Studies on radiocaesium in Estonian soils

The distribution of radiocaesium in natural soils in Estonia was studied by using low-background γ-spectroscopy. The average relaxation lengths for 134Cs and 137Cs were determined for 25 soil profiles from over 120 samples collected throughout Estonia. The average mass relaxation length values, ρ/α., are 42 ± 15 kgm−2 for the Chernobyl fallout and 110 ± 30 kg m−2 for the atmospheric nuclear weapons tests fallout. The distribution of the Chernobyl deposition is extremely uneven. About 60% of the total deposition (˜50 × 1012 Bq of 134Cs and ˜90 × 1012 Bq of 137Cs) has been recorded in north-east Estonia. The maximum 137Cs deposition reached 40 kBq m−2 in 1986, while the country-wide mean was 2.0 kBq m−2. The Chernobyl fallout approximately doubles the 137Cs mean deposition from the nuclear weapons tests (2.2 kBqm−2 in 1986) in Estonia