Thermoluminescence dating

The accumulation of trapped electrons, and the gaps left behind in the spaces they vacated, occurs at a measurable rate proportional to the radiation received from a specimen’s immediate environment.When a specimen is reheated, the trapped energy is released in the form of light (thermoluminescence) as the electrons escape.Because this accumulation of trapped electrons begins with the formation of the crystal structure, thermoluminescence can date crystalline materials to their date of formation; for ceramics, this is the moment they are fired.The major source of error in establishing dates from thermoluminescence is a consequence of inaccurate measurements of the radiation acting on a specimen.The complex history of radioactive force on a sample can be difficult to estimate.However, thermoluminescence proven acceptable in providing approximate dates in the absence of more exact measures.The amount of light produced is a specific and measurable phenomenon.If the specimen’s sensitivity to ionizing radiation is known, as is the annual influx of radiation experienced by the specimen, the released thermoluminescence can be translated into a specific amount of time since the formation of the crystal structure.

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Sample discs are mounted on a wheel and the readers are programmed to run heating and irradiation sequences.Powder samples (from pottery and bronze cores) are mixed with acetone and allowed to settle, so that fine grains, approximately 1/100mm. These grains are deposited and dried onto aluminium discs (for fine-grain analysis) or rhodium (for pre-dose analysis).Any remaining powder is dried and used for radioactivity measurements to complete the dating calculation. When the glue is dry, they are cut into slices 1/4mm thick with a fine diamond blade. Each slice is soaked in acetone after cutting to remove the glue. The remaining core is crushed and used for radioactive analysis to complete the dating calculation.During its lifetime the pottery absorbs radiation from its environment and it is this which creates thermoluminescence.The older the pottery, the more radiation it has absorbed and the brighter the pottery sample glows.