physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, optically stimulated luminescence (OSL) is a method for measuring doses from

ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...

. It is used in at least two applications: * Luminescence dating of ancient materials: mainly geological sediments and sometimes fired pottery, bricks etc., although in the latter case thermoluminescence dating is used more often *

Radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

dosimetry, which is the measurement of accumulated radiation dose in the tissues of health care, nuclear, research and other workers, as well as in building materials in regions of nuclear disaster The method makes use of

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s trapped between the valence and conduction bands in the

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

line structure of certain minerals (most commonly

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

). The trapping sites are imperfections of the lattice — impurities or defects. The ionizing radiation produces electron-hole pairs: Electrons are in the conduction band and holes in the valence band. The electrons that have been excited to the conduction band may become entrapped in the electron or hole traps. Under the stimulation of light, the electrons may free themselves from the trap and get into the conduction band. From the conduction band, they may recombine with holes trapped in hole traps. If the centre with the hole is a luminescence center (radiative recombination centre), emission of light will occur. The

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

s are detected using a photomultiplier tube. The signal from the tube is then used to calculate the dose that the material had absorbed. The OSL dosimeter provides a new degree of sensitivity by giving an accurate reading as low as 1 mrem for x-ray and gamma ray photons with energies ranging from 5 keV to greater than 40 MeV. The OSL dosimeter's maximum equivalent dose measurement for x-ray and gamma ray photons is 1000 rem. For beta particles with energies from 150 keV to in excess of 10 MeV, dose measurement ranges from 10 mrem to 1000 rem. Neutron radiation with energies of 40 keV to greater than 35 MeV has a dose measurement range from 20 mrem to 25 rem. In diagnostic imaging, the increased sensitivity of the OSL dosimeter makes it ideal for monitoring employees working in low-radiation environments and for pregnant workers. To carry out OSL dating, mineral grains have to be extracted from the sample. Most commonly these are so-called coarse grains of 100-200 μm or fine grains of 4-11 μm. Occasionally other grain sizes are used. The difference between

radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...

and OSL is that the former is used to date organic materials, while the latter is used to date minerals. Events that can be dated using OSL are, for example, the mineral's last exposure to sunlight; Mungo Man, Australia's oldest human find, was dated in this manner. It is also used for dating the deposition of geological sediments after they have been transported by air ( aeolian sediments) or rivers ( fluvial sediments). In archaeology, OSL dating is applied to ceramics: The dated event is the time of their last heating to a high temperature (in excess of 400 °C). Recent OSL dating of stone tools in Arabia pushed the "out-of-Africa" date hypothesis of human migration back 50,000 years and added a possible path of migration from the African continent to the Arabian peninsula instead of through Europe. The most widely-used OSL method is called single-aliquot regeneration (SAR).

References

{{reflist Particle detectors Dating methodologies in archaeology