Gamma radiation measurements and dose rates in commercially-used natural tiling rocks (granites)

The gamma radiation in samples of a variety of natural tiling rocks (granites) imported in Cyprus for use in the building industry was measured, employing high-resolution γ-ray spectroscopy. The rock samples were pulverised, sealed in 1-l plastic Marinelli beakers, and measured in the laboratory with an accumulating time between 10 and 14 h each. From the measured γ-ray spectra, activity concentrations were determined for 232Th (range from 1 to 906 Bq kg−1), 238U (from 1 to 588 Bq kg−1) and 40K (from 50 to 1606 Bq kg−1). The total absorbed dose rates in air calculated from the concentrations of the three radionuclides ranged from 7 to 1209 nGy h−1 for full utilization of the materials, from 4 to 605 nGy h−1 for half utilization and from 2 to 302 nGy h−1 for one quarter utilization. The total effective dose rates per person indoors were determined to be between 0.02 and 2.97 mSv y−1 for half utilization of the materials. Applying dose criteria recently recommended by the EU for superficial materials, 25 of the samples meet the exemption dose limit of 0.3 mSv y−1, two of them meet the upper dose limit of 1 mSv y−1 and only one clearly exceeds this limit.