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| Titel |
Carbonate and silicate rock standards for cosmogenic 36Cl |
| VerfasserIn |
Silke Mechernich, Tibor J. Dunai, Steven A. Binnie, Tomasz Goral, Stefan Heinze, Alfred Dewald, Lucilla Benedetti, Irene Schimmelpfennig, Fred Phillips, Shasta Marrero, Mehmet Akif Sarıkaya, Laura C. Gregory, Richard J. Phillips, Klaus Wilcken, Krista Simon, David Fink |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250146093
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| Publikation (Nr.) |
 EGU/EGU2017-10093.pdf |
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| Zusammenfassung |
| The number of studies using cosmogenic nuclides has increased multi-fold during the last
two decades and several new dedicated target preparation laboratories and Accelerator Mass
Spectrometry (AMS) facilities have been established. Each facility uses sample preparation
and AMS measurement techniques particular to their needs. It is thus desirable to have
community-accepted and well characterized rock standards available for routine processing
using identical target preparation procedures and AMS measurement methods as carried out
for samples of unknown cosmogenic nuclide concentrations. The usefulness of such natural
standards is that they allow more rigorous quality control, for example, the long-term
reproducibility of results and hence measurement precision, or the testing of new target
preparation techniques or newly established laboratories. This is particularly pertinent
for in-situ 36Cl studies due to the multiplicity of 36Cl production pathways that
requires a variety of elemental and isotopic determinations in addition to AMS 36Cl
assay.
We have prepared two natural rock samples (denoted CoCal-N and CoFsp-N) to serve as
standard material for in situ-produced cosmogenic 36Cl analysis. The sample CoCal-N is a
pure limestone prepared from pebbles in a Namibian lag deposit, while the alkali-feldspar
CoFsp-N is derived from a single crystal in a Namibian pegmatite. The sample preparation
took place at the University of Cologne, where first any impurities were removed
manually from both standards. CoCal-N was leached in 10 % HNO3 to remove
the outer rim, and afterwards crushed and sieved to 250-500 μm size fractions.
CoFsp-N was crushed, sieved to 250-500 μm size fractions and then leached in
1% HNO3 / 1% HF until 20% of the sample were removed. Both standards were
thoroughly mixed using a rotating sample splitter before being distributed to other
laboratories.
To date, a total of 28 CoCal-N aliquots (between 2 and 16 aliquots per facility) and 31
CoFsp-N aliquots (between 2 and 20 aliquots per facility) have been analyzed by six target
preparation laboratories employing five different AMS facilities. Currently, the internal
reproducibility of the measurements underlines the homogeneity of both standards. The
inter-laboratory comparison suggests low over-dispersion. Further measurements are pending
and should allow meaningful statistical analysis. Both standard materials are freely available
and can be obtained from Tibor Dunai (tdunai@uni-koeln.de). |
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