External gamma-ray dose rate and radon concentration in indoor environments covered with Brazilian granites |
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Authors: | Anjos R M Juri Ayub J Cid A S Cardoso R Lacerda T |
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Affiliation: | a LARA - Laboratório de Radioecologia, Instituto de Física, Universidade Federal Fluminense, Av. Gal Milton Tavares de Souza, s/no, Gragoatá, 24210-340 Niterói, RJ, Brazil b GEA-Instituto de Matemática Aplicada San Luis (IMASL), Universidad Nacional de San Luis, Consejo Nacional de Investigaciones Científicas y Técnicas, CCT-San Luis, Ej. de los Andes 950, D5700HHW San Luis, Argentina |
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Abstract: | Health hazard from natural radioactivity in Brazilian granites, covering the walls and floor in a typical dwelling room, was assessed by indirect methods to predict external gamma-ray dose rates and radon concentrations. The gamma-ray dose rate was estimated by a Monte Carlo simulation method and validated by in-situ measurements with a NaI spectrometer. Activity concentrations of 232Th, 226Ra, and 40K in an extensive selection of Brazilian commercial granite samples measured by using gamma-ray spectrometry were found to be 4.5-450 Bq kg−1, 4.9-160 Bq kg−1 and 190-2029 Bq kg−1, respectively. The maximum external gamma-ray dose rate from floor and walls covered with the Brazilian granites in the typical dwelling room (5.0 m × 4.0 m area, 2.8 m height) was found to be 120 nGy h−1, which is comparable with the average worldwide exposure to external terrestrial radiation of 80 nGy h−1 due to natural sources, proposed by United Nations Scientific Committee on the Effects of Atomic Radiation. Radon concentrations in the room were also estimated by a simple mass balance equation and exhalation rates calculated from the measured values of 226Ra concentrations and the material properties. The results showed that the radon concentration in the room ventilated adequately (0.5 h−1) will be lower than 100 Bq m−3, value recommended as a reference level by the World Health Organization. |
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Keywords: | 226Ra 232Th 40K 222Rn Radon exhalation rate Building material |
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