Concentration of radon and thoron in some dwellings of North-Eastern region

It has been well recognised all over the world that inhalation of indoor radon (222Rn), thoron (220Rn) and their daughter products contribute a major fraction of total dose to human beings from all possible sources of natural radioactivity. North-Eastern region, being in a zone of high seismicity, the indoor radon map of the region will provide a valuable database for any study related to radon anomalies. In the present work an attempt has been made to assess the levels of radon, thoron and their progeny in dwellings of a few cities in the North-Eastern region of India. Radon levels of different dwellings were analysed with reference to the nature of building materials, ventilation patterns and the type of underlying soil. The whole process was repeated to investigate into the seasonal variation in radon levels. The results were discussed under the light of exposure limits set by ICRP. (author)