Determination of Thoron Activity Concentration in Soils of Vi, Shaffa and Garta Sama Communities, Michika Local Government Area, Adamawa State, Nigeria

Abstract

Thoron (²²⁰Rn) is often disregarded in environmental radioactivity surveys because of its short half-life of 55.6 s, yet its short-lived decay products can contribute a non-trivial share of the inhalation dose received close to the ground surface, particularly in areas underlain by thorium-bearing lithologies. This study reports the activity concentrations of thoron and radon (²²²Rn) determined in soils of the Vi, Shaffa and Garta Sama communities of Michika Local Government Area, Adamawa State, Nigeria, an area associated with artisanal mineral extraction and previously reported enrichment in uranium- and thorium-series radionuclides. Twenty-five soil-gas stations were established at 50 m, 100 m, 200 m, 500 m and 2 km from fixed reference points within the two communities, and radon and thoron activity concentrations were obtained in situ with a RAD7 electronic radon/thoron detector coupled to a soil-gas probe. Thoron activity concentration ranged from 117 to 3,580 Bq/m³, with a mean of 1,345.4 Bq/m³, while radon ranged from 75 to 210 Bq/m³, with a mean of 133.0 Bq/m³. Mean thoron and radon levels were markedly higher in Vi, Shaffa (1,767.5 and 155.6 Bq/m³, respectively) than in Garta Sama (712.2 and 99.2 Bq/m³, respectively). A moderate-to-strong positive correlation was found between radon and thoron (r = 0.75, R² = 0.56), and the thoron-to-radon ratio averaged 9.5, confirming that thoron dominates the soil-gas radioactive inventory of the study area. These results are consistent with reports of elevated natural radionuclide content in Michika soils and highlight the need for routine thoron monitoring, alongside radon, in radiological risk assessments of mineralised terrains