Residual correction of ESR Al-centre signals in quartz

Electron spin resonance (ESR) signals in quartz minerals offers great potential for dating and resolving changes in rock cooling histories throughout the Quaternary period. The recently developed single aliquot regenerative dose (SAR) protocol for ESR measurements requires significantly reduced sample volumes and results in higher precision relative to multiple-aliquot additive dose methods. The SAR protocol incorporates an annealing step to reset the sample to its pre-irradiation condition, before regenerative doses are given to build the dose response curve. This annealing treatment generally involves heating at 400 °C for 4 min. However, measurements of quartz from the same lithology with varying natural equivalent dose values reveals that this annealing treatment is not universally applicable as some samples retain a signal exceeding 10% of the natural Al-centre signal (8% of the saturated Al-centre signal). This study employs a set of gneiss samples from the Aar massif in Switzerland to investigate different annealing conditions and to evaluate three different residual correction approaches. The results indicate that prolonged (>16 min) heating at 400 °C induces sensitivity changes, whereas short (<4 min) heating has no discernible effect on sensitivity. We advocate an approach whereby the residual is corrected for using the residual dose, rather than the residual signal intensity. This is achieved by adding the equivalent dose corresponding to the zero-dose-residual signal, to SAR dose response curve regenerative doses before interpolation of the sample equivalent dose onto the corrected dose response curve. • Residual ESR Al-signal was observed after the annealing treatment (zeroing) in SAR measurements. • Prolonged heating at high temperature can fully deplete the Al ESR signal in quartz but it causes sensitivity changes. • The correction approach of adding the equivalent residual dose corresponding to the zero-dose-residual signal to SAR regenerative doses before the DRC fitting is recommended.