Determination of specific activity of 226Ra, 232Th and 40K for assessment of radiation hazards from Turkish pumice samples

The specific activity of 226Ra, 232Th and 40K in 52 Turkish pumice samples collected from 11 geographical areas located in Central Anatolia, Eastern Anatolia, Mediterranean and Aegean regions was determined by gamma-ray spectrometry with a high-purity germanium (HPGe) detector. The specific activity of 226Ra, 232Th and 40K ranged from 12.7 ± 0.5 to 256.2 ± 9.1 Bq kg−1 with a mean of 89.1 ± 65.2 Bq kg−1, 12.3 ± 1.0 to 237.9 ± 12.2 Bq kg−1 with a mean of 87.0 ± 61.4 Bq kg−1 and 300.1 ± 5.5 to 1899.0 ± 30.8 Bq kg−1 with a mean of 1211.9 ± 419.8 Bq kg−1, respectively. Elemental concentrations were determined for U (from 1.0 to 20.7 ppm with a mean of 7.2 ± 5.3 ppm), Th (from 3.0 to 58.6 ppm with a mean of 21.4 ± 15.1 ppm) and K (from 1.0 to 6.1% with a mean of 3.9 ± 1.3%). The radium equivalent activity (Raeq), the activity index, the emanation coefficient, the 222Rn mass exhalation rate, the indoor absorbed dose rate and the effective dose rate were estimated for the radiation hazard of the natural radioactivity in all samples. The calculated mean Raeq value was 306.6 ± 177.7 Bq kg−1 (54.6 ± 5.5 to 737.6 ± 49.0 Bq kg−1) for all pumice samples. This value is lower than the recommended limit value of 370 Bq kg−1 for building raws and products. The emanation coefficient and the 222Rn mass exhalation rate of all samples ranged from 29.4 to 42.9% with a mean of 36.2% and from 11.0 to 196.4 μBq kg−1 s−1 with a mean of 73.5 μBq kg−1 s−1, respectively. The mean indoor absorbed dose rate and the corresponding mean effective dose rate were 274.6 ± 153.6 nGy h−1 (50.4–644.6 nGy h−1) and 1.35 ± 0.75 mSv y−1 (0.24–3.16 mSv y−1), respectively. For all pumice samples the mean indoor absorbed dose rate is about three times higher than the population-weighted average of 84 nGy h−1, while the mean effective dose rate values except for PUM 05, PUM 06, PUM 10 and PUM 15 exceed the dose criterion of 1 mSv y−1.