Assessing the reproducibility of quartz OSL lifetime determinations derived using isothermal decay

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Signal stability is a key consideration when using luminescence dating techniques. The stability, or lifetime, of a signal is one of the factors determining the upper age constraint for luminescence dating, and it has been suggested that the signal being used for dating should have a lifetime at least ten times the age being dated in order to limit age underestimation to an upper loss of 5%. Accurate derivations of signal stability and associated kinetic parameters, such as trap depth and frequency factor, are also important parameters for constraining rock cooling histories in thermochronometric techniques. This paper aims to assess the reproducibility of lifetime determinations derived using isothermal decay measurements. Variability arising from changing the isothermal decay protocol used is tested. Simulating Arrhenius plot from fixed trap depth and frequency values shows that whilst trap depth can be relatively well constrained, significant variability in the frequency factor, hence signal lifetime, should be expected. This paper also uses luminescence signals measured using different wavelengths to better understand the impact of signal from non-fast quartz OSL components in lifetime calculations. The presence of contributions from non-fast OSL components in the initial part of the OSL signal can result in the lifetime being calculated from charge contributions from multiple traps, not solely the 325 °C TL peak, as has been previously assumed. This effect can be reduced however by stimulating luminescence signals with longer wavelengths to better isolate signal from the fast component.