What is optically stimulated luminescence dating
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 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. Once we have calculated our equivalent dose, we need to measure the environmental radiation dose rate. This can be measured either at the sample location using a portable gamma spectrometer, through measurement of alpha, beta and gamma counts in the laboratory, or through direct measurement of uranium, thorium and potassium concentrations using inductively-coupled plasma mass spectrometry.
The OSL signal is reset by exposure to sunlight, so the signal is reset to zero while the sand is being transported (such as in a glacial meltwater stream).
In addition to radiation from the surrounding sediment, OSL samples are affected by a cosmic dose rate, which reduces as the amount of sediment the sample is buried under increases.
The cosmic dose is useful in other situations, as it can be used to determine how long rocks, for example, have been exposed on the Earth’s surface using Cosmogenic Nuclide Dating.
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.
From this curve we can calculate the dose that our sample must have received to produce the amount of light that we measured first.