Evaluation of indoor Rn and Rn concentrations in Dakshina Kannada, Karnataka, India.

Naturally occurring radioactive gases which tend to build up (radon and thoron) in indoor environs can cause deleterious health effects including the development of lung cancer. The present study aims to measure Rn and Rn levels in dwellings in different seasons in the environs of Dakshina Kannada region of India. The Rn and Rn concentrations were measured in the monsoon, autumn, winter, and summer seasons using Solid State Nuclear Track Detector (SSNTD, LR-115 type II) films fixed in single-entry pinhole cylindrical twin-cup dosimeters. The higher Rn levels in indoors were observed during winter with an average concentration of 38.8 Bq m and lower during summer with an average of 14.1 Bq m. The average indoor thoron concentration was also highest in winter with an average value of 25.5 Bq m and lowest in summer with 8.8 Bq m. The annual inhalation dose ranged from 0.44 to 1.06 mSv year with a mean value of 0.66 mSv year. The annual effective dose varied from 1.03 to 2.57 mSv year with an average value of 1.59 mSv year. The assessed values have been contrasted with the limit suggested by the UNSCEAR and the ICRP and were found to be within the permissible level. The normality of frequency distribution curves of Rn and Rn concentrations was assessed by the Kolmogorov-Smirnov test.