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Reduction of CO2-to-Graphite Conversion Time of Organic Materials for 14C AMS

Graphite is the most common type of target for 14C accelerator mass spectrometry (AMS). It is readily produced by catalytic reduction of CO2, but the presence of a small amount of impurities (e.g., sulfur compounds) may retard the reaction. We have tested some techniques to find a method that reduces the impurity content of CO2 produced by combustion of organic material. We found that using water during combustion reduces the average time for graphite conversion of CO2 from organic matter from >3 h to ca. 2 h. This is the time for graphite production from CO2 obtained by acid hydrolysis of calcite. Measurements of known-age and background samples show that this combustion method neither changes the isotopic ratios nor introduces any additional background.