what is thermoluminescrene dating?

Answer 1

Thermoluminescence dating
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Thermoluminescence (TL) dating is the determination by means of measuring the accumulated radiation dose of the time elapsed since material containing crystalline minerals was either heated (lava, ceramics) or exposed to sunlight (sediments). As the material is heated during measurements, a weak light signal, the thermoluminescence, proportional to the radiation dose is produced.

Natural crystalline materials : impurity ions, stress dislocations, and other phenomena that disturb the regularity of the electric field that holds the atoms in the crystalline lattice together. This leads to local humps and dips in its electric potential. Where there is a dip (a so called 'electron trap'), a free electron may be attracted and trapped. The flux of ionizing radiation—both from cosmic radiation and from natural radioactivity—excites electrons from atoms in the crystal lattice into the conduction band where they can move freely. Most excited electrons will soon recombine with lattice ions, but some will be trapped, storing part of the energy of the radiation in the form of trapped electric charge. Depending on the depth of the traps (the energy required to free an electron from them) the storage time of trapped electrons will vary- some traps are sufficiently deep to store charge for hundreds of thousands of years.

In thermoluminescence dating, these long-term traps are used to determine the age of materials: When irradiated crystalline material is again heated or exposed to strong light, the trapped electrons are given sufficient energy to escape. In the process of recombining with a lattice ion, they lose energy and emit photons (light quanta), detectable in the laboratory. The amount of light produced is proportional to the number of trapped electrons that have been freed which is in turn proportional to the radiation dose accumulated. In order to relate the signal (the thermoluminescence—light produced when the material is heated) to the radiation dose that caused it, it is necessary to calibrate the material with known doses of radiation since the density of traps is highly variable.

radiation dose can be measured, but this by itself is insufficient to determine the time since the zeroing event. The radiation dose rate - the dose accumulated per year-must be determined first. This is commonly done by measurement of the alpha radioactivity (the uranium and thorium content) and the potassium content (K-40 is a beta and gamma emitter) of the sample material. Ofthnical, but well written and well organized. There is a second edition.

Aitken, M.J., Introduction to Optical Dating, Oxford University Press (1998) – Good introduction to the field.

Answer 2

its spelled with -scence, not -screne...just so you are aware (typo i'm sure)

but...try here...
http://www.google.com/search?hl=en&q=Thermoluminescence+dating&btnG=Google+Search
http://en.wikipedia.org/wiki/Thermoluminescence
http://www.ati.ac.at/~vanaweb/papers/archview.pdf#search=%22what%20is%20thermoluminescence%20dating%22