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.Often the gamma radiation field at the position of the sample material is measured, or it may be calculated from the alpha radioactivity and potassium content of the sample environment, and the cosmic ray dose is added in.
In the site we found fluvial, fluvio-aeolian and aeolian deposits, paleosols, and organic infillings of the inactive river channels.
The purpose of the study was to determine stratigraphic position of the deposit units distinguished on the basis of lithofacial analysis, pedological description and thermoluminescence dating.
Once all components of the radiation field are determined, the accumulated dose from the thermoluminescence measurements is divided by the dose accumulating each year, to obtain the years since the zeroing event.
Thermoluminescence dating is used for material where radiocarbon dating is not available, like sediments.
Therefore, at that point the thermoluminescence signal is zero.
As time goes on, the ionizing radiation field around the material causes the trapped electrons to accumulate (Figure 2).
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.
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).
Natural crystalline materials contain imperfections: impurity ions, stress dislocations, and other phenomena that disturb the regularity of the electric field that holds the atoms in the crystalline lattice together.
The sample material is illuminated with a very bright source of infrared light (for feldspars) or green or blue light (for quartz).