Explain the process of thermoluminescence dating
Electrons from these substances get trapped in the mineral's crystalline structure, and continuing exposure of the rocks to these elements over time leads to predictable increases in the number of electrons caught in the matrices.
But when the rock is exposed to high enough levels of heat or light, that exposure causes vibrations in the mineral lattices and the trapped electrons are freed.
Better still, unlike radiocarbon dating, the effect luminescence dating measures increases with time.
As a result, there is no upper date limit set by the sensitivity of the method itself, although other factors may limit the method's feasibility.
When a small sample of ancient pottery is heated it glows with a faint blue light, known as thermoluminescence or TL.
During its lifetime the pottery absorbs radiation from its environment and it is this which creates thermoluminescence.
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.
We have 3 fully automated, computer operated Riso Minisys TL readers for measuring the TL.
The method is a direct dating technique, meaning that the amount of energy emitted is a direct result of the event being measured.The ancient piece : (a) is way above the background (c), and approximately midway between background and (b) The modern piece : (a) is only just above the background (c) and way below (b) Porcelain and certain other types of clay cannot be tested using the fine-grain method. The TL reader is programmed to measure changes in the 110C peak of quartz (the pre-dose peak) in the clay.Each time the sample is irradiated and then heated, the pre-dose peak increases. The first increase is due to the natural dose which the piece has absorbed over its life-time.The sample is then given a laboratory irradiation and a second increase is measured.From these measurements we can calculate the age of the piece.