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| Titel |
A fast semi-quantitative method for Plutonium determination in an alpine firn/ice core |
| VerfasserIn |
J. Gabrieli, G. Cozzi, P. Vallelonga, M. Schwikowski, M. Sigl, C. Boutron, C. Barbante |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029217
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| Zusammenfassung |
| Plutonium is present in the environment as a consequence of atmospheric nuclear tests carried
out in the 1960s, nuclear weapons production and releases by the nuclear industry over the
past 50 years. Plutonium, unlike uranium, is essentially anthropogenic and it was first
produced and isolated in 1940 by deuteron bombardment of uranium in the cyclotron of
Berkeley University. It exists in five main isotopes, 238Pu, 239Pu, 240Pu, 241Pu, 242Pu, derived
from civilian and military sources (weapons production and detonation, nuclear reactors,
nuclear accidents). In the environment, 239Pu is the most abundant isotope. Approximately 6
tons of 239Pu have been released into the environment as a result of 541 atmospheric weapon
tests
Nuclear Pu fallout has been studied in various environmental archives, such as sediments,
soil and herbarium grass. Mid-latitude ice cores have been studied as well, on Mont Blanc,
the Western Alps and on Belukha Glacier, Siberian Altai.
We present a Pu record obtained by analyzing 52 discrete samples of an alpine firn/ice
core from Colle Gnifetti (M. Rosa, 4450 m a.s.l.), dating from 1945 to 1991. The239Pu signal
was recorded directly, without preliminary cleaning or preconcentration steps, using an
ICP-SFMS (Thermo Element2) equipped with a desolvation system (APEX). 238UH+
interferences were negligible for U concentrations lower than 50 ppt as verified both in spiked
fresh snow and pre-1940 ice samples.
The shape of 239Pu profile reflects the three main periods of atmospheric nuclear weapons
testing: the earliest peak starts in 1954/55 to 1958 and includes the first testing period which
reached a maximum in 1958. Despite a temporary halt in testing in 1959/60, the Pu
concentration decreased only by half with respect to the 1958 peak. In 1961/62 Pu
concentrations rapidly increased reaching a maximum in 1963, which was about 40% more
intense than the 1958 peak. After the sign of the “Limited Test Ban Treaty” between USA and
URSS in 1964, Pu deposition decreased very sharply reaching a minimum in 1967. The third
period (1967-1975) is characterized by irregular Pu profiles with smaller peaks (about
20-30% compared to the 1964 peak) which could be due to French and Chinese
tests.
Comparison with the Pu profiles obtained from the Col du Dome and Belukha
ice cores by AMS (Accelerator Mass Spectrometry) shows very good agreement.
Considering the semi-quantitative method and the analytical uncertainty, the results are
also quantitatively comparable. However, the Pu concentrations at Colle Gnifetti
are normally 2-3 times greater than in Col du Dome. This could be explained by
different air mass transport or, more likely, different accumulation rates at each site. |
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