Positron

From Encyclopedia Jr, free information reference for Kids

The first detection of the positron in 1932 by Carl D. Anderson

The positron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1, a spin of 1/2, 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 gamma ray photons (see electron-positron annihilation).

A positron may be generated by positron emission radioactive decay, or the interaction of photon with a charged particle (such as an atom's nucleus) with energy greater than 2m_ec² = 2×0.511 MeV = 1.022 MeV with matter (m_e is the mass of one electron and c is the speed of light in vacuum). This process is called pair production, as it generates one electron and one positron from the energy of the photon.

The existence of positrons was first postulated in 1928 by Paul Dirac as a consequence of the Dirac equation. In 1932, positrons were discovered by Carl D. Anderson, who gave the positron its name. The positron was the first evidence of antimatter and was discovered by passing cosmic rays through a gas chamber and a lead plate surrounded by a magnet to distinguish the particles by bending differently charged particles in different directions.

Today, positrons are routinely produced in positron emission tomography (PET) scanners used in hospitals and in accelerator physics laboratories used in electron-positron collider experiments.

[edit] The positron in fiction

• The most famous use of the positron in fiction was Isaac Asimov's use in his robots' positronic brains. According to Asimov, in his book "The Relativity of Wrong", he decided to use positrons as they seemed a more interesting name for what is essentially an "electronic brain". Perhaps in an homage to Asimov, in the Star Trek universe the android Data, his "brother" Lore, "daughter" Lal, and other sundry related androids also have positronic brains.

• In Hideaki Anno's Neon Genesis Evangelion, the positron rifle, based upon the ATHENA tests in Europe, is used to defeat the invading Angels on numerous occasions; the most notable one being Ramiel.

• In the Japanese anime sci-fi series Mobile Suit Gundam SEED and its sequel, Mobile Suit Gundam SEED Destiny, large-scale positron cannons are used on some advanced warships for space-faring combat. Some characters in the series have moral issues with the use of positron cannons within the Earth's atmosphere, as the gamma radiation produced by annihilation reactions can irradiate the surrounding environment in the same way as a nuclear explosion, causing cancers and mutations.

• In the anime series Digimon Adventure 02, the powerful heroic Digimon known as Imperialdramon has an attack called "Positron Laser."

• In the film Ghostbusters, Peter Venkman refers to his proton pack as a "positron collider" while he and his fellow teammates trap their first ghost since going into business.

• In the film Barbarella, the villainous Duran Duran (from whom the pop group derived their name) was the developer of the Positronic ray.

[edit] See also

• Antimatter
• Beta particle
• Electron
• Radioactive decay
• List of particles
• Positron emission tomography
• Anti-gravity

[edit] External links

• What is a Positron? (from the Frequently Asked Questions :: Center for Antimatter-Matter Studies)
• Positron information search at SLAC
• Positron Annihilation as a method of experimental physics used in materials research.