Field Survey And Measurement Method Of The Characteristic Parameters Of Unattached Radon Progeny In Environment

Radon is one of the most important contributors to human exposure from natural sources,and its exposure dose mainly comes from short-lived radon progeny(²¹⁸Po,²¹⁴Pb,²¹⁴Bi)。The evaluation of radon exposure dose is of great significance for radon protection and management.Due to the unattached radon progeny have the characteristics of small particle size,large diffusion coefficient,and large dose conversion coefficient per unit exposure,the contribution of its exposure dose cannot be ignored.Carrying out accurate measurement of unattached radon progeny in the environment and field survey characteristic parameters of unattached radon progeny in typical environments is extremely important for the evaluation of radon exposure dose.This research focuses on the problems existing in previous studies,such as the measurement results of unattached radon progeny are not comparable,the unattached fraction of single radon progeny is difficult to obtain,the characteristic parameters of unattached radon progeny in typical dwelling environment are incomplete.Based on theoretical simulation and experimental measurement,this paper carried out three aspects of research:1)Research on the optimization and selection technology of collecting unattached radon progeny by single wire screen method.2)Research on accurate measurement and evaluation technology of unattached radon progeny activity concentration.3)Field measurement of characteristic parameters of unattached radon progeny in typical environment.The results show that at the sampling flow rate of 3 L·min^-1,the collection efficiency of different screens for unattached radon progeny is above 95%,and it increases with the increase of the mesh number of the screen.The collection efficiency of different screens for attached radon progeny is less than 1%,and it increases with the increase of screen mesh.Although the collection efficiency of different types of screens for attached radon progeny is relatively low,due to the attached radon progeny in typical indoor environment is relatively high,attached radon progeny will bring a systematic positive deviation（3.1%～9.5%）to the measurement results of unattached fraction,and the deviation increases with the increase of screen mesh.The experimental results of radon chamber agree with the theoretical calculation.At the sampling flow rate of 3 L·min^-1,due to the existence of"coarse particle mode"radon progeny,when 635 mesh wire mesh is used to measure the fraction of unattached radon progeny in outdoor and mine environment,the results will be seriously deviated.The positive deviation of the typical outdoor environment is about 40.3%,and the typical mine environment is about 113%.The revised Wicke algorithm can be applied to the accurate measurement of the fraction of unattached radon progeny and the activity concentration ratio of radon progeny in the field environment.The uncertainty of the measurement system can be reduced by the calibration of detection efficiency and sampling flow rate,as well as the evaluation of stability and accuracy.The experimental results of the customized RPM-FF01-2S radon progeny unattached fraction measurement device compared with EQF 3120 and BWLM-PLUS-2S show that the average value of the EEC measured by the three instruments is agree,and the relative deviation≤±3.0%.However,there are significant differences between the results of f_p.Different screen mesh,different sampling flow rate and the influence of attached radon progeny may be the main reasons.In the field measurement of characteristic parameters of unattached radon progeny in the typical environment,it was found that the f_p and the activity concentration ratios of radon progeny in different typical environments are quite different.The average f_p of city dwellings and rural dwellings are4.46%±2.19%and 3.79%±1.71%,respectively,the average f_p of office environment is 5.11%±0.86%,and the average f_p of outdoor is 5.37%±3.09%.The activity concentration ratios of radon progeny and unattached radon progeny in typical city dwelling environment are 1:0.94:0.70 and 1:0.07:0.06,those in rural dwelling environment are 1:0.88:0.66 and 1:0.09:0.07,and those in outdoor environment are 1:0.88:0.77 and 1:0.11:0.11.The optimized selection and evaluation technology of single screen in this study can judge whether the selection of screen is optimized,the influence of attached radon progeny in field measurement can be evaluated,and a good idea for standardization of unattached radon progeny measurement technology can be provided in the future.This study obtained the characteristic parameters of unattached radon progeny in the typical environment will enrich the data of radon progeny characteristic parameters in China.It can be directly applied to the calculation of radon exposure dose conversion coefficient in dwellings environment,and fill the gaps in this field in China.