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It has been suggested that Matter creation be merged into this article or section. (Discuss) Proposed since February 2010. |
| Light–matter interaction |
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| Low-energy phenomena: |
| Photoelectric effect |
| Mid-energy phenomena: |
| Compton scattering |
| High-energy phenomena: |
| Pair production |
Pair production refers to the creation of an elementary particle and its antiparticle, usually when a photon (or another neutral boson) interacts with a nucleus. For example an electron and its antiparticle, the positron, may be created. This is allowed, provided there is enough energy available to create the pair – at least the total rest mass energy of the two particles – and that the situation allows both energy and momentum to be conserved. Other pairs produced could be a muon and anti-muon or a tau and anti-tau. However all other conserved quantum numbers (angular momentum, electric charge, lepton number) of the produced particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, or if one particle has strangeness of +1 then another one must have strangeness of −1. The probability of pair production in photon-matter interactions increases with increasing photon energy and also increases with atomic number approximately as Z2.
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Examples [link]
In nuclear physics, this occurs when a high-energy photon interacts with a nucleus. The energy of this photon can be converted into mass through Einstein's equation E = m c2 where E is energy, m is mass and c is the speed of light. The photon must have enough energy to create the mass of an electron plus a positron. The mass of an electron is 9.11 × 10−31 kg, the same as a positron. Without a nucleus to absorb momentum, a photon decaying into electron-positron pair (or other pairs for that matter) can never conserve energy and momentum simultaneously. [1]
Energy [link]
Photon-nucleus pair production can only occur if the photons have an energy exceeding twice the rest energy (me c2) of an electron (1.022 MeV). These interactions were first observed in Patrick Blackett's counter-controlled cloud chamber, leading to the 1948 Nobel Prize in Physics. The same conservation laws apply for the generation of other higher energy particles such as the muon and tau.
In semiclassical general relativity, pair production is also invoked to explain the Hawking radiation effect. According to quantum mechanics, particle pairs are constantly appearing and disappearing as a quantum foam. In a region of strong gravitational tidal forces, the two particles in a pair may sometimes be wrenched apart before they have a chance to mutually annihilate. When this happens in the region around a black hole, one particle may escape while its antiparticle partner is captured by the black hole.
Pair production is also the hypothesized mechanism behind the pair instability supernova type of stellar explosion, where pair production suddenly lowers the pressure inside a supergiant star, leading to a partial implosion, and then explosive thermonuclear burning. Supernova SN 2006gy is hypothesized to have been a pair production type supernova.
In 2008 the Titan laser aimed at a 1-millimeter-thick gold target was used to generate positron–electron pairs in large numbers.[2]
See also [link]
- Electron–positron annihilation
- Meitner–Hupfeld effect
- Pair-instability supernova
- Two-photon physics
- Dirac equation
References [link]
- ^ Hubbell, J. H. (June 2006). "Electron positron pair production by photons: A historical overview". Radiation Physics and Chemistry 75 (6): 614–623. Bibcode 2006RaPC...75..614H. DOI:10.1016/j.radphyschem.2005.10.008.
- ^ "Laser technique produces bevy of antimatter". MSNBC. 2008. https://www.msnbc.msn.com/id/27998860/. Retrieved 2008-12-04. "The LLNL scientists created the positrons by shooting the lab's high-powered Titan laser onto a one-millimeter-thick piece of gold."
External links [link]
https://wn.com/Pair_production
Dragonlance
Dragonlance is a shared universe created by Laura and Tracy Hickman, and expanded by Tracy Hickman and Margaret Weis under the direction of TSR, Inc. into a series of popular fantasy novels. The Hickmans conceived Dragonlance while driving in their car on the way to TSR for a job interview. At TSR Tracy met Margaret Weis, his future writing partner, and they gathered a group of associates to play the Dungeons & Dragons role-playing game. The adventures during that game inspired a series of gaming modules, a series of novels, licensed products such as board games, and lead miniature figures.
In 1984, TSR published the first Dragonlance novel, Dragons of Autumn Twilight. It began the Chronicles trilogy, a core element of the Dragonlance world. While the authoring team of Tracy Hickman and Margaret Weis wrote the setting's central books, numerous other authors contributed novels and short stories to the setting. Over 190 novels have used the Dragonlance setting, and have been accompanied by supplemental Dungeons & Dragons campaign setting material for over a decade. In 1997, Wizards of the Coast LLC purchased TSR, and licensed Dragonlance to Sovereign Press, Inc in 2001 to produce game materials; this licensing agreement expired in 2007.
Creation (American band)
Creation was an American teen musical group from New York City. The band members were Sam Hellerman (drums and percussion), Raechel Rosen (lead vocals), Derek Orshan (bass, backing vocalist), Josh Shackett (rhythm guitar), and Tory Geismar (lead guitar and backing vocalist). Their first album, World Without Windows, was released in November 2005 and featured guest musician Clarence "Big Man" Clemons on one of the tracks.
It was said the idea for the band came from a cafe, the group was there. The stated goal of the group is "to help create a more peaceful world for the future, and to educate kids about multiculturalism, diversity, and peace." To help achieve that end, the band announced that all gross proceeds from their first album were to go towards the We Are Family Foundation. They also worked with Building with Books and U.S. Doctors for Africa. Creation's philanthropic mission was featured in many media outlets including USA Today, Time For Kids, The Montel Williams Show, Girls' Life Magazine, and The Jewish Week.
Gloria (heating system)
Gloria (meaning glory in Spanish) was a central heating system used in Castile beginning in the Middle Ages. It was a direct descendant of the Roman hypocaust, and due to its slow rate of combustion, it allowed people to use smaller fuels such as hay instead of wood.
Description
The Gloria consisted of a firebox, generally located outside (in a courtyard, for example), which burned hay, and one or more ducts that ran under the floors of the rooms to be heated. The warm exhaust gases from the combustion would pass through these ducts and then be released outside through a vertical flue.
The system is more efficient than a fireplace, because the rate of combustion (and therefore the heat output) can be regulated by restricting the airflow into the firebox. Moreover, the air required for combustion does not have to pass through the interior of the building, which reduces cold drafts. Finally, because the firebox is not open to the interior, there is no risk of filling the interior with smoke.
Gloria (1931 film)
Gloria is a 1931 French-German drama film directed by Hans Behrendt and starring Gustav Fröhlich, Brigitte Helm and Rolf Drucker. It was a co-production between the Munich-based Bavaria Film and France's Pathé-Natan. A separate French-language version Gloria was also released. Such multi-language versions were common during the early years of sound.
Cast
References
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Gloria (Them song)
"Gloria" is a song written by Northern Irish singer-songwriter Van Morrison and originally recorded by Morrison's band Them in 1964 and released as the B-side of "Baby, Please Don't Go". The song became a garage rock staple and a part of many rock bands' repertoires. It is particularly memorable for its "G–L–O–R–I–A" chorus. It is easy to play, as a simple three-chord song, and thus is popular with those learning to play guitar.
History
Morrison said that he wrote "Gloria" while he performed with the Monarchs in Germany in the summer of 1963, at just about the time he turned eighteen years old. He started to perform it at the Maritime Hotel when he returned to Belfast and joined up with the Gamblers to form the band Them. He would ad-lib lyrics as he performed, sometimes stretching the song to fifteen or twenty minutes. After signing a contract with Dick Rowe and Decca, Them went to London for a recording session at Decca Three Studios in West Hampstead on 5 July 1964; "Gloria" was one of the seven songs recorded that day. Besides Morrison, present were Billy Harrison on guitar, Alan Henderson on bass, Ronnie Millings on drums and Patrick John McCauley on keyboards. Rowe brought in session musicians Arthur Greenslade on organ and Bobby Graham on drums, since he considered the Them members too inexperienced. There remains some dispute about whether Millings and McCauley were miked up, but Alan Henderson contends that Them constituted the first rock group to use two drummers on a recording. Although some sources claim that Jimmy Page played second guitar, other sources deny this.
