The Alpha Spectrometry Method Of Measuring Radon Progeny And Thoron Progeny Concentration By Least Squares Method

Radon(²²²Rn)and thoron(²²⁰Rn)belong to radioactive inert gases and are one of the main sources of natural radiation exposure.However,²²²Rn/²²⁰ Rn progeny have a higher dose to humans than ²²²Rn/²²⁰ Rn itself.In the early stage,the project team has established an optimized energy spectrum method for measuring ²²²Rn/²²⁰ Rn progeny,measured the relative parameters of the filter and the energy spectrum apparatus,and realized the rapid and accurate measurement of²²²Rn/²²⁰ Rn progeny within 2 hours.Then by delphi software programming,to achieve any time interval to read spectral data at any energy range function,to achieve fully automated measurment except the sampling process.In order to obtain ²²²Rn/²²⁰ Rn progeny concentration more accurately,in this paper,based on the theoretical formula of optimized energy spectrum method,the concentration counts of ²²²Rn/²²⁰ Rn in multiple time periods were measured and the concentration formulas ofmultiple progeny were established in parallel.The weighted least square method was used to process the data.The concentration matrix of each progeny is obtained by partial derivation of the sum of squared residuals and the concentration of each progeny.The matrix of the relative deviation of each progeny is deduced according to the error formula.The four key parameters of sampling time,total measurement time,measurement count and weighing fator in the error formula of theoretical model are optimized.Through the matlab simulation and optimization,the total alpha and alpha energy spectrum measurements were taken to measure the sampling time and total measurement time of²²²Rn/²²⁰ Rn.For the ²²² Rn progeny,the optimized sampling time of the total alpha method was 5 minute and the optimized sampling time of the alpha energy spectrum method was 15 minute.For the ²²⁰ Rn progeny,the optimized sampling time of the total alpha and alpha energy spectrum was 30 minute.After the efficiency factor was proposed,the total measurement time was further optimized.For the ²²² Rn progeny,the total measurement time optimized of the total alpha method and alpha energy spectrum was 70 minute.For the ²²⁰ Rn progeny,the total measurement time optimized of total alpha method and alpha energy spectrum was 170 minute.Through multi-stage recombination experiment,the line chart of the relative deviation accumulation of Ra B,Ra C,Th B and Th C was made,and the optimal measurement counting interval was between 12 and15 segments.The weight factor optimized by experimental research and theoretical analysis is Ni.By comparing different methods,the reliability of ²²²Rn/²²⁰ Rn progeny measured by alpha energy spectrum method was verified.And in the case of low concentrations,alpha energy spectrum multistage method has a smaller relative deviation.Finally,we write the MATLAB-GUI interface program of ²²²Rn/²²⁰ Rn sub-system,which makes data processing easy and reduces the cumbersome manual calculation.In this project,we improved and perfected the original alpha energy spectrum method and obtained the ²²²Rn/²²⁰ Rn concentration more accurately.