Scavenged 239Pu, 240Pu, and 241Am from snowfalls in the atmosphere settling on Mt. Zugspitze in 2014, 2015 and 2016

Abstract

Concentrations of 239Pu, 240Pu, and 241Am, and atomic ratio of 240Pu/239Pu in freshly fallen snow on Mt. Zugspitze collected in 2014, 2015 and 2016 were determined by accelerator mass spectrometry (AMS). For the sub-femtogram (10−15 g) - level of Pu and Am analysis, a chemical separation procedure combined with AMS was improved and an excellent overall efficiency of about 10−4 was achieved. The concentration of 239Pu ranges from 75 ± 13 ag/kg to 2823 ± 84 ag/kg, of 240Pu from 20.6 ± 5.2 to 601 ± 21 ag/kg, and of 241Am was found in the range of 16.7 ± 5.0–218.8 ± 8.9 ag/kg. Atomic ratios of 240Pu/239Pu for most samples are comparable to the fallout in middle Europe. One exceptional sample shows a higher Pu concentration. High airborne dust concentration, wind directions, high Cs concentrations and the activity ratio of 239+240Pu/137Cs lead to the conclusion that the sample was influenced by Pu in Saharan dust transported to Mt. Zugspitze.

Cryoconite: an efficient accumulator of radioactive fallout in glacial environments

“…The deposition of plutonium, which is still occurring on the Alpine snowpack, is too weak to influence the isotopic fingerprint of cryoconite. Pu activity in fresh snow ranges from 0.4 to 11.5 µBq kg −1 (Gückel et al, 2017), roughly 6 orders of magnitude lower than the average activity of cryoconite, which is 41 Bq kg −1 . This has important implications because it suggests that cryoconite is more influenced by past atmospheric fallout rather than contemporary fallout, Table 1.…”

“…On average, more than 99 % of the Pu found in cryoconite from the Morteratsch glacier is from global fallout, while for the Forni glacier the average contribution is 95 %, suggesting a non-negligible influence from the Chernobyl accident (∼ 5 %). By comparing the 240 Pu/ 239 Pu ratio of global fallout and of modern snow deposited in the Alps (Gückel et al, 2017), it is possible to further discuss the Pu sources in cryoconite. Modern Alpine snow has a slightly higher ratio than global fallout (0.21 vs. 0.18), probably because of the partial influence of resuspended Chernobyl radioactive fallout, which Figure 4.…”

“…Data about the fraction of Pu and 137 Cs related to global fallout in cryoconite samples from the Morteratsch and Forni glaciers and from other glaciers. To calculate global fractions, reference ratios defined by Ketterer et al (2008), Cagno et al (2014), Gückel et al (2017) and Wilflinger et al (2018) 2018Waldemarbreen 9Svalbard 93 ± 4 56 ± 25 Łokas et al (2019) at least when considering Pu. The only source that can provide cryoconite FRNs from past atmospheric deposition is ice accumulated within the period of maximum deposition of atmospheric radioactivity, when it was dominated by global stratospheric fallout.…”

Cryoconite as an efficient monitor for the deposition of radioactive fallout in glacial environments

“…The deposition of plutonium which is still occurring on the Alpine snowpack, is too weak to influence the isotopic fingerprint of cryoconite. Pu activity in fresh snow ranges from 0.4 to 11.5 μBq kg -1 (Gückel et al, 2017), roughly six orders of magnitude lower than the average activity of cryoconite, which is 41 Bq kg -1 . This has important implications because it suggests that cryoconite is more influenced by a historic atmospheric fallout rather than the contemporary one, at least when considering Pu.…”

“…By comparing the 240 Pu/ 239 Pu ratio of global fallout and of modern snow deposited in the Alps (Gückel et al, 2017), it is possible to further discuss the Pu sources in cryoconite. Modern Alpine snow has a slightly higher ratio than global fallout 290 (0.21 vs. 0.18), probably because of the partial influence of re-suspended Chernobyl radioactive fallout, which is more enriched in 240 Pu than global fallout (Ketterer and Szechenyi, 2008).…”