Quartz luminescence dating
Most excited electrons will soon recombine with lattice ions, but some will be trapped, storing part of the energy of the radiation in the form of trapped electric charge (Figure 1).Depending on the depth of the traps (the energy required to free an electron from them) the storage time of trapped electrons will vary as some traps are sufficiently deep to store charge for hundreds of thousands of years.Where there is a dip (a so-called "electron trap"), a free electron may be attracted and trapped.The flux of ionizing radiation—both from cosmic radiation and from natural radioactivity—excites electrons from atoms in the crystal lattice into the conduction band where they can move freely.Thermoluminescence dating (TL) 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).As a crystalline material is heated during measurements, the process of thermoluminescence starts.
Optically stimulated luminescence dating is a related measurement method which replaces heating with exposure to intense light.
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.
These imperfections lead to local humps and dips in the crystalline material's electric potential.
It will often work well with stones that have been heated by fire.
The clay core of bronze sculptures made by lost wax casting can also be tested.