Radiocarbon Dating by Accelerator Mass Spectrometry: Some Recent Results and Applications

¹⁴C differs from other nuclides measured by accelerator mass spectrometry (AMS) in that an extensive database of dates already exists. AMS dates should therefore have comparable accuracy, and the measurement of isotopic ratios to better than 1%, which was an important technical goal, has been reached. The main advantage of being able to date samples 1000 times smaller than previously lies in the extra selectivity that can be employed. This is reflected in the results and applications. Selection can apply at several levels; from objects that formerly contained too little carbon, to the choice of archaeological material, to the extraction of specific chemical compounds from a complex environmental sample. This is particularly useful in removing uncertainty regarding the validity of a date, since a given sample may comprise carbon atoms from different sources each with their own ¹⁴C `age'. Examples from archaeological and environmental research illustrating these points are given. ¹⁴C dating by AMS differs from conventional radiocarbon dating by having the potential to measure much lower levels of ¹⁴C, and therefore should double the time span of the method. This potential has not yet been realized because of sample contamination effects, and work in progress to reduce these is described.