Study on ²²⁰Rn Equilibrium Factor in China Traditional Dwellings

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