Thoron exposure in the radon-thoron prone area of the Adamawa Region, Cameroon

The radon-prone area of the Adamawa region is characterized by high radon concentrations, where no low-risk area was observed. This study aims to investigate about indoor thoron concentration in this area, using RADUET detectors, thoron progeny monitors and DTPS/DRPS. The indoor thoron concentration ranged between 17 and 1000 Bq m(-3), with an average of 131 Bq m(-3). 36% of dwellings have thoron concentration less than 100 Bq m(-3) while 28% are above 300 Bq m(-3). The thoron equilibrium factor of 0.04 was found to be two times higher than the globally assumed value. Thoron progeny contributes on average to 26% (1.9 mSv y(-1)) of the total inhalation dose. The excess lifetime cancer risk due to thoron progeny is about 5%. These results justify that thoron cannot be neglected when assessing radiation doses. As only radon is regulated, such study will contribute to accelerate the regulation on thoron.