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Radiocarbon dating: radioactive carbon decays to nitrogen with a half-life of years. In dead material, the decayed 14C is not replaced and its concentration in the object decreases slowly. To obtain a truly absolute chronology, corrections must be made, provided by measurements on samples of know age. The most suitable types of sample for radiocarbon dating are charcoal and well-preserved wood, although leather, cloth, paper, peat, shell and bone can also be used. Because of the somewhat short half-life of 14C, radiocarbon dating is not applicable to samples with ages greater than about 50, years, because the remaining concentration would be too small for accurate measurement.
Pottery dating from thermoluminescence
Nederlands Indisch Cultureel Centrum - Den Haag
Apparatus sectioned for thermoluminescent dating of pottery, comprising a heating chamber, a photomultiplier and a gamma particle counter with a spare gamma counting ring. The photomultiplier converts thermoluminescent TL light to an electric current which is amplified. By the judicious use of filters the unwanted infa-red radiation and the red and yellow light of background incandescence in the oven is eliminated, allowing only blue light to reach the cathode. Here the light is converted to electrons and the signal is amplified in the photomultiplier cells. This electron signal is fed to a chart recorder producing a glow curve or plot of TL intensity versus temperature.
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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. Thermoluminescence emits a weak light signal that is proportional to the radiation dose absorbed by the material.
Thermoluminescence dating is very useful for determining the age of pottery. Electrons from quartz and other minerals in the pottery clay are bumped out of their normal positions ground state when the clay is exposed to radiation. This radiation may come from radioactive substances such as uranium , present in the clay or burial medium, or from cosmic radiation. The longer the exposure to the radiation, the more electrons that are bumped into an excited state, and the more light that is emitted upon heating. The process of displacing electrons begins again after the object cools.
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