Intercomparison of 14 C Dating of Wood Samples at Lund University and ETH-Zurich AMS Facilities: Extraction, Graphitization, and Measurement

We conducted an interlaboratory comparison between our radiocarbon-related research group at Lund University and the established ETH-Zurich facility to test the quality of the results obtained in Lund and to identify sources of potential background differences and scatter. We did find differences between the 2 laboratories in the contributions of chemical preparation, graphitization, and measurements to the overall background. The resulting overall background is, however, almost similar. Multiple measurements on 2 wood samples of known calendar age yield consistent and accurate 14 C ages in both laboratories. However, one of our known samples indicates that IntCal09 is ≃38 ± 16 14 C BP too young at 7020 calendar yr BP, which is consistent with one of the raw data sets contributing to IntCal09. Overall, our results show that a systematic approach to compare the different steps involved in 14 C age determination is a useful exercise to pinpoint targets for improvement of lab routines and assess interlaboratory differences. These effects do not necessarily become apparent when comparing 14 C measurements that integrate over the whole process of preparation and measurement of different laboratories.