Natural radioactivity at beach sands in Ilha Grande, Southeastern Brazil

In order to analyze temporal variability on the gamma dose absorbed in the air in beaches in Ilha Grande, Brazil, in 2011–2012 new measurements were made in four of ten beaches analyzed previously in 2001. The measurements were performed directly with a proportional detector. The values varied between 47 ± 5 (Lopes Mendes) and 97 ± 11 nGyh−1 (Caxadaco) Praia Preta. The average annual effective dose was 0.08 ± 0.02 mSv year−1 , in line with the world average of effective external doses, 0.07 mSv year−1 according to UNSCEAR. No statistically significant change was observed after 10 years.