JP6169888B2 - Radioactivity measuring device - Google Patents

Description

  The present invention relates to a radioactivity measurement apparatus.

  Conventionally, for a radiation detector, a method for measuring the peak efficiency of all absorption peaks of a plurality of energy using a plurality of standard radiation sources and calculating a peak efficiency curve by fitting a predetermined function to a plurality of measurement points Is known (see, for example, Non-Patent Document 1).

"Radioactivity measurement series 7 Gamma-ray spectrometry using germanium semiconductor detector", Ministry of Education, Culture, Sports, Science and Technology, 1992, p.95.

By the way, in the method according to the above-described prior art, it is desired to evaluate the uncertainty of the radioactivity determination accompanied by the efficiency calibration of the radiation detector using the peak efficiency curve.
This invention is made | formed in view of the said situation, and it aims at providing the radioactivity measuring apparatus which can evaluate appropriately the uncertainty of radioactivity determination of a sample.

In order to solve the above problems and achieve the object, the present invention employs the following aspects.
(1) A radioactivity measurement apparatus according to an aspect of the present invention includes a radiation detector that detects radiation emitted from a sample (for example, the radiation detector 15 in the embodiment), information on the sample, and the radiation. Peak efficiency calculation means for calculating the peak efficiency at the energy of the total absorption peak and the uncertainty of the peak efficiency from the total absorption peak of the energy spectrum of the radiation detected by the detector (for example, calculation in the embodiment) Unit 23), the peak efficiency function generating means for generating a peak efficiency function indicating the energy dependence of the peak efficiency according to the peak efficiency calculated by the peak efficiency calculating means and the energy of the total absorption peak (For example, the calculation unit 23 in the embodiment also serves as a predetermined probability density in the peak efficiency range corresponding to the uncertainty of the peak efficiency) Set a number, generate a random number according to the probability density function, and generate pseudo peak efficiency according to the random number in a simulated manner (for example, the calculation unit 23 in the embodiment also serves), According to the pseudo peak efficiency generated for each random number by the pseudo peak efficiency generating means and the energy of the total absorption peak, a pseudo peak efficiency function indicating the energy dependence of the pseudo peak efficiency is represented by each random number. A plurality of pseudo peak efficiency functions corresponding to the plurality of random numbers generated by the pseudo peak efficiency function generation unit (for example, the calculation unit 23 in the embodiment also serves as the generation unit) To generate a frequency distribution of the value of the pseudo peak efficiency function at an appropriate energy, and based on the frequency distribution, the frequency at the appropriate energy Uncertainty setting means for setting the uncertainty of the value of the similar peak efficiency function and setting the uncertainty as the uncertainty of the value of the peak efficiency function at the appropriate energy (for example, the calculation unit 23 in the embodiment also serves as) And comprising.

(2) A radioactivity measurement apparatus according to an aspect of the present invention includes a radiation detector that detects radiation emitted from a sample (for example, the radiation detector 15 in the embodiment), information on the sample, and the radiation. Variable calculation means for calculating a variable at a predetermined energy and uncertainty of the variable related to efficiency calibration of the radiation detector (for example, the calculation unit 23 in the embodiment) from the energy spectrum of the radiation detected by the detector. And variable function generating means for generating a variable function indicating energy dependency of the variable in accordance with the variable calculated by the variable calculating means and the predetermined energy (for example, calculation in the embodiment) A predetermined probability density function in a variable range corresponding to the uncertainty of the variable, and generating a random number according to the probability density function, Pseudo-variable generating means (for example, the arithmetic unit 23 in the embodiment also serves as a pseudo-variable), the pseudo-variable generated by the pseudo-variable generating means for each random number, and the predetermined variable A pseudo variable function generating means for generating a pseudo variable function indicating the energy dependence of the pseudo variable for each random number according to energy (for example, the arithmetic unit 23 in the embodiment also serves), and the pseudo variable function A frequency distribution of values of the pseudo-variable function at an appropriate energy is generated by the plurality of pseudo-variable functions corresponding to the plurality of random numbers generated by the generating means, and the appropriate energy is generated based on the frequency distribution. Uncertainty setting means for setting the uncertainty of the value of the pseudo variable function of the variable function and setting the uncertainty as the uncertainty of the value of the variable function at the appropriate energy (for example, It comprises a doubles as) calculating unit 23 in the facilities form.

  According to the radioactivity measuring apparatus according to the aspect described in (1) above, it is specified by statistical errors of detection by the radiation detector and known uncertainties (for example, uncertainty of quantification of a sample for efficiency calibration). Uncertainty in peak efficiency at a given energy is calculated. Based on the uncertainty of the peak efficiency at this specific energy, the uncertainty of the value of the peak efficiency function at an appropriate energy is set by a simulation process using random numbers. As a result, the uncertainty associated with the calibration of the efficiency of the radiation detector can be set appropriately, and the uncertainty of the radioactivity quantification of the sample can be appropriately evaluated.

  According to the radioactivity measuring apparatus according to the aspect described in (2) above, as variables related to the calibration of the efficiency of the radiation detector, various variables used for correction of self-absorption and sum effect in peak efficiency are used. Thus, the uncertainty at a specific energy is calculated based on the statistical error and the previously known uncertainty. Based on the uncertainty of the variable at this specific energy, the uncertainty of the value of the variable function at an appropriate energy is set by a simulation process using random numbers. As a result, the uncertainty associated with the calibration of the efficiency of the radiation detector can be set appropriately, and the uncertainty of the radioactivity quantification of the sample can be appropriately evaluated.

It is a block diagram of the radioactivity measuring apparatus which concerns on embodiment of this invention. The peak efficiency of all absorption peaks detected by the radiation detector according to the embodiment of the present invention, the uncertainty of the peak efficiency, and a predetermined probability density function set in the peak efficiency range according to the uncertainty of the peak efficiency are shown. FIG. It is a figure which shows the pseudo peak efficiency function which shows the energy dependence of the pseudo peak efficiency produced | generated by the radioactivity measuring apparatus which concerns on embodiment of this invention.

Hereinafter, a radioactivity measurement apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the radioactivity measuring apparatus 10 according to the present embodiment includes an input device 11, an output device 12, a processing device 13, a pulse height analyzer 14, a radiation detector 15, and a power supply 16. I have.
The input device 11 includes, for example, various switches and a keyboard that output signals according to the input operation of the operator, and transmits various command signals according to the input operation of the operator to the processing device 13.
The output device 12 includes, for example, a speaker and a display device, and outputs various types of information received from the processing device 13.

The wave height analyzer 14 is, for example, a multi-channel analyzer, and calculates the wave height distribution of the output signal pulse output from the radiation detector 15, that is, the count value for each of a plurality of channels set according to the wave height value. For example, when an output signal pulse having a peak value corresponding to the energy of radiation emitted from the sample is output from the radiation detector 15, the pulse height analyzer 14 uses the energy distribution as the pulse height distribution of the output signal pulse of the radiation detector 15. Create a spectrum.
The radiation detector 15 is a semiconductor detector such as germanium, and detects radiation (for example, γ-rays, X-rays, etc.) emitted from the sample. The radiation detector 15 is supplied with power from a power source 16.

The processing device 13 includes a communication unit 21, a storage unit 22, and a calculation unit 23.
The communication unit 21 transmits and receives various signals between the processing device 13 and the wave height analyzer 14.
The storage unit 22 stores, for example, various types of preset data, calculation result data of the calculation unit 23, data output from the wave height analyzer 14, and the like.

The calculation unit 23 calculates the peak efficiency at the energy of the total absorption peak from the information of the sample for efficiency calibration and the count value (peak area) of the total absorption peak of the energy spectrum of the radiation detected by the radiation detector 15. Calculate the uncertainty of the peak efficiency. Information on the sample for efficiency calibration includes information on the shape, size, material, weight, and amount of radioactivity of the sample, and information on uncertainty set in advance for each piece of information.
For example, as illustrated in FIG. 2, the calculation unit 23 calculates the detected value s (for example, s1,..., S9) of the peak efficiency ε of all absorption peaks of a plurality of different energies E (for example, E1,..., E9). Then, the uncertainty u (for example, u1,..., U9) of the detected value s of the peak efficiency ε is calculated. The computing unit 23 adapts a predetermined function according to the calculated detection value s of peak efficiency ε and the energy E of all absorption peaks, and shows a peak efficiency function f indicating the energy dependence of the detection value s of peak efficiency ε. (E) is generated.

The calculation unit 23 sets a predetermined probability density function in a peak efficiency range corresponding to the uncertainty of the peak efficiency for each total absorption peak, generates a random number according to the probability density function, and generates a pseudo peak corresponding to the random number. Simulate efficiency. A pseudo peak efficiency function indicating the energy dependence of the pseudo peak efficiency is generated according to the pseudo peak efficiency generated for each random number and the energy of all absorption peaks.
For example, as shown in FIG. 2, when the uncertainty u of the detection value s of the peak efficiency ε is defined by the 95% confidence level for each total absorption peak, the calculation unit 23 determines that the peak efficiency ε is A probability density function g (ε) such as a normal distribution function is set such that the probability of occurrence within the peak efficiency range (s ± u) with the detected value s as the median value is 95%. Then, for each total absorption peak, a random number Rj (j = 1,..., N; N is a statistically sufficient number, for example, 10,000) according to the probability density function g (ε) is generated. The probability density function g (ε) has a 95% confidence interval (M ± 2σ; σ = standard deviation) with respect to the median value M of the peak efficiency ε according to the random number Rj (j = 1,..., N). The function corresponds to (s ± u).

For example, for the arbitrary natural number k (for example, k = 1,..., 9), the calculation unit 23 sets the probability density set in each peak efficiency range (sk ± uk) for each energy Ek of all absorption peaks. A random number Rj (k) according to the function g (ε) k is generated. As a result, as shown in FIG. 3, a different random number Rj (k) is generated for each energy Ek (E1,..., E9) of all absorption peaks, and the i-th random number Ri of each random number Rj (k). By (k), pseudo peak efficiencies r1 (i), ..., rk (i), ..., r9 (i) are generated in a simulated manner. That is, the random number Ri (k) is a different random number for each reference by the natural number k. For example, the i-th random number Ri (1) of the random number Rj (1) (j (1) = 1,..., N) of the energy E1. ) Generates a pseudo peak efficiency r1 (i), and a pseudo peak efficiency r2 (i) by an i-th random number Ri (2) of random numbers Rj (2) (j (2) = 1,..., N) of energy E2. In the same manner, pseudo peak efficiencies r3 (i),..., R9 (i) are generated.
The calculation unit 23 matches the pseudo peak efficiencies r1 (i),..., Rk (i),. ..., a pseudo peak efficiency function f (E, i) indicating the energy dependence of r9 (i) is generated. The calculation unit 23 performs pseudo peak efficiency function f (E, j) (j = 1,..., For each of the plurality of random numbers Rj (k) (that is, each R1 (k),..., RN (k)). N).
The calculation unit 23 uses a plurality of pseudo peak efficiency functions f (E, j) (j = 1,..., N) corresponding to a plurality of random numbers Rj (k) to obtain a pseudo peak efficiency function f () at an appropriate energy Ex. Ex, j) (j = 1,..., N) value frequency distribution is generated, and the uncertainty of the value of the pseudo peak efficiency function at an appropriate energy Ex is set based on the standard deviation of the frequency distribution. This uncertainty is defined as the uncertainty of the value of the peak efficiency function f (Ex) at an appropriate energy Ex.

  As described above, according to the radioactivity measurement apparatus 10 according to the present embodiment, statistical errors in detection by the radiation detector 15 and previously known uncertainties (for example, uncertainties in quantification of a sample for efficiency calibration, etc.) To calculate the uncertainty of the peak efficiency at a specific energy (that is, each energy E of all absorption peaks). Based on the uncertainty of the peak efficiency at this specific energy, the value of the peak efficiency function f (Ex) at an appropriate energy Ex is obtained by a simulation process using random numbers Rj (j = 1,..., N). Uncertainty is set. Thereby, for example, the uncertainty related to the efficiency calibration of the radiation detector 15 can be set appropriately without the need for performing complicated calculation of error propagation, and the uncertainty such as the radioactivity quantification of the sample can be appropriately set. Can be evaluated.

In the above-described embodiment, the calculation unit 23 sets the uncertainty of the value of the peak efficiency function f (Ex) at an appropriate energy Ex by simulation processing. However, the present invention is not limited to this. Uncertainty at an appropriate energy Ex can be set by the above-described simulation processing for variables used in various arithmetic processing such as correction of self-absorption and correction of the sum effect.
That is, the calculation unit 23 calculates appropriate variables and uncertainty of variables related to the efficiency calibration of the radiation detector 15 from the count value (peak area) of the total absorption peak of the energy spectrum of the radiation detected by the radiation detector 15. And a variable function indicating the energy dependence of the variable is generated. Then, a predetermined probability density function is set in the variable range corresponding to the uncertainty of the variable, a random number according to this probability density function is generated, a pseudo variable corresponding to the random number is generated in a simulated manner, and the energy dependence of the pseudo variable A pseudo variable function indicating the sex is generated for each random number. Then, by using a plurality of pseudo variable functions corresponding to a plurality of random numbers, a frequency distribution of values of the pseudo variable function at an appropriate energy is generated, and the uncertainty of the value of the pseudo variable function at an appropriate energy is based on the frequency distribution. The uncertainty is set as the uncertainty of the value of the variable function at an appropriate energy.

  In the above-described embodiment, the radiation detector 15 is a semiconductor detector such as germanium. However, the detector is not limited to this and may be another detector such as a scintillation detector.

DESCRIPTION OF SYMBOLS 10 ... Radioactivity measuring device 11 ... Input device 12 ... Output device 13 ... Processing device 14 ... Wave height analyzer 15 ... Radiation detector 16 ... Power supply 21 ... Communication part 22 ... Memory | storage part 23 ... Calculation part (peak efficiency calculation means, peak Efficiency function generating means, pseudo peak efficiency generating means, pseudo peak efficiency function generating means, uncertainty setting means, variable calculating means, variable function generating means, pseudo variable generating means, pseudo variable function generating means)

Claims (3)

A radiation detector for detecting radiation emitted from the sample for efficiency calibration ;
Information including the shape, dimensions, material, weight, and amount of radioactivity of the sample, uncertainty information preset for the information, and total absorption of the energy spectrum of the radiation detected by the radiation detector Peak efficiency calculation means for calculating the peak efficiency at the energy of the total absorption peak and the uncertainty of the peak efficiency from the peak;
Peak efficiency function generating means for generating a peak efficiency function indicating energy dependency of the peak efficiency according to the peak efficiency calculated by the peak efficiency calculating means and the energy of the total absorption peak;
A pseudo peak efficiency that sets a predetermined probability density function in a peak efficiency range according to the uncertainty of the peak efficiency, generates a random number according to the probability density function, and generates a pseudo peak efficiency according to the random number in a simulated manner Generating means;
Wherein a pseudo peak efficiency generated for each prior Symbol random number by the pseudo peak efficiency generating means, in response to said energy of the whole peak, a pseudo peak efficiency function representing the energy dependence of the pseudo peak efficiency before Pseudo peak efficiency function generating means for generating each random number;
A frequency distribution of the values of the pseudo peak efficiency function at an appropriate energy is generated by the plurality of pseudo peak efficiency functions corresponding to the plurality of random numbers generated by the pseudo peak efficiency function generating means, and the frequency distribution An uncertainty setting means for setting the uncertainty of the value of the pseudo-peak efficiency function at the appropriate energy based on the uncertainty and setting the uncertainty as the uncertainty of the value of the peak efficiency function at the appropriate energy;
A radioactivity measurement apparatus comprising: A radiation detector for detecting radiation emitted from the sample for efficiency calibration ;
From the information including the shape, dimensions, material, weight, and radioactivity of the sample, uncertainty information preset for the information, and the energy spectrum of the radiation detected by the radiation detector, Variable calculation means for calculating a variable at a predetermined energy and an uncertainty of the variable according to efficiency calibration of the radiation detector;
Variable function generating means for generating a variable function indicating energy dependence of the variable according to the variable calculated by the variable calculating means and the predetermined energy;
A pseudo variable generating means for setting a predetermined probability density function in a variable range corresponding to the uncertainty of the variable, generating a random number according to the probability density function, and generating a pseudo variable corresponding to the random number;
And the pseudo variables generated before each Symbol random number by the pseudo variable generation unit, wherein in accordance with the predetermined energy, quasi for generating a pseudo-variable function showing the energy dependence of the pseudo-variable before each Symbol random number Variable function generation means;
A plurality of pseudo variable functions corresponding to the plurality of random numbers generated by the pseudo variable function generating means generate a frequency distribution of the values of the pseudo variable function at an appropriate energy, and based on the frequency distribution Uncertainty setting means for setting the uncertainty of the value of the pseudo variable function at an appropriate energy, and making the uncertainty an uncertainty of the value of the variable function at the appropriate energy;
A radioactivity measurement apparatus comprising: A radiation detector for detecting radiation emitted from the sample for efficiency calibration;
Information including the shape, dimensions, material, weight, and amount of radioactivity of the sample, uncertainty information preset for the information, and total absorption of the energy spectrum of the radiation detected by the radiation detector Variable calculation means for calculating a variable at a predetermined energy related to the efficiency calibration of the radiation detector and an uncertainty of the variable from the peak;
Variable function generating means for generating a variable function indicating the energy dependence of the variable according to the variable calculated by the variable calculating means and the energy of the total absorption peak;
A pseudo variable generating means for setting a predetermined probability density function in a variable range corresponding to the uncertainty of the variable, generating a random number according to the probability density function, and generating a pseudo variable corresponding to the random number;
A pseudo variable that generates, for each random number, a pseudo variable function indicating the energy dependence of the pseudo variable in accordance with the pseudo variable generated for each random number by the pseudo variable generating means and the energy of the total absorption peak. Function generation means;
A plurality of pseudo variable functions corresponding to the plurality of random numbers generated by the pseudo variable function generating means generate a frequency distribution of the values of the pseudo variable function at an appropriate energy, and based on the frequency distribution Uncertainty setting means for setting the uncertainty of the value of the pseudo variable function at an appropriate energy, and making the uncertainty an uncertainty of the value of the variable function at the appropriate energy;
A radioactivity measurement apparatus comprising:

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