Radionuclide analysis in the soil of Kumaun Himalaya, India, using gamma ray spectrometry

Environmental release of low levels of radioactivity can occur as a consequence of normal radionuclides present in the earth's crust. We present here the results of a survey undertaken in 2003 on the radionuclide concentration in different rock formations in the eastern part of Kumaun Himalaya. The activity concentration and gamma-absorbed dose rates of the terrestrial radionuclides caused by Ra-226, Th-232 and K-40 were determined in the soil samples collected from the eastern part of Kumaun Himalaya. The mean concentration of U-238 and Th-232 in the earth's crust varied from 0.5 to 5 ppm (6 to 60 Bq/kg) and 2 to 20 ppm (8 to 80 Bq/kg) respectively. The reported activity concentration for the different rock formations varied from 32.6 to 1305.5 Bq/kg for U-238, 16.3 to 136.3 Bq/kg for Th-232 and 124.6 to 1758.0 Bq/kg for K-40. The distribution of the radionuclides varied with rock type due to different chemical properties of the measured radionuclides and the rocks. The result shows that high activity levels were found in Saryu Formation consisting of augen-gneiss, granite interbedded with schists and flaggy quartzite. The total air-absorbed dose rate in air above 1 m height was calculated from the three radionuclides (Ra-226, Th-232 and K-40), which varied from 39.1 to 226.8 nGy h(-1). The internal and external health-hazard indices were calculated based on the concentration of Ra-226, Th-232 and K-40. Strong positive correlations were observed between U-235 and Ra-226, Th-232 and Ra-226, K-40 and Th-232 as well as K-40 and Ra-226. However, no significant correlation was observed between U-238 and Ra-226 because of radioactive disequilibrium between them.