Positron emission is a type of beta decay, referred to as "beta plus" (β+).
In beta plus decay, a proton is converted to a neutron via the weak nuclear force and a beta plus particle (a positron) and a neutrino are emitted.
Isotopes which emit positrons include Carbon-11, Nitrogen-13, Oxygen-15 and Fluorine-18; for example:
These isotopes are used in positron emission tomography.
See also