Dependence of (anomalous) fading of infra-red stimulated luminescence on trap occupancy in feldspars

Dose dependency of anomalous fading of infra-red stimulated luminescence (IRSL) from feldspars has been investigated using radiations of different ionisation qualities. The rate of fading of the IRSL signal after proton irradiation (9.4–30%/decade) is on an average almost twice compared to that after 90Sr/90Y beta particle irradiation (3.5–15%/decade) for all the measured feldspar mineral specimens. Similarly, the fading rates after x-rays of 50 kV and 10 kV fall in between those of beta particle and proton irradiations. Our results suggest that rate of anomalous fading in feldspars depends on the number density of the trapped charge carriers. These results support the hypothesis that anomalous fading occurs across randomly distributed donor-acceptor distances as opposed to pairs with a fixed distance. -- Highlights: • Proton irradiated IRSL in feldspar fades twice as fast as that of beta particles. • Systematic increase of fading rates with beta particles, x-rays and proton. • Observation suggests the dose rate is dose dependent i.e., burial age. • Tunnelling model with randomly distributed sites is favoured by the results