Clean quartz matters for cosmogenic nuclide analyses: An exploration of the importance of sample purity using the CRONUS-N reference material |
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| Institution: | 1. Rubenstein School for Environment and Natural Resources, University of Vermont, Burlington, VT, USA;2. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA, USA;3. Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA;4. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA;5. Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales, Australia;6. Scottish Universities Environmental Research Centre, East Kilbride, UK;7. Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, UK |
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| Abstract: | Reference materials are key for assessing inter-laboratory variability and measurement quality, and for placing analytical uncertainty bounds on sample analyses. Here, we investigate four years of data resulting from repeated processing of the CRONUS-N reference material for cosmogenic 10Be and 26Al analyses. At University of Vermont, we prepared a CRONUS-N aliquot with most of our sample batches from 2013 to 2017; these reference material samples were then distributed to four different accelerator mass spectrometry facilities, yielding 73 10Be analyses and 58 26Al analyses. We determine CRONUS-N 10Be concentrations of (2.26 ± 0.14) x 105 atoms g?1 (n = 73, mean, 1 SD) and 26Al concentrations of (1.00 ± 0.08) x 106 atoms g?1 (n = 58, mean, 1 SD). We find a reproducibility of 6.3% for 10Be and 7.7% for 26Al (relative standard deviations). We also document highly variable 27Al and Mg concentrations and a 10Be dispersion twice as large as the mean AMS analytic uncertainty. Analyses of the CRONUS-N material with and without density separation demonstrate that non-quartz minerals are present in the material and have a large impact on measured concentrations of 27Al, 10Be, and impurities; these non-quartz minerals represent only a very small portion of the total mass (0.6–0.8%) but have a disproportionally large effect on the resulting data. Our results highlight the importance of completely removing all non-quartz mineral phases from samples prior to Be/Al extraction for the determination of in situ cosmogenic 10Be and 26Al concentrations. |
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| Keywords: | Geochronology Cosmogenic nuclides Accelerator mass spectrometry Quality control Beryllium-10 |
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