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Encyclopedia > Thermoluminescence dating

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). As the material is heated during measurements, a weak light signal, the thermoluminescence, proportional to the radiation dose is produced. Radiation has a variety of different meanings. ... It has been suggested that crystallization processes be merged into this article or section. ... In physics, heat is defined as energy in transit. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικος (keramikos, having to do with pottery). The term covers inorganic non-metallic materials whose formation is due to the action of heat. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ...


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. This leads to local humps and dips in its electric potential. 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. 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. 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. // An ion is an atom or a group of atoms (a chemical substance), or subatomic particle, with a net electric charge. ... In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ... Properties In chemistry and physics, an atom (Greek άτομον meaning indivisible) is the smallest possible particle of a chemical element that retains its chemical properties. ... Electric potential is the potential energy per unit of charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In semiconductors and insulators, the conduction band is the range of electron energy, higher than that of the valence band, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ...


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. In the process of recombining with a lattice ion, they lose energy and emit photons (light quanta), detectable in the laboratory. The amount of light produced is proportional to the number of trapped electrons that have been freed which is in turn proportional to the radiation dose accumulated. In order to relate the signal (the thermoluminescence—light produced when the material is heated) to the radiation dose that caused it, it is necessary to calibrate the material with known doses of radiation since the density of traps is highly variable. In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... In physics, a quantum refers to an indivisible, and perhaps, elementary entity. ... Biochemistry laboratory at the University of Cologne. ... Calibration is the determination, by measurement or comparison with a standard, of the correct value of each reading on a measuring instrument. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ...


Thermoluminescence dating presupposes a "zeroing" event in the history of the material, either heating (in the case of pottery or lava) or exposure to sunlight (in the case of sediments), that removes the pre-existing trapped electrons. 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. In the laboratory, the accumulated radiation dose can be measured, but this by itself is insufficient to determine the time since the zeroing event. The radiation dose rate - the dose accumulated per year-must be determined first. 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. 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. An alpha particle is deflected by a magnetic field Alpha particles (named after the first letter in the Greek alphabet, α) are a highly ionizing form of particle radiation which have low penetration. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... Alpha radiation consists of helium nuclei and is readily stopped by a sheet of paper. ... This article is about electromagnetic radiation. ... An emitter is any device used to emit any signal, beacon, light, odor, liquid, fragrance, or the like. ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ...


Thermoluminescence dating is used for material where radiocarbon dating is not available, like sediments. Its use is now common in the authentication of old ceramic wares, for which it gives the approximate date of the last firing. Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of carbonaceous materials up to ca 60,000 years. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ...


Optical dating is a related measurement method which replaces heating with exposure to intense light. The sample material is illuminated with a very bright source of infrared light (for feldspars) or green or blue light (for quartz). Ultraviolet light emitted by the sample is detected for measurement. Optical dating is a method of determining how long ago minerals were last exposed to daylight. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Quartz is amongst one of the most common minerals in the Earths continental crust. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ...


See also

--220.233.68.71 09:44, 5 June 2006 (UTC)a tool which archaeologists use A Thermoluminescent dosimeter is a small device used to measure radiation exposure by measuring the amount of visible light emitted from a crystal in the detector when the crystal is heated. ...


References

  • Quaternary TL Surveys - Guide to thermoluminescence date measurement
  • Frequently asked questions about TL dating
  • Aitken, M.J., Thermoluminescence Dating, Academic Press, London (1985) – Standard text for introduction to the field. Quite complete and rather technical, but well written and well organized. There is a second edition.
  • Aitken, M.J., Introduction to Optical Dating, Oxford University Press (1998) – Good introduction to the field.

  Results from FactBites:
 
Dating Exhibit (402 words)
Thermoluminescence dating is used for rocks, minerals and pottery.
Therefore, thermoluminescence dating is actually determining the last time a crystal was heated and electrons were released.
The minerals that are used for thermoluminescence dating are quartz, feldspar, diamond and calcite.
Thermoluminescence dating - Wikipedia, the free encyclopedia (711 words)
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).
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 dating presupposes a "zeroing" event in the history of the material, either heating (in the case of pottery or lava) or exposure to sunlight (in the case of sediments), that removes the pre-existing trapped electrons.
  More results at FactBites »

 
 

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