The radioactivity concentrations of 226Ra, 232Th and 40Kwere measured using gamma-ray spectroscopy with NaI (Tl) detectors in four tantalitemining sites in the Oke-Ogun area, South-Western Nigeria. The measured values of theactivities of 40K, 226Ra and 232Th in the soil sampleswere found to lie in the ranges 123.7 ± 3.8 – 1372.3 ± 8.6, 16.8 ± 1.6 – 71.1 ± 2.53 and3.0 ± 0.7 – 31.9 ± 1.0 Bq kg–1, respectively. These samples were also found to have radiumequivalent activity in the range 74.2–121.0 Bq kg-1. Values of 0.2–0.3 for the externaland 0.3–0.4 for the internal hazard indices were estimated for the samples and the annualeffective dose varied from 70.3 ± 13.5 to 100.8 ± 42.8 µSv with a mean of 87.5 ± 18.6 µSvy–1. The annual effective dose is higher than the world average.
