Start Optically stimulated luminescence dating wiki

Optically stimulated luminescence dating wiki

Exposure of mineral grains to light or heat (at least 300˚C) reduces the luminescence to a low and definable residual level.

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.

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.

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.

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.

The radioactive decay of 40K releases beta and gamma radiation, whereas the decay in the U and Th series generates mostly alpha particles and some beta and gamma radiation.

(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.

95% reduction in OSL within 4 seconds of exposure to light from blue diodes Optically stimulated luminescence (OSL) dating or optical dating provides a measure of time since sediment grains were deposited and shielded from further light or heat exposure, which often effectively resets the luminescence signal (Fig.1).