Richard Gillespie

Chronology of guitarrero cave, peru.

Dating by accelerator mass spectrometry of wooden artifacts, cord, and charcoal samples from Guitarrero Cave, Peru, supports the antiquity of South Americas earliest textiles and other perishable remains. The new dates are consistent with those obtained from disintegration counters and leave little doubt about the integrity of the lower Preceramic layers and their early cultivars. Re-evaluation of the mode of deposition suggests that most of the remains resulted from short-term use of the cave in the eighth millennium B.C., with a possible brief human visit as early as 12,560 years ago.

Laboratory contamination in radiocarbon accelerator mass spectrometry

Abstract Factors which influence contamination during laboratory conversion of sample carbon to graphite are discussed. Careful attention to the cleaning of apparatus and the use of disposable components can reduce the extent of laboratory-induced contamination. Some examples of contamination from conservation treatments are also given.

Status of the Oxford radiocarbon accelerator

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).

Recent developments in archaeological dating using an accelerator

Abstract The main function of the Oxford Radiocarbon Accelerator Laboratory, to provide a continuing facility for archaeological dating, has been realised in the last few months. The current state of technical development allows us to tackle the majority of archaeological projects, although limitations in measurement accuracy and in the ability to estimate the contamination background impose some constraints. Within these limitations, about 50 archaeological dates have been determined on a variety of materials, to an accuracy of about 1.5% (for recent dates), over the time period extending back to about 30 000 years. Some of the specific archaeological projects to which accelerator dating has made a special contribution are described.