Nuclear fission
In 1936, Szilárd attempted to create a chain reaction using beryllium and indium, but was unsuccessful. Nuclear fission was discovered by Otto Hahn and Fritz Strassmann in December 1938 and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch. A few months later, Frédéric Joliot-Curie, H. Von Halban and L. Kowarski in Paris searched for, and discovered, neutron multiplication in uranium, proving that a nuclear chain reaction by this mechanism was indeed possible.