Abstract
The Oxford accelerator has been used exclusively for 14C measurements, and has progressed to the point where reliable dates can be obtained. Evidence for the present performance is presented, including a histogram of the reproducibility of over 100 wire pairs used in actual dating. The errors of measurement on known-age materials are also shown. Machine improvements which have lead to the present performance are described; two problems in particular remain: a variation of the 13C/ 12C ratio with beam current, and a variation of beam position and distribution from one target to another. Graphite targets continue to be made on tantalum wires. We have built another source in which the target is rotated during sputtering, but this has not been tested. The greatest age obtained is 62 000 ± 2000 years BP from geological graphite, but this is almost certainly limited by sample contamination. In practice, the background is limited by laboratory contamination (detailed in a companion paper).
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