Measurement of natural radioactivity of Iranian granite samples using beta–gamma coincidence spectrometer and maximum likelihood method

Any exposure to ionizing radiation can cause undesirable biological effects. To estimate the direct radiation exposure to the public, an accurate investigation of the natural radioactivity level from building materials is required. Granite stone contains primordial radionuclides and commonly used as a decorative material in dwellings. In this paper, the radioactivity contents of 48 granite samples were measured using a gamma–beta-radiation spectrometer and the absorbed dose rate due to gamma radiations, radium equivalent activity, annual effective dose rate and internal and external hazard indices associated with these materials were assessed. The results showed that the most of the studied granite samples that incorporated in constructions appear to be safe as building material but some samples have hazard indices more than the maximal permitted values for building materials (1 mSv year⁻¹) and are not quite safe to be used indoors.