Indoor radon, thoron, and thoron daughter concentrations in Korea

A nationwide survey for radon (222Rn), thoron (220Rn), and thoron daughters has been conducted. The arithmetic mean of annual radon concentration in Korean dwellings was 53.4±57.5 Bq/m3. The indoor radon concentration showed a lognormal distribution with a geometric mean and its standard deviation of 43.3±1.8 Bq/m3. The arithmetic mean of annual thoron and its progeny concentrations in Korean dwellings were 45.2±110.1 and 0.99±1.00 Bq/m3, respectively. The equilibrium factor between thoron and its progeny was 0.022. The arithmetic mean indoor gamma dose rate was 212±52 nGy/h. The radon concentrations in the traditional and modern style houses were about two times higher than those in apartments. The average annual effective doses to the general public from radon, thoron, and gamma dose rate were 1.35, 0.23, and 1.03 mSv/y, respectively.