Measurement of indoor radon concentration in kindergartens in Sofia, Bulgaria

As a part of the systematic survey of indoor radon in Bulgaria, indoor radon concentration was measured in 292 kindergartens buildings of Sofia city during 3 month (January – April), 2013 using the CR-39 nuclear tracts detectors. In any building at least two frequently occupied rooms (mainly playrooms) were observed. Altogether 922 measurements were performed. The frequency distribution was well described by the lognormal function. The measured radon concentrations range between 9 and 1415 Bq m-3 with a geometric mean of 101 Bq m-3 (2.08) and arithmetic mean 132 Bq m-3 with a standard deviation of 118 Bq.m-3. The radon concentrations obtained in this survey were compared with radon concentration in Sofia dwellings obtained from previous study. A detailed statistical analysis of the building factors was present.