Enrico Fermi of Italy irradiates uranium with neutrons. He believes he has produced the first transuranic element but unknowingly achieves the world’s first nuclear fission.

Frederic and Irene Joliot-Curie of France discover artificial radioactivity, like the radioactivity of atoms produced in transmutation experiments.  

Leo Szilard files for patent amendments for "the liberation of nuclear energy for power production and other purposes through nuclear ’transmutation.’ " He proposes a "chain reaction" for the first time.