COMPUTER-SIMULATIONS OF OPTICAL BLEACHING OF TL AND OSL SIGNALS

We describe the results obtained from a computer simulation of bleaching of thermoluminescence (TL), generation of phototransferred TL (PTTL) and production of optically stimulated luminescence (OSL) during optical stimulation. The model used in these simulations includes shallow trapping levels, thermally ''active'' traps from which charge is thermally excited during TL readout, deep thermally disconnected traps which are stable during TL readout, radiative recombination centers and non-radiative recombination centers. In the model described, optical excitation of electrons is assumed to occur from the thermally disconnected traps only. Recombination of optically excited electrons with trapped holes is an important aspect of the model. PTTL, TL and OSL curves are simulated as functions of absorbed radiation dose and as functions of illumination time during optical excitation. The results indicate that a model such as this, in which the key feature is the recombination of freed electrons with trapped holes, cannot be discounted as the mechanism for optical bleaching, PTTL and OSL in sedimentary materials.