Contribution of Thoron and Its Progeny to the Effective Dose by Inhalation in the Uranium-Thorium Bearing Regions of Mayo Kebbi and Guéra in Chad

Abstract

Abstract In recent years, technological developments and hypotheses made by some researchers have revealed that the effective inhalation dose from thoron and its progeny was underestimated. This study uses direct measurements to show the significant contribution of thoron progeny to the effective inhalation dose. To achieve this, radon-thoron discriminative detectors (RADUET) and thoron progeny monitors were used for the simultaneous measurement of radon, thoron, and thoron progeny in 150 selected houses in the townships of Bitkine, Mongo, Léré, and Pala in southern Chad. By solid-state detection, concentrations of radon, thoron, and thoron progeny were measured and associated effective doses evaluated. The mean concentrations of radon, thoron, and thoron progeny were 62 (1), 60 (2), and 7.6 (2.1) Bq m−3, respectively. These concentrations are above the corresponding global average values. The equilibrium factor of the thoron varied considerably from one municipality to another. The average total annual effective dose by inhalation was estimated to be 4.23 mSv. The contribution of thoron and its progeny to the total inhalation dose ranged from 5% to 86% with an average of 62%. Considering the above, public exposure to thoron and its associated progeny is a public health concern in a similar way to radon.