The results of the lithuanian radon survey

A national survey of indoor radon levels in Lithuania was performed between 1995 and 1998. The main objective of this survey was to evaluate the average of indoor radon concentrations in Lithuania and to determine whether there were significant variations with different areas.
Measurements have been carried out in 400 randomly selected detached houses. The duration of one measurement was at least 3 weeks. The levels in two commonly used rooms on the lowest level were measured using passive electrets. Measurements were carried out during the cold weather season, 1 October and 30 April, i.e., when doors and windows generally are closed and the heating on. Information on house construction and layout, including the age of the house, the building materials and whether there was a basement, the type of water supply, as well as the ambient gamma dose rate, were also recorded. The results show that the arithmetic mean of indoor radon in the randomly selected detached houses is (554) Bq m (confidence level 95%) and the geometric mean is 22 Bq m-3. A separate set of measurements was performed in Birzai karst region. The arithmetic and geometric mean values in detached houses in this region are (9816) and 50 Bq m, respectively. Five regions (excluding the karst region ) where the indoor radon concentrations are two or more times higher than the average concentrations in the rest of Lithuania have been found. The source of indoor radon in Lithuania is the bedrock and the soils. The type and construction of house have significant influence on the indoor radon concentrations. The levels in houses built during the last 14 years are on average half those in houses built before 1985. The radon concentration in ground water is less than 30 Bq l-1. No statistically significant differences between winter and summer indoor radon concentrations have been found. The annual effective doses as a result of indoor radon have been estimated and are presented, the average value for detached houses being 0.97 mSv. The national standards for restricting exposures to natural radiation sources have been adopted, action levels and intervention determined on the basis of the results obtained, intervention being different for dwellings and for workplaces.