Theory
Scattering
Atoms
αβγ decay
Decay Series
Law
Half-life
Geiger
Carbon-14
Fission
Chain Reaction
Nuclear Energy
Nuclear reactors
Fusion

The search for artificially radioactive substances led to the discovery of fission.

The discovery of fission led to the atomic bomb.

Fission was discovered in 1939, by two Germans, Hahn and Strassmam

They bombarded Uranium with neutrons and found the products of the reaction to be Barium and Krypton.

Fission
Fission is the splitting of a large nucleus into two or more fragments of comparable size with the release of energy. It occurs when a neutron, travelling at a suitable speed, collides with a heavy nucleus. Usually a number of neutrons accompany the fission fragments. The energy released is far greater than in other types of nuclear reaction.
Fission differs from other types of nuclear reaction in a number of ways. Nuclear reactions that are the consequence of natural or artificial radioactivity, involve the ejection of relatively light particles such as an alpha particle or proton, which left behind a modified nucleus, and resulted in the release of energy (perhaps several MeV).
In contrast, fission leaves behind a shattered nucleus, and results in the release of much more energy (perhaps 200 MeV).

Fission was discovered in 1939, by two Germans, Hahn and Strassman, when they bombarded Uranium with neutrons and found the products of the reaction to be Barium and Krypton.
                 
It was quickly realised that because neutrons cause fission and other neutrons are released in the reaction, that a self-sustaining reaction ought to be possible.