Radiometric analysis of Brazilian commercial ornamental stones

The term "commercial ornamental stones" comprises different natural stones with different mineralogical components and the distribution and amount of natural radionuclides depended on the mineralogy. Few studies on natural radioactivity in ornamental stones carried out in Rio de Janeiro (Brazil) and the present work were carried out in order to analyze the distribution of activity concentration in these materials. The activity concentration of ²³⁸U, ²³⁵U, ²²⁶Ra, ²³²Th and ⁴⁰K in Ornamental Stones measured using γ-ray spectrometry to estimate the radiation hazard as well as establishing a database for radioactivity levels. Samples were collected in stores in Rio de Janeiro, carefully transported, weighed, packed with PVC film and left to rest for at least 45 days to reach secular equilibrium. Samples analyzed by gamma spectrometry using a hyper pure germanium detector (HPGE). Detection efficiency for each sample was obtained using LabSOCS software. The activity concentrations for samples were within the ranges (0.83 ± 0.15 to 39.96 ± 1.19, 8.04 ± 2.54 to 111.36 ± 13.33, 0.43 ± 0.03 to 264.58 ± 0.98, BDL to 8.17± 0.65 and 1.30 ± 0.57 to 1567.01 ± 65.08) Bq⋅kg^-1 for ²³⁸U, ²²⁶Ra, ²³²Th, ²³⁵U and ⁴⁰K, respectively. The world average for building materials is 50 Bq⋅kg^-1 for ²³⁸U, 50 Bq.kg^-1 for ²³²Th and 500 Bq⋅kg^-1 for ⁴⁰K. In the present work, the average for granite was 19.43 ± 0.39 Bq⋅kg^-1 for ²³⁸U, 56.70 ± 1.13 Bq⋅kg^-1 for ²³²Th and 1113.28 ± 20.27 Bq⋅kg^-1 for ⁴⁰K, thus the values for ²³²Th and ²³⁸U are above the world average. Analyzing for the granite that showed the highest concentrations of activity the average values of Transport Rate was 3.12 ± 0.04 Bq⋅m^-2⋅s^-1, Emanation Rate was 0.16 ± 0.00 Bq⋅kg^-1⋅s^-1, Exhalation Flow was 530.26 ± 6.05 Bq⋅m^-3, Effective Equivalent Dose Due to Radon Exposure was 0.78 ± 0.01 WLM⋅year^-1 and Annual Effective Dose Due to Radon and Thoron was 7.02 ± 0.10 mSv⋅year^-1. Annual Effective Dose Due to Radon and Thoron it is above the annual limit for public individuals which is 1 mSv⋅year^-1 and below the occupationally exposed individual, which is 20 mSv⋅year^-1 in an average of 5 years, it does not exceed the maximum level recommended by ICRP-60.