阅读说明：本技术 一种确定活性炭滤盒中放射性碘-131活度及分布的方法 (Method for determining activity and distribution of radioactive iodine-131 in activated carbon filter box ) 是由 夏文 叶宏生 陈克胜 宋鑫鹏 林敏� 徐利军 于 2020-12-02 设计创作，主要内容包括：本公开属于放射性测量技术领域,具体涉及一种确定活性炭滤盒中放射性碘-131活度及分布的方法。该方法是通过对活性炭滤盒深度-效率函数的测量,并采用待测样品正反方向测量后求解超越方程的方式,同时获得待测样品活度及分布参数。利用该方法进行样品活度及活度分布的测量使得不确定度在10％以内。(The disclosure belongs to the technical field of radioactivity measurement, and particularly relates to a method for determining activity and distribution of radioactive iodine-131 in an activated carbon filter box. The method is characterized in that the activity and distribution parameters of the sample to be measured are obtained simultaneously by measuring the depth-efficiency function of the activated carbon filter box and solving an transcendental equation after the forward and reverse directions of the sample to be measured are measured. The method is used for measuring the activity and the activity distribution of the sample, so that the uncertainty is within 10 percent.)

1. A method for determining activity and distribution of radioactive iodine-131 in an activated carbon filter box is characterized in that the method is to measure a depth-efficiency function of the activated carbon filter box, solve an transcendental equation after positive and negative measurement of a sample to be measured is carried out, and obtain activity and distribution parameters of the sample to be measured.

2. The method of claim 1, wherein the depth-efficiency function is measured by comparing the depth-efficiency function to a threshold value¹³¹Preparing a filter paper plane standard source with specific activity by using the I standard solution, preparing a series of activated carbon filter box sources distributed at different depths through activated carbon filling and depth positioning, and respectively carrying out efficiency calibration on a measured sample measuring position to obtain a depth-efficiency function f (x) of the iodine monitor on the activated carbon filter box sources.

3. The method of claim 1, wherein the preparing the series of depth distributed activated carbon filter cartridges is performed by fixing a planar standard source to the activated carbon containing member in the activated carbon filter cartridge at different heights in axial position by a positioning device.

4. The method of claim 1, wherein the positioning device is a positioning ring.

5. The method of claim 1, wherein the forward-reverse measurement of the sample to be tested results in a forward-reverse count rate N₁Counter-direction count rate N_-1(ii) a The transcendental equation has the equation:

wherein A is the activity of the sample to be detected, alpha is a distribution parameter, A₀The activity of the surface unit thickness delta D of the sample to be detected, D is the total thickness of the activated carbon of the sample to be detected, e is a natural constant, and D is the distance from the positive surface of the sample to be detected.

6. The method according to claim 1, wherein the standard source activity of the filter paper plane is 10-10⁶Bq。

7. The method according to claim 1, wherein the series of depth-distributed activated carbon filter cartridge sources can be distributed uniformly or non-uniformly in depth, and the number of the series of sources is 1-20.

8. The method according to claim 1, wherein the series of depth-distributed activated carbon filter cartridge sources can be distributed in a non-uniform depth manner, and the number of the series of sources is 5-10.

9. The method of claim 1, wherein the number of the series of different depth-distributed activated carbon cartridge sources is 1 or more.

10. The method according to claim 2 or 5, wherein the depth-efficiency function f (x) is fitted using an exponential fit or a linear fit; the solution of the transcendental equation may be a graphical solution, newton's tangent, a power series solution, or a computer programmed solution.

Technical Field

The disclosure belongs to the technical field of radioactivity measurement, and particularly relates to a method for determining activity and distribution of radioactive iodine-131 in an activated carbon filter box.

Background

In the air¹³¹I is the key radionuclide of the nuclear facility operation monitoring and environment monitoring, the monitoring is usually carried out by an iodine monitor, an active carbon filter box is generally adopted to adsorb iodine in air, and a NaI (Tl) gamma spectrometer is used for measuring iodine in the filter box¹³¹I activity concentration. Due to adsorption by the cartridge¹³¹I is exponentially distributed along with the depth, and the gamma ray detection efficiency at different depths is different, so that difficulty is brought to the activity fixed value of the filter box. At present, users of the iodine monitor mostly adopt uniformly distributed filter box sources to carry out efficiency calibration, larger measurement errors exist,through research, when the index distribution parameter is more than 2, the detection efficiency of uniformly distributed filter box source scales is adopted to carry out activity measurement calculation, and the result error is more than 50%.

Disclosure of Invention

Objects of the invention

In light of the problems with the prior art, the present disclosure provides a method for measuring activity and activity distribution of a sample with uncertainty within 10%.

(II) technical scheme

In order to solve the problems existing in the prior art, the method is realized by the following technical scheme:

a method for determining activity and distribution of radioactive iodine-131 in an activated carbon filter box is characterized in that the activity and distribution parameters of a sample to be measured are obtained simultaneously by measuring a depth-efficiency function of the activated carbon filter box and solving an transcendental equation after positive and negative measurement of the sample to be measured is carried out.

Preferably, the depth-efficiency function is measured by¹³¹Preparing a filter paper plane standard source with specific activity by using the I standard solution, preparing a series of activated carbon filter box sources distributed at different depths (only one standard source is placed in each filter box) by filling activated carbon and performing depth positioning, and performing efficiency calibration on a measured sample measuring position to obtain a depth-efficiency function f (x) of the iodine monitor on the activated carbon filter box sources.

Preferably, the preparation series of depth-distributed activated carbon filter cartridges are prepared by fixing the planar standard source at different heights at the axial position of the activated carbon containing part in the activated carbon filter cartridge by the positioning device.

Preferably, the positioning device is a positioning ring.

Preferably, the forward and reverse counting rate N is obtained by performing forward and reverse measurement on the sample to be measured₁Counter-direction count rate N_-1(ii) a The transcendental equation has the equation:

wherein A is the activity of the sample to be detected, alpha is a distribution parameter, A₀The activity of the surface unit thickness delta D of the sample to be detected, D is the total thickness of the activated carbon of the sample to be detected, e is a natural constant, and D is the distance (depth) from the positive surface of the sample to be detected.

Preferably, the standard source activity of the filter paper plane is 10-10⁶Bq。

Preferably, the standard source activity of the filter paper plane is 10²～10⁴Bq。

Preferably, the series of depth-distributed activated carbon filter box sources can adopt a depth uniform distribution or non-uniform distribution mode, and the number of the series of sources is 1-20.

Preferably, the series of depth-distributed activated carbon filter box sources can adopt a depth uniform distribution or non-uniform distribution mode, and the number of the series of sources is 5-10.

Preferably, the series of depth-distributed activated carbon filter box sources can adopt a depth non-uniform distribution mode, and the number of the series of sources is 5-10.

Preferably, the number of the series of activated carbon filter cartridge sources distributed at different depths is more than 1.

Preferably, the depth-efficiency function f (x) may be fitted using an exponential fit or a linear fit, and the transcendental equation may be solved using a graphical solution, a newton's tangent, a power series solution, or a computer programming solution. .

Preferably, when solving the transcendental equation, boundary condition inputs are required, namely:

thus, it is possible to obtain:the human-representative side can solve the system of equations.

(III) advantageous effects

By adopting the method provided by the disclosure, the activity and distribution parameters of the sample to be measured are obtained simultaneously by measuring the depth-efficiency function of the activated carbon filter box and solving the transcendental equation after the forward and reverse directions of the sample to be measured are measured. The uncertainty of the obtained relative expansion of the iodine-131 activity measurement result is reduced to be within 10% from 20% -30% of the uncertainty of the relative expansion of the traditional method, and the accuracy of the nuclear facility operation monitoring and environment monitoring results is improved.

Detailed Description

The present application will be further described with reference to specific examples.

A method for determining activity and distribution of radioactive iodine-131 in an activated carbon filter box is characterized in that the activity and distribution parameters of a sample to be measured are obtained simultaneously by measuring a depth-efficiency function of the activated carbon filter box and solving an transcendental equation after positive and negative measurement of the sample to be measured is carried out. The specific operation is as follows:

(1) by using¹³¹I, preparing a filter paper plane standard source by using a standard solution, and calculating the activity value of the filter paper plane standard source;

(2) respectively positioning the plane standard source to the positions of 0mm, 4.8mm, 8.8mm, 12.8mm, 16.8mm and 20.4mm in the direction of the source probe of the activated carbon filter box, and filling activated carbon up and down to the original mass;

(3) the activated carbon filter boxes with different depths are respectively placed at the measuring position (0 cm) of a sample to be measured for measurement, and the filter box pair of the measuring position detector can be obtained¹³¹The depth-efficiency relationship function of I is f (x) 0.082873 · e^-0.046511x；

(4) The sample to be tested (known as A: 814.8Bq, alpha: 0.32 mm)^-1) The counting rate N is respectively measured in the positive and negative directions of the measuring position₁＝61.49s^-1、N_-1＝31.62s^-1；

(5) Establishing an transcendental equation as follows, solving to obtain the activity A of the sample to be measured which is 846.8Bq and the distribution parameter alpha which is 0.325mm^-1。

(6) Similarly, the standard source with known activity and distribution is used as the sample to be measured to perform measurement verification at other measurement positions, and the results are shown in the following table, which indicates that the deviation of the measurement result of the activity of the sample to be measured is less than 5%, and the relative expansion uncertainty is within 10%.

Therefore, by using the method provided by the embodiment, the relative expansion uncertainty of the obtained iodine-131 activity measurement result is reduced to be within 10% from 20% -30% of that of the traditional method, and the accuracy of the nuclear facility operation monitoring and environment monitoring results is improved.

Example 2

A method for determining activity and distribution of radioactive iodine-131 in an activated carbon filter box is characterized in that the activity and distribution parameters of a sample to be measured are obtained simultaneously by measuring a depth-efficiency function of the activated carbon filter box and solving an transcendental equation after positive and negative measurement of the sample to be measured is carried out. The specific operation is as follows:

(1) by using¹³¹I, preparing one filter paper plane standard source by using the standard solution, and calculating the activity value of the filter paper plane standard source;

(2) positioning the plane standard source to the position 0mm in the direction of the source probe of the activated carbon filter box, and filling activated carbon below the plane standard source to the original mass;

(3) the activated carbon filter box is respectively placed in the measurement position (0cm position) of a sample to be measured in the forward and reverse directions for measurement, namely the measurement is respectively carried out at two different depths of a plane source 0mm position and a plane source 20.4mm (total depth of the filter box), and the measurement position detector can be obtained by fitting¹³¹The depth-efficiency relation function of I is f (x) 0.0195. e^-0.028875x；

(3) The sample to be tested (known as A. 2565.0 Bq. alpha. 0.37 mm)^-1) The counting rate N is respectively measured in the positive and negative directions of the measuring position₁＝46.42s^-1、N_-1＝30.09s^-1；

(4) Establishing an transcendental equation as follows, and solving to obtain the activity A of the sample to be measured as 2565.4Bq, distribution parameter alpha 0.372mm^-1。

(5) Through uncertainty analysis, the uncertainty of the synthetic standard of the activity measurement result of the sample to be measured is solved in the measurement, the uncertainty of the relative expansion is within 10%, and compared with the traditional method, the uncertainty is 20% -30%, so that the accuracy of the operation monitoring and environment monitoring results of the nuclear facility is obviously improved.