gamma radiation

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 very short wavelength (high frequency). Wavelengths of the longest gamma radiation are less than 10^-10 m, with frequencies greater than 10¹⁸ hertz (cycles per sec). Gamma rays are essentially very energetic X rays; the distinction between the two is not based on their intrinsic nature but rather on their origins. X rays are emitted during atomic processes involving energetic electrons. Gamma radiation is emitted by excited nuclei (see nucleus) or other processes involving subatomic particles; it often accompanies alpha or beta radiation, as a nucleus emitting those particles may be left in an excited (higher-energy) state. The applications of gamma radiation are much the same as those of X rays, both in medicine and in industry. In medicine, gamma ray sources are used for cancer treatment and for diagnostic purposes. Some gamma-emitting radioisotopes are also used as tracers (see radioactive isotope). In industry, principal applications include inspection of castings and welds. Data from artificial satellites and high-altitude balloons have indicated that a flux of gamma radiation is reaching the earth from outer space, thus opening up the field of research known as gamma-ray astronomy.

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).

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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