Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating. It is useful to geologists and archaeologists who want to know when such an event occurred.
It uses various methods to Optical dating and measure luminescence.
All sediments and soils contain trace amounts of radioactive isotopes of elements such as potassiumuraniumthoriumand rubidium. These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as Optical dating and potassium feldspar.
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. Stimulating these mineral Optical dating using either light blue or green for OSL; infrared Optical dating IRSL or heat for TL causes a luminescence signal to be emitted as the stored unstable electron energy is the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.
Most luminescence dating methods rely on the assumption that the mineral grains were sufficiently "bleached" at the time of the event being dated. Quartz OSL ages can be determined typically from toyears BP, and can be reliable when suitable methods are used and proper checks are done.
The concept of using luminescence dating in archaeological contexts was first suggested in by Farrington Daniels, Charles A. Boyd, and Donald F. Saunders, who thought the thermoluminescence response of pottery shards could date the last incidence of "Optical dating."
InAitken et al. Inthe principles behind optical and thermoluminescence dating were extended to include surfaces made of granite, basalt and such as carved rock from ancient monuments and artifacts. Ioannis Liritzisthe initiator of ancient buildings luminescence dating, has shown this in several cases of various monuments. The radiation dose rate is calculated from measurements of the radioactive elements K, U, Th and Rb within the sample and its surroundings and the radiation dose rate from cosmic rays.
The dose rate is usually in the range 0. The total absorbed radiation dose is determined by exciting, with light, specific "Optical dating" usually quartz or potassium feldspar extracted from the sample, and measuring the amount of light emitted as a result. The photons of the emitted light must have higher energies than the excitation photons in order to Optical dating measurement of ordinary photoluminescence.
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; Optical dating excited it will not emit any such photons. The older the sample is, the more light it emits, up to a saturation limit. The minerals that are measured are usually either quartz or potassium feldspar sand-sized grains, or unseparated silt-sized grains.
There are advantages and disadvantages to using each.
For quartz, blue or green excitation frequencies are normally used and the near ultra-violet emission is measured. Optical dating potassium feldspar or silt-sized grains, near infrared excitation IRSL is normally used and violet emissions are measured.
Unlike carbon datingluminescence dating methods do not require a contemporary organic component of the sediment to be dated; just quartz, potassium feldspar, or certain other mineral grains that have been fully bleached during the event Optical dating dated.
In a study of the chronology of arid-zone lacustrine sediments from Lake Ulaan in southern MongoliaLee et al. The sediments with disagreeing ages were determined to be deposited by aeolian Westerly winds delivered an influx of 14 C -deficient carbon from adjacent soils and Paleozoic carbonate rocks, a process that is also active today.
This reworked carbon changed the measured isotopic ratios, giving a false older age. However, the wind-blown origin of these sediments were ideal for OSL dating, as most of the grains would have been completely bleached by sunlight exposure during transport and burial.
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K-feldspars optical response stimulation spectra". Silesian University Optical dating Technology, Poland. Mediterranean Archaeology and Archaeometry.
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Fluorine absorption Nitrogen dating Obsidian hydration Seriation Stratigraphy. Retrieved from " https: Geochronological dating methods Dating methodologies in archaeology.