Reproducibility of thermal pretreatment prior to optically stimulated luminescence measurements: implications for overdispersion

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Most protocols using optically stimulated luminescence (OSL) signals for equivalent dose meas-urement involve heating the sample prior to measurement – this is called preheating. Whilst tempera-ture control of the hotplate on commercially available luminescence instruments is very precise, it has been known for many years that the temperature of the sample is commonly lower than that of the hotplate. The problem is exacerbated when ramping the temperature of the hotplate, especially at higher heating rates (> 5 K/s). Thermal lag [1] may be due to poor contact between the hotplate and the substrate the sample is mounted on, or poor contact between the substrate and the sample. In practice the former is most common. Thermal lag is of major concern in two situations. The first is where the temperature is being used as part of some physical characterisation of a defect, such as methods for estimating values of E and s; here differences between the measured and actual tempera-ture may lead to significant errors in parameter estimates. The second source of concern is where the thermal lag varies from one preheat step to another, leading to additional scatter in measurements, and additional overdispersion in equivalent dose values. It is this second issue that is the focus of this study. This paper proposes a procedure that can be incorporated into single aliquot methods of equivalent dose measurement for automatically monitoring the reproducibility of the preheat treatment at each stage of the protocol. For quartz OSL SAR measurements, the impact of poor reproducibility in pre-heat is limited at low temperatures, but becomes significant above 240°C. The consequences of poor reproducibility in preheating are even more significant for measurements of the thermally-transferred OSL (TT-OSL) signal from quartz and the infrared stimulated luminescence (IRSL) or post-IR IRSL signal from feldspar. Quantification of the reproducibility of the preheat procedure means it can be used as a rejection criterion for individual aliquots. Application of this criterion results in a reduction in scatter in equivalent dose. The implications of poor reproducibility in preheating for the reproduci-bility of equivalent dose values and the impact on overdispersion in single aliquots and single grains is discussed.
Cyfnod12 Medi 2017
Teitl y digwyddiad15th International Conference on Luminescence and Electron Spin Resonance Dating
Math o ddigwyddiadCynhadledd
LleoliadCape Town, De AffricaDangos ar fap
Graddau amlygrwyddRhyngwladol