gamma ray

Penetrating very short-wavelength electromagnetic radiation, similar to an X-ray but of higher energy, that is emitted spontaneously by some radioactive substances (see gamma decay; radioactivity). Gamma radiation also originates in the decay of certain subatomic particles and in particle-antiparticle annihilation (seealso antimatter). Gamma rays can initiate nuclear fission, can be absorbed by ejection of an electron (see photoelectric effect), and can be scattered by free electrons (see Compton effect).

Learn more about gamma ray with a free trial on Britannica.com.

Subgroup of the globulins. In humans and many other mammals, most antibodies are in the gamma globulin fraction of blood. A human gamma globulin preparation may be administered (by injection) to persons lacking immunity, either generally or to a particular disease, after exposure or before expected exposure.

Learn more about gamma globulin with a free trial on Britannica.com.

Type of radioactivity in the most common form of which an unstable atomic nucleus dissipates energy by gamma emission, producing gamma rays. Gamma decay also includes two other processes, internal conversion and internal pair production. In internal conversion, excess energy in a nucleus is transferred to one of its own orbiting electrons and the electron is ejected from the atom. In internal pair production, excess energy is converted into an electron and a positron, which are emitted together. Typical half-lives (see half-life) for gamma emission range from about 10⁻⁹ to 10⁻¹⁴ second.

Learn more about gamma decay with a free trial on Britannica.com.

Gamma (uppercase Γ, lowercase γ; Γάμμα) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. It was derived from the Phoenician letter Gimel . Letters that arose from Gamma include the Roman C and G and the Cyrillic letters Ge Г and Ghe Ґ.

In Modern Greek, it represents either a voiced velar fricative /ɣ/ or a voiced palatal fricative /ʝ/. In Ancient Greek, it represented a voiced velar stop /ɡ/. Before velars, it represents a velar nasal /ŋ/ in Modern as well as Ancient Greek, and a double gamma represents a prenasalized voiced velar stop (/ŋɡ/).

Gamma combinations

The gamma can be combined with other letters or itself.

• A double gamma (γγ) is pronounced like the ng in "jumping"
• A gamma with xi (γξ) is pronounced roughly like the nx in "Sphinx"
• (γχ) is pronounced like the nkh in "ankh"
• A gamma combined with kappa (γκ) is pronounced like the nk in "banker"

Use as a symbol or a term

Gamma is often used to denote a variable in mathematics and physics. In certain areas it has a specific meaning, such as representing gamma radiation in nuclear physics and the Lorentz factor in theory of relativity. In mathematics, there is a gamma function (usually written as Γ-function.)

See also

• Г, г - Ge (Cyrillic)
• G, g - Latin