The share of radon in the formation of radiation background in North-Estonian settlements (ecological aspect)

The paper presents data on the emanation of radon in Estonian rocks and soils. The regions which could pose a threat to inhabitants of Estonia in terms of radon exhalation are listed. It is shown that radon-evoked effective equivalent doses depend on the type of construction and the duration of exposure. The share of radon in the total effective equivalent dose received by people is assessed. The region between Tallinn and Narva in North Estonia poses the greatest threat in terms of radon emanation. In this region the concentration of radionuclides in rocks is anomalously high. Measurements conducted in the basements or excavations to a depth of 3 m below land surface showed that the amount of radon emanated by soils and rocks was the highest in the eastern part of Estonia between Kohtla-Jaerve and Narva, and it was somewhat lower in the west, in the area of Tallinn and Maardu: from 1758-2180 Bq/m3 to 3430 Bq/m3 , and from 252-1715 Bq/m3 to 3404 Bq/m3, respectively. These figures are 132-439 times higher than the corresponding indicator in the air near land surface. In comparison with underground constructions, radon concentration on the ground floor of overground buildings is ca. 24 times lower (from 25-57 Bq/m3 to 300 Bq/m3, which is, however, 43 times as much as in the open air), while on the upper floor it is 70 times lower (from 8-45 Bq/m3 to 100 Bq/m3, i. e. 14 times higher than in the open air). In different regions the concentration of radon in the living and working rooms was higher than 50 Bq/m3 in 24-71% of cases, higher than 100 Bq/m3 in 9-57% of cases, and higher than 200 Bq/m3 in 17-43% of cases. The effective radiation dose received by people whose working place is in the basement is four and more times higher than the total permissible dose (5 mS/yr). The sole source is radon and its daughter elements. In the overground buildings the dose is from 6.4-1.6 to 3.9 mSv/yr (from 8-32 to 39-76% of the total permissible dose), reaching occasionally 20.6-39 mSv/yr. (author). 6 tabs., refs