Estudo da radioatividade natural em areias de praias do extremo sul da Bahia utilizando métodos de análises nucleares

Abstract

The natural radioactivity was determined in the beaches sands from extreme south of Bahia in seven locations: Arraial D'Ajuda, Porto Seguro, Trancoso, Caraíva, Cumuruxatiba, Prado and Caravelas. Neutron Activation Techniques Analysis (Instrumental Neutron Activation Analyses was used for determination of 232Th and Delayed Neutrons Analysis for determination of uranium) and Gamma Spectrometry Analysis (for determination of the 226Ra, 214Pb, 228Ac and 40K). The mean specific activity for 238U was higher in Cumuruxatiba and Alcobaça than in others locations studied. The values of the specific activities of 226Ra and 232Th in Cumuruxatiba, Trancoso and Alcobaça are above average worldwide, the mean of 40K was higher in Cumuruxatiba than in others locations. The rate absorbed dose in ar, annual effective dose and gamma ray radiation hazard also were measured. The dose absorbed in the outdoor air at 1 m ranged from 21 to 14,450 nGy h-1 with value average of 1792 nGy h-1. The highest average value was found in Cumuruxatiba (15,100 nGy h-1). The effective dose annual ranged between 0.025 and 18.50 mSv a-1, with average of 2.162 mSv a- 1. Values in Arraial D'Ajuda, Trancoso, Alcobaça, Caraíva and Cumuruxatiba were greater than global average (0,07 mSv a-1). The mean value of annual effective dose rate outdoor in Cumuruxatiba (17.72 mSv a-1) is considered as a region with high background (HBRA). Values of gamma ray radiation hazard considered the sands from Caraíva, Alcobaça and Cumuruxatiba unsafe for use as building material. In this work use the MCNP-5 code, based on the method Monte Carlo, to compare the experimental aboslute efficiency curve obtained by the simulated aboslute efficiency curve. The experimental data showed agreement with the simulated, however for the lower energies were disagreement, because the sensitive volume of the germanium crystal it is not considered.