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 μm grains is modelled using Geant4 to predict the degree of charge imbalance a grain will experience when exposed to i) the ⁹⁰Sr/⁹⁰Y beta source of a Risø TL/OSL reader, ii) a 200 keV electron beam, and iii) the ‘infinite-matrix’ ⁴⁰K β 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.