Thermoluminescence

The thermoluminescence is the use of a physical property of certain crystals which was developed in the Années 1950 like method of Datation, mainly of ceramics.

Simplified basic principle

A certain number of crystals, like the quartz, the Feldspar, the Zircon have the property to accumulate during time, in the form of energy at the atomic level, the natural and cosmic irradiation of the place where they are. When they are then subjected to a very strong temperature, they restore the energy accumulated in the form of light (Photon S). Once cooled, accumulation can begin again.

Practical use

The crystals present in materials used for the clothes industry of potteries, restore the totality of the energy load accumulated during geological time during their cooking. It is then enough to subject a sample once again to a high Température in order to measure the emitted light which will be proportional to the time passed between the two operations. By taking account of the radiation level natural of the medium where remained ceramics to date and from the nature of the crystals concerned, one obtains by a calculation the precise dating of the sample. This technique is also applicable to grounds of hearth, furnaces, lava, and in general in any medium containing the sensitive crystals and having been subjected to important temperatures in the past.

Limits of this method

measurement can be distorted by any unknown event which would have strongly heated the sample, like a fire. For the furnaces of potter, one will obtain only the dating of the last use. In addition, the accidental exposure of the sample to an artificial radioactive source scrambles calculations definitively.
the crystals have a natural limitation of storage of the natural radioactivity. Beyond of a certain threshold, they do not react any more. One estimates at 700.000 years the measurable maximum seniority with the method of thermoluminescence.

Field of application and measuring accuracy

One uses it mainly in two disciplines:

the Archeology: dating of potteries, architectural elements out of terra cotta, terra cotta sculptures, furnaces, bronzes (core), burned stones of the hearths, heated flint tools and glares.
the Geology: igneous rocks (volcanites), calcite (stalagmites), loess, dunes, craters of meteorite.

Precision on the ages (relative error on average):

the sphere of activity is approximately 100 years with almost 1 million years.
Inaccuracy from 5% to 15% taking into account the external amount measured on site, being able to go up to 20% on the objects out of the archaeological context.

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