Chronological Methods 12 - Luminescence Dating Scientists in North America first developed thermoluminescence dating of rock minerals in the s and s, and the University of Oxford, England first developed the thermoluminescence dating of fired ceramics in the s and s.
During the s and s scientists at Simon Frasier University, Canada, developed standard thermoluminescence dating procedures used to date sediments. Inthey also developed optically stimulated luminescence dating techniques, which use laser light, to date sediments.
How does Luminescence work?
The microscopic structure of some minerals and ceramics trap nuclear radioactive energy. This energy is in constant motion within the minerals or sherds. Most of the energy escapes as heat, but sometimes this energy separates electrons from the molecules that make up the minerals or ceramics.
Usually the electrons will reconnect with the molecules, but some will not. The electrons that dont reconnect eventually encounter imperfections in the microscopic structure of the ceramics or minerals, and they become trapped by these imperfections.
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Over time energy in the form of more and more trapped electrons is stored in these structural imperfections. By heating the ceramic or mineral to above degrees Celcius, these trapped electrons are released, creating a flash of light called thermoluminescence.
When a laser light source is used to stimulate the release of electrons, the process is called optically stimulated luminescence.
Luminescence Profile In the process of making a ceramic vessel, the soft clay vessel must be heated in a kiln to harden it. The process of firing the vessel releases the trapped electrons energyand resets the thermoluminescence clock to zero.
The process of accumulation of electrons energy and then release when heated occurs every time the ceramic vessel is reheated.
What an archaeologist would be able to measure using this technique is the last time the vessel was heated above degrees Celcius, either at the time the vessel was first fired or the last time it was heated if it was used as a cooking vessel. In the laboratory, the release of electrons can be induced through heating or the use of a laser beam.
The intensity of the light emmisions luminescence can be measured to determine the amount of time that has passed since the vessel was last heated and the present laboratory heating of the vessel. How is a Luminescence Sample Processed? A small sample is cut out of the artifact being dated.
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An equivalent dose DE of nuclear radiation is determined for every artifact through the application of artificial doses of nuclear radiation through heating or exposure to a laser light beam to subsamples of the artifact to scale the signal.
Next the burial dose rate DR is determined by measuring the radioactivity in portions of the sample grains and surrounding sediments.
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This method is applicable to samples that range in age from a few hundred years to several hundred thousand years. The Limitations of Luminescence Dating Using this technique, almost any rock mineral or ceramic sample can be directly dated. However, it works best when dating heated grains in ceramics, obsidian, burned flint, and burned sediments.
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