Electrons are in the conduction band and holes in the valence band. The electrons that have been excited to the conduction band may become entrapped in the electron or hole traps.
- Thermoluminescence dating.
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Under stimulation of light the electrons may free themselves from the trap and get into the conduction band. From the conduction band they may recombine with holes trapped in hole traps. If the centre with the hole is a luminescence center radiative recombination centre emission of light will occur.
The photons are detected using a photomultiplier tube. The signal from the tube is then used to calculate the dose that the material had absorbed.
The OSL dosimeter provides a new degree of sensitivity by giving an accurate reading as low as 1 mrem for x-ray and gamma ray photons with energies ranging from 5 keV to greater than 40 MeV. The OSL dosimeter's maximum equivalent dose measurement for x-ray and gamma ray photons is rem. For beta particles with energies from keV to in excess of 10 MeV, dose measurement ranges from 10 mrem to rem. Neutron radiation with energies of 40 keV to greater than 35 MeV has a dose measurement range from 20 mrem to 25 rem.
In diagnostic imaging the increased sensitivity of the OSL dosimeter makes it ideal for monitoring employees working in low-radiation environments and for pregnant workers. To carry out OSL dating, mineral grains have to be extracted from the sample.
Optically Stimulated Luminescence
Occasionally other grain sizes are used. The difference between radiocarbon dating and OSL is that the former is used to date organic materials, while the latter is used to date minerals. Events that can be dated using OSL are, for example, the mineral's last exposure to sunlight; Mungo Man , Australia's oldest human find, was dated in this manner. In archaeology, OSL dating is applied to ceramics: Recent OSL dating of stone tools in Arabia pushed the "out-of-Africa" date hypothesis of human migration back 50, years and added a possible path of migration from the African continent to the Arabian peninsula instead of through Europe.
From Wikipedia, the free encyclopedia. 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. OSL dating can be used to date sediments from decades up to , years in exceptional circumstances 1 although the technique is more commonly applied to sediments up to , years old.
Explaining the science of Antarctic glaciers
The biggest challenge for OSL dating in glacial environments is partial bleaching resetting of the luminescence signal. This occurs if the grains of sand are not exposed to sufficient sunlight prior to deposition within a landform such as a glacial moraine.
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. 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.
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A second challenge for OSL dating in glacial environments is that the luminescence sensitivity brightness of the quartz is often very low. Recent advances in OSL dating techniques for feldspar 2 , 3 may result in this becoming the preferred mineral for OSL dating of glacial sediments, although feldspars are often more severely affected by partial bleaching than quartz.
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OSL has been widely used to date glacial sediments, because organic material required for radiocarbon dating is often absent. In Prep have sampled a suite of modern glaciofluvial sediments from Jostedalen, Southern Norway, to quantify the unbleached residuals of different glacial sediments and also to explore whether the luminescence signature of quartz and feldspars provides information about the different depositional pathways that sediments are transported along.
OSL dating can also be used effectively with other dating techniques such as cosmogenic nuclide dating. Quaternary Geochronology 5 , — Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts.
Optically stimulated luminescence
Radiation Measurements 43 , A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments. Boreas 41 , Depositional pathway tracing in glacial catchments using the OSL of coarse-grained quartz and K-feldspar.
Quaternary Science Reviews In Prep. Optically stimulated luminescence dating of glaciofluvial sediments on the Canterbury Plains, South Island, New Zealand. Quaternary Geochronology 8 , Journal of Quaternary Science 24 , Quaternary Research, 65 1: Quaternary glaciation of Mount Everest. Quaternary Science Reviews, 28 Photographs taken by Geoff Duller Aberystwyth University. Blue diodes are most commonly used to stimulate the OSL signal from quartz, which is then detected in the UV emission spectrum.
The proglacial delta at Nigardsbreen, Jostedalen, Southern Norway. Sampled for OSL dating in August . Road cut through glacial outwash sediments, Patagonia. OSL sample locations are highlighted.