Terrestrial Gamma Radiation in Phuket Island, Thailand
Keywords:Gamma dose rate, absorbed dose rate, 226Ra, 232Th, 40K.
The aim of this study was to evaluate the level of terrestrial radioactivity on Phuket Island, which used to be the richest tin province in Thailand. We measured 124 survey points of terrestrial gamma dose rate at one meter above the surface of local soil along roads in the environs of Phuket Island. Another 31 survey points were examined inside an old ore-dressing plant. The terrestrial gamma dose rate of the Island (excluding the abandoned area of the old dressing plant) ranges from 20 to 900 nGy h-1, while the geometric mean Island value was 190 nGy h-1. Soil samples were also collected from selected areas having high gamma dose rates to analyze for activity concentrations of 226Ra, 232Th and 40K. Based on these soil activities, the calculated terrestrial gamma dose rate found to range between 25 and 520 nGy h-1. The corresponding annual effective doses varied between 0.03 and 0.6 mSv y-1. The results of the terrestrial gamma dose rate obtained from direct measurement in the old tin dressing plant ranged from 110-17,170 nGy h-1 with a mean value of 1410 nGy h-1. The terrestrial gamma dose rate calculated from soil samples in the dressing plant ranged from 590 to 206,080 nGy h-1 which corresponding to annual effective dose of 0.7-250 mSv y-1. Thus, the dose rates on much of Phuket Island are within typical background values while the dose rates within the old tin dressing plant are elevated by as much as 16 times background.
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