Radon-thoron discriminative measurements in the high natural radiation areas of southwestern Cameroon.

Although indoor radon was initially measured in the uranium regions of Poli and Lolodorf using Electret Ionization Chambers, discriminative RADUET detectors were deployed in 70 houses of the high natural radiation areas of Bikoue and Ngombas in the uranium region of Lolodorf in Southwestern Cameroon. Radon and thoron concentrations were determined using Image-J and Microscope Methods for track evaluation. Radon and thoron concentrations follow lognormal distributions and ranged respectively from 27 ± 26 to 937 ± 5 Bq m(-3) and from 48 ± 40 to 700 ± 128 Bq m(-3). The arithmetic means of radon and thoron concentrations were found to be 92 ± 3 Bq m(-3) and 260 ± 13 Bq m(-3.) Less than 2% of houses have indoor radon above the reference level of 300 Bq m(-3) and 30% of houses have thoron concentrations above 300 Bq m(-3.) Inhalation doses due to radon and thoron range respectively between 0.6-17.7 mSv yr(-1) and 0.2-3 mSv yr(-1) with the mean values of 1.4 mSv yr(-1) and 1 mSv yr(-1). The contribution of indoor thoron to the total inhalation dose ranges between 15%- 78.5% with the mean value of 47%. Thus thoron cannot be neglected when assessing radiation dose.