Nuclear fission was discovered on 19 December 1938 in Berlin by German chemists Otto Hahn and Fritz Strassmann and physicists Lise Meitner and Otto Robert Frisch.
Nuclear fission involves splitting the atom, more specifically the nuclei of the atom to break the bond, that releases energy.
This is done by bombarding the material with a neutron to make the atom unstable so that it breaks down to lighter nuclie and release energy.