Nuclear contamination sources in surface air of Finnish Lapland in 1965–2011 studied by means of 137Cs, 90Sr, and total beta activity

Abstract

Radionuclides 137 Cs and 90 Sr and total beta activity were determined from air filters collected in Rovaniemi (Finnish Lapland) in 1965–2011. Nuclear contamination sources present in the air filter samples as well as temporal changes in radionuclide concentrations were examined. Ozone observations and meteorological modeling were used in combination with radionuclide analyses to study the reasons behind the observed seasonal concentration variation. In general, the magnitude and variation in activity concentrations of 137 Cs and 90 Sr and total beta activity in the surface air of Rovaniemi in 1965–2011 corresponded well with values from other countries. However, the obtained results prove in practice that hardly any refractory or intermediate radionuclides from the destroyed Chernobyl reactor fuel were introduced to Finnish Lapland. The main source of 137 Cs and 90 Sr and total beta activity in the surface air of Rovaniemi in 1965–2011 has been intense atmospheric nuclear weapon testing in 1950s–1960s and later tests performed in 1965–1980, as well as leakages from underground nuclear tests in Semipalatinsk, 1966, and Novaya Zemlya, 1987. For 137 Cs and total beta activity, the influence of Chernobyl and Fukushima accidents was detected.

Measurements and modelling of airborne plutonium in Subarctic Finland between 1965 and 2011

“…The activity ratio 238 Pu/ 239+240 Pu cannot be determined for the period immediately after the Chernobyl accident because the activity concentrations of 238 Pu and 239+240 Pu were below the detection limit during April-December 1986. This finding is in agreement with the previous assumptions about hardly any Chernobyl-derived refractory elements in Finnish Lapland (Salminen-Paatero et al 2019).…”

“…The major part of 241 Am in the samples originates from the decay of 241 Pu after the sampling and only a minor part of 241 Am originates directly from nuclear events. The results for 137 Cs, 90 Sr, and total beta activity have been reported elsewhere (Salminen-Paatero et al 2019). The activity ratio 238 Pu/ 239+240 Pu and the mass ratio 240 Pu/ 239 Pu in Rovaniemi have been presented pictorially with other global ratio values in the article by Thakur et al (2017), but the ratio values of Rovaniemi were not discussed in detail there.…”

“…of Sr (5.2±1.1 µBq m -3 ) in the same air filter samples in April-June 1986 (Salminen-Paatero et al 2019). It has been suggested that the initial contamination plume from the destroyed Chernobyl reactor contained intermediate ( 90 Sr) and refractory elements (Pu isotopes) and that plume passed over Central and Southern parts of Finland, while the volatile elements like 137 Cs were mostly in the later contamination plumes which reached also Lapland (Saxén et al 1987).…”

“…Slight peaks in the 239+240 Pu concentration can be seen in 1974, 1978 and 1981, evidently due to the atmospheric nuclear tests performed by People's Republic of China between 1973 and1980. The effect of these nuclear tests on the radionuclide concentration level in Finnish Lapland was already observed in the concentration variation of 137 Cs (Salminen-Paatero et al 2019). Like with 238 Pu, the concentration of 239+240 Pu was below the detection limit in April-June 1986 following the Chernobyl accident.…”

“…Then the filters were combined to suitable sets for the gamma measurement and determination of 137 Cs concentration. The details of air sampling, combining air filters and measurements for gamma activity of 137 Cs and total beta activity have been given in Salminen et al (2019).…”