Optically stimulated luminescence dating

This prevents exposure of the grains to light, a process known as bleaching, which would lead to the light-sensitive OSL traps being emptied and the OSL “clock” being reset. The most typical would be to hammer opaque plastic or metal tubes into a cleaned section wall; the sediment at both ends of the tube will then be discarded in the lab, and the inner light-safe portion will be used for the measurement of the OSL signal.Alternatively, samples can be collected by scraping sediment into black light-tight bags while covered by a black tarpaulin to keep light out; a red-light torch can be used for illumination since red wavelengths do not affect the electron traps.Optically stimulated luminescence (OSL) dating of sedimentary quartz grains and thermoluminescence (TL) dating of burnt stones are the methods most commonly applied in archaeological contexts, and the former is the subject of this entry.

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The grains are then sieved again to provide a narrow range of sizes (e.g., 180–212 μm diameter) and mounted in a monolayer on a 9.8 mm diameter stainless steel or aluminum disk, which has been pre-sprayed with silicone oil so that the grains stay adhered during the measurement procedure.

In the case of single-grain dating, each grain is placed in an individual hole drilled into the surface of an aluminum disk, each disk designed to hold 100 single grains.

The lighting level in the luminescence laboratory is low and usually red, similar to the conditions in a photographic darkroom.

The grains, 90–300 μm in diameter (sand sized), are usually extracted from the bulk sediment sample by wet or dry sieving and are then chemically treated with hydrochloric (HCl) acid to remove carbonates and hydrogen peroxide (H) solution to digest any organic matter.

OSL dating can also be applied to heated materials, such as burnt stones and pottery, but TL dating remains the method of choice for such materials.

Bøtter-Jensen and Duller (The OSL dating technique is based on the fact that natural minerals (such as quartz and feldspar) are not perfectly formed but contain defects in their crystal lattices that are able to trap negatively charged electrons within positively charged vacancies (“holes”).Photostimulated Luminescence (PSL or POSL) is also called Optically Simulated Luminescence (OSL) and can be used for a wide range of dosimetric purposes.It is gaining importance in radiation protection dosimetry, personal dosimetry, medical dosimetry and space dosimetry due to the high sensitivity of some phosphors and is a good alternative for film dosimetry.The physical basis has been discussed in detail for the nonspecialist by Feathers ().The former covered early work on sites in Africa, Western Europe, East Asia, Siberia, Australia, and the Americas, whereas the latter reviewed the more recent applications as part of a history of the last 50 years of luminescence dating in archaeology.Once the sediment sample has been collected and taken back to the laboratory, the mineral grains can be stimulated with a green laser or blue light-emitting diode, which will release the trapped electrons in the form of light emission ( (equivalent dose) corresponds to the radiation dose absorbed by the mineral grains since they were last exposed to sunlight or heat, Gy (or gray) is a unit of radiation absorption equal to 1 J of radiation per kg of sample, and ka is 1,000 years.

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