Photonics, the science and technology based on and concerned with the controlled flow of photons, or light particles. It is the optical equivalent of electronics, and the two technologies coex...

Bose-Einstein statistics, class of statistics that applies to elementary particles called bosons, which include the photon, pion, and the W and Z particles. Bosons have integral values of the ...

Elementary ParticlesFor each of these particles, except the photon, gluon, and Z-boson, there is an antiparticle with the same mass and opposite charge. In most cases the antiparticle is denot...

Statistical mechanics, quantitative study of systems consisting of a large number of interacting elements, such as the atoms or molecules of a solid, liquid, or gas, or the individual quanta o...

Gamma radiation, high-energy photons emitted as one of the three types of radiation resulting from natural radioactivity. It is the most energetic form of electromagnetic radiation, with a ver...

Photochemistry, study of chemical processes that are accompanied by or catalyzed by the emission or absorption of visible light or ultraviolet radiation. A molecule in its ground (unexcited) s...

Compton effect [for A. H. Compton], increase in the wavelengths of X rays and gamma rays when they collide with and are scattered from loosely bound electrons in matter. This effect provides s...

Ionization chamber, device for the detection and measurement of ionizing radiation. It consists basically of a sealed chamber containing a gas and two electrodes between which a voltage is mai...

Pion or pi meson, lightest of the meson family of elementary particles. The existence of the pion was predicted in 1935 by Hideki Yukawa, who theorized that it was responsible for the force of...

Laser [acronym for light amplification by stimulated emission of radiation], device for the creation, amplification, and transmission of a narrow, intense beam of coherent light. The laser is ...