Methods for high precision 14C AMS measurement of atmospheric CO2 at LLNL

Development of {sup 14}C analysis with precision better than 2{per_thousand} has the potential to expand the utility of {sup 14}CO{sub 2} measurements for carbon cycle investigations as atmospheric gradients currently approach traditional measurement precision of 2-5{per_thousand}. The AMS facility...

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Bibliographic Details
Published in:Radiocarbon 2006-10, Vol.49 (2)
Main Authors: Graven, H D, Guilderson, T P, Keeling, R F
Format: Article
Language:English
Subjects:
ACCELERATORS
ACCURACY
AIR
ATOMS
BEAM CURRENTS
CARBON CYCLE
DATA
GEOSCIENCES
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
LAWRENCE LIVERMORE NATIONAL LABORATORY
MASS SPECTROSCOPY
OXALIC ACID
SPUTTERING
WHEELS
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Summary:Development of {sup 14}C analysis with precision better than 2{per_thousand} has the potential to expand the utility of {sup 14}CO{sub 2} measurements for carbon cycle investigations as atmospheric gradients currently approach traditional measurement precision of 2-5{per_thousand}. The AMS facility at the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, produces high and stable beam currents that enable efficient acquisition times for large numbers of {sup 14}C counts. One million {sup 14}C atoms can be detected in approximately 25 minutes, suggesting that near 1{per_thousand} counting precision is economically feasible at LLNL. The overall uncertainty in measured values is ultimately determined by the variation between measured ratios in several sputtering periods of the same sample and by the reproducibility of replicate samples. Experiments on the collection of one million counts on replicate samples of CO{sub 2} extracted from a whole air cylinder show a standard deviation of 1.7{per_thousand} in 36 samples measured over several wheels. This precision may be limited by the reproducibility of Oxalic Acid I standard samples, which is considerably poorer. We outline the procedures for high-precision sample handling and analysis that have enabled reproducibility in the cylinder extraction samples at the
ISSN:0033-8222
1945-5755