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  • Author: Vasilis Pagonis x
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Simulation of OSL Pulse-Annealing at Different Heating Rates: Conclusions Concerning the Evaluated Trapping Parameters and Lifetimes

Pulse annealing has been the subject of several studies in recent years. In its basic form, it consists of relatively short-time optically stimulated luminescence (OSL) measurements of a given sample after annealing at successively higher temperatures in, say, 10°C increments. The result is a decreasing function with a maximum OSL at low temperatures and gradually decreasing to zero at high temperature. Another presentation is that of the percentage OSL signal lost per annealing phase, associated with minus the derivative of the former curve, which yields a thermoluminescence (TL)-like peak. When the heating is performed at different heating rates, the TL various heating rates (VHR) method can be utilized to evaluate the trapping parameters. Further research yielded more complex pulse-annealing results in quartz, explained to be associated with the hole reservoir. In the present work, we simulate numerically the effect, following the experimental steps, in the simpler form when no reservoir is involved, and in the more complex case where the reservoir plays an important role. The shapes of the reduction-rate curves resemble the experimental ones. The activation energies found by the VHR method are very close to the inserted ones when the retrapping probability is small, and deviate from them when retrapping is strong. The theoretical reasons for this deviation are discussed.

Abstract

The thermoluminescence (TL) glow curves from feldspars have been the subject of numerous studies, because of their importance in luminescence dating and dosimetry. This paper presents new experimental TL glow curves in a plagioclase feldspar, measured using the T max-T stop technique of glow curve analysis. Kinetic analysis of the experimental results is carried out for a freshly irradiated sample, as well as for a sample which has undergone optical treatment using infrared light for 100 s at 50°C. Application of the initial rise method of analysis indicates that the TL signals from both samples can be characterized by a continuous distribution of energy levels. By subtracting the TL glow curves measured at successive T stop values, a series of TL glow curves is obtained which are analyzed using the empirical general order kinetics. It is found that all TL glow curves obtained by this subtractive procedure can be described accurately by the same general order parameter b ∼1.7. In a second attempt to analyze the same TL glow curves and possibly extract information about the underlying luminescence process, the shape of TL glow curves is analyzed using a recently proposed physical kinetic model which describes localized electronic recombination in donor-acceptor pairs. Within this model, recombination is assumed to take place via the excited state of the donor, and nearest-neighbor recombinations take place within a random distribution of centers. This recent model has been used recently to describe successfully several types of luminescence signals. This paper shows that it is possible to obtain good fits to the experimental data using either one of these two approaches.

Abstract

The present paper presents a comparative experimental study of two commonly measured Optically Stimulated Luminescence (OSL) signals in quartz. The experimental study measures both the continuous wave OSL (CW-OSL) and the linearly modulated (LM-OSL) signals from the same quartz sample for a range of stimulation temperatures between 180 and 280°C, while the former is transformed to pseudo LM-OSL (ps LM-OSL). A computerized deconvolution curve analysis of the LM-OSL and ps LM-OSL signals was carried out, and the contributions of several OSL components to the initial OSL signal (0.1 s) were shown to be independent of the stimulation temperature used during the measurement. It was also found that the composite OSL (0.1 s) signal consists mainly of the first two OSL components present in the OSL curves. The equivalence of the ps LM-OSL (transformed CW-OSL) and of LM-OSL measurements was also examined by an appropriate choice of the experimental stimulation times, and of the stimulation power of the blue LEDs used during the measurement.