Volumetric Variations of Indoor Radon and Thoron

The volumetric variations of indoor radon and thoron were measured in rooms ranging in volume from 30-310 m(3) in different dwellings at various locations in Bangalore, India. The rooms selected were similar in quality of construction, age, type of walls, and type of floor. Twin cup plastic track detectors were installed in the rooms of 42 dwellings to record indoor (222)Rn and (220)Rn levels. Higher concentrations were observed in rooms with lower volumes than in rooms with higher volumes. The (222)Rn and (220)Rn concentrations in the dwellings ranged from 4.0-93.0 Bq m(-3), whereas the concentrations of their daughter products ranged from 0.01-2.5 mWL. When the room volume increased tenfold, the concentration of (222)Rn reduced by 23% and that of (220)Rn reduced by 13%, provided all other conditions remained the same. The concentrations did not increase linearly with the volumes of the rooms. The annual effective exposure dose rate because of (222)Rn, (220)Rn and their daughter products ranged from 0.1-0.4 mSv year(-1) with a mean of 0.2 +/- 0.1 mSv year(-1).