†e-mail: Keith.Fifield@anu.edu.au

The extremely high sensitivity of accelerator mass spectrometry (AMS), and its applicability to a range of isotopes, is facilitating the determination of chronologies for many problems in Quaternary studies. At the ANU, the AMS system based on the 15 million-volt 14UD accelerator in the Department of Nuclear Physics is making contributions in the areas listed below. Most of these projects entail collaborations with groups in RSES and/or the Department of Geology, and some will be reported in more detail in other presentations to this meeting. My intention will be to highlight the special capabilities of AMS as well as the symbiosis between physicist and earth scientist that is making these advances possible.

1. Establishing chronologies for marine cores via radiocarbon dating of individual species of foramanifera hand-picked from short sections of core. Typically, less than 1 mg of carbon is available for dating.
2. Determination of atmospheric levels of ¹⁴C back to 50 ka before present by comparison of U/Th and radiocarbon dates on corals from the Huon Peninsula, PNG. The small-sample capability of AMS permits both a stringent chemical pretreatment of the samples, and checks on its efficacy, that would not be possible with conventional radiometric methods.
3. Improvement in the age limit of radiocarbon dating. This is resulting in radiocarbon evidence for human occupation of Australia beyond 40 ka B.P., and lends support to other dating techniques, OSL in particular, which have been indicating such earlier occupation for some time.
4. Establishing glacial chronologies on the Kosciusko Massif and in Tasmania via exposure-age dating using the accumulation of ¹⁰Be and ³⁶Cl in moraine boulders and glacially-polished bedrock surfaces. These isotopes are produced in situ by the action of cosmic rays, and concentrations are so low that only AMS offers the sensitivity to be able to measure them.
5. Recently, in a collaboration with the Institute of Geological and Nuclear Sciences at Lower Hutt in New Zealand, we have shown that it is possible to date ice in temperate-climate glaciers using ³²Si, which has a 140 year half-life. This isotope is produced in the atmosphere by cosmic-ray interactions with argon, and falls out in precipitation at the rate of ~10³ atoms/cm²/yr. While radiometric methods have been applied to rainwater or snow, where hundreds of litres may be readily obtained, the situation is rather different for glacial ice where typically only a kilogram is available for dating. In this case, only AMS has the requisite sensitivity for determining the extremely low concentrations of the isotope.