Radionuclides content of building materials and associated gamma dose rates in dwellings

Irradiation of the human body from external sources is mainly by gamma radiation from radionuclides in the 238U and 232Th series and from 40K. In the uranium series, the decay chain segment starting from 226Ra is radiologically the most important and, therefore, reference is often made to radium instead of uranium. This study deals with the determination of natural radioactivity in twenty igneous rocks used in Italian building construction and with their associated gamma dose rates in dwellings. Common applications of these rocks are for cladding and flooring, but some of these are used, at times, as structural building materials. The radioactivity concentrations of 226Ra, 232Th and 40K were measured using a gamma spectrometer with a HPGe detector. The average values of the measured activities are in the order of 100, 100, and 1000 Bq kg-1, respectively, for the above radionuclides. The calculations of the annual effective dose due to external exposure have been carried out with a methods developed by Markkannen (1995). The dose rate is calculated for a rectangular source of uniform density and activity concentration. The indoor dose rate is calculated by summing the separately calculated dose rates caused by walls, floor and ceiling. Conversion factor of 0.7 Sv Gy-1 is used for converting the absorbed dose in air to the effective dose. The calculated effective dose ranges between 0.1 and 2 mSv y-1.