HOW DOES THERMOLUMINESCENCE DATING WORK? The thermoluminescence technique is the only physical means of determining the absolute age of pottery presently available. It is an absolute dating method, and does not depend on comparison with similar objects (as does obsidian hydration dating, for example). Luminescence Dating of Pottery from Owens Valley and Death Valley the late prehistoric period into distinct chronological units using radiocarbon dates is difﬁcult. Sherds are typically divided into three categories (rim, body, and basal pieces) and then tabulated; rarely is .
The thermoluminescence technique is the only physical means of determining the absolute age of pottery presently available. It is an absolute dating method, and does not depend on comparison with similar objects as does obsidian hydration dating, for example. Most mineral materials, including the constituents of pottery, have the property of thermoluminescence TLwhere part of the energy from radioactive decay in and around the mineral is stored in the form of trapped electrons and thermoluminescence dating pottery marks released as light upon strong heating as the electrons are dating woman going through divorce and combine with lattice ions. By comparing this light output with that produced by known doses of radiation, thermoluminescence dating pottery marks amount of radiation absorbed by the material may be found. When pottery is fired, it loses all its previously acquired TL, and on cooling the TL begins again to build up.
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.
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 Figure 2. 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 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.
Relation to radiocarbon dating[ edit ] 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. An example of this can be seen in Rink and Bartoll, Electrons from these substances get trapped in the mineral's crystalline structure, and continuing exposure of the rocks to these elements over time leads to predictable increases in the number of electrons caught in the matrices.
But when the rock is exposed to high enough levels of heat or light, that exposure causes vibrations in the mineral lattices and the trapped electrons are freed. The exposure to radioactive elements continues, and the minerals begin again storing free electrons in their structures. If you can measure the rate of acquisition of the stored energy, you can figure out how long it has been since the exposure happened.
The energy released by stimulating the crystals is expressed in light luminescence. The intensity of blue, green or infrared light that is created when an object is stimulated is proportional to the number of electrons stored in the mineral's structure and, in turn, those light units are converted to dose units. The equations used by scholars to determine the date when the last exposure happened are typically: The most recent heating measured in pottery sherds is assumed to represent the manufacturing event; the signal arises from quartz or feldspar in the clay or other tempering additives.
Although pottery vessels can be exposed to heat during cooking, cooking is never at sufficient levels to reset the luminescence clock. Luminescence can also be used to determine the original firing temperature. Raw material such as flints and cherts have been dated by TL; fire-cracked rock from hearths can also be dated by TL as long as they were fired to sufficiently high temperatures.
The best success from TL dates on chipped stone artifacts likely are from events when they were deposited into a hearth and accidentally fired. Surfaces of buildings and walls: The buried elements of standing walls of archaeological ruins have been dated using optically stimulated luminescence; the derived date provides the age of burial of the surface.
In other words, the OSL date on a foundation wall of a building is the last time that foundation was exposed to light before being used as the initial layers in a building, and hence when the building was first built. Some success has been found dating objects such as bone tools, bricks, mortar, mounds, and agricultural terraces.