Radon concentration in Beijing underground buildings and assessment of the internal dose equivalent

The measurement results of the average radon concentration in 220 underground buildings in Beijing by the passive integrating activated charcoal method are given. Except nature cave, the indoor radon concentrations in 198 underground buildings appear a lognormal distribution. Geometric mean and geometric standard deviation are 0.79 and 2.3 pCi/L respectively, arithmetic mean is 1.10 pCi/L. The annual effective dose equivalent of population and occupation in the underground buildings due to exposure to radon and its daughters are 1.39 and 1.20 mSv respectively, 31% and 13% more than that of corresponding groups in the ground buildings respectively