Radiological risk estimation from indoor radon, thoron, and their progeny concentrations using nuclear track detectors.

Abstract

In this paper, we report the results of seasonal variations of indoor radon and thoron concentrations, equilibrium factors for gas progeny, and radiological risks to dwellers in the hilly area of Guwahati City, Assam, India. Twin-cup dosemeters with LR-115 (II) nuclear track detectors were used in this study. The findings show that values vary significantly, with winter having the highest values and summer having the lowest, with spring and autumn having moderate values. In winter, radon concentrations range from 61.6 ± 11.2Bqm-3 (Mud) to 115.3 ± 34.3Bqm-3 (AT), with geometric mean values of 69.2 ± 13.8Bqm-3 and 109.4 ± 27.9Bqm-3, and in summer, they range from 21.1 ± 5.9Bqm-3 (Mud) to 28.4 ± 8.3Bqm-3 (AT), with geometric mean values of 22.7 ± 6.3Bqm-3 and 26.1 ± 7.1Bqm-3, whereas thoron concentrations range from 13.1 ± 5.1Bqm-3 (Mud) to 58.8 ± 12.6Bqm-3 (AT), with geometric mean values of 27.6 ± 7.0Bqm-3 and 52.9 ± 10.1Bqm-3 in winter, respectively, and in summer, from 8.8 ± 2.3Bqm-3 (Mud) to 13.0 ± 5.5Bqm-3 (Mud), with a geometric mean value of 1.87 ± 1.29Bqm-3. Radon and thoron progeny levels are reported to vary from 4.1 ± 0.3 mWL (Mud) to 15.1 ± 4.3 mWL (AT) and 2.6 ± 0.9 mWL (Mud) to 14.3 ± 4.2 mWL (AT) in winter and from 1.5 ± 0.7 mWL (AT) to 3.0 ± 2.5 mWL (Mud) and 0.9 ± 0.3 mWL (AT) to 2.7 ± 0.5 mWL (Mud) in summer, respectively. The equilibrium factors for radon and its progeny have been reported to range from 0.23 ± 0.1 (Mud) to 0.51 ± 0.3 (AT) in winter, whereas from 0.23 ± 0.1 (AT) to 0.48 ± 0.4 (Mud) in summer, respectively. The equilibrium factors for thoron and its progeny have been estimated in the range of 0.02 ± 0.01 (Mud) to 0.09 ± 0.06 (AT) in winter, whereas 0.02 ± 0.02 (AT) to 0.07 ± 0.05 (Mud) in summer, respectively. The inhalation dose rates differed from house to house, having values in the range of 1.2 ± 0.2mSvyear-1 (Mud) to 4.6 ± 1.3mSvyear-1 (AT) in winter, whereas 0.5 ± 0.3mSvyear-1 (AT) to 0.9 ± 0.5mSvyear-1 (Mud) in summer, respectively. The effective doses (EDs) due to the exposure of radon and thoron in the study area have been found to range from 2.5 ± 0.3mSv (Mud) to 9.1 ± 2.7mSv (AT) in winter and 0.9 ± 0.4mSv (AT) to 1.8 ± 1.3mSv (Mud) in summer, respectively. The levels of radon and thoron in similar types of construction were found to be significantly different from one house to another. The estimated radon and thoron concentrations in the houses of that region during winter are found to be substantially higher than the global averages as reported by UNSCEAR.