Gamma ray
hideGamma rays (denoted as γ) are electromagnetic radiation of high energy. They are produced by sub-atomic particle interactions, such as electron-positron annihilation, neutral pion decay, radioactive decay, fusion, fission or inverse Compton scattering in astrophysical processes. Gamma rays typically have frequencies above 1019 Hz and therefore energies above 100 keV and wavelength less than 10 picometers, often smaller than an atom. Gamma radioactive decay photons commonly have energies of a few hundred KeV, and are almost always less than 10 MeV in energy.
Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium. Alpha and beta "rays" had already been separated and named by the work of Ernest Rutherford in 1899, and in 1903 Rutherford named Villard's distinct new radiation "gamma rays."
Hard X-rays produced for by linear accelerators ("linacs") and astrophysical processes often have higher energy than gamma rays produced by radioactive gamma decay. In fact, one of the most common gamma-ray emitting isotopes used in nuclear medicine, technetium-99m produces gamma radiation of about the same energy (140 kev) as produced by a diagnostic X-ray machine, and significantly lower energy than the therapeutic treatment X-rays produced by linac machines in cancer radiotherapy.
In the past, distinction between the X-rays and gamma rays was arbitrarily based on energy (or equivalently frequency or wavelength), but because of the wide overlap and increasing use of megavoltage X-ray sources, now the two types of radiation are usually defined by their origin: X-rays are emitted by electrons outside the nucleus (and when produced by therapeutic linacs are often simply called "photons"), while gamma rays are specifically emitted by the nucleus (that is, produced by gamma decay). In theory, there is no lower limit to the energy of such photons, and thus "ultraviolet gamma rays" have been postulated.
In certain fields such as astronomy, gamma rays and X-rays are still sometimes defined by energy, as the processes which produce them may be uncertain.
As a form of ionizing radiation, gamma rays can cause serious damage when absorbed by living tissue, and they are therefore a health hazard.
For more information about Gamma ray, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with gamma rays
Fermi Telescope Detects Gamma-Ray From 'Star Factories' in Other Galaxies
Nov 02, 2009 |
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Nearby galaxies undergoing a furious pace of star formation also emit lots of gamma rays, say astronomers using NASA's Fermi Gamma-ray Space Telescope. Two so-called "starburst" galaxies, plus a satellite ...
Starburst galaxy sheds light on longstanding cosmic mystery
Nov 02, 2009 |
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(PhysOrg.com) -- An international collaboration that includes scientists from the University of Delaware's Bartol Research Institute in the Department of Physics and Astronomy has discovered very-high-energy ...
Astronomers explore 'last blank space' on map of the Universe
Oct 28, 2009 |
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(PhysOrg.com) -- The most distant object ever discovered is described in this week's edition of the science journal Nature. Two international teams of astronomers report their observations of a gamma-ray burst ...
Gamma-ray photon race ends in dead heat; Einstein wins this round
Oct 28, 2009 |
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Racing across the universe for the last 7.3 billion years, two gamma-ray photons arrived at NASA's orbiting Fermi Gamma-ray Space Telescope within nine-tenths of a second of one another. The dead-heat finish ...
Fermi Telescope Caps First Year With Glimpse of Space-Time (w/ Video)
Oct 28, 2009 |
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During its first year of operations, NASA's Fermi Gamma Ray Space Telescope mapped the extreme sky with unprecedented resolution and sensitivity. It captured more than one thousand discrete sources of gamma ...
Heart of a galaxy emits gamma rays
Oct 02, 2009 |
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(PhysOrg.com) -- Quite a few distant galaxies turn out to be cosmic delivery rooms. Large numbers of massive stars are born in the hearts of these starburst galaxies, and later explode as supernovae. In the ...
Very High Energy Gamma Rays
Sep 25, 2009 |
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(PhysOrg.com) -- Gamma-rays are the most energetic known form of electromagnetic radiation, with each gamma ray being at least one hundred thousand times more energetic than an optical light photon. The most ...
Large Area Telescope First Year Data Released
Aug 27, 2009 |
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(PhysOrg.com) -- Ever since the Large Area Telescope launched aboard the Fermi Gamma-ray Space Telescope in June 2008, the LAT team has been analyzing data, searching for answers to some of the most pressing ...
Has PAMELA Already Seen Dark Matter?
Aug 25, 2009 |
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(PhysOrg.com) -- Back in 2006, PAMELA (a Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) was launched with the purpose of detecting cosmic radiation and looking for clues pointing ...
Dark Matter May be Easier to Detect than Previously Thought
Aug 10, 2009 |
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(PhysOrg.com) -- The Milky Way, like many other galaxies, is thought to be embedded in massive, lumpy amounts of dark matter that release gamma rays and other emissions. Although at first these emissions seem ...
Large Area Telescope explores high-energy particles
Jul 28, 2009 |
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(PhysOrg.com) -- NASA's Fermi Gamma-ray Space Telescope is making some exciting discoveries about cosmic rays and the Large Area Telescope aboard Fermi is the tool in this investigation. Scientists in the ...
Fermi telescope finds gamma-ray galaxy surprises
Jul 14, 2009 |
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Back in June 1991, just before the launch of NASA's Compton Gamma-Ray Observatory, astronomers knew of gamma rays from exactly one galaxy beyond our own. To their surprise and delight, the satellite captured ...
Astrophysicists solve mystery in Milky Way galaxy
Jul 09, 2009 |
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A team of astrophysicists has solved a mystery that led some scientists to speculate that the distribution of certain gamma rays in our Milky Way galaxy was evidence of a form of undetectable "dark matter" ...
VLBA locates superenergetic bursts near giant black hole
Jul 02, 2009 |
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(PhysOrg.com) -- Using a worldwide combination of diverse telescopes, astronomers have discovered that a giant galaxy's bursts of very high energy gamma rays are coming from a region very close to the supermassive ...
Fermi Telescope reveals a population of radio-quiet gamma-ray pulsars
Jul 02, 2009 |
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(PhysOrg.com) -- A new class of pulsars detected by NASA's Fermi Gamma-ray Space Telescope is solving the mystery of previously unidentified gamma-ray sources and helping scientists understand the mechanisms ...
