Principles of thermoluminescence dating
Depending on the type of stimulation source, the phenomenon is termed thermally stimulated luminescence (TL) or optically stimulated luminescence (OSL).The OSL is further divided, based on the colour (wavelength) of the excitation light source, into Blue Light Stimulated Luminescence (BLSL) and Infrared Stimulated Luminescence (IRSL)Luminescence dating requires a proper resetting of the previously acquired (pre depositional) luminescence in the natural minerals into a very low level (natural zeroing event), either by exposure to sun light during pre-depositional transportation (by wind, water etc.) or by a thermal event (pottery making, baking by lava, fusion crest of meteorites), before deposition.The accumulation of trapped electrons, and the gaps left behind in the spaces they vacated, occurs at a measurable rate proportional to the radiation received from a specimen’s immediate environment.When a specimen is reheated, the trapped energy is released in the form of light (thermoluminescence) as the electrons escape.The time elapsed since sedimentation, i.e., Age = Paleodose Annual Dose In practice, the paleodose is calculated by measuring the luminescence intensity in the natural mineral and regenerate the equivalent luminescence intensity by artificial radiation dose from a calibrated beta source attached to the TL/OSL instrument.For calculating the annual dose rate, the elemental concentration of U, Th and K (by XRF or ICP-MS) in the sediment and water content in the sediment are required.
The longer the pottery is in the ground, the more radiation dose it will absorb, causing more electrons to be excited into trap states.
The technique is particularly useful for dating materials ranging in age from a few decades to around 100,000–150,000 years.
In this chapter, following a brief outline of the historical development of the dating method, basic principles behind the technique are discussed.
Sample collection methods are also reviewed, as well as types of materials that can be dated.
Continuing refinements in both methodology and equipment promise to yield luminescence chronologies with improved accuracy and extended dating range in the future and these are briefly discussed.© 2016 The Author(s). This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Luminescence Dating: Applications in Earth Sciences and Archaeology, Luminescence - An Outlook on the Phenomena and their Applications, Jagannathan Thirumalai, Intech Open, DOI: 10.5772/65119. Luminescence Dating: Applications in Earth Sciences and Archaeology, Luminescence - An Outlook on the Phenomena and their Applications, Jagannathan Thirumalai, Intech Open, DOI: 10.5772/65119.
This is followed by a look at measurement equipment that is employed in determining age and its operation.