Survey of radon, thoron and its decay products in two coal mines in Fangshan area of Beijing

The concentrations of radon and thoron as well as thoron decay products (220RnD) have been measured by using passive integral monitors in two coal mines of Beijing areas during summer and winter. The results show that the annual average concentrations of 222Rn, 220Rn and 220RnD in two mines were 292 and 4919 Bqm-3, 91 and 2638 Bqm-3, 0.9 and 6.0 EEC Bqm-3, respectively. The average annual effective doses to the miner from radon and thoron were 2.54-42.9 mSv·a-1 and 0.13-1.43 mSv·s-1, of which only 4.9% and 3.2% of the total doses from thoron. Radon is still the mostly dose source for the miner. A significant seasonal variation in a coal mine was observed. 222Rn and 220Rn concentrations in some sites in summer exceed 10000 Bqm-3. To heighten ventilation in coal mine is important, in order to avoid the miner exposed to the higher radiation. (authors)