Thermoluminescence and ESR studies and dating of naturalcalcite minerals

In this study, the calcite type travertine samples collected from Denizli and Cankiri regions were investigated and dated by Thermoluminescence and Electron Spin Resonance Spectroscopy. On the natural glow curves of Denizli and Cankiri travertines, two glow peaks were observed at 280 deg. C, 330 deg. C and at 270 deg. C and 330 deg. C respectively. Upon irradiating the samples artifically, glow peaks at t80 deg. C and 170 deg. C respectively were observed in Denizli and Cankiri travertines. Heating of the samples before irradiation caused an increase in the thermoluminescence sensitivity for all peaks, except the one at 330 deg. C. It was also found that this increase depends on both pre-heating temperature and time. An attempt was made to explain this increase in sensitivity by increasing of the rate of diffusion of impurity ions in the crystal during heating. The relationship between thermoluminescence sensitivity and pre-irradiation dose was also examined, and beyond a threshold value of pre-irradiation dose an increase in the thermoluminescence sensitivity of all peaks, except the one at 330 deg. C, was found for every sample. As the glow peaks at 330C were saturated at very low artificial dose values for the dating purpose, the peaks at 2BOoC and 270 deg. C respectively used Denizli and Cankiri travertines. It was found that the thermal life time of the trapped electrons z, corresponding to these peaks, is about l00 years. It is therefore concluded that the samples older than 106 years could be dated by using these glow peaks. In order to investigate the alteration ot thermoluminescence glow peak intensity with irradiation dose, virgin travertines and samples consolidated with impregnated polymers were irradiated and the growth curves were obtained. ED (Equivalent Dose) and JD (Geological Dose) values were calculated using the Barabas model and the least square method. It was found that the values found both for natural and consolidated samples were in good correlation within the limits of confidence. Furthermore, it was also found that these values were not effected from different dose rates. Annual dose of the samples were calculated by combining the results of two methods which give internal and external doses received. To determine internal dose rate, the amount of radioactive elements 238U, 232Th and 40K in the samples were measured. Neutron activation analysis was performed for this measurement. For external dose rate measurement CaSO4, Dy dosimeters were used. The ages of each travertine sample were thus calculated by using annual dose, ED and JD values. The age of Denizli travertine is determined to be 774.000 t 66.000 years and that of Cankiri travertine is 103.000 t 9.000 years. The ESR spectra of the same samples were also taken at room temperature. The ESR signals in the spectra were assigned to C03 3 . C03 and COZ centres that were originated from the ionization of C03 z groups, which is the major constituent of calcite after irradiation. The heating of irradiation samples at different temperatures above room temperature for equal periods showed that 180 deg. C, 280 deg. C peaks in Denizli travertines, and 170 deg. C, 270 deg. C glow peaks in Cankiri travertines, are correlated with C03 3 and COz centres and the peaks at 330 oC are correlated with C03 centres. The ages of the same samples were also calculated by ESR method and the ages of Denizli and Cankiri travertines are found to be 1.110.000 t 110.000, 230.000 t 22.000 years respectively. The differences in ages determined by these two methods are explained by the nature of thermoluminescence method. The decreacing ot the luminescence emission sensitivity of the trapped electrons with respect to different parameters is assumed to be the main reason for the low value obtained by the thermoluminescence