Fundamental investigations of natural and laboratory generated SAR dose response curves for quartz OSL in the high dose range

• Double saturation exponential laboratory dose response.
• Behaviour is inherent to quartz.
• Natural dose response curves enter saturation earlier than laboratory dose response curves.
• Initial dose dependent sensitivity changes may lead to poor dose recovery at very high doses.

SAR-OSL investigations on quartz from Romanian loess resulted in non concordant fine and coarse-grain ages for equivalent doses higher than ∼100 Gy. The laboratory dose response for both grain sizes is well represented by a sum of two saturating exponential functions, fine and coarse grains characterised by D01 and D02 values of ∼140 and ∼1400 Gy and ∼65 and ∼650 Gy respectively. Pulsed OSL experiments confirmed that this behaviour is almost certainly inherent to quartz and not caused by contamination with another mineral. Natural dose–response curves do not follow the same pattern and enter saturation much earlier. Analysis of time resolved spectra indicated similar luminescence lifetimes for both fine and coarse quartz grains, and natural and laboratory generated OSL signals seem to use the same non-dose-dependent recombination pathways. The natural signals of a sample with an expected equivalent dose of 2000–2500 Gy were found to be below the saturation level of the laboratory dose response curve for both grain sizes; this also applied to the luminescence signals measured after >5000 Gy given on top of natural doses.