Natural radiation in the sands of the Brazilian regions with different rock formations
M. A. Silveira 1*, B. R. Pereira 1, N. H. Medina 2
1 Departamento de Física, Centro Univeristário da FEI
2 Instituto de Física da Universidade de São Paulo
The present work investigated southeastern Brazilian beaches in order to analyze the dose from total external natural radiation. We have applied the gamma-ray spectrometry technique to measure the activities from the radionuclides 40K and the elements from the series of 238U and 232Th, and the associated effective dose levels in air present in each area studied. In order to determine the mineral responsible for the high activity found in one specific site, the sand samples were analyzed with a scanning electron microscope, using Energy-Dispersive X-Ray Spectroscopy (EDS) microanalysis. Sands has been studied with evidence of different rock formations in the region of the beach of Morro Branco Ceara, Itacare beach in Bahia and beaches of the southern state of Sao Paulo. We determined the activities of radionuclides 40K, 238U and 232Th present in each sample and calculated the effective dose in [mSv / year] of each one. A sample collected on the beach in Itacare showed a value of effective dose of 2.5 (a) mSv / year. This value is higher than the international average dose of 0.48 mSv / year (annual typical range (0.3 - 0.6 mSv) indicated by the United Nations Scientific Committee on the Effects of Atomic Radiation), mainly due to the presence of 238U in an amount greater than is typically found. The values found for other samples were 0.162 (56) mSv / year to the white sand , 0.114 (34) mSv/year for the orange sand , 0.0925 (43) mSv/year for the red sand of the sea cliffs in Ceará; and 0.0135 (31)mSv/year for the Praia Grande beach, in São Paulo state.