Outdoor radon and thoron concentrations in different seasons in Tumkur district, Karnataka

Radon is a colorless gas produced due to the decay of ²²⁶Ra. Though the outdoor radon dose is smaller than that of the indoor, it also contributes to considerable amount of radiation dose to the population. In the present research work, the concentrations of radon, thoron and their progenies were determined using twin cup dosimeters fitted with Solid State Nuclear Track Detectors (SSNTD). In the southern part of Tumkur, five taluks were identified and in each taluk eight geographically different places were selected for the measurement of radon and thoron concentration for different seasons of a year. The average radon concentration from all the seasons was found to be highest in Kunigal with 16.90 and lowest in Turuvekere with 12.18 Bqm^-3. In some regions of Kunigal the underground regions contains large amount of granite formations. Also, the outdoor radon and thoron concentrations were found to be higher in winter season (16.32 and 3.52 Bqm^-3) and lower in summer season (12.42 and 2.06 Bqm^-3). The highest annual outdoor inhalation dose was found in Kunigal with 0.13 mSv and the lowest was observed in Turuvekere with 0.10 mSv. The average annual inhalation dose due to outdoor radon, thoron and their progeny were found to be 0.151 mSv. (author)