Thermoluminescence and electron spin resonance properties of some travertines from Turkey

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 degrees C increases the sensitivity of all radiation-induced TL peaks except the 330 degrees C glow peak. Results of gamma-ray dose calibration in travertine (CaCO3 crystal of trigonal symmetry) indicate that the 180 and 280 degrees C TL peak amplitudes increase exponentially with dose. We show that second-order kinetics characterizes the 180 and 280 degrees C glow peaks reasonably well. The Mn2+ 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 CO33- and CO2- centres. An isochronal thermal anneal sequence experiment showed that 180 and 280 degrees C peaks in travertines are correlated with CO33- and CO2- centres in the same way that the peak at 330 degrees C is correlated with SO2- centres, A model for the recombination mechanism is suggested on the basis of the TL and ESR measurements, (C) 1999 Elsevier Science Ltd. All rights reserved.