Dosimetric impact of natural terrestrial radioactivity on residents of lower Himalayas, India.

A comprehensive radio-ecological evaluation of soil samples of Solan and Shimla districts of Himachal Pradesh has been carried out for risk and dose assessment. Twenty-six randomly selected environmental soil samples were analysed for natural radionuclide concentrations (226 Ra, 232 Th and 40 K) using NaI(Tl) scintillator detector. The average concentration of 226 Ra, 232 Th and 40 K was observed as 37, 59 and 430 Bq kg-1 , respectively, which exceeded the worldwide average of 33, 45 and 412 Bq kg-1 reported by UNSCEAR (Sources and effects of ionizing radiation. Report to the general assembly with scientific annexes, New York, 2008). Radium equivalent activity (Raeq ), hazard indices (Hex , Hin ) and radioactivity level indices (Iϒr , Iα , AUI) and Clark value were checked against their threshold limits, and their mean values were safely below the recommended criteria. This confirms the soil applicability for construction purposes. Indoor and outdoor dose rates (Ḋ), age-dependent annual effective doses (AED), organ-specific doses and lifetime attributable cancer risk (both cancer incidence and cancer mortality) were also computed. Strong positive correlation was established between radon/thoron exhalation rate and their parent radionuclides. Multivariate statistical technique was employed to explore spatial distribution of radionuclides and homogeneity between various radiological parameters.