The  positrons, the anti-particle of the electron, were postulated by Dirac in 1930 and have been discovered by Andersen 3 years later.  This particles are present in nature, but their lifetime is short, since we happen to live in a world dominated by matter, when they encounter an electron they annihilate producing photons.  Mohorovicic (1934) postulated the existence of the e+e– bound state. Ruark (1945) baptized it  “positronium” and gave a qualitative discussion of the spectroscopic structure. In Deutsch (1951): Experimental detected  in gas and  measured for the first time the  lifetime of o-Ps to ±10%They are a unique tool  for studying problems in particle physics and astrophysics as well as solid state physics and material science. We use positron sources and slow positron beams to make experiments  in  fundamental physics and for nanoscale investigation in condensed matter. As a source of positrons we use an isotope of Sodium (²²Na), which emits them when a proton makes a beta decay: