Gamma dose rates and distribution of natural radionuclides in sand beaches—Ilha Grande, Southeastern Brazil

In order to study the process of dispersion and the activity concentration of 232Th and 238U series and 40K radionuclides in two island beaches in southeastern Brazil, analyses was made of sand samples of 0–10 cm profile, during a 12-month period. Moreover, the monthly variations of gamma dose rates were studied to determine the local environment absorbed dose rate. The average activity concentration of primordial radionuclides 232Th, 238U and 40K at Preta beach, they were 239, 121 and 110 Bq kg−1, while at Dois Rios beach they were 48, 39 and 412 Bq kg−1, respectively. The absorbed dose rate in air, observed at 1 m above the ground, ranged from 54 to 228 nGy h−1 at Preta beach and from 39 to 110 nGy h−1 at Dois Rios beach. The annual effective dose equivalent corresponding to Preta beach is 0.15 mSv a−1 and to Dois Rios 0.08 mSv a−1.