A spin one-half particle, it was observed in cloud chamber photographs of cosmic rays, and it is ejected by proton-rich radioactive nuclei in positive beta decay.  
This accounts for the superfluous negative energy states of an electron as predicted by the relativistic quantum mechanical theory proposed by Dirac.  A spin one-half particle, it was observed in cloud chamber photographs of cosmic rays, and it is ejected by proton-rich radioactive nuclei in positive beta decay.  FTP, identify this particle, discovered in 1932 by Carl Anderson.
This accounts for the superfluous negative energy states of an electron as predicted by the relativistic quantum mechanical theory proposed by Dirac.  
positron or anti-electron