Estimation of indoor gamma dose rate

An expression was derived from an air cavity inside an infinite medium with homogeneous natural radionuclide distribution for use as an upper limit for the indoor dose rate. Correction coefficients were calculated for wall thickness for rooms of various shapes and dimensions and the presence of doors and windows was accounted for. A mean indoor dose rate of 6.8 μrad/hr was obtained for an assumed distribution of buildings of various materials. Average outdoor dose rates, based on the average natural radioactivity of soils, were calculated as 4.8 μrad/hr and 5.4 μrad/hr respectively for open areas and streets. Assuming that the populations of industrial countries spend 80%, 15% and 5% of the time indoors, in open spaces and in streets respectively, a mean annual dose of 40 μrad was calculated. This estimate is 20% higher than that of UNSCEAR. (U.K.)