Radioactivity of building materials in Mahallat, Iran - an area exposed to a high level of natural background radiation - attenuation of external radiation doses

In this study, mass activity of naturally occurring radioactive materials were measured in twenty-three building material samples, use extensively in the area exposed to a high level of natural background radiation (Mahallat, Iran), to determine the radioactivity index and changes to the level of indoor gamma radiation. The mass activity of Th-232, Ra-226 and K-40 were within the ranges from 18 +/- 3 to 44 +/- 10 Bq/kg (average of 27 +/- 6 Bq/kg), 22 +/- 5 to 53 +/- 14 Bq/kg (average of 34 +/- 6 Bq/kg) and 82 +/- 18 to 428 +/- 79 Bq/kg (average of 276 +/- 58 Bq/kg), respectively. The gamma dose rates for population were estimated between 48 +/- 9 and 111 +/- 26 nGy/h with exception of radon exhalation from building materials. Since the air kerma rate in the town varies from 0.8 to 4 mu Gy/h, the attenuation coefficient was calculated for buildings made of the afore-mentioned materials. Additionally, the annual gamma radiation doses for inhabitants were calculated based on time spent outdoors and indoors.