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| Titel |
81Kr-dating is now available |
| VerfasserIn |
Z.-T. Lu, W. Jiang, A. Sharma, K. Bailey, P. Mueller, T. P. O'Connor, S.-M. Hu, R. Purtschert, N. C. Sturchio |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061179
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| Zusammenfassung |
| Due to its simple production and transport processes in the terrestrial environment, the
long-lived noble-gas isotope 81Kr is the ideal tracer for old water and ice in the age
range of 105-106 years, a range beyond the reach of 14C. 81Kr-dating, a concept
pursued over the past four decades by numerous laboratories employing a variety
of techniques, is now available for the first time to the earth science community
at large. This is made possible by the development of ATTA-3, an efficient and
selective atom counter based on the Atom Trap Trace Analysis method and capable of
measuring both 81Kr/Kr and 85Kr/Kr ratios of environmental samples in the range of
10-14-10-10. The instrument was calibrated with 12 samples whose 85Kr/Kr ratios were
independently measured using Low Level Decay Counting, including six samples that were
measured in a blind arrangement. Compared to the previously reported ATTA-2
instrument, the counting rates of ATTA-3 are higher by two orders of magnitude and
the required sample size lower by one order of magnitude. For 81Kr-dating in the
age range of 200 – 1,500 kyr, the required sample size is 5 – 10 micro-L STP of
krypton gas, which can be extracted from approximately 100 – 200 kg of water or 40
– 80 kg of ice. Moreover, a laser-induced quenching scheme was developed to
enable measurements of both the rare 81,85Kr and the abundant 83Kr, whose isotopic
abundances differ by 11 orders of magnitude. This scheme allows ATTA-3 to directly
determine 81Kr/Kr and 85Kr/Kr ratios without other supplemental measurements.
Combining the significant reduction in sample size with numerous advances in
the measurement procedure, ATTA-3 represents the state-of-the-art instrument for
routine analysis of these rare noble gas tracers in a wide range of earth science
applications.
More information regarding ATTA-3 is posted at http://www.phy.anl.gov/mep/atta/. This
work is supported by the U.S. DOE, Office of Nuclear Physics, under contract
DE-AC02-06CH11357; and by NSF, Division of Earth Sciences, under Award No.
EAR-0651161. |
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