Dose rate calculation caused by natural radioactivity in granite samples used as building materials in Iran

All building materials contain various amounts of natural radioactive nuclides. Materials derived from rock and soil contain mainly natural radionuclides of the uranium (238U) and thorium (232Th) series, and the radioactive isotope of potassium (40K). Radiation exposure due to building materials can be divided into external and internal exposure. The external exposure is caused by direct gamma radiation. The internal exposure is caused by the inhalation of radon (222Rn), thoron (220Rn) and their short-lived decay products. In this study, the external exposure caused by direct gamma radiation from granite samples as the building materials is considered. Total absorbed dose rate and annual effective dose rate in air due to under test granite samples were calculated. The obtained values for absorbed dose rate in all samples, except for sample No. 2 is more than the corresponding population-weighted world-averaged value of 60 nGy h−1. Applying dose criteria recommended by the European Commission Report on Radiological Protection Principles Concerning the Natural Radioactivity of Building Materials, 1999 for superficial materials, all investigated samples meet the exemption dose limit of 0.3 mSv y-1.