Geospatial trends of radon, thoron, and their progeny, and inhalation dose prediction in the diamond mining areas of Yokadouma and Mobilong, Eastern Cameroon

Radon (²²²Rn) and thoron (²²⁰Rn) with their progeny (RnP and TnP) are naturally occurring gases posing health risks when accumulated indoors. This study presents the first geostatistical mapping of indoor exposure to these radionuclides in the diamond mining regions of Yokadouma and Mobilong, eastern Cameroon. Over 101 days, activity concentrations were measured in 50 dwellings using radon - thoron discriminative detectors (RADUET) and progeny sensors (DRPS/DTPS). Data were log-linearly normalised and spatially interpolated by ordinary kriging in ArcGIS to assess long-term human and environmental impacts in radiologically enriched mining areas. Radon concentrations ranged from 12.3 to 198.7 Bq m^-³, thoron from 9.8 to 389 Bq m^-³, with progeny levels of 0.3-2.7 Bq m^-³ (RnP) and 0.2-2.1 Bq m^-³ (TnP). Estimated annual effective doses varied from 0.3 to 9.7 mSv y^-¹. Active mining sites accounted for over 50 % of RnP and TnP levels due to granite and thorium-rich bedrock. Inhalation doses averaged 5.4 ± 0.8 mSv y^-¹ in active mines, 4.8 ± 0.7 mSv y^-¹ in nearby villages, and 3.6 ± 0.5 mSv y^-¹ in Yokadouma. About 26 % of homes exceeded the ICRP's 6 mSv y^-¹ limit, mainly in poorly ventilated mining zones. Kriging and variogram modelling identified high-risk zones requiring intervention. Spatial variability correlated with building materials and ventilation. The inactive Mobilong site showed minimal influence (< 5 %). Findings emphasise mining's role in enhancing indoor radiological hazards and support targeted monitoring and mitigation policies.