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Quartz luminescence dating

Mineral separations are performed by standard techniques using heavy liquids and hydrofluoric acid (HF) to digest non-quartz minerals and etch the outer 10 to 20 µm of quartz grains which are affected alpha radiation.The purity of the quartz extract is primal for effective dating because a small amount contamination (1%) by potassium feldspar and other minerals can dominate the luminescence emissions.Zöller, L., Richter, D., Masuth, S., Wunner, L., Fischer, M., and Antl-Weiser, W. Luminescence chronology of the Grub-Kranawetberg site, Austria.

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.Spectral purity of quartz is often determined by excitation by infrared light from a diode array with subsequent light emissions associated presumably with feldspar contaminants.However, some quartz grains yield considerable emissions with infrared excitation and may host feldspathic or other mineral inclusions; such grains should be analyzed as feldspar grains.Many types of sediment receive prolonged ( 1 hr) light exposure with transport and deposition, particularly in eolian, littoral and sublittoral sedimentary environments.In addition, the inherent residual level is influenced by the susceptibility of the luminescence signal of a specific mineral to solar resetting.OSL dating provides an estimate of the time elapsed with latest period of burial and thus, yields a depositional age (Fig. (c) With burial and exposure to ionizing radiation free electrons are stored in charge defects within grains crystal lattice.(d) Further light exposure of grains with erosion and transport zeros the luminescence.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.Often this luminescence “cycle" occurs repeatedly in many depositional environments with signal acquisition of mineral grains by exposure to ionizing radiation during the burial period and signal resetting (“zeroing") with light exposure concurrent to sediment erosion and transportation. (a) Luminescence is acquired in mineral grains with exposure to ionizing radiation and trapping of electrons.Often mineral grains that are fresh from a bedrock sources have significantly lower luminescence emissions per radiation dose in comparison to grains that have cycled repeatedly. (b) The luminescence for grains is zeroed by exposure to sunlight with erosion and transport.

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