Natural radiation distribution of soils at Kotagiri Taluk of the Nilgiris biosphere in India

The systematic study of background radiation and the distribution of radionuclides in the environment of Nilgiris biosphere in South India, have been carried out with an objective of establishing reliable baseline data on the background radiation level of the region. Soil samples have been collected at various places of Kotagiri taluk in Nilgiris biosphere and are analyzed for radioactivity measurements of primordial radionuclides by 3'x3' Nal(TI) gamma-ray spectrometer. It is observed that the average activity of 232Th series, 238U series and 40K in soil samples is found to be 102 Bq x kg-1, 41 Bq x kg-1 and 229 Bq x kg-1, respectively which contributes to a total gamma-dose of 86 nGy x h-1. Results of this systematic investigation establish the existence of wide range of variation in 232Th series, 238U series and 40K activities, which may be attributable to the existence of wide variety of lithological compounds in the zone under study. The ambient gamma-radiation dose measured is found to vary from 91 to 193 nGy x h-1 with a mean of 142.8 nGy x h-1. The measured ambient gamma-dose is more than 50% of the dose calculated from soil activities, which is due to the higher cosmic ray contribution to the total dose in the environment. The data is compared with different places around the world and the results are discussed in this paper. (author)