INDOOR AND OUTDOOR GAMMA-RADIATION IN FINLAND

This study measured the dose rate in air in the dwellings of 350 perso ns, selected randomly from the central population register of Finland. TLD dosemeters were employed for half-year measurements in 1991. Addi tionally, the results were compared with outdoor gamma radiation calcu lations based on data from a previous survey conducted in 1978-80. The absorbed dose rate in air in low-rise residential buildings and in bl ocks of flats had ranges of 24-144 nGy.h(-1) and 45-184 nGy.h(-1) resp ectively, the population weighted mean values being 58 and 100 nGy.h(- 1). The weighted mean for the total population was 73 nGy.h(-1). In th e figures given, the dose rate due to cosmic radiation, 32 nGy.h(-1), was subtracted. The population weighted mean terrestrial dose rate out doors was 71 nGy.h(-1). In houses and in hats the mean indoor/outdoor dose rate ratios were 0.84 and 1.33 respectively. This gave a populati on weighted mean for this ratio of 1.00. A statistically significant i ncrease caused by the Chernobyl fallout was observed, these results be ing in agreement with shielding factor studies. This increment due to the Chernobyl fallout, which was subtracted, was 0.3-19 nGy.h(-1), on average 3 nGy.h(-1). The national annual average effective dose due to natural terrestrial radiation was 0.45 mSv and owing, in 1991, to the Chernobyl fallout 0.03 mSv.