Positron

This article is about the positron particle. For the computer game, see Positron (game).

A positron is the antiparticle of the electron. It is antimatter, has an electric charge of +1, a spin of 1/2, and the same mass as an electron. When a positron annihilates with an electron, their mass is converted into energy in the form of two gamma ray photons. See Electron-positron annihilation.

A positron may be generated by positron emission radioactive decay, or the interaction of photons of energy greater than 1.022 MeV with matter. This process is called pair production, as it generates both an electron and a positron from the energy of the photon.

The existence of positron was first postulated in 1928 by Paul Dirac. In 1932, a positron was observed by Carl D. Anderson, who gave the positron its name. Interestingly, Anderson also suggested, unsuccessfully, to rename electrons to "negatron."

The Positron in Fiction

The most famous use of the positron in fiction was Isaac Asimov's use in his robots' Positronic brains. It is likely that he chose to use positrons because they were relatively newly-discovered when he was first writing about the robots. 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 occassions. Positrons might soon, however, be used a source of energy. It is possible to travel to Mars with only about 5 grams of positrons, and it would only take several days to do so.

In the Japanese anime sci-fi series Mobile Suit Gundam SEED and it's sequel, Mobile Suit Gundam SEED Destiny, large scale positron cannons are used on some advanced warships for spacefaring 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 annhilation reactions can irradiate the surrounding environment in the same way that a nuclear explosion can, causing cancers and mutations. Either way, these cannons are typically portrayed as the single most powerful conventional weapon that can be deployed on a battlefield, more than enough to take down anything from a battlecruiser to an entire naval fleet in a single hit. A positron cannon was also deployed to break apart the remains of Junius Seven, a colony destroyed in the war that had fallen out of its orbit and was rapidly descending to Earth.

See also

• electron
• radioactive decay
• list of particles
• positron emission tomography