Preliminary results regarding the first map of residential radon in some regions in Romania.

Radon represents the most important contribution of population exposure to natural ionising radiation. This article presents the first indoor radon map in some regions of Romania based on 883 surveyed buildings in the Ştei-BăiŢa radon-prone region and 864 in other regions of Romania. Indoor radon measurements were performed in the last 10 y by using CR-39 nuclear track detectors exposed for 3-12 months on ground floor levels of dwellings. Excluding the Ştei-BăiŢa radon-prone region, an average indoor radon concentration of 126 Bq m(-3) was calculated for Romanian houses. In the Ştei-BăiŢa radon-prone area, the average indoor concentration was 292 Bq m(-3). About 21 % of the investigated dwellings in the Ştei-BăiŢa radon-prone region exceed the threshold of 400 Bq m(-3), while 5 % of the dwellings in other areas of Romania exceed the same threshold. As expected, indoor radon concentration is not uniformly distributed throughout Romania. The map shows a high variability among surveyed regions, mainly due to the differences in geology. The radon emanation rate is substantially influenced by the soil characteristics, such as the soil permeability and soil gas radon concentration. Since higher permeability enables the increased migration of soil gas and radon from the soil into the building, elevated levels of indoor radon can be expected in more permeable soil environments.