Abstract
A hyper-pure germanium detector-based, gamma-ray spectroscopy, low-background counting system was used to determine the level of natural radioactivity from beach sand samples collected from various locations along the Andaman coast of Thai peninsula following the 2004 tsunami. The activity concentrations of 226Ra, 232Th and 40K were found to lie in the range of 1.6±0.1↔52.5±0.8, 0.3±0.1↔73.9±1.5 and 2.8±0.1↔1,111.9±116.5 Bq.kg-1 respectively for the west coast and 3.5±0.1↔83.1±1.2, 4.5±0.1↔42.0±0.9, and 9.6±1.1↔1,376±144 Bq.kg-1 respectively for the east coast. The radioactivity concentrations of 226Ra, 232Th and 40K along the Andaman coast are comparable to that of the east coast, which was not exposed to the tsunami. The activity concentration of artificial radionuclides (ie. 137Cs) was found to be below the minimum detectable activity. The derived values for external and internal hazard indices for sand samples obtained in this study ranges from 0.01-0.50 and 0.01-0.72 respectively while the radium equivalent activity varied from 2.8-184.8 Bq.kg-1 which are lower than the internationally approved values of <1 for Hex and Hin and <370 Bq.kg-1 for Raeq. None of beach sand samples which were studied could be considered as a radiological hazard to people who were exposed to them. The monitored areas are at the typical local level of radioactivity from natural background radiation. The gamma absorbed dose rates due to 226Ra, 232Th and 40K in the sand samples varied in the range 1.3±0.1 to 86.4±2.5 nGy.h-1 with an average value of 48±1 nGy.h-1. Assuming a 20% outdoor occupancy factor, the corresponding annual effective dose varied from 1.6±0.1 to 105.9±3.1 μSv.y-1 with a mean value of 59.1±0.3 μSv.y-1 , significantly lower than the worldwide average value of 0.07 mSv.y-1 for the annual outdoor effective dose as reported by UNSCEAR(2000).