Concentrations of 222Rn, 220Rn and their progeny in residences in Hong Kong

The standardized charcoal canisters of diameter 4″ recommended by USEPA for passive measurements of 222Rn concentrations were modified for active air sampling. Through calibrations, the concentrations of 222Rn and 220Rn in air can be simultaneously obtained by counting the areas under the γ-ray peaks for 222Rn and 220Rn progenies using an HPGe γ-spectrometer. 222Rn and 220Rn concentrations in 62 residences in Hong Kong were surveyed. In addition, the potential α-energy concentrations (PAEC) of 222Rn and 220Rn progeny were simultaneously recorded at the same sites. The mean values of gas concentration, PAEC and equilibrium factor for 222Rn are 27±9 Bq m-3, 1.8±1.4 mWL and 0.24±0.13, respectively, and the corresponding values for 220Rn are 11±4 Bq m-3, 1.2±0.9 mWL and 0.029±0.015, respectively. Factors affecting the concentrations of 222Rn and 220Rn and progeny were also studied, including the air-cooling method, building characteristics, site location and meteorological parameters.