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| Titel |
First dating of groundwater with Atom Trap Trace Analysis of 39Ar - technique |
| VerfasserIn |
Florian Ritterbusch, Sven Ebser, Joachim Welte, Thomas Reichel, Arne Kersting, Roland Purtschert, Werner Aeschbach-Hertig, Markus K. Oberthaler |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082958
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| Zusammenfassung |
| The importance of 39Ar as a dating tracer for the time range between 50 and 1000
years has clearly been identified [1]. So far, it has been routinely accessible only by
Low-Level-Counting (LLC) in the underground laboratory in Bern requiring a sample size of
several tons of water and a measuring time of several weeks [2]. Here we report on the first
dating results with 39Ar using an atom optical technique known as Atom Trap Trace
Analysis (ATTA). This method has been developed for rare krypton isotopes in the past
decade and is now available for routine analysis [3]. However, the applicability
of ATTA to 39Ar has only been demonstrated in a proof of principle experiment
[4].
We will discuss the essential experimental improvements that were necessary for bringing
this method to the level of dating real samples. Our apparatus achieves an atmospheric
39Ar-count-rate of 4.1(3) atoms/h, which corresponds to an 18-fold improvement over the
reported results in [4]. Based on that, we dated a groundwater sample of the upper Rhine
Graben to 360(68) years within one day of measurement. Further samples of the investigated
aquifer system are dated similarly in order to obtain the age information for a comprehensive
hydrological study.
The apparatus has the potential to measure 39Ar-concentrations on small samples down to
less than 1 ccSTP of Argon, corresponding to about 100 ml of air, 2.5 l of water or 1 kg of
ice. This opens up the way for a broader application of 39Ar as a tracer e.g. in oceanography
or glaciology, where the sample sizes are typically limited to 10 l of water or 1 kg of ice
respectively.
[1] Loosli, H. H. (1983), A dating method with 39Ar, Earth and Planetary Science Letters, 63,
51-62.
[2] P. Collon, W. Kutschera, and Z.-T. Lu. Tracing noble gas radionuclides in the
environment. Annual Review of Nuclear and Particle Science, 54(1): 39-67, 2004.
[3] W. Jiang et al., An atom counter for measuring 81Kr and 85Kr in environmental samples.
Geochimica et Cosmochimica Acta, 91(0):1-6, 2012.
[4] Jiang, W. et al. (2011), 39Ar detection at the 10-16 isotopic abundance level with Atom
Trap Trace Analysis, Phys. Rev. Lett. 106, DOI: 10.1103/PhysRevLett.106.103001. |
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