Paper No. 11
Presentation Time: 9:00 AM-6:30 PM


CORBETT, Lee B., Department of Geology and Rubenstein School of Environment and Natural Resources, University of Vermont, Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405, BIERMAN, Paul, Department of Geology, University of Vermont, Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405 and ROOD, Dylan H., AMS Laboratory, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF, United Kingdom,

Optimizing laboratory methodology for the preparation of 10Be samples has a direct positive effect on data quality. Methodological optimization can be implemented in any laboratory, and produces purer samples that perform more consistently during accelerator mass spectrometry (AMS). Tracking sample composition throughout the laboratory procedures (e.g., by using ICP-OES) provides quality control. Optimization strategies that can have large benefits include testing quartz purity, verifying the performance of column chromatography, testing final Be yield and purity, and minimizing background 10Be levels.

For the ~800 samples prepared following optimization of University of Vermont procedures in 2009, ICP-OES measurements of the final beryllium column fraction indicated that little Be was lost during processing; final Be yields were ~95% of the original Be load in the sample (added through a ~250 μg 9Be spike). Al, Fe, and Ti, which are known to decrease the efficiency of AMS if present in the Be fraction, were effectively removed during column chromatography, leaving <20 μg of each elemental impurity. Samples ran on the Lawrence Livermore National Laboratory AMS with an average 9Be3+beam current of 21.4 ± 3.9 μA (n = 814), and performed as well as the standards; the ratio of sample beam currents normalized to beam currents for the first run of all standards was 1.0±0.2.

96 of the samples analyzed in this experiment were cobbles embedded within the Greenland Ice Sheet (GIS). These samples had very low 10Be concentrations and most would not have been measurable before methodological optimization. Background 10Be levels were minimized by using beryl 9Be carrier produced at UVM and repeatedly run as a process blank (4.2 ± 1.7 x 10-16, n = 22), using dedicated labware and hood space for low-level samples, and counting blank cathodes to near exhaustion on the AMS. The GIS samples had 9Be3+ beam currents of 23.3 ± 3.4 μA, measured ratios from 4.2 x 10-16 to 2.7 x 10-13, and 10Be concentrations of several hundred to several thousand atoms per gram. This case study suggests that methodological optimization targeted at producing high-precision, low-detection limit samples is a prerequisite to addressing scientific questions involving 10Be analysis of very young samples, long-buried samples, or profiles with high erosion rates.