Estimation of seasonal variation in Radon, thoron and their progeny levels in some dwellings

Radon and its progeny are the major contributors in the radiation dose received by general population of the world. Keeping this in mind the environmental radon, thoron and their progeny measurements have been carried out in some dwellings. The radon thoron twin dosimeter cups designed by environmental assessment division of Bhabha Atomic Research Centre (BARC) Mumbai, India have been used for this study. Three pieces of LR-115 type II solid-state nuclear track detectors are fixed in the dosimeters. The dosimeters were suspended in the dwellings for three months during a season. The specially designed twin cup dosimeter used in present study consists of two chambers of cylindrical geometry separated by a wall in the middle with each having a length of 4.5 cm and radius of 3.1 cm. This dosimeter employs three SSNTDs out of which two detectors were placed in each chamber and a third one was placed on the outer surface of the dosimeter. One chamber is fitted with glass fiber filter so that radon and thoron both can diffuse into the chamber while in other chamber, a semi permeable membrane made of latex or cellulose nitrate, having a thickness of 25 µm is used. The membrane mode measures the radon concentration alone as it can diffuse through the membrane but suppresses the thoron. The twin cup dosimeter also has a provision for bare mode enabling it to register tracks due to radon, thoron and their progeny in total. To observe the effect of environmental conditions the measurements have been carried out during different seasons of the year. The radon-thoron progeny levels and annual dose received by the inhabitants in the dwellings under study have also been calculated. The levels are found to be higher during winter season as compare to other seasons of the year.