Soil-gas Thoron Concentration Associated with Seismic Activity

Abstract

Radon is the by-product of the natural decay of radium that is derived from the decay series of uranium. Radon-220 (or thoron) is one of the three naturally occurring radio isotopes of radium. The half-life of thoron is 55 seconds. Continuous soil gas thoron monitoring was done using SSNTD (LR-115 type II film), manufactured by Kodak Pathe, France. The study was carried out from March 2012 to February 2013 at Mat Bridge (23°18¢N, 92°48¢E) along Mat Fault in Serchhip District, Mizoram (India), which lies in seismic zone V of the seismic zonation map of India. The exposed SSNTDs were processed in a constant temperature bath. The average value of thoron concentration was recorded to be 203.08 tracks/cm2 with a standard deviation of 130.84 tracks/cm2. An attempt has been made to correlate thoron data to earthquakes that occurred during the observation period. The effect of meteorological parameters (viz. relative humidity, rainfall and air temperature) on thoron data was also taken into consideration. The study showed a positive correlation with earthquake for one event. Positive correlation was found between thoron data and all the meteorological parameters.