Abstract
Abstract. The activity concentrations of 238,239,240Pu and 241Am (for determining its mother nuclide, 241Pu) as well as activity ratios of 238Pu/239+240Pu, 241Pu/239+240Pu and 239+240Pu/137Cs and the mass ratio of 240Pu∕239Pu were determined from air filter samples collected in Rovaniemi (Finnish Lapland) in 1965 to 2011. The origin of plutonium in surface air was assessed based on these data from long time series. The most important Pu sources in the surface air of Rovaniemi were atmospheric nuclear-weapon testing in the 1950s and 1960s, later nuclear tests in 1973–1980 and the SNAP-9A satellite accident in 1964, whereas the influence from the 1986 Chernobyl accident was only minor. Contrary to the alpha-emitting Pu isotopes, 241Pu from the Fukushima accident in 2011 was detected in Rovaniemi. Dispersion modeling results with the SILAM (System for Integrated modeLling of Atmospheric composition) model indicate that Pu contamination in northern Finland due to hypothetical reactor accidents would be negligible in the case of a floating reactor in the Shtokman natural gas field and relatively low in the case of an intended nuclear power plant in western Finland.
Highlights
The distribution of anthropogenic radionuclides in global fallout from nuclear-weapon testing is uneven, and even more inhomogeneous is their distribution in regional and local fallout from different sources
The activity concentrations of 238,239,240Pu and 241Am as well as activity ratios of 238Pu/239+240Pu, 241Pu/239+240Pu and 239+240Pu/137Cs and the mass ratio of 240Pu/239Pu were determined from air filter samples collected in Rovaniemi (Finnish Lapland) in 1965 to 2011
The radionuclides of 137Cs and 90Sr and total beta activity of 238,239,240Pu and 241Am were determined from the air filter samples that were collected in Rovaniemi (Finnish Lapland) in 1965–2011. 241Am (t1/2 – half-life – of 432.2 years) was analyzed for calculating the activity concentration of its mother nuclide, the relatively short-lived beta emitter 241Pu (t1/2 of 14.35 years)
Summary
The distribution of anthropogenic radionuclides in global fallout from nuclear-weapon testing is uneven, and even more inhomogeneous is their distribution in regional and local fallout from different sources. There are only a few contiguous long-term radioactivity data series from Subarctic and Arctic areas where the changes in concentration levels and isotope ratios can be followed and nuclear events can be identified as contamination sources in a particular environment. Radionuclide concentration and isotope ratio data from 1965 to 2011 have been used for estimating nuclear contamination sources in the surface air of the Finnish Subarctic over almost 5 decades. Atmosphericdispersion modeling completed the experimental data by providing risk estimates and reference values for future accidental releases of nuclear material in and close to Arctic regions, as well as indicating the importance of the accurate source term in calculating the amount of radioactivity released into the atmosphere after Fukushima
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