STUDY OF RADIATION EXPOSURE DUE TO RADON, THORON AND PROGENY IN THE INDOOR ENVIRONMENT OF YAMUNA AND TONS VALLEYS OF GARHWAL HIMALAYA.

Long-term measurements of indoor radon, thoron and their progeny concentrations have been carried out in dwellings of Yamuna and Tons Valleys of Uttarkashi, Garhwal Himalaya to investigate the health risk associated with inhalation of radon, thoron and progeny. The experimentally determined values of radon, thoron and progeny concentrations were used to estimate the annual inhalation doses and annual effective doses. The annual inhalation dose has been found to vary from 0.8 to 3.9 mSv y(-1) with an average of 1.8 mSv y(-1). The annual effective dose from the exposure to radon and its progeny in the study area has been found to vary from 0.1 to 2.4 mSv with an average of 1.2 +/- 0.6 mSv. Similarly, the annual effective dose due to thoron and its progeny has been found to vary from 0.2 to 1.5 mSv with an average of 0.6 +/- 0.4. The measurement techniques and results obtained are discussed in detail.