Variation of natural radioactivity in sediments of beach placers along the eastern coast of India

Natural radiation measurements for 232Th and 238U were undertaken for the first time in the subsurface area, at the eastern coastal part of India. The primary objective of the present study was to study the dependence of specific grain sizes exhibiting higher abundance of radioactivity, irrespective of their depths. This would enable to optimize the fraction with specific grain size for effective mining in view of the resource potential. The relationship between the radioactivity counts of 232Th and 238U with grain size has been established in this article for the first time. The site of coring has been chosen based on handheld Gamma survey meter. The sand size range between 125 and 180 µm contains more 232Th and 238U counts as compared to the more extensive size range. The average activity concentrations of radioactive elements such as 232Th and 238U were obtained using a HPGe detector and found to be 371.42 ppm, 211.17 ppm, and 405.66 ppm for 232Th and 13.05 ppm, 10.77 ppm and 19.16 ppm for 238U, respectively, for Core-1, 2 and 3. Core-1, being close to the Rushikulya river, the deposition of sediments is affected by fluvial and allied marine processes. The upper part of Core-3 is more affected by various processes, but the deeper part is less affected and deposition as well as sedimentation played a crucial role in subsurface enrichment. The enhanced Th/U ratio in the entire study area, irrespective of grain size and depth provides an opportunity for Th exploration for recent advance in technological application and defence system. The major providers for the enhanced level of 232Th and 238U are monazite and zircons, the SEM analysis also confirmed the presence of monazite and zircons.