Yogesh Prasad

Soil-gas radon as seismotectonic indicator in Garhwal Himalaya

Research on earthquake-related radon monitoring has received enormous attention recently. Anomalous behaviour of radon in soil and groundwater can be used as a reliable precursor for an impending earthquake. While earthquake prediction may not yet be possible, earthquake prediction research has greatly increased our understanding of earthquake source mechanisms, the structural complexities of fault zones, and the earthquake recurrence interval, expected at a given location. This paper presents some results of continuous monitoring of radon in soil-gas in Garhwal Himalaya, India. Daily soil-gas radon monitoring with seismic activity and meteorological parameters were performed in the same laboratory system, located at H.N.B. Garhwal University Campus, Tehri Garhwal, India. Radon anomalies along with meteorological parameters were found to be statistically significant for the seismic events within the magnitudes M2.0-M6.0 and epicentral distances of 16-250 km from the monitoring station. The frequent positive and negative anomalies with constant environmental perturbation indicate the opening and closing of micro cracks within the volume of dilatancy by strain energy. The spike-like and sharp peak anomalies were recorded before, during and after earthquakes occurred in the area. The variations in radon concentrations in soil-gas are found to be correlated with seismic activities in the Garhwal Himalaya. The correlation between radon level and meteorological parameters is also discussed.

226Ra, 232Th and 40K contents in soil samples from Garhwal Himalaya, India, and its radiological implications

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).

Radon Emanation from Soil and Groundwater and Surface Gamma Dose Rate in Budhakedar, Garhwal Himalayas, India

Radon was measured in soil-gas and groundwater in the Budhakedar area of Tehri Garhwal, India and related to the gamma dose rate in the same area. A laboratory experiment was also performed to measure the radon exhalation rate from soil samples collected from the same area. Radon exhalation rate from collected soil samples was found to vary from 0.1×10-5 Bq·kg-1·h-1 to 5.7×10-5 Bq·kg-1·h-1 with an average of 1.5×10-5 Bq·kg-1·h-1. Radon concentration in soil and groundwater of the Budhakedar area varies from 1098 to 31,776Bq·m-3 with an average value of 7456Bq·m-3, and from 8 to 3047Bq·L-1 with an average value 510Bq·L-1, respectively. Surface gamma dose rate in the study area varied from 32.4 to 83.6μR·h-1 with an overall mean of 58.7μR·h-1. The observed value of the gamma dose rate was not found to be related to the value of radon concentration in ground-water but a weak positive correlation was observed between the gamma dose rate and soil-gas radon concentration. 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.