The effect of single grain luminescence characteristics on single aliquot equivalent dose estimates

Abstract

We report an investigation of the effect of different single grain OSL behaviours on multiple-grain (single aliquot) De estimates. This was done by creating ‘synthetic aliquots’ in which signals are summed from collections of individual grains. The samples used were taken from aeolian linear dune sediments, from sites located in the Kalahari. We note this is a type of sample for which single multiple-grain aliquots are routinely used for dating. Several grain behavioural types were identified in our samples but the only grain type that systematically affected multiple-grain De estimates was the ‘over-saturating’ type (the case where the natural signal (Ln/Tn) is significantly greater than the regenerated Lx/Tx signal at saturation), the presence of which lead to higher estimates of De. The magnitude of this effect is controlled by the contribution of ‘over-saturating’ grains to the total light sum of the multiple-grain aliquot and the maximum increase observed in this study was ∼15 Gy. Of the four samples investigated here, inter-aliquot variations in the signal contribution of ‘over-saturating’ grains led to a significant increase in dispersion in just one of the samples. More generally, the presence/absence of these grains is considered to be a likely source of significant ‘intrinsic’ scatter in single aliquot dating and likely to broaden multiple-grain De distributions. We suggest all samples are screened for this behaviour before single aliquot dating is attempted.