James Chadwick

Discovered the neutron

The experiment

Alpha particles were shot through certain elements and ejected protons from the nuclei of atoms, this was due to the neutrons in the particles.

Discovery

Chadwick's contribution to atomic theory was the discovery of neutrons. He discovered them by hitting elements like gold foil or beryllium with alpha particles. Chadwick found that doing this released an unknown radiation and that ejected protons from the nucleus of atoms.
James Chadwick article

Tells of his background and discoveries.

James Chadwick Cartoon: Discovery of the Neutron