Luminescence dosimetry: Does charge imbalance matter?

We use both modelling and high dose experiments to investigate the effects of charge imbalance on luminescence. Charge entering and leaving irradiated 50 mu m grains is modelled using Geant4 to predict the degree of charge imbalance a grain will experience when exposed to i) the Sr-90/(90) Y beta source of a Rise, TL/OSL reader, ii) a 200 keV electron beam, and iii) the 'infmite-matrix' K-40 beta spectrum. All simulations predict that between 1.4% and 2.9% more electrons enter a grain than leave, resulting in a net negative charge in the grain. The possible effects of this charge imbalance on luminescence production are discussed and experiments designed to test the resulting hypotheses; these involve giving very high doses (hundreds of kGy) to silt-sized quartz grains using low energy electrons (200 keV). Up to 700 kGy, we observe an increase in both luminescence output resulting from these high doses, and in sensitivity; above 700 kGy, both decrease. These observations, together with a slower luminescence decay during stimulation following higher doses, are consistent with the hypothesis of a decrease in hole population as a result of net accumulation of electrons during irradiation.