Measurement of radon/thoron exhalation rates and gamma-ray dose rate in granite areas in japan

Radon and thoron exhalation rates and gamma-ray dose rate in different places in Hiroshima Prefecture were measured Exhalation rates were measured using an accumulation chamber method. The radon exhalation rate was found to vary from 3 to 37 mBq m-2 s-1, while the thoron exhalation rate ranged from 40 to 3330 mBq m-2 s-1). The highest radon exhalation rat(37 mBq m-2 s-1) and gamma-ray dose rate (92 nGy hs-1, were found in the same city (Kure City). In Kure City, indoor radon and thoron concentrations were previously measured at nine selected houses using a radon-thoron discriminative detector (Raduet). The indoor radon concentrations varied from 16 to 78 Bq m-3, which was higher than the average value in Japan (15.5 Bq m-3). The indoor thoron concentration ranged from ND (not detected: below a detection limit of approximately 10 Bq m-3) to 314 Bq m-3. The results suggest that radon exhalation rate from the ground is an influential factor for indoor radon concentration. (authors)