Reference levels of natural radioactivity for the beach sands in a Brazilian southeastern coastal region

Gamma dose rates of ten beaches in Ilha Grande, an island of Brazilian southeastern cost, were measured in situ using an environmental radiation detector. The values ranged from 62 nGy h-1 at Dois Rios Beach to 126 nGy h-1 at Preta Beach. The activity concentrations of radionuclides 232Th series, 238U series and 40K in three different sand profiles (0-10, 10-20 and 20-30 cm) were measured using gamma ray spectrometry and the result is shown in Bq kg-1. In most of the cases, eight out of ten beaches, 40K was the main contributor to the calculated local gamma dose rate. The annual effective doses were 0.15±0.03 mSv yr-1 for Preta and 0.10±0.02 mSv yr-1for Caxadaço beaches, while in the others beaches the mean value of annual effective doses was 0.08 mSv yr-1. None of the beaches analysed were considered a radiological risk.