Thermoluminescence dating is the use of heat on archeological or geological samples to produce a light signal that is proportional to an accumulated radiation dose. It is used to date rocks, minerals and ceramics for dates between approximately 300 to 10,000 B.P. (before present). It is usually used in conjunction with other methods of historical dating, such as carbon 14 or stratigraphy.
When a material is heated or exposed to sunlight, electrons are excited and can be trapped in small imperfections in the molecular lattice of the sample, for example pottery or sediment. When the sample is exposed to heat, these trapped electrons are once again excited and recombine with the parent material. When this happens, they give off energy in the form of light that can be measured.
Thermoluminescence dating requires two measurements for a successful date estimate. The first measurement is how much radiation the sample has been exposed to over the years. The second evaluates how much natural radiation is found both within and around the sample. Using these measurements, you can calculate how long the sample has been exposed to the radiation. This gives you the estimate for how long it has been since the sample was last heated.
Since thermoluminescence dating requires information about radiation levels at the site the sample was taken from, if that site is destroyed or inaccessible, it may not be possible to use thermoluminescence dating techniques. With this knowledge in mind, you can plan ahead and remove the necessary background material along with the sample to make thermoluminescence dating possible.
Thermoluminescence dating can only be used to date the object to the last time that it was heated to 350 degrees Celsius or higher, such as a clay vessel being fired, or a rock used as part of a fire hearth. It cannot be used on organic material. This method also does not take into account any significant changes that may have occurred over the years to the sample or its environment. Results are best if a number of samples from the same area or archaeological dig can be compared. There can be a fairly large margin of error in this method, which is why it is best to corroborate the results with other dating methods if possible.
Thermoluminescence dating can be used on samples for which radiocarbon dating is not possible. It is commonly used on pottery, ceramics, rocks, minerals and geological sediments. It can also be useful for comparing samples, even if the absolute age is not closely determined.
Thermoluminescence dating requires the sample to be exposed to heat over a period of time, which means that the sample may be compromised in the process.