Optimization of the ‘double SAR’ procedure for polymineral fine grains

The “double SAR” protocol has been used to measure the equivalent dose of polymineral grains from fine-grained samples. However, the optical ages obtained with this protocol using the different luminescence signals from a sample are not always consistent. Quartz optical ages are believed to be more reliable than feldspar ages. The post-IR OSL signals from polymineral fine grains are believed to be dominated by the signal from quartz. The ages obtained with the “double SAR” protocol using the post-IR OSL signals from polymineral fine grains are therefore considered to be more reliable than those obtained using the IRSL signals. Thus, the feldspar contribution to the post-IR OSL signals should be reduced as much as possible. In this paper, the effects of IR-stimulation temperature and duration before OSL measurement on the post-IR OSL signals from quartz extracts and polymineral grains, and their equivalent dose values were tested. The results show that the IR stimulation causes the quartz post-IR OSL signals to be reduced even at room temperature if the IR stimulation lasts long enough, but does not affect quartz equivalent dose estimation using post-IR OSL signals. In the ‘double SAR’ procedure, the IR-stimulation time should be determined by an IR-bleaching DeDe plateau test, and the bleaching should preferably be performed at room temperature.