Problems in determining lifetimes of esr signals in natural and burned flint by isothermal annealing signals in natural and burned flint by

ESR signals in microcrystalline quartz (flint) are zeroed by burning and their regrowth can be used to date flint artifacts. We have attempted to determine the mean lives of the dating signals, E′ and A1, in natural and burned flint by two methods, isothermal annealing and steady state/saturation. Isothermal annealing experiments were conducted at 100°C < T < 400°C and the mean lives at 15°C were extrapolated from these data. Flint that has been heated either archaeologically or in the laboratory gives anomalously low mean lives, <- 100 yr, for both signals. This is inconsistent with the observation that experiments carried out on burned flint recovered from archaeological sites give equivalent dose values comparable to exposure histories of > 105 yr. The isothermal annealing experiments on natural flint gave mean lives of circa 10⁷ yr for the E′ signal, and the steady state/saturation method gave values of 10⁵-10⁶ yr for both signals. These values are consistent with observed saturation doses and with archaeological lifetimes. We suggest that there must be a change in the kinetics of charge recombination in burned flints at some temperature below 100°C, which is undetectable in isothermal heating experiments of reasonable duration. Isothermal annealing experiments suggest that preheating procedures previously used to anneal unstable components in flint must be revised.