In 1919 there was a surprising discovery made by the British physicist Ernest Rutherford. He started by producing a beam of alfa particles using radium. Rutherford had studied alfa particles during many years and had earlier showed that they were helium nuclei. Then he let the beam of helium nuclei collide with nitrogen atoms in gas form. The peculiarity was that there were hydrogen nuclei produced in the collisions. The first nuclear reaction had been identified,

                  
The hydrogen nucleus was called proton, which in Greek means the first.

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