The exposure of human beings to ionising radiation from natural sources is a continuing and inescapable feature of life on earth. Natural radionuclides are widely distributed in various geological formations and ecosystems such as rocks, soil groundwater and foodstuffs. In the present study, the distribution of (226)Ra, (232)Th and (40)K was measured in soil samples collected from different lithological units of the Thauldhar and Budhakedar regions of Garhwal Himalaya, India. The collected soil samples were analysed using gamma ray spectrometry. The activity concentrations of the naturally occurring radionuclides (226)Ra, (232)Th and (40)K in these soil samples were found to vary from below detection level (BDL) to 131 +/- 18 Bq kg(-1), 9 +/- 6 to 384 +/- 53 Bq kg(-1) and 471 +/- 96 to 1406 +/- 175 Bq kg(-1), respectively. The distribution of radionuclides depends upon the rock formation and chemical properties within the earth. The activity concentrations vary widely depending on the sample origin. The external absorbed gamma dose rates due to (226)Ra, (232)Th and (40)K were found to vary from 49 to 306 nGy h(-1). The average radium equivalent activity from these soil samples was 300 Bq kg(-1).

In the present study, the distribution of natural radionuclides in soil samples collected from different geological units of Kumaun Himalayas are assessed using gamma ray spectrometer with Nal (Tl) detector. The naturally occurring radioactivity concentration of 226 Ra, 232 Th and 40 K were found to vary from 36.4 Bq/kg to 166.6 Bq/kg, 15.3 Bq/kg to 94.7 Bq/kg and 645.9 Bq/kg to 1378.9 Bq/kg, respectively. The total absorbed gamma dose rate was found to vary from 80 nGy/h to 179.6 nGy/h. The resulting dose due to the presence of these radionuclides was estimated from radiation protection point of view. The significance of this investigation is also discussed in details.

: Radon was measured in soil-gas and groundwater in the Budhakedar area of Tehri Garhwal, India in summer and winter to obtain the seasonal variation and its correlation with radon exhalation rate. The environmental surface gamma dose rate was also measured in the same area. The radon exhalation rate in the soil sample collected from different geological unit of Budhakedar area was measured using plastic track detector (LR-115 type II) technique. The variation in the radon concentration in soil-gas was found to vary from 1098 to 31,776 Bq.m -3 with an average of 7456 Bq.m -3 in summer season and 3501 to 42883 Bq.m -3 with an average of 17148 Bq.m -3 in winter season. In groundwater, it was found to vary from 8 to 3047 Bq.l -1 with an average value 510 Bq.l -1 in summer and 26 to 2311 Bq.l -1 with an average value 433 Bq.L -1 in winter. Surface gamma dose rate in the study area varied from 32.4 to 83.6 mR.h -1 with an overall mean of 58.7 mR.h -1 in summer and 34.6 to 79.3 mR.h -1 with an average value 58.2 mR.h -1 in winter. Radon exhalation rate from collected soil samples was found to vary from 0.1 × 10 -5 to 5.7 × 10 -5 Bq.kg -1 .h -1 with an average of 1.5 × 10 -5 Bq.kg -1 .h -1 in summer season and 1.7 × 10 -5 to 9.6 × 10 -5 Bq.kg -1 .h -1 with an average of 5.5 × 10 -5 Bq.kg -1 .h -1 . A weak negative correlation was observed between radon exhalation rate from soil and radon concentration in the soil. Radon exhalation rate from the soil was also not found to be correlated with the gamma dose rate, while it shows a positive correlation with radon concentration in water in summer season. Inter-correlations among various parameters are discussed in detail.

The natural pollution level due to gamma radiation was measured in about 22 residential houses around the Tehri Dam Project in Uttarakhand state by using Environmental Radiation Dosimeter. Both urban and rural houses were selected for the measurements. The recorded gamma dose rate in indoor atmosphere was found to vary from 25.