What is optically stimulated luminescence dating
We prepare the sample through treating it with acids to remove any calcium carbonate or organic material, and sieve it to get a specific grain size (usually between 0.018 – 0.025 mm diameter), which we then measure in a specialised instrument.
In the Aberystwyth Luminescence Laboratory our instruments are made by a Danish manufacturer and are called “Risø OSL/TL readers”.
If the OSL signal is not fully reset, it may result in an age overestimation.
OSL specialists overcome these challenges through only sampling certain glacial landforms, where greater sunlight exposure is likely to have occurred prior to deposition e.g. Quartz luminescence dating of Anglian Stage (MIS 12) fluvial sediments: Comparison of SAR age estimates to the terrace chronology of the Middle Thames valley, UK.
Once the sand grain has been buried and it is no longer exposed to sunlight, the OSL signal starts to accumulate. Testing an approach to OSL dating of Late Devensian glaciofluvial sediments of the British Isles.
OSL works because all sediments have some natural radioactivity, caused by the presence of uranium, thorium and potassium isotopes in heavy minerals such as zircons.
Once the equivalent dose and dose rate have been measured, sample age can be calculated: Age (ka) = Equivalent dose (Gy) / dose rate (Gy/ka) OSL dating can be used to date sediments from decades up to 400,000 years in exceptional circumstances although the technique is more commonly applied to sediments up to 100,000 years old. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts.
The biggest challenge for OSL dating in glacial environments is partial bleaching (resetting) of the luminescence signal.
The gamma spectrometer has been put into the sample hole (see the lead going from the gamma spectrometer crystal to the control box).
We analyse the quartz or feldspar minerals in sand deposits.
When these quartz or feldspar minerals are exposed to the ionising radiation emitted by the radioactive isotopes in zircons, electrons within the crystals migrate and become trapped in their crystal structure.
The number of trapped electrons depends on the total amount of radiation that the mineral has been exposed to.
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.