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Positron emission is a type of beta decay, sometimes referred to as "beta plus" (β+). In beta plus decay, a proton is converted, via the weak force, to a neutron, a positron (also known as the "beta plus particle", the antimatter counterpart of an electron), and a neutrino. Isotopes which undergo this decay and therefore emit positrons include carbon-11, nitrogen-13, oxygen-15, fluorine-18, and iodine-121. As an example, the following equation describes the beta plus decay of carbon-11 to boron-11, emitting a positron e+ and a neutrino νe: ^hbox; o;^hbox;+;e^+;+; u_e. These isotopes are used in positron emission tomography, a technique used for medical imaging. Electron capture is a competing decay mode to this process and is energetically favored, but as the energy difference goes up so does the branching ratio towards positron emission.
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