Improvements in dating tooth enamel by ESR.

ESR dating requires that growth curves be determined by interpreting complex spectra. Spectra, however, can vary significantly in shape and field position between different samples, or occasionally between subsamples, even though the mineralogy remains the same. In some cases, this spectral variability does not affect the resulting accumulated dose calculation. In other cases, signal subtraction may be needed. However, some samples that until recently might have been considered unsuitable for dating are now shown to yield accurate and precise results because a broad interference peak is integral to the hydroxyapatite signal. By studying the spectrum at the Q-band frequency, it can be shown that the interfering signal in most cases is not a problem for dating. A second concern has been that artificially irradiating sample aliquots can introduce a short-lived component that is simply an unstable enhancement of the dating signal. The apparent accumulated dose from growth curves created immediately after irradiation is considerably greater than that after annealing, although the curve's shape remains unchanged. Annealing both the natural and artificially irradiated signal shows the dating signal's lifetime to be greater than 10(10) years.