Chadwick, James
The Englishman Sir James Chadwick (1891 - 1974), son of a cotton spinner, was an experimental physicist.
In 1932, he devised a apparatus consisting of a cylinder containing a polonium source and beryllium target. The resulting radiation was directed at paraffin wax. The displaced particles, which were protons, would go into a small ionization chamber where they could be detected. After only about two weeks of experimentation, he sent a letter to Nature titled: Possible Existence of a Neutron.
A few years later, he determined the neutron mass to be between 1.0084 and 1.0090 atomic units.
See also
Last modified:10 January 2026 2.23 p.m.