Optically stimulated luminescence osl dating
This is because water attenuates (scatters) the radiation, reducing the total radiation dose that the sample has been exposed to. 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. In the Aberystwyth Luminescence Laboratory our instruments are made by a Danish manufacturer and are called “Risø OSL/TL readers”. This instrument stimulates the luminescence signal of the sand through shining the sample with blue or infrared light-emitting-didoes (LEDs), which give the electrons enough energy to escape their traps and recombine elsewhere, emitting a photon of light. 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. 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”). 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.
We call this measurement our “equivalent dose”, because it is equivalent to the dose that the sample received in nature. 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 age is obtained by measuring the radiation dose received by the sample since it was last bleached by sunlight, and dividing this estimate by the dose rate from environmental sources of ionising radiation.
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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.