Optically Stimulated Luminescence

Optically stimulated luminescence dating of fluvial deposits definition

We analyse theThe number of trapped electronsFor quartz blue

The number of trapped electrons depends on the total amount of radiation that the mineral has been exposed to. Optically stimulated luminescence dating of glaciofluvial sediments on the Canterbury Plains, South Island, New Zealand. The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried. Once we have calculated our equivalent dose, we need to measure the environmental radiation dose rate.

Photograph used with permission

For quartz, blue or green excitation frequencies are normally used and the near ultra-violet emission is measured. Photograph used with permission of Geoff Duller. We analyse the quartz or feldspar minerals in sand deposits.

Optically Stimulated Luminescence

Road cut through glacial outwash sediments, Patagonia. Photographs taken by Geoff Duller Aberystwyth University. Saunders, who thought the thermoluminescence response of pottery shards could date the last incidence of heating. This reworked carbon changed the measured isotopic ratios, giving a false older age. From this curve we can calculate the dose that our sample must have received to produce the amount of light that we measured first.

Quaternary glaciation of Mount Everest. Sediment transport in glacial environments is often over short distances in turbid meltwater streams, which can limit the sunlight exposure that the grains of sand receive.

We then give our sand sample a range of laboratory radiation doses and measure the luminescence that each dose produces to develop a calibration curve. This occurs if the grains of sand are not exposed to sufficient sunlight prior to deposition within a landform such as a glacial moraine. These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar. There are advantages and disadvantages to using each.

If we assume that the radiation dose rate of the sediment has remained constant over time, then if we measure that dose rate, we can calculate the sample age. This is because water attenuates scatters the radiation, reducing the total radiation dose that the sample has been exposed to.