy spectrum is stopped. By itself, the effect of avoiding an increase in error due to incorrect calibration processing can be obtained.

In the above embodiment, Na is used as the detector.
Although an example of a configuration using an I (Tl) scintillator has been described, the present invention is applicable not only to the case where another scintillator is used, but also to the case where a detector other than the scintillator (for example, a semiconductor detector) is used. It is possible.

[0044]

As described above, according to the present invention,
When the radiation state of the environment is determined to be abnormal, the energy calibration process based on the energy spectrum is not performed, so that erroneous energy calibration that increases an error in the measurement result can be prevented.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing an overall configuration of an environmental radiation monitor according to the present invention.

FIG. 2 is a diagram illustrating an example of an energy spectrum of environmental radiation.

FIG. 3 is a diagram showing an example of setting contents of a temperature calibration table.

FIG. 4 is a flowchart illustrating a procedure of an energy calibration process according to the embodiment.

[Explanation of symbols]

10 probe section, 12 NaI (Tl) scintillator, 14 photomultiplier tube, 16 high voltage power supply (HV), 1
8 preamplifiers, 20 main amplifiers, 22 wave height analyzers,
24 DSP, 26 dose calculation unit, 28 output unit, 30
Spectrum memory, 32 spectrum utilization calibration processing unit, 34 reference value memory, 40 temperature sensor, 42 A
/ D converter, 44 temperature utilization calibration processing unit, 46 temperature calibration table, 50 abnormality determination unit, 52 calibration control unit, 5
4 memory, 60 table update unit.

Claims (5)

(57) [Claims] 1. An environmental radiation monitor for detecting radiation in the environment with a radiation detector and calculating an environmental radiation dose based on a detection pulse output from the radiation detector. Pulse height analysis means for obtaining an energy spectrum by performing pulse height analysis, spectrum-based calibration means for performing energy calibration based on a peak for a predetermined natural radionuclide in the obtained energy spectrum, and environmental radiation based on environmental radiation measurement results. Abnormality determining means for determining whether the state is normal or abnormal, and calibration control means for stopping energy calibration processing by the spectrum using calibration means when it is determined that the radiation is abnormal, environmental radiation monitor. 2. An environmental radiation monitor for detecting radiation in the environment by a radiation detector and calculating an environmental radiation dose based on a detection pulse output from the radiation detector, wherein the detection output from the radiation detector Pulse height analysis means for obtaining an energy spectrum by pulse height analysis, spectrum-based calibration means for performing energy calibration based on a peak of a predetermined natural radionuclide in the obtained energy spectrum, and temperature detection for detecting the temperature of a radiation detector Means, a temperature calibration table in which a calibration coefficient corresponding to each temperature is set, and a calibration coefficient corresponding to the temperature of the radiation detector are searched from the temperature calibration table, and a temperature utilization for performing energy calibration using the calibration coefficient. Whether the environmental radiation status is normal or abnormal based on calibration means and environmental radiation measurement results Abnormality determining means for determining, if it is determined normal, the spectrum use calibration means to perform energy calibration, if it is determined to be abnormal, the temperature control means to perform energy calibration, calibration control means, An environmental radiation monitor, comprising: 3. The environmental radiation monitor according to claim 2, wherein when energy calibration is performed by the spectrum-based calibration unit, a calibration coefficient in the calibration is obtained, and the calibration coefficient and the temperature detection unit detect the calibration coefficient. An environmental radiation monitor, comprising: a table updating unit that updates setting contents of the temperature calibration table according to the set temperature. 4. The environmental radiation monitor according to claim 1, wherein the abnormality determination unit performs an abnormality determination based on a determination criterion in which a condition regarding a concentration change of radon and thoron in the atmosphere is added. Environmental radiation monitor characterized by the following. 5. The environmental radiation monitor according to claim 4, wherein the abnormality determination unit has a plurality of determination criteria corresponding to each weather condition, and performs an abnormality determination using the determination criteria corresponding to the weather condition. An environmental radiation monitor characterized in that: