Nuclear fission

Researchers bombarded uranium (element 92) with slow neutrons to explore the emission of two alpha particles and possible formation of a radium isotope (element 88). Instead they found barium (element 56) which puzzled scientists. This process was eventually confirmed and called fission.
 Otto Hahn and Lise Meitner Germany and Austria 1939 Nuclear fission

Researchers bombarded uranium (element 92) with slow neutrons to explore the emission of two alpha particles and possible formation of a radium isotope (element 88). Instead they found barium (element 56) which puzzled scientists. This process was eventually confirmed and called fission.