Study On Continuous Measurement Method Of The Unattachend Radon Progeny

Radon(²²²Rn) decay produces a series of solid radionuclides,called radon progeny.Since radon progeny can attach to the respiratory epithelium and mucous membranes in different parts of the respiratory tract,the doses caused by these decay products exceed their parent nuclides.There are two forms of radon progeny in the air,the unattached and the attached.Due to the large diffusion coefficient of the unattached radon progeny,it is not easy to be exhaled after being adsorbed in the respiratory tract,so it has attracted much attention.This study aims to develop a continuous measurement method for the unattached radon progeny without changing the wire screen.The measurement method and variation of the particle size distribution and unattached fraction of radon progeny and the influence of flow rate on sampling parameters were studied to improve the sensitivity.Ensure the accuracy of the result through the accurate measurement and calculation of sampling parameters.On the basis of realizing the radon progeny concentration measured by the imaging plate,30-,100-,200-,and 400-mesh wire screens and filter membranes were used to form a graded screen array?GSA?.The particles of 0.1-1000 nm are segmented,and the capture efficiency of particles of each size segment in the GSA is calculated theoretically.After sampling,the radon progeny concentration was measured with an imaging plate,and then EM algorithm and Towmey algorithm were used to infer the particle size distribution.The unattached AMD of RaA is 0.91±0.03 nm,and that of the attached AMD is 291.0±19.3 nm;the unattached AMD of RaB is 0.94±0.05 nm,and that of the attached AMD is 306.6±16.4 nm.Comparing the results of the two algorithms,the AMD of the unattached radon progeny is consistent,and that of the attached raodon progeny is basically the same,with a relative deviation of8.9%.The particle size distribution and unattached fraction under different temperature and humidity conditions were explored.No obvious regular change in particle size distribution with temperature and humidity was observed,and the unattached fraction decreased with increasing humidity.The capture efficiency and the FT ratio of the 30-,100-,200-,and400-mesh wire screens at low and higher flow rates were measured using the imaging plates,and compared with the predictions of Cheng-Yeh theory and Alonso theory.It is concluded that Cheng-Yeh theory is applicable to the condition that the Reynolds number is less than 3.4,and Alonso theory is applicable to the condition that the Reynolds number is greater than 3.4.An iterative subtraction algorithm was introduced for continuous measurement of the unattached radon progeny.Continuous measurement experiments were performed at different radon concentration levels,and compared with a single measurement method:the maximum deviation of C_RaA is 31.2%and the maximum deviation of C_RaB is 40.7%,due to the low concentration level of RaC,the maximum deviation of C_RaC is54.5%.According to the error transfer theory,the errors caused by the statistical fluctuations of the continuous measurement and single measurement at different radon concentration levels were calculated.The results showed that the error of the continuous measurement will not exceed 1.36 times of the single measurement,and the reliability of the method meets the requirements.