On the detection of OSL age overestimation using single-aliquot techniques

Optically stimulated luminescence (OSL) dating is a quantitative dating method to determine the time of last exposure of sand and silt to (sun) light. However, insufficient resetting of the optically stimulated luminescence signal prior to sediment deposition can result in overestimation of the age of a sample. Therefore detection of so-called poor bleaching is of prime importance in OSL dating. Several methods proposed in the literature for detection of poor bleaching are based on the scatter in equivalent doses obtained by singlealiquot methods. In this paper numerical simulations are used to assess the validity of these methods. The simulations show that scatter in equivalent doses is largely dependent on the number of grains contributing to the luminescence signal of each aliquot, and proportion of poorly-bleached grains in the mixture under study. Thresholds for detection of poor bleaching based on inter-aliquot scatter in equivalent doses are therefore not valid. It is concluded that tight, symmetrical dose distributions obtained on small aliquots (ultimately consisting of a single grain) provide the best indication that the sample is homogeneously bleached.