Investigation on the applicability of quartz isothermal thermoluminescence (ITL) signal to dating Quaternary sediments: Dose recovery experiments

초록

In this paper, we explored the applicability of quartz ITL (Isothermal ThermoLuminescence) signals to dating Quaternary sediments, the depositional ages of which are beyond the datable age ranges of the conventional OSL dating methods. Firstly, the decrease in quartz ITL signal sensitivity was examined using quartz from alluvial fan and modern beach environments. In this experiment, the degree of quartz ITL sensitivity decrease was observed to be dependent on the size of radiation doses absorbed by quartz and probably on the depositional environments. In the dose recovery experiment, the laboratory doses given to the samples were all overestimated. Further, we observed that, for the laboratory-irradiated quartz samples, the TL signals that are directly related to isothermal TL signal production (325 degrees C and 375 degrees C TL signals) had not been effectively removed by exposure to light for 1000 seconds. This seems to suggest that, besides the sensitivity decrease in ITL signals, the overestimation of the given doses in the dose recovery experiment may be, at least partly, attributed to the presence of less light -sensitive luminescence signal components remaining after optical stimulation. Based on these, after subtracting the residual dose, we could recover the given dose accurately. This study shows that, although quartz ITL ages are presumed to overestimate the depositional ages, the quartz ITL dating method is useful, at least, for constraining the upper limit of depositional ages.

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