Thermoluminescence and ESR in an aragonite speleothem

Mechanisms of thermoluminescence (TL) in aragonite have been studied using electron spin resonance (ESR) techniques. Natural aragonite shows a prominent TL glow peak at 613 K. Additional gamma irradiation enhanced this glow peak but displaces it slightly to 593 K, and induces two glow peaks at 393 and 493 K. Pre-annealing at 653 K for 10 min and subsequent gamma irradiation also induces and enhances two glow peaks at 393 and 493 K. The authors show that second-order kinetics characterizes all the glow peaks reasonably well. Results of dose calibration in aragonite indicate that the 393 K peak increases linearly with dose, whereas the others exhibit anomalous behaviours. On the other hand, aragonite presents a complex ESR spectrum. The pre-anneal and subsequent irradiation procedure is found to enhance Pb³⁺ and CO₃^- ESR hole centres. An isochronal thermal anneal sequence experiment indicates that these ESR centres can be related to two glow peaks at 393 and 493 K. A model for the recombination mechanism is suggested on the basis of TL and ESR measurements.