Quartz luminescence dating

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As sediment is transported by wind, water, or ice, it is exposed to sunlight and zeroed of any previous luminescence signal.

Once this sediment is deposited and subsequently buried, it is removed from light and is exposed to low levels of natural radiation in the surrounding sediment.

In our laboratory, these sediments are exposed to an external stimulus (blue-green light) and the trapped electrons are released.

The released electrons emit a photon of light upon recombination at a similar site.

In order to relate the luminescence given off by the sample to an age, we first need to obtain the dose equivalent to the burial dose.

Following the single-aliquot regenerative (SAR) method of Murray and Wintle (2000), the dose equivalent (De) is calculated by first measuring the natural luminescence of a sample.

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Free electrons are generated within the mineral matrix by exposure to ionizing radiation from the radioactive decay of daughter isotopes in the 235U, 238U and 232Th decay series, and a radioactive isotope of potassium, 40K, with lesser contributions from the decay of 85Rb and cosmic sources.OSL is an acronym for Optically-Stimulated Luminescence.Optically-Stimulated Luminescence is a late Quaternary dating technique used to date the last time quartz sediment was exposed to light.Discoveries in the 1980s and 1990s that exposure of quartz and feldspar grains to a tunable light source, initially with lasers and later by light emitting diodes, yield luminescence components that are solar reset within seconds to minutes, expanded greatly the utility of the method (Huntley et al., 1985; Hütt et al., 1988; Aitken, 1998).In the past 15 years there have been significant advances in luminescence dating with the advent of single aliquot and grain analysis, and associated protocols with blue/green diodes that can effectively compensated for laboratory induced sensitivity changes (Murray and Wintle, 2003; Wintle and Murray, 2006; Duller, 2012) and render accurate ages for the past ca. Most recently, the development of protocols for inducing the thermal-transfer of deeply trapped electrons has extended potentially OSL dating to the 106 year timescale for well solar-reset quartz and potassium feldspar grains from eolian and littoral environments (Duller and Wintle, 2012).The OSL signal of potassium feldspar is usually more resista nt to solar resetting than most quartz.There is significant variability in the luminescence properties of quartz and potassium feldspar grains related to crystalline structure, minor and rare-earth impurities, solid-solution relations, number of luminescence cycles (Fig. Thus, because of this inherent variability in dose sensitivity of quartz and feldspar, analytical procedures for dating often need to be tailored for a specific geologic provenance.Through geologic time, quartz minerals accumulate a luminescence signal as ionizing radiation excites electrons within parent nuclei in the crystal lattice.A certain percent of the freed electrons become trapped in defects or holes in the crystal lattice of the quartz sand grain (referred to as luminescent centers) and accumulate over time (Aitken, 1998).Thus, the population of stored electrons in lattice-charge defects increases with prolonged exposure to ionizing radiation and the resolved luminescence emission increases with time.Exposure of mineral grains to light or heat (at least 300˚C) reduces the luminescence to a low and definable residual level.

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