Considering the role of radon in epidemiology, an attempt was made to make a nation-wide map of indoor (222)Rn and (220)Rn for India. More than 5000 measurements have been carried out in 1500 dwellings across the country comprising urban and nonurban locations. The solid state nuclear track detectors based twin cup (222)Rn/(220)Rn discrimination dosimeters were deployed for the measurement of indoor (222)Rn, (220)Rn and their progeny levels. The geometric means of estimated annual inhalation dose rate due to indoor (222)Rn, (220)Rn and their progeny in the dwellings was 0.94 mSvy(-1) (geometric standard deviation 2.5). It was observed that the major contribution to the indoor inhalation dose was due to indoor (222)Rn and its progeny. However, the contribution due to indoor (220)Rn and its progeny was not trivial as it was found to be about 20% of the total indoor inhalation dose rates. The indoor (222)Rn levels in dwellings was significantly different depending on the nature of walls and floorings.
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