Dose response of ESR signals in tooth enamel

Radiation-induced growth in the g = 2.0018 signal in fossil tooth enamel can be used to determine the age of fossil teeth. Porat and Schwarcz (1994) [Integrative Paths to the Past: Paleoanthropological Advances in Honor of F.C. Howell (eds Corrucini R. and Ciochon R.), pp. 521–530. Prentice- Hall, Englewood Cliffs] suggested that the radiation sensitivity of all tooth enamel is quite similar, and have constructed a Universal Growth Curve (UGC) to estimate equivalent dose (DE). To further test this concept, we use a saturating exponential of the form I = Imax (1 - exp[- D/D0]) to fit normalized ESR intensity (I) data for teeth from various sites. We show that the ranges of fitting parameters Imax and D0 overlap for modern and fossil enamels. This suggests that no significant diagenetic changes in the enamel have occured to affect the ESR signal in most samples. Sensitivity, as measured by normalized intensity at D = 32 Gy, varies by 22% (n = 24); modern samples have the same mean sensitivity, but show less variation (8%). The normalized dose-response curve (natural intensity vs DE) is a good predictor of DE, although there are some outliers. Imax is strongly correlated with D0, suggesting a relationship between trap concentration and capture cross-section for migrating charges.