8
THE RESULTS OF THE LITHUANIAN RADON SURVEY

Gendrutis Morkunas 1 , Gustav Akerblom 2
1 Radiation Protection Centre, Kalvariju 153, LT-2042, Vilnius, Lithuania
Tel. 3702 754693, fax. 3702 754692, e-mail genmo@takas.lt 2 Swedish Radiation Protection Institute, SE-171 16, Stockholm, Sweden
Tel. 468 7297150, fax.468 7297108, e-mail gustav.akerblom@ssi.se

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
(55....4) Bq m -3 (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 (98....16) and 50 Bq m -3 , 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.

Key words: Lithuania, radon, concentration, surveys.