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Evaluation of Direct-Precipitation and Gas-Evolution Methods for Radiocarbon Dating of Ground Water

Published online by Cambridge University Press:  18 July 2016

In Che Yang*
Affiliation:
US Geological Survey, Mail Stop 407 PO Box 25046, Denver Federal Center Denver, Colorado 80225
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Abstract

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The extraction of dissolved carbonate species for age dating from a 100L water sample by the direct-precipitation method (DPM) and by the gas-evolution method (GEM) has been investigated. Stable carbon-isotope fractionation between initial and final carbon dioxide evolved was ca 11‰ by GEM and 1‰ by DPM. GEM will produce isotopically lighter carbon dioxide compared with DPM if carbonate recovery is low. Extraction efficiency of > 95% can be achieved by GEM in 3 hours using nitrogen gas at a sweeping rate of 2000cc per minute. DPM requires precipitates to settle overnight to assure > 95% recovery. GEM is little affected by a high concentration of sulfate ions, whereas DPM is greatly affected by sulfate resulting in less yield.

Type
V. General Aspects of 14C Technique
Copyright
Copyright © The American Journal of Science 

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