Radioactivity dosage evaluation of brazilian ornamental granitic rocks based on chemical data, with mineralogical and lithological characterization

Abstract

One hundred samples of granitic rock were collected fram granite traders in Belo Horizonte. Autoradiography, optical microscopy, diffractometry and chemical analysys (x-ray spectrometry, x-ray fluorescence, neutron activation, gravimetry and electron probe microanalysis) were used to determine the mineral assemblages and lithotypes.Chemical analysis revealed uranium concentrations minor 30 ppm and thorium. minor 130 ppm. Higher concentrations generally correlated with high concentrations of light rare earths in silica-rich rocks of granitic composition. Calculations were made of radioactive doses for samples, of floor tiles in a standard room, with total concentration of uranium and thorium greater than 60 ppm. On the basis of calculations of 232Th, 40K and 226 Ra from analysis of Th, K, and U, the doses calculated were between 0.11 and 0.34 mSv/year, which are much lower than the acceptable international exposure standard of 1.0 mSv/year.