History of Nuclear Fission

Enrico Fermi and his collaborators were the first to study elements that have been bombarded by neutrons resulting in new radioactive elements being formed. However this process was not interpreted as fission until several years later.
Fermi had predicted that the neutron would be a useful nuclear projectile. He thought this because neutrons are uncharged and receive no electric forces from the nucleus when reaching the nuclear surface. Fermi's prediction was proven correct later on by other physicists.

Otto Hahn and Fritz Strassman tested uranium salts by bombarding these solutions with neutrons. Later through chemical analysis they found a number of new radioactive elements present. Hahn and Strassman conducted repeated tests to prove that barium was produced during this process.

Otto Frisch was able to show that a uranium nucleus, which had absorbed a neutron could split into roughly two equal parts one of which was barium. During this process there were large amounts of energy being released. Frisch named this the process of fission.