Study on 220Rn equilibrium factor in China traditional dwellings

The spatial distribution and seasonal variation of 220Rn concentration (CTn) and its progeny concentration (Cp,Tn) in China traditional dwellings constructed with soil were studied. The results show that the spatial distribution of CTn appears a significant concentration gradient, and decreases exponentially from the distance of source (bare walls or ground), while there is a good linearity and repeatability. The seasonal variation of CTn displays maximum value in autumn and minimum value in winter. The seasonal variation of Cp,Tn comparing with CTn and Cp,Rn is similar, and its spatial variation can be ignored. Therefore, fixing the distance distance of 220Rn form source, there is a definite relationship between CTn and Cp,Tn. 220Rn equilibrium factors FTn respectively are 0.003±0.001 and 0.017±0.014 at the distances of 2.5 cm and 20 cm from wall. The Cp,Tn results of actual measurement in traditional houses are in good agreement with the calculated values by using FTn. The measurement to 220Rn gas is more easily achieved comparing with 220Rn progenies. The introduction of FTn provides a simple and reliable method for assessment of 220Rn exposure. (authors)