How Robust are Single Aliquot Regeneration paleo-doses using single grains of Quartz: The role of change in luminescence sensitivity during the measurement of natural luminescence

NAVEEN CHAUHAN, Haresh Rajapara, James Feathers, Stephen Garnett, Robert James Wasson, Manoj Jaiswal, Ashok Kumar Singhvi

Luminescence dating using quartz is generally carried out using the single aliquot regeneration (SAR) protocol (Murray et al., 2021; Murray and Wintle, 2000). Singhvi et al. (2011) suggested a methodological improvement in the SAR protocol to account for the changes in the luminescence sensitivity during the readout of natural OSL signal. It was suggested that such changes are common and if not corrected for, can lead to systematic offsets in the SAR based luminescence ages. Singhvi et al. (2011) proposed a Natural Correction Factor (NCF) to correct for such changes in the luminescence sensitivity.
This suggestion implied that, in the absence of any experimental procedure to routinely measure changes in the luminescence sensitivity of individual grains, currently used automated single grain measurements and age determination based on them could be erroneous (Chauhan and Singhvi, 2019). This contribution examines a possible way such that automated single grain measurements can be used through segregation of luminescence signals from grains whose signal potentially have a NCF closer to unity.
Examination of SAR measurements on single grain data provided three important observations viz.;
a) dispersion in single grain paleo- doses decreased with the signal to background ratio(R),
b) the dose recovery tests on young samples (with low natural doses), additionally irradiated with a larger laboratory dose, indicated that, majorly the samples with high signal / background ratio (R), typically > 100, returned paleodoses closer to the expected dose. Grains with lower R gave lower paleo-doses with a higher dispersion;
c) Optical decay curves of samples with R > 3 and R > 100 differed and only grains, with similar and near ideal decay shapes comprising only the fast component, yielded concordant paleo-doses.
These led to a suggestion that segregation of paleo-doses based on their R values and optical decay shapes could possibly provide a diagnostic filter for grains that do not suffer sensitivity changes and, ages based on such grains would be more reliable. At this stage this study is presented as an idea with reasonable premise and promise, some encouraging results on the proof of the concept and we suggest for a community wide effort towards a reevaluation of reported single grain paleo-doses based on two criteria viz. the R value and optical decay shapes, so that more realistic single grain luminescence ages are obtained.