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Positron (antielectron)
PositronDiscovery.jpg
Cloud chamber photograph by C.D. Anderson of the first positron ever identified. A 6 mm lead plate separates the upper half of the chamber from the lower half. The positron must have come from below since the upper track is bent more strongly in the magnetic field indicating a lower energy.
Composition: Elementary particle
Statistical behavior: Fermion
Group: Lepton
Generation: First
Interaction: Gravity, Electromagnetic, Weak
Symbol(s): β+, e+
Antiparticle: Electron
Theorized: Paul Dirac (1928)
Discovered: Carl D. Anderson (1932)
Mass: 9.10938215(45)×10 −31 kg[1]

5.4857990943(23)×10 −4 u[1]
[1822.88850204(77)]−1 u[note 1]
0.510998910(13) MeV/c2[1]

Electric charge: +1 e
1.602176487(40)×10 −19 C[1]
Spin: 12

The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1, a spin of 12, and the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two or more gamma ray photons (see electron-positron annihilation). The existence of positrons was first postulated in 1928 by Paul Dirac as a consequence of the Dirac equation.

Positrons may be generated by positron emission radioactive decay (through weak interactions), or by pair production from a sufficiently energetic photon.

Contents

History

The first scientist deemed to have detected positrons through electron–positron annihilation was Chung-Yao Chao, a graduate student at Caltech in 1930, though he did not realize what they were at that time. Positrons were discovered in 1932 by Carl D. Anderson, who gave the positron its name.[2] The positron was the first evidence of antimatter and was discovered by passing cosmic rays through a cloud chamber and a lead plate surrounded by a magnet to distinguish the particles by bending differently charged particles in different directions. The positron was theoretically predicted by the Dirac equation in 1928, although Paul Dirac himself was slow to accept that the observed positron was actually the particle predicted by his equation.

Today, positrons, created through the decay of a radioactive tracer, are detected in positron emission tomography (PET) scanners used in hospitals and in accelerator physics laboratories used in electron–positron collider experiments. In the case of PET scanners, positrons provide a mechanism to show areas of activity within the human body, which is now widely used in cancer imaging and also brain imaging. In addition to the two above-mentioned applications of positrons in medicine and fundamental physics, an experimental tool called positron annihilation spectroscopy (PAS) is used in materials research.

New research has dramatically increased the quantity of positrons that experimentalists can produce. Physicists at the Lawrence Livermore National Laboratory in California have used a short, ultra-intense laser to irradiate a millimetre-thick gold target and produce more than 100 billion positrons.[3][4]

See also

Notes

  1. ^ The fractional version’s denominator is the inverse of the decimal value (along with its relative standard uncertainty of 4.2×10 −10).

References

  1. ^ a b c d The original source for CODATA is:
    Mohr, P.J.; Taylor, B.N.; Newell, D.B. (2006). "CODATA recommended values of the fundamental physical constants". Reviews of Modern Physics 80: 633–730. doi:10.1103/RevModPhys.80.633.  
    Individual physical constants from the CODATA are available at:
    "The NIST Reference on Constants, Units and Uncertainty". National Institute of Standards and Technology. http://physics.nist.gov/cuu/. Retrieved 2009-01-15.  
  2. ^ Anderson, Carl D. (1933). "The Positive Electron". Physical Review 43 (6): 491–494. doi:10.1103/PhysRev.43.491.  
  3. ^ Bland, E. (1 December 2008). "Laser technique produces bevy of antimatter". MSNBC. http://www.msnbc.msn.com/id/27998860/. Retrieved 2009-07-16. "The LLNL scientists created the positrons by shooting the lab's high-powered Titan laser onto a one-millimeter-thick piece of gold."  
  4. ^ "Laser creates billions of antimatter particles". Cosmos Online. http://www.cosmosmagazine.com/news/2345/laser-creates-billions-particles-antimatter.  

External links


Wiktionary

Up to date as of January 14, 2010

Definition from Wiktionary, a free dictionary

See also positron, and positrón

German

Noun

Positron, n. (plural: Positronen)

  1. positron

Gaming

Up to date as of February 01, 2010

From Wikia Gaming, your source for walkthroughs, games, guides, and more!

Positron


Cover of City of Heroes, V2 #3

Statistics
Real name Dr. Raymond Keyes
Status Active
Affiliations Freedom Phalanx
Previous affiliations Stanford University
Notable powers Flight, Radiation Blasts, Radiation Emission
Notes Smart and explosive.


Positron is the Iron Man/Captain Atom of the Freedom Phalanx, and the alter-ego of dev Matthew Miller.

History

Before becoming a superhero, Dr. Raymond Keyes was a professor of nuclear physics at Stanford. After his budget was cut and his access to the university's linear accelerator became limited, he took a corporate job in an effort to work for the greater good. However, he soon find out that not all companies shared his ideal. In an unfortunate (or perhaps fortunate) "industrial accident," Dr. Keyes found himself able to generate and control anti-matter. With his extended knowledge of nuclear physics, Dr. Keyes understood very well the capabilities of his power, and their danger.

In order to better control and focus his powers, he constructed a crude suit able to contain the anti-matter. This allowed him to fire anti-matter in the form of blasts, as well as a limited form of flying. He put his powers to the test when a group of Devouring Earth monsters attacked an amusement park and killed dozens of citizens. In the name of justice, Dr. Keyes tracked them down to their base and destroyed them. As a result, Devouring Earth has become his most hated enemies, and the feeling is mutual. When the media had asked him what his "hero name" was, he told them "Positron". Thus a hero was born.

The important thing to remember about Positron, however, is his high level of instability. While he once had control over his powers, after being injured in the Rikti War he became trapped in his suit. A large enough leak could mean bad news for all of Paragon (similarly to how the Siren's Call zone was destroyed by an out-of-control hero).

In-Game

Positron stands guard in the center of Steel Canyon and gives out a Task Force to heroes leveled 10-15. This Task Force features the Clockwork, Circle of Thorns and Vahzilok, and is widely regarded as one of the worst in the game due to the long length, repetitive tasks and lack of a big finale fight.


This article uses material from the "Positron" article on the Gaming wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.

Simple English

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A positron is the antimatter equivalent to an electron. It has the same mass as an electron, however it has a positive charge, whereas an electron has a negative charge. Like all antimatter, when it meets its so-called counterpartner, each are annihilated and turned into energy. There is no known name for this type of energy, as it is neither mechanical, radiation, chemical, electrical, nuclear, nor thermal. Although the energy does emit light photons when annihilated, it is converted from some form of energy which we, as a scientific community, cannot name.

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