Simulation of electron transport during beta irradiation

Abstract

Optimisation of the laboratory beta irradiation for luminescence dosimetry requires a detailed understanding of the processes involved. For this purpose, we have developed a Monte-Carlo transport based model of the 90Sr/ 90Y source used on Risø TL/OSL readers. Here, we test this model against experimental data for an unshielded source. It is shown to be able to represent well the general form of the dependence of dose rate on depth and substrate. In contrast to data from film dosimetry (a measure of true energy deposition), we found CaF 2 luminescence dosimetry deviated systematically from the predicted values. We suggest that these differences must arise from an LET dependence of the luminescence efficiency on the electron spectrum depositing dose. This modelling begins to provide an analytical basis for the recent observation that the beta to gamma apparent dose rate ratio is phosphor dependent, even for phosphors with essentially identical energy absorption characteristics (e.g. quartz, feldspar, Al 2 O 3 ).