Optically stimulated luminescence dating of fluvial deposits
The radiation dose that is equivalent to the natural luminescence emission of isolated quartz and feldspar grains is referred to as the equivalent dose (D: measured in grays: 100 rads = 1 gray) and is one half of the OSL age equation (Eq. In most dating applications quartz is often the favored mineral because of its abundance in sediments, ease of physical separation and known stability of luminescence emissions.
In contrast, feldspar minerals are often less abundant, and have a troubling signal instability (anomalous fading), though yield considerably brighter OSL emissions.
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.
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.
Alpha particles are about 90 to 95% less effective in inducing luminescence compared to beta and gamma radiation.
The advent of single aliquot regenerative (SAR) dose procedures for quartz (Murray and Wintle, 2003; Wintle and Murray, 2006) has provided the needed analy tical flexibility to compensate for variable luminescence properties of quartz and feldspar grains and laboratory-induced sensitivity changes, particularly associated with preheat treatments and with laboratory beta irradiation.These charge defects are potential sites of electron storage with a variety of trap-depth energies.A subpopulation of stored electrons with trap depths of ~1.3 to 3 e V is a subsequent source for time-diagnostic luminescence emissions.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).Common silicate minerals like quartz and potassium feldspar contain lattice-charge defects formed during crystallization and from subsequent exposure to ionizing radiation.