Thermoluminescence and electron spin resonance properties of some travertines from Turkey

Abstract

For the sake of dating certain calcite geological samples, the TL and ESR properties of travertines from Denizli (in the southwestern part of Turkey) were studied and the effects of pre-heating temperature and pre-heating time on the sensitivity of the samples to radiation evaluated. Heat treatment above 350°C increases the sensitivity of all radiation-induced TL peaks except the 330°C glow peak. Results of gamma-ray dose calibration in travertine (CaCO 3 crystal of trigonal symmetry) indicate that the 180 and 280°C TL peak amplitudes increase exponentially with dose. We show that second-order kinetics characterizes the 180 and 280°C glow peaks reasonably well. The Mn 2+ lines of the ESR spectra are used to investigate the thermal decomposition processes of travertine samples, showing very good agreement with those of thermogravimetry. Glow mechanisms of TL in travertine have also been studied using ESR analysis. The pre-heating and subsequent laboratory irradiation procedure is found to enhance the TL and ESR signals of CO 3 3− and CO 2 − centres. An isochronal thermal anneal sequence experiment showed that 180 and 280°C peaks in travertines are correlated with CO 3 3− and CO 2 − centres in the same way that the peak at 330°C is correlated with SO 2 − centres. A model for the recombination mechanism is suggested on the basis of the TL and ESR measurements.