It includes techniques such as optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), and thermoluminescence dating (TL)."Optical dating" typically refers to OSL and IRSL, but not TL.All sediments and soils contain trace amounts of radioactive isotopes of elements such as potassium, uranium, thorium, and rubidium.These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar.In a study of the chronology of arid-zone lacustrine sediments from Lake Ulaan in southern Mongolia, Lee et al.discovered that OSL and radiocarbon dates agreed in some samples, but the radiocarbon dates were up to 5800 years older in others.-deficient carbon from adjacent soils and Paleozoic carbonate rocks, a process that is also active today.A sample in which the mineral grains have all been exposed to sufficient daylight (seconds for quartz; hundreds of seconds for potassium feldspar) can be said to be of zero age; when excited it will not emit any such photons.The older the sample is, the more light it emits, up to a saturation limit.
These methods also do not suffer from overestimation of dates when the sediment in question has been mixed with “old carbon”, or -deficient carbon that is not the same isotopic ratio as the atmosphere.
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Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating.
The radiation causes charge to remain within the grains in structurally unstable "electron traps".
The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.