Accelerator mass spectrometry (AMS) differs from other forms of mass spectrometry in that it accelerates ions to extraordinarily high kinetic energies before mass analysis. The special strength of AMS among the mass spectrometric methods is its power to separate a rare isotope from an abundant neighboring mass (“abundance sensitivity”, e.g. 14C from 12C). The method suppresses molecular isobars completely and in many cases can separate atomic isobars (e.g. 14N from 14C) also. This makes possible the detection of naturally occurring, long-lived radio-isotopes such as 10Be, 36Cl, 26Al and 14C. Their typical isotopic abundance ranges from 10−12 to 10−18. AMS can outperform the competing technique of decay counting for all isotopes where the half-life is long enough. source: wikipedia
Christopher Ramsey at Oxford University has been most concerned with the development of high precision techniques and their applications to archaeological and environmental problems. His area of research invovles the Accelerator Mass Spectrometry (AMS) techniques including the development of gas ion sources for AMS that allows the measurement of very small samples and a technique, GC-AMS with applications in the environmental and biological sciences.
Precision and accuracy in accelerator mass spectrometry (AMS) dating relies on the systematic reduction of errors at all stages of the dating process, from sampling to AMS measurement. With new AMS systems providing much better precision and accuracy for the final stage of the process, we need to review the process as a whole to test the accuracy of reported results. A new High Voltage Engineering Europa (HVEE) AMS system was accepted at Oxford in September 2002. Since then, the system has been in routine use for AMS dating and here we report on our experiences during the first year. The AMS system itself is known to be capable of making measurements on single targets to a precision of better than 0.2% for the (super 14) C/ (super 13) C ratio and better than 0.1% for the (super 13) C/ (super 12) C ratio. In routine operation, we measure known-age wood to a precision of just above 0.3%, including uncertainties in background and pretreatment. At these levels, the scatter in results is no higher than reported errors, suggesting that uncertainties of + or -25 to + or -30 (super 14) C yr can be reliably reported on single target measurements. This provides a test of all parts of the process for a particular material in a particular state of preservation. More generally, sample pretreatment should remove as much contamination as feasible from the sample while adding as little laboratory contamination as possible. For more complex materials, such as bone, there is clearly more work needed to prove good reproducibility and insignificant offsets in all circumstances. Strategies for testing accuracy and precision on unknown material are discussed here, as well as the possibilities of one day reaching precisions equivalent to errors of or -20 (super 14) C yr.
C B Ramsey et al, Towards high precision AMS: Progress and Limitations: RadioCarbon Journal, Vol 46, No 1, 2004
The 2007 Biblical Archaeology Society Publication Awards recognize the best books on archaeology and the Bible published in 2005 and 2006 and have been presented since 1985. The book comprises 27 chapters which stemmed from an invited meeting in Oxford organised by Levy and Higham in 2004.