Evaluation of Radon ́s Emission in Ornamental Rocks

The representative organizations of the sector of ornamental rocks had looked the Commission of Nuclear Energy by means of the Center of Mineral Technology Espirito Santo (CETEM-ES) requesting aid how much the evaluation of levels of radiation in Brazilian ornamental rocks, exported to U.S.A. for use as material coverings in residences. Exhalation of radon (Rn) from these exotic granites may expose the occupants to an increased risk of contracting lung cancer. The objective of this work was to evaluate the risk associated with the exhalation of radon of indoor covering plates in environments, by means of nuclear techniques and to use models of calculation of dose endorsed internationally. For in such a way, the characterizations radiometric and mineralogical of three types of silicatic rocks used for covering have been carried through, determining the rates of exhalation and concentration of radon ́s activity in the chosen materials. Introduction The Brazilian industrial sector produces a great variety of granites, marbles, quartzite etc., reaching to all about 500 different types of rocks. Normally, these ornamental rocks are classified by corporate names, the producing state, the geologic origins and mineralogical composition. However, they are not classified by radiological activity. The study of radioelement ́s concentrations in granites rocks is important for the classification granite petrography for application in civil construction. Granites are an example of rocks that contain a natural enrichment of uranium 238 (U); thorium 232 (Th) and potassium 40 (K). The concentrations of these elements in the rock vary significantly from sample to sample. However studies have shown that the general petrography characteristic is closely correlated to the concentration of these radioactive elements (Whitfiel et al. 1959). In terms of surface mobility, uranium and potassium can easily be oxidized into water soluble compounds that can be leached from the surface matrix and deposited in sediments far from the origin of the rock. On the other hand, Thorium, which is less water soluble, is less susceptible to leaching and tends to stay within the rock matrix. Thus, over time this difference in solubility results