ABSTRACT
Objective:To study the levels and variation of equilibrium factor in indoor environment.Methods:A one-year continuous measurement of radon concentration and equilibrium equivalent radon concentration was carried out in an indoor office building of Nanning city. The effective data acquisition rates of radon gas and radon progeny were 99.9% and 86.7%, respectively.Results:The annual average activity concentration and equilibrium equivalent radon concentration in indoor environment were (50.9±20.7)and (15.5±10.1)Bq/m 3, both of which had the same diurnal and seasonal variation. The average annual value of equilibrium factor was 0.30±0.12, showing no obvious diurnal variation. The distribution of monthly mean value of equilibrium factor showed a similar trend to that of radon and radon progeny. The highest and the lowest value appeared in November and June, respectively, with 0.47±0.24 and 0.19±0.06. Conclusions:Due to the large variation range of monthly mean value of equilibrium factor in indoor environment, when annual effective dose of radon exposure was estimated based on radon gas concentration, attention should be paid to choose the quantity value of equilibrium factor and the uncertainty caused by the change of equilibrium factor should be considered.