Assessment of ambient gamma dose rate around a prospective uranium mining area of South India - A comparative study of dose by direct methods and soil radioactivity measurements

Indoor and outdoor gamma dose rates were evaluated around a prospective uranium mining region - Gogi, South India through (i) direct measurements using a GM based gamma dose survey meter, (ii) integrated measurement days using CaSO4: Dy based thermo luminescent dosimeters (TLDs), and (iii) analyses of 273 soil samples for Ra-226, Th-232, and K-40 activity concentration using HPGe gamma spectrometry. The geometric mean values of indoor and outdoor gamma dose rates were 104 nGy h(-1) and 97 nGy h(-1), respectively with an indoor to outdoor dose ratio of 1.09. The gamma dose rates and activity concentrations of Ra-226, Th-232, and K-40 varied significantly within a small area due to the highly localized mineralization of the elements. Correlation study showed that the dose estimated from the soil radioactivity is better correlated with that measured directly using the portable survey meter, when compared to that obtained from TLDs. This study showed that in a region having localized mineralization in situ measurements using dose survey meter provide better representative values of gamma dose rates. (C) 2014 The Authors. Published by Elsevier B.V.