Deposition of 125Sb, 106Ru, 144Ce, 134Cs and 137Cs in Finland after the Chernobyl accident

In this study the deposition characteristics of 125 Sb, 106 Ru, 144 Ce, 134 Cs and 137 Cs in Finland after the Chernobyl accident was investigated based on gamma spectrometric analysis of 97 lichen, peat and surface soil samples. The aim of this study was to determine the fallout pattern of 125 Sb, 106 Ru , 124 Cs, and 144 Ce in Finland, to verify the fallout pattern of 137 Cs reported in earlier works, and to obtain an estimate of the total amounts of these nuclides deposited in Finland. The highest deposition values of 144 Ce were found in a zone extending from southwestern Finland to Kuhmo area close to the Russian border. The deposition pattern of 144 Ce resembled the deposition patterns of refractory nuclides, such as 95 Zr and transuranium elements. The regional deposition of cesium isotopes 134 and 137 differed from that of 144 Ce owing to the different volatility properties of these nuclides. Our results confirm the earlier observations of high deposition values of 137 Cs in southwestern Finland, Varkaus-Kuopio region, Kuhmo region and Kotka-Kouvola region. A comparison of previous results to our results suggests an overestimated deposition in the Oulu region in this study due to the lack of samples in the region. The observed average 134 Cs to 137 Cs activity ratio, 0.527 ±0.010 decay-corrected to 1 May 1986, is in agreement with earlier studies and corresponds to a burnup of 13 GWd tU -1 . Although ruthenium is a refractory element, the behaviour of 103 Ru and 106 Ru has been shown to resemble the behaviour of volatile elements. This has been explained by the formation of volatile ruthenium oxides. The deposition pattern of 125 Sb resembled those of cesium isotopes. This suggests that antimony behaved like volatile nuclides in the destroyed reactor. It was calculated that depending on the nuclide, 0.017%-1.5% of the reactor core inventory and 0.6%-13% of the atmospheric emissions were deposited in Finland. These percentages were proportional to the volatility of the nuclides.