Time Period: 1891 - 1974

Background: English physicist James Chadwick, graduate of Manchester University, is credited for his discovery of the neutron in 1932. He worked as assistant director of radioactive research in Cambridge and as professor at the University of Liverpool. He was knighted the 1935 Nobel Prize in Physics.

Belief: Intrigued by Rutherford's speculation about a subatomic particle with no charge, Chadwick delved into the branches of physics and chemistry from mathematics. He began a series of experiments to prove the existence of such a particle, although with no avail. However, in 1930, Both and Becker had described an unusual type of gamma ray produced by bombarding the metal beryllium with alpha particles. Chadwick recognized that the properties of this radiation was more consistent than Rutherford's described neutral particle. Subsequent experiments from the derived information allowed Chadwick to prove the existence of of the neutron.

Contribution: By this point in time, the main parts of the atom and its structure had been developed. James Chadwick successfully placed the last piece of the puzzle in, and successfully, the atom was made, and a thorough understanding established.