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Purity of the separate is accessed through microscopic inspection and point counting of grain mineralogy.
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.
Exposure of mineral grains to light or heat (at least 300˚C) reduces the luminescence to a low and definable residual level.
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.
The recent development of charge transfer techniques for potassium feldspar (e.g. A common approach in OSL dating is to use SAR protocols on quartz aliquots with the protocols customized for a specific sample, a study site or area (Fig. The SAR approach is predicated on a number of assumptions.
post IR290) that use elevated preheats (~290˚C) to transfer electrons from stable deeper to shallower traps for ease of measurement has extended dating possibilities to 10 timescales for well solar reset grains (Duller and Wintle, 2012). 3: (a) Determination of equivalent dose (in grays) using the single aliquot regenerative (SAR) protocols, where the natural luminescence emission is Ln/Tn and the regenerative dose is Lx/Tx; sensitivity changes are corrected by the administration of a small text dose (e.g. First, that the fast component of luminescence emissions, light released within the first 4 seconds, is the dominant signal, usually 30 aliquots of quartz or feldspar grains (Fig. Each aliquot often contains 10’s to 100’s of quartz grains; the total number dependent on grain size (e.g. Statistical analyses of equivalent dose distributions are critical to render accurate OSL ages with specific age models (Galbraith and Roberts, 2012).
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.
Sediment grains act as long-term radiation dosimeters when shielded from further light exposure with the luminescence signal a measure of radiation exposure during the burial period.
This residual level is the point from which the geological OSL signal accumulates post burial.
Many types of sediment receive prolonged ( 1 hr) light exposure with transport and deposition, particularly in eolian, littoral and sublittoral sedimentary environments.
(d) Further light exposure of grains with erosion and transport zeros the luminescence.
(e) The grains are buried again and luminescence is acquired with exposure to ionizing radiation.