Distribution of 226Ra, 232Th, and 40K in soils of Rio Grande do Norte (Brazil)

A survey programme aimed at studying the environmental radioactivity in the Brazilian state of Rio Grande do Norte was undertaken. Fifty-two soil samples, together with two rock and two uraniferrous ore samples were collected from the eastern and central regions of this state. Concentrations of radioelements in samples were determined by γ-ray spectrometry. The average concentrations of 226Ra, 232Th, and 40K in the surveyed soils were 29.2 ± 19.5 (SD), 47.8 ± 37.3, and 704 ± 437Bq kg−1, respectively. Higher values were found in the rock samples. The distributions of 226Ra and 232Th were fitted by log-normal curves. Radiological measurements carried out with a portable scintillometer at the sampled sites revealed an average absorbed dose rate of 55 ± 27 (SD) nGy h−1. Computed dose rates obtained through the Beck formula ranged from 15–179nGy h−1, with a mean value of 72.6 ± 38.7 (SD) n Gyh−1, and their distribution fitted a log-normal curve. An annual average effective dose equivalent of 552 μSv (range: 117–1361 μSv) was estimated for 51 sites in Rio Grande do Norte.