|Composition: ||Elementary particle |
|Family: ||Fermion |
|Group: ||Lepton |
|Generation: ||First |
|Interaction: ||Gravity, Electromagnetic, Weak |
|Antiparticle: ||Electron |
|Theorized: ||Paul Dirac, 1928|
|Discovered: ||Carl D. Anderson, 1932|
|Symbol: ||β+, e+ |
|Mass: ||9.1093826(16) × 10−31 kg |
|Electric charge: ||1.602176462(63) × 10−19 C |
|Spin: ||½ |
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). The first scientist deemed to have captured 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 may be generated by positron emission radioactive decay (a weak interaction), or by pair production from a sufficiently energetic 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.
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".
- In the Star Trek universe the android Data, his "brothers" Lore and B4, "daughter" Lal, and kindred Soong-type androids have positronic brains.
- ALPHA Collaboration
- Paul Dirac
- Carl D. Anderson
- 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 Durand Durand was the developer of the Positronic ray.
- In the video game Castlevania: Aria of Sorrow, completing the Boss Rush under a certain time will grant the player access to the Positron Rifle. Its description reads: "Fires positive electrons."
- In the video game Pikmin, one of the spaceship parts that needs to be collected is named "Positron Generator". Its description says it can generate unlimited amounts of energy.
- In the video game Freelancer, the positron is the basis for a defensive shield.
- In comics the Black superhero Icon created by Milestone Media and published by DC Comics has the ability to generate and blast positron energy from his hands.
- In the sitcom Friends, Phoebe's ex boyfriend David moved to Minsk to work on "positronic distillation of subatomic particles".
- ^ Anderson, Carl D. (1933). "The positive electron". Phys. Rev., 43(6):491–494 doi: 10.1103/PhysRev.43.491.