What is a Positron?
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 in contact with conventional matter, it explodes in a shower of pure energy, bombarding everything in the vicinity with gamma rays. Like electrons, positrons respond to electromagnetic fields, and can be kept contained using confinement techniques. They can couple together with antiprotons and antineutrons to make antiatoms and antimolecules, though only the simplest of these have ever been observed. Positrons exist in a low density throughout the cosmic medium, and antimatter harvesting techniques have even been proposed to exploit their energy. The positron’s existence was first postulated by the famous physicist Pau
A positron is an anti-matter electron (yes, there is such a thing as anti-matter!). It is identical to the electron in mass, but has an opposite charge of +1 (the electron is defined to have a charge of -1) Where do positrons come from? Positrons can come from a number of sources. However, in PET they are all produced by nuclear decay. Basically unstable nuclei are produced in a cyclotron by bombarding target material with protons. A typical reaction is to have a bombarding proton enter the nucleus of the target material and kick a neutron out in the process. For example, bombarding 18-O (an isotope of oxygen that has two extra neutrons relative to the familiar 16-O) results in the proton being captured and a neutron being ejected from the target nucleus. Changing the number of protons in the nucleus changes the atomic species and in this case the atom is changed from oxygen to fluorine. You can represent this as [18-O + proton => 18-F + neutron]. Other reactions are also possible, e.g
