Photo dating radio
Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating.
It is useful to geologists and archaeologists who want to know when such an event occurred.
The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.
Stimulating these mineral grains using either light (blue or green for OSL; infrared for IRSL) or heat (for TL) causes a luminescence signal to be emitted as the stored unstable electron energy is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.
In multiple-aliquot testing, a number of grains of sand are stimulated at the same time and the resulting luminescence signature is averaged .
Single Quartz OSL ages can be determined typically from 100 to 350,000 years BP, and can be reliable when suitable methods are used and proper checks are done.For quartz, blue or green excitation frequencies are normally used and the near ultra-violet emission is measured.For potassium feldspar or silt-sized grains, near infrared excitation (IRSL) is normally used and violet emissions are measured.These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar.
The radiation causes charge to remain within the grains in structurally unstable "electron traps".In a study of the chronology of arid-zone lacustrine sediments from Lake Ulaan in southern Mongolia, Lee et al.