Key Words Radon exhalation · Building materials · Track detector

Inhalation of indoor radon has long been recognised as a risk to health. The major sources of the indoor radon and also its daughters are building materials, natural gas and an underground-derived water supply. In this work a set of radon measurements was carried out, using the CR-39 solid state nuclear track detector, in dif-ferent rooms of dwellings in Cairo. These compartments were located in apartment complexes built of the same building materials. The results showed that the radon concentration and exhalation rate in these houses varied from 47.94 to 84.32Bq·m3 and 2.59 to 4.04mBq·m2·h1, respectively. The mean values of radon concentration in living rooms, bedrooms, bathrooms and kitchens were 50.981.94, 53.183.69, 79.362.96 and 81.291.93Bq·m3, respectively. The mean values of exhalation rate were 2.680.11, 2.790.19, 4.010.18 and 4.220.12mBq·m2·h1, respectively. This data showed that bathrooms and kitchens had a significantly higher radon concentration and exhalation rate com-pared with both other rooms and the outdoor levels