Microscopic Observations and Natural Radioactivity Hazzard Indices in Granites Used in Dwelling

Abstract: The distribution of 226Ra, 232Th and 40K in 62 granitoid samples obtained from 13 plutons of Iran was microscopically and isotopically studied in detail. Microscopic observations and systematic data analyses are consistent and reveal the presence of radioactive minerals (e.g. zircon, apatite and titanite) particularly for samples which are rich in radioactive element concentration. The average activities of the measured radionuclides varied up to 128 Bq kg-1 for 226Ra, up to 118.6 Bq kg-1 for 232Th, and up to 1385.46 Bq kg-1 for 40K, with mean values of 60.39, 78.47, and 884.72 Bq kg-1, respectively, which are higher than the standard values given for granites worldwide. To asses the radiation hazards associated with granite sampes, average radium equivalent activity (240.72 Bq kg-1), outdoor and indoor external hazard indices (0.65012-0.325061), internal hazard index (0.81334), annual effective dose rate (0.13759 mSv/yr), excess life cancer risk (0.48155 mSv/yr), and gamma radiation index (0.88856) were calculated. The average hazard indices of Iranian granites are smaller than the permited limit given by UNSCEAR for public porposes, however there is some radiological risk from the usage of samples studied as internal decorative and ornamental building materials in dwellings. Due to higher radiological hazard indices in granites of Birgand, Kordestan, Zanjan, Azerbayjan and Takab, certain caution is required when using these granites in private locations.