Radioluminescence
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Radioluminescence is the phenomenon by which light is produced in a material by bombardment with ionizing radiation such as alpha particles, beta particles, or gamma rays.
Contents
[hide]Mechanism
Radioluminescence occurs when an incoming particle of ionizing radiation collides with an atom or molecule, exciting an orbital electron to a higher energy level. The particle usually comes from the radioactive decay of an atom of a radioisotope, an isotope of an element that is radioactive. The electron then returns to its ground energy level by emitting the extra energy as a photon of light. A chemical that releases light of a particular color when struck by ionizing radiation is called a phosphor. Radioluminescent light sources usually consist of a radioactive substance mixed with, or in proximity to, a phosphor. Some sufficiently radioactive elements such as actinium or einsteinium have the ability to ionize the air and release a glow without any additives.
Common materials
- Radium: one of the earliest radioluminescent materials, it was commonly used in dial clocks and a variety of quack products. Due to its radiation hazard (it also gives off radon gas which is also harmful) it has been replaced by safer alternatives.
- Promethium: unlike radium, promethium is only a relatively low-energy beta-emitter, which, unlike alpha emitters, does not degrade the phosphor lattice and the luminosity of the material does not degrade so fast. The isotope promethium-147 is commonly used. Unlike radium, its half-life is only 2.62 years, meaning it cannot be used for more than a few years.
- Tritium: The latest generation of the radioluminescent materials is based on tritium, a radioactive isotope of hydrogen with half-life of 12.32 years that emits very low-energy beta radiation. The low-energy 5.7 keV beta particles emitted by tritium cannot pass through the enclosing glass tube and even if they could, they are not able to penetrate human skin.
