  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 gamma-ray spectroscopy. The rock samples were
pulverized, sealed in 1 litre plastic Marinelli beakers, and measured in the
laboratory with an accumulating time between 10 and 14 hours each. From the
measured gamma-ray spectra, activity concentrations were determined for Th-232
(range from 1 to 906 Bq/kg), U-238 (from 1 to 588 Bq/kg) and K-40 (from 50 to
1606 Bq/kg). The total absorbed dose rates in air calculated from the
concentrations of the three radionuclides, Th-232 and U-238 series and K-40,
ranged from 7 to 1209 nGy/h for full utilization of the materials, from 4 to
605 nGy/h for half utilization and from 2 to 302 nGy/h for one quarter
utilization. The total effective dose rates per person indoors were determined
to be between 0.02 to 2.97 mSv/y 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, two of
them meet the upper dose limit of 1 mSv/y and only one exceeds clearly this
limit.
