RESUMO
The aim of this study was to evaluate the concentrations of naturally occurring radioactive nuclides 226Ra, 232Th and 40K and corresponding dose rates over atomic mineral occurrences of Dharmapuri shear zone in parts of Salem, Dharmapuri, Krishnagiri, and Vellore districts of Tamilnadu, India. In this paper, area-wise ternary diagrams of Ra, Th and K were plotted to study their relative concentration in the samples. Correlation study was also carried out to delineate the contribution of individual radionuclides toward the measured gamma dose rate. The concentrations of Ra, Th and K were determined by gamma ray spectrometry system using a 5" × 4" NaI (Tl) detector assembly. The geometric mean values of the estimated annual effective outdoor dose equivalent (AEDE) in mSv/y in the four areas were 2.35, 0.72, 1.88 and 0.36. A good linear correlation was observed between the estimated and measured annual effective dose equivalent.