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Stimulating samples using infrared light causes luminescence, the intensity of which varies depending on the amount of radiation absorbed.
Exposure to sunlight resets the luminescent signature and so the time period since the sediment was buried can be calculated.
Once evicted from the ‘traps’ the electrons are attracted are attracted back to the ‘holes’ created by ionisation and, on recombination at these centres emit energy in the form of photons.
These are measured by a photomultiplier tube within a luminescence reader and are used to estimate the Equivalent Dose (De) of absorbed radiation required to create that signal, and is measured in Grays (1 Gy = 1J/kg).
Following the natural zeroing event and subsequent burial, the natural minerals begin luminescence acquisition afresh from the ionizing radiation (alpha, beta and gamma) constantly provided by the decay of radioactive elements (U238, Th232, K40, Rb) present in the sediments and also from the cosmic rays.
For calculating the age, the radiation energy stored in the mineral (known as Paleodose) and the annual radioactivity rate (annual dose) from the surrounding sediments has to be calculated.
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.
Hollie Wynne (Aberystwyth University) stirs OSL samples being treated with acid in the preparation lab of the Aberystwyth Luminescence Research Laboratory. We make an approximation of the number of trapped electrons by measuring the light that they emit following stimulation by light (hence the name of the technique, “Optically stimulated luminescence”).
Although a relatively new technique, particularly in subaqueous sediments, Strata Data have pioneered its industrial application in dating superficial seabed deposits for geohazard risk assessment.
Suitable for samples up to about 150Ka containing quartz. Ideal for young sediments with no biogenic material present or where the age of the sediments exceeds the range of 14C dating (c. Requires precise measurement of sample water content and salinity.
This page was contributed by Dr Georgina King from the Aberystwyth Luminescence Research Laboratory in the Institute for Geography and Earth Sciences. OSL is used on glacial landforms that contain sand, such as sandur or sediments in glacial streams.
| Calculating Age | Challenges for OSL | Case studies of OSL dating in glacial environments | References | Comments | Another way of dating glacial landforms is optically stimulated luminescence dating (OSL).
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).