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The radioactivity concentrations of 226Ra, 232Th and 40K were measured using gamma-ray spectroscopy with NaI (Tl) detectors in four tantalite mining sites in the Oke-Ogun area, South-Western Nigeria. The measured values of the activities of 40K, 226Ra and 232Th in the soil samples were found to lie in the ranges 123.7 ± 3.8 - 1372.3 ± 8.6, 16.8 ± 1.6 - 71.1 ± 2.53 and 3.0 ± 0.7 - 31.9 ± 1.0 Bq kg-1, respectively. These samples were also found to have radium equivalent activity in the range 74.2-121.0 Bq kg-1. Values of 0.2-0.3 for the external and 0.3-0.4 for the internal hazard indices were estimated for the samples and the annual effective dose varied from 70.3 ± 13.5 to 100.8 ± 42.8 μSv with a mean of 87.5 ± 18.6 μSv y-1. The annual effective dose is higher than the world average. [ABSTRACT FROM AUTHOR]