James Chadwick proved the existence of neutrons in 1932, according to Book Rags. As uncharged particles in atoms, neutrons play a key part in nuclear fission, or the splitting of atoms.
Chadwick's research greatly increased understanding of the structure of the atomic nucleus, according to the Nobel Prize website. Before his discovery, scientists knew of the existence of protons in the nucleus, but not neutrons.
Unlike protons and electrons, neutrons have no electrical charge. This means the charged particles of other elements cannot prevent them from penetrating and splitting their nuclei.
Chadwick won the 1935 Nobel Prize in Physics, according to Book Rags. His work led to the fission of uranium 235, and the subsequent development of the atomic bomb.