Direct Measurement of Activity Concentrations and Assess to Cancer Risk of Radon and Thoron in Homes the Towns of Moanda and Franceville, South-East Gabon

The purpose of the present study was to carry out measurements of the activity concentrations of radon (222Rn) and thoron (220Rn) in homes, to calculate the annual effective inhalation dose and the induced risk of lung cancer associated with the exposure to 222Rn and 220Rn, for individuals living in the towns of Moanda and Franceville, in Gabon. One hundred (100) radon-thoron detectors of the brand RADUET were deployed in these localities, 50 per city, i.e., one detector per home. The results of the radon concentrations varied in the range 91-156 Bq m-3 in Moanda, with arithmetic and geometric mean values of 113.2 ± 2.8 Bq m−3 and 111.8 (1.0) Bq m−3, respectively, and in the range 76-139 Bq m-3 in Franceville, with arithmetic and geometric mean values of 105.0 ± 1.9 Bq m−3 and 104.2 (1.0) Bq m−3, respectively. These mean values are above the United Nations Committee on the Effects of Atomic Radiation (UNSCEAR) worldwide average values of 40 Bq m−3 (arithmetic mean) and 45 Bq m−3 (geometric mean). For thoron, the concentrations varied in the range 3-945 Bq m−3, with arithmetic and geometric mean values of 69.5 ± 0.4 Bq m−3 and 24.4 (3.9) Bq m−3 at Moanda, and in the range 4-78 Bq m−3, with arithmetic and geometric mean values of 18.4 ± 0.4 Bq m−3 and 11.6 (0.4) Bq m−3 in Franceville. This shows that the mean concentration values of thoron were significantly higher than the UNSCEAR world average value of 10 Bq m−3. Overall, the highest concentration values were recorded in the town of Moanda and the lowest in the town of Franceville. The dose values estimated in the present study demonstrate that the population in Moanda and in Franceville may be exposed to a relatively significant potential risk of radon-and thoron-induced cancer.