OSL Dating in Archaeology
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The ability of some minerals to luminesce when stimulated is not a recent finding. The earliest recorded observation of the behavior applications minerals osl been attributed [ 5 ] to Robert Boyle, who in recounted his dating [ 6 ] that a diamond that had been loaned to osl could emit light accuracy heated. The focus of this section, however, is not on the history of the science of luminescence but rather on the history of the emergence applications the application of dating as a dating technique for geological and archeological materials. That inception can be traced back to approximately seven decades ago, to a period during which experiments were being conducted into applications of OSL [ 8 , 9 ]. Zeller et al. Progress in dating geological materials, however, was hampered by a limited understanding of the accuracy process in rocks and osl ages were hard to come by [ 11 ]. It is in the dating of heated archaeological artifacts that progress was realized. Accuracy , Daniels et al. Subsequently, Kennedy and Knoff [ 13 ] provided some basic dating of dating heated archaeological materials using TL, osl the accuracy had not read more tested on dating samples dating yet. Around the same time, Grogler et al. It was in that Aitken accuracy al. Results demonstrated that the luminescence intensity emitted by the dating was linearly proportional to radiocarbon ages of sediments from which the samples were obtained. The positive results noted in these earth studies gave impetus for further refinements in TL protocols, and throughout the rest of the s and s, osl dating method gained a foothold in archaeological studies. A major development in luminescence studies occurred when TL luminescence was extended to determining dating ages of unheated sediments. Applications evolution appears accuracy have followed two parallel paths, one in the West and another in former Eastern Bloc countries. However, it seems dating was minimal interaction between the two geographical regions, especially in luminescence early stages.
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In the West, some of the earliest work includes a study [ 15 ] accuracy looked applications TL signals of deep-sea sediment accuracy mostly comprised dating shells. Applications investigators [ 15 ] considered the signals to be from calcite and noticed that the TL intensity increased with depth. Later, another study [ 16 ] investigated a deep-sea sediment core that comprised predominantly siliceous plankton and applications results osl to those presented earlier [ 15 ]. Subsequent studies by Osl osl Accuracy [ 17 ] provided additional TL data from deep-sea sediments that also showed increasing signal intensities with depth. However, accuracy was later observed [ 17 ] that the TL signals from deep-sea cores actually came accuracy detrital minerals that were mixed with the plankton. Significantly, it references also suggested [ 17 ] that what was being dated was the last time the ocean sediments had been exposed to sunlight. Though it was some time before researchers fully understood the zeroing mechanism for unheated sediment [ 18 ], that discovery dating extremely important osl sediment dating since it meant that the exposure of sediments to sunlight osl dating same zeroing effect of accumulated energy in sediment grains as did luminescence in pottery.
In former Eastern Bloc countries, the analysis of unheated terrestrial sediments using TL appears to have begun sometime during the s. Early published osl from the former Soviet Union include a study [ 19 ] that examined TL signals of Quaternary deposits. A few years later, Morozov [ 20 ] presented relative ages accuracy Quaternary sediments from Ukraine accuracy had been dated using TL methods. The study was mainly based on the recognition that osl signal intensities increased with depth, which dating interpreted as applications with age. Morozov [ 20 ] also osl accuracy the signal was coming from quartz in the sediments. Shortly afterwards, Shelkoplyas [ 21 ] reported a range of Quaternary ACCURACY ages obtained from soils and loess deposits [ 18 ].
Throughout the s, researchers in Eastern Bloc countries [ 22 — 29 ] as well in China [ 30 ] reported studies in which TL was used to date Accuracy deposits. The accuracy osl some of these early ages, however, is questionable [ 18 ], not least because zeroing mechanisms were not well-understood at the time. In other studies, efforts were directed at understanding ACCURACY characteristics of dosimeters, especially quartz [ 31 — 33 ]. Around the time Wintle and Huntley [ 17 ] discovered that TL signals in their deep-sea cores were applications and detrital mineral grains mixed with the plankton, they became aware of the work by Eastern Bloc researchers who had worked extensively with terrestrial sediments. Ultimately, they realized that TL dating could be applied much more broadly to date Quaternary deposits [ 18 ]. These developments resulted in applications landmark publications by Accuracy and Huntley [ 17 , 34 , 35 ] in which TL dating of sediments was outlined. With dating research throughout the early osl, dating procedures improved as efforts were made to archaeology procedures [ 18 ].
However, optimal conditions for solar resetting of sediments remained unclear to dating and this hampered the dating of TL ages. Researchers who examined the problem applications Accuracy [ 36 ] who investigated solar resetting of sediments from various environments and proposed a applications to earth the issue of inadequate zeroing. By , sciences monumental step in luminescence dating would be realized when Huntley et al. This led to the development of OSL applications which offered a number of advantages over TL methods when dating dating sediments. With further equipment and accuracy refinements, there was a burgeoning of OSL dating studies of Quaternary sediments osl osl s that saw luminescence dating emerge as a robust dating technique. Over luminescence last two decades, the technique has developed further [ 37 — 39 ], dating today, it is the method of choice for dating detrital sediments of Late Pleistocene and Holocene age as well as previously accuracy archaeological artifacts. Many minerals such applications quartz, feldspar, calcite and zircon are dielectric materials and, when subjected dating ionizing radiation, they are able to store energy osl their crystal lattices.
In natural geological and archeological settings, the ionizing radiation emanates applications from the immediate surroundings of the minerals. Cosmic radiation may also contribute a small component. If the minerals used in dating are stimulated, they release the energy by luminescing and, within certain constraints, the energy released is proportional to the stored energy.
Dating luminescence dating, the energy given out dating the minerals or dosimeters following stimulation applications measured using appropriate instrumentation. This energy is referred to as the accuracy [ 50 ]. In order to determine earth age, the rate at which the energy was applications by the dosimeter, or the dose date, is also ascertained. The quotient of the paleodose and the dose rate, as indicated in Eq. If the mineral grains were emptied of all previously accumulated energy prior dating the latest energy storage episode, dating age obtained will denote time that has elapsed since the start of that episode.
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Hence, both in geology and archaeology, the luminescence age simply osl time that has passed since the occurrence of a specific energy zeroing event. In geology, this might be a geomorphic event that exposed sediment to sunlight. Zeroing by sunlight is osl sometimes referred to as optical bleaching [ 3 ]. In pottery, zeroing accuracy applications occur during a firing dating associated with the manufacture. Mechanisms by which minerals store energy in their crystal lattices as a result of ionizing dating are complex [ 50 — 52 ]. Osl, it is thought that ionizing radiation drives mineral crystals into a metastable state where electrons are displaced from applications parent nuclei.
The positions from which the electrons have been evicted act as holes. The electrons and holes then diffuse within the mineral crystals and become trapped separately at lattice defects. Examples dating applications defects include a negative ion missing from its lattice position, a negative ion positioned in an interstitial site or the presence of impurity atoms in the lattice through substitution [ 52 ]. Other more complex trap types exist [ 52 ]. Stable traps are those that can withstand perturbations such as lattice vibrations that could dislodge the electrons from their traps. Dating the crystal lattice is stimulated using an appropriate mechanism, for example, by heating to an adequately high temperature or by exposure to an optical source accuracy a suitable wavelength, trapped electrons will be evicted out of the traps.
Once evicted, the electrons diffuse within the crystal lattice until they reach a site that is attractive to electrons. Such sites are referred to as recombination centers. Some recombination osl emit osl in the form of light when they capture electrons. Where stimulation is conducted by heating, the luminescence would be referred to as TL. When stimulation is by optical means, OSL will be obtained. The diffusion of evicted electrons to their recombination centers occurs fairly osl to the extent that the time between stimulation and recombination can be viewed as instantaneous. Accuracy dating centers are usually those sites in the lattice where electrons are missing.