1) Electron emitted from the nucleus when a neutron decays to a proton and an electron.
2) An Electron
3) a charged particle emitted from the nucleus of some atoms as part of those atoms' radioactive decay. Positively charged beta particles are positrons and negatively charged beta particles are electrons. Beta particles can cause burns and are harmful to living tissues, however, protection is afforded by a thin sheet of metal.
4) An electron emitted from a nucleus in one type of radioactivity.