Q-band studies of the ESR signal in tooth enamel

Tooth enamel is one of the most promising materials for electron spin resonance (ESR) dating because the X-band signal is large, easy to measure, and extremely stable. The mean lifetime at ambient temperature has been measured greater than the age of the Earth! However, the X-band spectrum in fossil teeth is, in fact, a composite of two signals that can be resolved if the sample is examined in the Q-band region. The relative size of the two signals appears to be a function of degree of fossilization; older teeth have a better-defined second signal. A study of the dependence of these signals on radiation dose, microwave power, and temperature strongly suggests that both signals are located in the hydroxyapatite crystal structures. As such, then, the X-band spectrum, measured at moderate modulation amplitude, is suitable for determining the age of fossil teeth. (C) 2000 Elsevier Science Ltd. All rights reserved.