Radon is a radioactive gas that is formed naturally by the breakdown of uranium in soil, rock and water. Recent epidemiological findings from residential studies demonstrate a statistically significant increase of lung cancer risk from prolonged exposure to indoor radon. The new requirements of ICRP and WHO include the control of indoor exposure due radon and establishment of a reference level for the annual average activity concentration up to 300 Bq/m3 for existing dwellings and public buildings.
In this paper the results of indoor radon survey in Plovdiv city are presented. Radon measurementswere made in 44 dwellings and 91 kindergartens by using CR-39 nuclear track detectors. The detectors in dwellings were exposed for 6 months from October 2011 to May 2012 while the detectors in kindergartens for 3 month from January to April 2014. The average annual indoor radon concentration (GM) for dwelling was found to be 100 Bq/m3 and for kindergartens 230 Bq/m3. The maximum measurement value of radon concentration in dwellings was 930 Bq/m3 and for kindergartens 1094 Bq/m3. The radon concentrations in dwellings were compared with that in kindergartens and the results show that kindergartens have a high indoor radon concentration than dwellings. A detailed statistical analysis of the building factors was presented as well as the risk from radon exposure was assessed.
Keywords: indoor radon, passive detectors, dwellings, kindergartens.