Assessment of the natural radioactivity in the Brazilian state of Rio Grande do Norte

Fifty-one soil samples were collected to a depth of 30 cm in the central and eastern region of the Brazilian state of Rio Grande do Norte. Concentrations of background radionuclides in soil samples were determined by gamma ray spectrometry with an HPGe detector. The average concentrations of 226Ra, 232Th, and 40K in the surveyed soils were 29.0 +/- 19.4 Bq kg-1, 46.6 +/- 36.2 Bq kg-1, and 677.8 +/- 434.9 Bq kg-1, respectively. The bedrock of Santana do Matos (Rio Grande do Norte) showed fairly high radioactivity (90 Bq kg-1 of 226Ra, 285.6 Bq kg-1 of 232Th, and 1,414 Bq kg-1 of 40K). Radiological measurements carried out in Santana do Matos with a hand-held scintillometer revealed external gamma radiation ranging from 200-330 nGy h-1 in the down-town area. Higher values were recorded in the surroundings of that town.