Comparison of ESR signal dose-responses in modern and fossil tooth enamels

The dose response of ESR signals in enamels extracted from young archaeological (modern) teeth aged less than 200 y were compared with fossil teeth ranging in age from about 50 to 110 ka. We aimed to test the accuracy of equivalent dose (ED) determinations on modern teeth with a known (near zero) ED because zeroing the signal in tooth enamel is not possible. The modern teeth showed departure from true single saturating exponential dose response, but generally gave very good agreement with the expected near zero ED (+/- 5-10% in the worst cases). Linear fitting was better than SSE fitting within the lower dose ranges. However, the fossil teeth showed significant variability and departure from the well-behaved dosing characteristics of modern enamels. When the natural signal was excluded, EDs were found to be strongly dependent upon the choice of the first added dose in both cases studied using a modulation amplitude of 0.32 mT, and strongly dependent upon choice of modulation amplitude in another case. These latter observations, when considered in relation to modern enamel behaviour, raise questions about the possibility of diagenetic change in the fossil enamel. (C) 1997 Elsevier Science Ltd.