Positrons are the antimatter equivalent of electrons, with a positive charge and low prevalence in the universe. They can be used in particle accelerator experiments and positron emission tomography for diagnostic purposes. Proposed applications include antimatter warfare and energy production, but are unlikely due to their indiscriminate effects and high energy requirements.
A positron is the antimatter equivalent of an electron. Like the electron, the positron has a spin of ½ and an extremely low mass (about 1/1836 of a proton). The only differences are its charge, which is positive rather than negative (hence the name), and its prevalence in the universe, which is much lower than that of the electron. Being antimatter, if a positron comes into contact with conventional matter, it explodes in a shower of pure energy, bombarding everything nearby with gamma rays.
Like electrons, positrons respond to electromagnetic fields and can be kept contained using confinement techniques. They can mate with antiprotons and antineutrons to make antiatoms and antimolecules, although only the simplest of these have ever been observed. Positrons exist in a low density throughout the cosmic medium, and even antimatter harvesting techniques have been proposed to harness their energy.
The existence of the positron was first postulated by the famous physicist Paul Dirac in 1930 and discovered only two years later, in 1932, in an experiment with a particle accelerator. Because they are small and react to magnetic fields, positrons are just as likely to be used in particle accelerator experiments as electrons are.
Today, positrons are used most frequently in positron emission tomography, where a small amount of a radioisotope with a short half-life is injected into a patient and, after a short waiting period, the radioisotope concentrates in the tissue of interest and begins to break down, releasing positrons. These positrons travel a few millimeters in the body before colliding with an electron and releasing gamma rays, which can be picked up by the scanner. This is used for a variety of diagnostic purposes, whether to study the brain or to track the movement of a drug throughout the body.
Proposed futuristic applications of positrons include antimatter warfare and energy production. However, both applications are not particularly likely to be widely used, due to their indiscriminate effect in warfare – modern warfare is more based on precision – and radioactive emissions similar to nuclear bombs. Unless extremely efficient means of harvesting positrons from space are developed, it is unlikely that positrons will be used to produce energy, because nearly as much energy is needed to create them as is extracted from annihilation with conventional matter.
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