SAMPLE DILUTION FOR AMS ~14C ANALYSIS OF SMALL SAMPLES (30-150 mug C)

摘要

We investigated sample dilution as a techriique for accelerator mass spectroraetry (AMS) radiocarbon analysis of very small samples (down to 30 mug). By diluting such samples up to a total weight of 200 mug, we can still perform reliable AMS measurements and improve the success rate significantly for targets that are difficult to measure. A disadvantage of this dilution technique is a loss of measurement precision. In addition, calculations of the ~14C/~12C isotope ratios and the uncertainties therein are not straightforward because of peculiarities in isotope fractionation processes in the AMS system. Therefore, to make sample dilution a routine method in our laboratory, we did extensive theoretical and experimental research to find the optimum conditions for all relevant parameters. Here, we report on the first detailed study dealing with all aspects of sample dilution. Our results can be applied in general. As an illustrative test case, we analyze ~14C data for CO_2 extracted from an ice core, from which samples of 35 mug C or less are available.