For a real world application, see PET scans. Positron emission tomography, a common imaging technique in healthcare, relies upon certain radioactive isotopes that undergo beta decay. That is to say, an up quark in a proton flips to down, and turns the proton into a neutron, and ejects a positron (antimatter electron). When the positron meets an electron, they annihilate and release gamma rays, which are detected.