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 226Ra, 232Th and 40K were determined in the soil samples collected from the eastern part of Kumaun Himalaya. The mean concentration of 238U and 232Th 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 238U, 16.3 to 136.3 Bq/kg for 232Th and 124.6 to 1758.0 Bq/kg for 40K. 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 (226Ra, 232Th and 40K), 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 226Ra, 232Th and 40K. Strong positive correlations were observed between 235U and 226Ra, 232Th and 226Ra, 40K and 232Th as well as 40K and 226Ra. However, no significant correlation was observed between 238U and 226Ra because of radioactive disequilibrium between them.