JPH09304542A - Radiation measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation measuring apparatus in which an energy value can be calibrated simply without using a radiation source for calibration. SOLUTION: An environmental radiation is detected by a detection part 10, and the energy spectrum of the environmental radiation is found by a multichannel analyzer 22. A peak detection part 32 investigates a prescribed search range in the energy spectrum, and it detects the photoelectric peak of<40> K which is distributed widely in an environment. In a reference-value storage part 34, the correct energy value of the photoelectric peak of the<40> K is stored as a reference value. In a comparison processing part 33, the channel of the photoelectric peak detected by the peak detection part 32 is compared with the channel of the reference value stored in the reference-value storage part 34. On the basis of a compared result, a voltage or a gain instruction part 35 adjusts a voltage instruction value to a high-voltage power supply 14 or a gain instruction value to a main amplifier 18 in such a way that the channel of the photoelectric peak is brought close to the reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring apparatus, and more particularly to energy calibration in the radiation measuring apparatus.

[0002]

2. Description of the Related Art In a scintillation detector or a semiconductor detector, when radiation is detected, a detection pulse proportional to the energy lost by the radiation in the detector is obtained. Radiation measuring devices utilizing such properties include, for example,
A device that obtains the energy spectrum of the radiation from the measurement target by performing a pulse height analysis of the detection pulse using a multi-channel analyzer, and a dose rate by counting and weighting each detection pulse according to the wave height. There is also a device for obtaining the dose equivalent rate.

However, in the radiation measuring apparatus, the wave height of the detection pulse corresponding to the radiation of the same energy changes with time due to the change with time of the characteristics of the photomultiplier tube, the detector, and the amplifier, and as a result, the radiation Energy may not be obtained correctly. In the radiation measuring apparatus, energy calibration is regularly performed to avoid such a situation.

Conventionally, in the energy calibration process of a radiation measuring apparatus, a calibration radiation source such as ¹³⁷ Cs is set in the vicinity of the detector, the radiation source is measured to obtain an energy spectrum, and the photopeak ( The voltage applied to the detector and the gain of the amplifier were adjusted so that the total absorption peak) or the Compton end was in the correct channel corresponding to the photoelectric peak of the radiation source or the energy at the Compton end.

[0005]

In such a conventional energy calibration method, since a radiation source for calibration is used, it is necessary to possess and manage the radiation source, and the operator needs to carry out the calibration process. I had to go to the radiation measuring device with the radiation source.

The present invention has been made to solve such a problem, and energy calibration can be easily performed without using a calibration radiation source, and an operator can perform special energy calibration processing. It is an object of the present invention to provide a radiation measuring apparatus that does not require the work of

[0007]

In order to achieve the above-mentioned object, a radiation measuring apparatus according to the present invention detects radiation emitted from an object to be measured by a detector, and a pulse height of a detection pulse output from the detector. In a radiation measuring device for calculating a predetermined measurement result by using, a reference value storage means for storing a reference value relating to energy of radiation emitted from a predetermined natural radionuclide existing in the environment, and the detector from the environment Spectrum generating means for detecting the energy spectrum of the environmental radiation by detecting the radiation of the, and detecting the peak corresponding to the predetermined natural radionuclide from the obtained energy spectrum, based on this peak index point of the energy spectrum Comparing the peak detection means to be obtained and the energy value of the index point with the reference value stored in the reference value storage means , And having a calibration means for performing the energy calibration process based on the comparison result.

In this configuration, energy calibration is performed without using a special radiation source for calibration by using a specific natural radionuclide that is present in a relatively large amount in the environment as a reference. The reference value storage means stores a reference value relating to the energy of the radiation emitted from such a predetermined natural radionuclide, for example, the correct energy value at the photoelectric peak or Compton edge. The spectrum generation means measures the radiation from the environment and obtains its energy spectrum in accordance with the calibration processing execution command from the operator. The peak detecting means detects a peak corresponding to the predetermined natural radionuclide from the energy spectrum, and obtains an index point of the energy spectrum based on the peak. The calibration means compares the energy value at this index point with the reference value and performs energy calibration based on the comparison result.
The energy calibration referred to here includes, for example, processing such as adjustment of the voltage applied to the detector and adjustment of the gain of the amplifier that proportionally amplifies the detection pulse.

According to this configuration, since the calibration process can be performed using the natural radionuclide existing in the environment,
Eliminates the need to own and manage a calibration radiation source. Also,
As a result, it becomes possible to perform the calibration process while there is no operator, and the burden on the operator can be reduced.

In this configuration, for example, ⁴⁰ K or ²⁰⁸ Tl can be used as a natural radionuclide used as a calibration standard. If the peak detecting means can specify the energy range for peak detection, The peak can be detected at high speed.

Further, in a preferred aspect of the present invention, the radiation measuring apparatus further has a time measuring means capable of setting a start time of the calibration processing or a time until the calibration processing is started, and the time measuring means is used for the above-mentioned. When it is detected that the set time or the set time has been reached, the detector, the reference value storage means, the spectrum generation means, the peak detection means, and the calibration means are activated to perform the calibration process.

According to this structure, since the calibration process can be performed at the time or time set in the time measuring means, the calibration process can be performed at a time when the normal measurement process is not performed, such as at night, and the measurement time can be reduced. Eliminates the need for scraping for the calibration process.

Further, in the present invention, the determination means for determining the spread of the energy spectrum in the vicinity of the peak detected by the peak detection means and determining whether or not the peak is suitable for the energy calibration process from this result is provided. Further, it is possible to further provide and not use the peak determined to be unsuitable by the determination result of the determination means for the energy calibration process. According to this calibration, if the detected peak is affected by the artificial radionuclide, it is possible to prevent the peak from being used for the energy calibration process. Can be prevented.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a radiation measuring apparatus according to the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a functional block diagram showing a configuration of a first embodiment of a radiation measuring apparatus according to the present invention. In this embodiment, energy calibration is performed using ⁴⁰ K, which is a natural radionuclide widely distributed in nature such as concrete of buildings.

The detector 10 of the radiation measuring apparatus comprises a scintillator 11 and a photomultiplier tube 12. As the scintillator 11, a solid scintillator such as NaI (Tl) may be used, or a plastic scintillator may be used. A high voltage is applied to the photomultiplier tube 12 from a high voltage power supply 14.

The scintillator 11 emits light upon incidence of radiation, and the photomultiplier tube 12 converts the light into an electrical detection pulse and outputs it. The detection pulse output from the photomultiplier tube 12 is amplified by the preamplifier 16, then proportionally amplified by the main amplifier 18, and digitized by the A / D converter 20. The multi-channel analyzer 22 performs wave height analysis of the digitized detection pulse and counts the detection pulse for each channel of each wave height to obtain the energy distribution of incident radiation, that is, the energy spectrum. The energy spectrum obtained by the multi-channel analyzer 22 is output from the output unit 24.

The measurement control unit 30 controls the measurement work having the above configuration. In the measurement control unit 30,
The main control unit 31 controls normal measurement processing such as start and end of measurement, and also controls energy calibration processing. The main control unit 31 is connected to the instruction input unit 26 through which the user inputs an operation instruction. The main control unit 31 controls the measurement process by issuing a predetermined control command to the multi-channel analyzer 22 or the like according to the user's operation instruction received from the instruction input unit 26.

The reference value storage unit 34 stores a reference value for energy calibration. Here, the reference value refers to the correct value of the energy value at the index point of the energy spectrum of the reference natural radionuclide ( ⁴⁰ K in this embodiment). In addition, the index point of the energy spectrum is a point that is a feature of the pattern of the energy spectrum, and in this embodiment, the photoelectric peak or Compton edge is used as the index point.

For example, the scintillator 11 has a NaI (T
l) When using an inorganic crystal scintillator such as a scintillator, the photoelectric peak (total absorption peak) is used as the index point of the energy spectrum. Therefore, in this case, ⁴⁰
Energy E of gamma rays radiated from K (1461 ke
V) is stored in the reference value storage unit 34 as a reference value.

On the other hand, when a plastic scintillator is used as the scintillator 11, the Compton end is used as the index point of the energy spectrum. Therefore, in this case,
The energy value Ec (124) at the Compton end obtained from the energy E of γ-rays emitted from the calibration radiation source by the following equation.
4 keV) is stored in the reference value storage unit 34 as a reference value.

[0022]

[Equation 1] The peak detection unit 32 receives the information of the energy spectrum from the multi-channel analyzer 22 and detects the characteristic peak of the energy spectrum. The characteristic peak is a peak serving as a reference for obtaining the index point, and is a photoelectric peak (when using NaI (Tl) scintillator) or a peak due to Compton effect (when using plastic scintillator). Point to. The comparison processing unit 33 obtains an index point (that is, a photoelectric peak or Compton edge) of the energy spectrum based on the characteristic peak detected by the peak detection unit 32, and the energy value of this index point is stored in the reference value storage unit 34. Compare with the reference value.

The voltage / gain command section 35 comprises a comparison processing section 3
Based on the comparison result of No. 3, the voltage command value for the high-voltage power supply 14 or the gain command value for the main amplifier 18 is adjusted.
The high-voltage power supply 14 and the main amplifier 18 include the voltage / gain command unit 3
According to the command value given from 5, the output voltage or the gain is adjusted.

In the timer 36, the time to start the energy calibration process or the time until the energy calibration process is started is set. This set value is input from the instruction input unit 26 and set in the timer 36 via the main control unit 31. When the setting is completed, the timer 36 performs a time counting process, and supplies a calibration start signal to the main control unit 31 when detecting that the set start time has come or the set time has elapsed.

Each element of the measurement control unit 30 may be configured by hardware or software.

Next, the flow of energy calibration processing in the radiation measuring apparatus of FIG. 1 will be described using the flowchart of FIG. The example of FIG. 2 shows an example in which the start time is set in the timer 36.

In this example, the operator inputs the instruction input unit 26.
The timer 36 sets the start time of the calibration process (S1). This setting process is performed at the end of the measurement process for one day, or when the measurement process has several tens of minutes necessary for the calibration process before the next measurement. When the time is set, the timer 36 starts the time counting process (S
2). Then, when the set start time comes, the timer 3
6 outputs a calibration start signal to the main controller 31.
Upon receiving the calibration start signal, the main control unit 31 activates the radiation measuring apparatus and starts measuring background (environmental) radiation. Then, measurement is performed for about 10 minutes to obtain a sufficient count value, and an energy spectrum of background radiation is generated (S3). An example of the energy spectrum of this background radiation is shown in FIGS. 3 and 4. FIG. 3 is an energy spectrum when a NaI (Tl) scintillator is used for the detector, and FIG. 4 is an energy spectrum when a plastic scintillator is used for the detector. In the spectra of FIGS. 3 and 4, the vertical axis represents the count value (or count rate) and the horizontal axis represents energy in channels (ch). In the plastic scintillator, the photoelectric effect does not occur so much and the Compton effect is the main, so that the photoelectric peak does not appear in the energy spectrum, only the peak due to the Compton effect appears.

The information of this energy spectrum is input to the peak detector 32. The peak detector 32 detects a peak corresponding to ⁴⁰ K from this energy spectrum (S4). In order to detect this peak, the peak detection unit 32 has a search range set in advance. For example, when using a NaI (Tl) scintillator, 14
The predetermined channel range near 61 keV is set as the search range when the plastic scintillator is used, and the predetermined channel range near 1100 keV is set.

As shown in FIG. 3 or FIG. 4, the energy spectrum obtained by the measurement is generally a plot of count values for each channel and is not a smooth curve. Then, the process of approximating the energy spectrum to a smooth curve is performed. In this embodiment, the energy spectrum is approximated to an assumed spectrum curve that is obtained in advance based on the Gaussian distribution. To this end, the least squares method is applied to the data at each point of the graph to identify the assumed spectral curve that best fits the energy spectrum. And
Peak detection is performed on the smooth spectrum curve thus obtained. Alternatively, the energy spectrum may be smoothed by a known smoothing process to be shaped into a smooth curve, and a peak may be detected from this curve.

Then, in the thus obtained smooth energy spectrum curve, the count value of each channel in the set search range is compared to obtain the channel with the highest count value, and that channel is set as the peak channel.

It should be noted, above, by preliminarily limiting the search range of the peak, but an even examples which enables detection of a peak of ⁴⁰ K, the range restriction is not essential. That is, by adjusting the maximum value of the energy value to be measured in advance, the peak at ⁴⁰ K can be set to be the peak on the highest energy side in that range. In this case, the energy spectrum is set to the highest energy side. The peak detected first by searching from can be regarded as the ⁴⁰ K peak. Therefore, in such a case, it is not necessary to set the search range.

When the detection of the ⁴⁰ K peak is completed in this way, the peak detection section 32 obtains an index point of this energy spectrum based on the detected peak. here,
When a NaI (Tl) scintillator is used as the detector, a photoelectric peak is detected, so the peak itself is used as an index point of the energy spectrum. On the other hand, when a plastic scintillator is used as the detector, since the peak of the Compton effect is detected, the Compton edge is obtained from this peak and used as the index point. in this case,
As shown in FIG. 4, half of the count value N of the characteristic peak in the energy spectrum, that is, the point of the count value of N / 2 is defined as the Compton edge.

Next, the comparison processing unit 33 compares the energy value (channel) of the index point thus obtained with the reference value read from the reference value storage unit 34 (S).
5). That is, the comparison processing unit 33 converts, for example, the reference value into a channel unit value and compares the reference value with the channel of the index point. When a NaI (Tl) scintillator is used as the detector, the comparison processing unit 33 compares the channel of the index point with the channel corresponding to the energy of the photoelectric peak of ⁴⁰ K (1461 keV). On the other hand, when a plastic scintillator is used as the detector, the comparison processing unit 33 sets the channel of the index point to the energy (1244 ke) at the Compton end of ⁴⁰ K.
V) and the corresponding channel.

The comparison result of the comparison processing unit 33 is the result of the main control unit 3.
Input to 1. When the channel of the index point coincides with the channel of the reference value, it means that the radiation measuring apparatus has been correctly energy calibrated, and the main control unit 31 ends the series of calibration processes. On the other hand, when the channel of the index point does not match the channel of the reference value, the main control unit 31 inputs the comparison result to the voltage / gain command unit 35. When the channel of the index point is larger than the channel of the reference energy value, the voltage / gain command unit 35 causes the photomultiplier tube 12 to operate.
The command value to the high-voltage power supply 14 or the main amplifier 18 is adjusted so that the voltage applied to the main amplifier 18 or the gain of the main amplifier 18 is reduced by a predetermined amount (S6). On the contrary, when the channel of the index point is smaller than the channel of the reference energy value, the voltage / gain command unit 35 increases the voltage applied to the photomultiplier tube 12 or the gain of the main amplifier 18 by a predetermined amount. 14
Alternatively, the command value to the main amplifier 18 is adjusted (S7). The amount of adjustment of the applied voltage or gain at this time may be an amount by which the index point of the energy spectrum moves up or down by about one channel. In this case, the adjustment amount for one time is about 0.2 to 0.3 V for the voltage applied to the photomultiplier tube. Which of the applied voltage and the gain is adjusted depends on the setting of the operator.

When the adjustment of the applied voltage or the gain is completed, the process returns to the above-mentioned S3 (measurement). And
The above measurement (S3), peak detection (S4), until the channel at the index point matches the channel at the reference value,
The processes of comparison (S5) and adjustment (S6, S7) are repeated.

As described above, according to this embodiment, the energy spectrum of the environmental radiation is obtained, and the energy calibration is performed based on the peak corresponding to the specific natural radionuclide ( ⁴⁰ K) in the energy spectrum. It becomes unnecessary to possess and manage the radiation source of Further, according to the present embodiment, the energy calibration process can be performed at night when there is no operator or in the idle time between the measurements, so that the time can be effectively used.

[Second Embodiment] Next, an embodiment in which the present invention is applied to an environment γ-ray continuous monitor will be described. This device is
For example, when installed outdoors in a nuclear power plant,
It is a device for measuring the dose equivalent rate of a line.

FIG. 5 shows the configuration of the environmental γ-ray continuous monitor of this embodiment. As shown in FIG. 5, in the present embodiment, a NaI (Tl) scintillator 40 having good sensitivity to γ rays is used as a detector. A high voltage bias voltage is applied to the photomultiplier tube 42 from a high voltage power supply 44. The photomultiplier tube 42 converts the light emission of the NaI (Tl) scintillator 40 into an electrical detection pulse and outputs it. This detection pulse is proportionally amplified by the main amplifier 46 and then A /
It is input to the D converter 48. The A / D converter 48 has a function of a multi-channel analyzer, detects the wave height of the input detection pulse, and outputs a digital signal according to the wave height level. A DSP (digital signal processor) 50 calculates a weight value according to the level (corresponding to the pulse height) of the digital signal by a preset calculation or conversion table, and supplies it to the counting circuit 52. The counting circuit 52 calculates the dose equivalent rate based on the result of sequentially adding the respective weight values. The dose equivalent rate is displayed on the display unit 54.

The apparatus of this embodiment can calculate and display the dose equivalent rate of γ rays in the environment as described above. In this device, in order to calculate the correct dose equivalent rate, at least the pulse output from the main amplifier 46 is
The wave height must correspond to the energy of the incident radiation. For this reason, this embodiment has a mechanism for energy calibration.

The spectrum memory 56 and the spectrum analysis circuit 58 in FIG. 5 are the mechanism for this energy calibration. In the present embodiment, this spectrum memory 5
6 and the spectrum analysis circuit 58 execute the energy calibration process in parallel with the measurement process during normal monitoring.

The digital signal output from the A / D converter 48 is input to the spectrum memory 56. The spectrum memory 56 has a plurality of channels corresponding to the respective crest levels, and every time a digital signal corresponding to each detection pulse is input, a count is added to the channel corresponding to the level value of the digital signal. To go. By executing this processing for a predetermined time, the wave height distribution of the environment γ rays, that is, the energy spectrum is formed in the spectrum memory 56.

The spectrum analysis circuit 58 analyzes the energy spectrum thus obtained and detects the total absorption peak of a specific natural radionuclide (for example, ⁴⁰ K). The processing for this peak detection may be the same as the processing of the first embodiment. That is, the spectrum memory 56
The energy spectrum obtained from the above is approximated to a smooth curve by the method as shown in the first embodiment, and the peak of the curve, that is, the point of the maximum count value is obtained in a predetermined search range. As the search range, a range of a predetermined number of channels before and after a correct energy value (or a value obtained by converting this into a channel value) of all absorption peaks of a specific natural radionuclide serving as a reference is set in advance. In this embodiment,
Since the calibration process is performed in parallel with the measurement, the position of the peak of the energy spectrum does not suddenly change significantly, so the search range may be a relatively narrow range.

Then, the spectrum analysis circuit 58 shows that the total absorption peak of the natural radionuclide detected in this way is
It is determined whether or not it is in a preset correct channel (that is, energy −1461 keV in the case of ⁴⁰ K). If the result of determination is that all absorption peaks are not in the correct channel position, the spectrum analysis circuit 5
8 adjusts the voltage of the high voltage power supply 44 or the gain of the main amplifier 46 so that all absorption peaks are in the correct channel. That is, the spectrum analysis circuit 58 holds the information on the adjustment amount of the voltage or the gain necessary for shifting the wave height distribution by one channel, for example, and the channels of all absorption peaks detected from the wave height distribution and the total absorption peaks The difference from the correct channel is obtained, the adjustment amount of the voltage or gain required to eliminate the difference is calculated, and a control signal for changing the voltage or gain by the adjustment amount is sent to the high-voltage power supply 44 or the main amplifier 46. Supply. As a result, the applied voltage to the photomultiplier tube 42 or the gain of the main amplifier 46 is adjusted, and the main amplifier 46 outputs a pulse having a wave height that corresponds correctly to the energy of the incident radiation.

As described above, according to the environmental γ-ray continuous monitor of this embodiment, in the energy spectrum of environmental radiation, all absorption peaks corresponding to a specific natural radionuclide widely distributed in the environment are detected, and this peak is detected. Since the energy calibration is performed based on, the energy calibration can be performed in parallel with the normal monitoring process. That is,
The apparatus of this embodiment is always in a state where energy calibration is performed. In the present embodiment, ²⁰⁸ Tl (total absorption peak 2.6 MeV) can be used in addition to ⁴⁰ K as a natural radionuclide as a standard for energy calibration, or both can be used together.

In the continuous environment gamma ray monitor as in the present embodiment, artificial radioactive nuclide radiation may enter from facilities such as nuclear power plants in addition to natural radioactive nuclides.
In such a case, a peak due to the artificial radionuclide appears in the energy spectrum. When such a peak due to an artificial radionuclide appears near the peak due to a natural radionuclide that is used as a reference for energy calibration, the peak of the artificial radionuclide was mistakenly recognized as a peak of the natural radionuclide in the peak detection, and was mistaken. There is a possibility that calibration will be performed. For example, at ⁴⁰ K, there are some artificial radionuclides that emit relatively close energy radiation, such as ⁶⁰ Co, and this situation may occur. In the present embodiment, in order to avoid such a situation, the spectrum analysis circuit 58 performs the following processing.

That is, the spectrum analysis circuit 58 performs peak detection within a predetermined search range and then calculates the spread of the energy spectrum in the vicinity of the detected peak. That is, on both sides of the detected peak, for example, points having a count value of 1/2 of the peak are detected, and the number of channels between these two points is calculated as the spread of the spectrum. When the peak due to the artificial radionuclide is close to the peak of the natural radionuclide, the count value of each channel around those peaks is large due to the overlapping of the two peaks, and the spread of the energy spectrum is large. Become. Therefore, the spectrum analysis circuit 58
When the spread of the calculated energy spectrum is larger than a predetermined threshold value, it is considered that the peak receives an artificial radionuclide, and therefore the energy calibration process is not performed on the peak. This can prevent erroneous energy calibration processing from being performed.

The γ-rays emitted by ²⁰⁸ Tl have a considerably large energy, and in a normal environment where an environment γ-ray continuous monitor is installed, there are almost no artificial radionuclides emitting γ-rays having an energy close to this. Therefore, when the ⁴⁰ K peak is determined to be inappropriate as the energy calibration reference by the above process, the energy calibration process may be performed using the ²⁰⁸ Tl peak.

The embodiments of the radiation measuring apparatus according to the present invention have been described above. In each of the above embodiments, an example in which a scintillation detector is used as a detector has been described, but the present invention is also applicable to the case where a semiconductor detector is used.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a configuration of a radiation measuring apparatus according to a first embodiment.

FIG. 2 is a flowchart showing a flow of energy calibration processing of the radiation measuring apparatus according to the first embodiment.

FIG. 3 is a diagram showing an example of an energy spectrum of environmental radiation when a NaI (Tl) scintillator is used as a detector.

FIG. 4 is a diagram showing an example of an energy spectrum of environmental radiation when a plastic scintillator is used as a detector.

FIG. 5 is a block diagram showing a configuration of an environment γ-ray continuous monitor according to a second embodiment.

[Explanation of symbols]

10 detector, 11 scintillator, 12 photomultiplier tube, 14 high voltage power supply, 16 preamplifier, 18 main amplifier, 20 A / D converter, 22 multi-channel analyzer, 24 output section, 26 instruction input section, 30 measurement control Section, 31 main control section, 32 peak detection section, 33 comparison processing section, 34 reference value storage section, 35 voltage / gain command section, 36 timer, 56 spectrum memory, 58 spectrum analysis circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Tateishi 6-22-1 Mure, Mitaka City, Tokyo Aloka Co., Ltd.

Claims (6)

[Claims] 1. A radiation measuring apparatus for detecting radiation emitted from a measurement object by a detector and calculating a predetermined measurement result by using a wave height of a detection pulse output from the detector, in a predetermined environment existing in an environment. Reference value storage means for storing a reference value relating to energy of radiation emitted from a natural radionuclide, spectrum generating means for detecting radiation from the environment by the detector to obtain an energy spectrum of environmental radiation, and the obtained energy A peak corresponding to the predetermined natural radionuclide is detected from the spectrum, peak detection means for obtaining an index point of the energy spectrum based on the peak, and an energy value of the index point are stored in the reference value storage means. And a calibration means that compares with a reference value and performs energy calibration based on the comparison result. The radiation measuring device according to claim. 2. The radiation measuring apparatus according to claim 1, wherein the predetermined natural radionuclide is ⁴⁰ K. 3. The radiation measuring apparatus according to claim 1, wherein the predetermined natural radionuclide is ²⁰⁸ Tl. 4. The radiation measuring apparatus according to claim 1, wherein an energy range in which peak detection is performed by the peak detecting unit can be designated. 5. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus further comprises a clocking unit capable of setting a start time of the calibration process or a time until the calibration process is started. When the time measuring means detects that the set time or the set time has come, the detector, the reference value storing means, the spectrum generating means, the peak detecting means, and the calibrating means are activated to perform the calibration process. Radiation measuring device characterized by performing. 6. The radiation measuring apparatus according to claim 1, wherein the spread of the energy spectrum in the vicinity of the peak detected by the peak detecting means is determined, and from this result, the peak is subjected to energy calibration processing. A radiation measuring apparatus comprising: a determining unit that determines whether or not it is suitable, and a peak that is determined to be unsuitable based on the determination result of the determining unit is not used for energy calibration processing.