Luminescence dating - Wikipedia
We describe data on the thermoluminescence (TL) of ocean sediments which leads us to propose that exposure to sunlight prior to deposition reduces any. IN the last decade thermoluminescence dating has been developed for use on archaeological material, principally pottery, that was heated in. 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).
Where there is a dip a so-called " electron trap"a free electron may be attracted and trapped.
- Luminescence dating
- Thermoluminescence dating
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. 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.
In practical use[ edit ] Another important technique in testing samples from a historic or archaeological site is a process known as Thermoluminescence testing.Optical dating
Which involves a principle that all objects absorb radiation from the environment. This process frees electrons within elements or minerals that remain caught within the item. Thermoluminescence testing involves heating a sample until it releases a type of light.
This light is then measured to determine the last time the item was heated. When irradiated crystalline material is again heated or exposed to strong light, the trapped electrons are given sufficient energy to escape. Minerals[ edit ] The minerals that are measured are usually either quartz or potassium feldspar sand-sized grains, or unseparated silt-sized grains.
Thermoluminescence dating - Wikipedia
There are advantages and disadvantages to using each. For quartz, blue or green excitation frequencies are normally used and the near ultra-violet emission is measured. For potassium feldspar or silt-sized grains, near infrared excitation IRSL is normally used and violet emissions are measured.
Comparison to radiocarbon dating[ edit ] Unlike carbon datingluminescence dating methods do not require a contemporary organic component of the sediment to be dated; just quartz, potassium feldspar, or certain other mineral grains that have been fully bleached during the event being dated. In a study of the chronology of arid-zone lacustrine sediments from Lake Ulaan in southern MongoliaLee et al.
Westerly winds delivered an influx of 14 C-deficient carbon from adjacent soils and Paleozoic carbonate rocks, a process that is also active today.
Chronological Methods 12 - Luminescence Dating Scientists in North America first developed thermoluminescence dating of rock minerals in the s and s, and the University of Oxford, England first developed the thermoluminescence dating of fired ceramics in the s and s.
During the s and s scientists at Simon Frasier University, Canada, developed standard thermoluminescence dating procedures used to date sediments.
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Inthey also developed optically stimulated luminescence dating techniques, which use laser light, to date sediments.
How does Luminescence work?
The microscopic structure of some minerals and ceramics trap nuclear radioactive energy. This energy is in constant motion within the minerals or sherds.
Most of the energy escapes as heat, but sometimes this energy separates electrons from the molecules that make up the minerals or ceramics. Usually the electrons will reconnect with the molecules, but some will not.