The story of the discovery of the
neutron and its properties is central to the extraordinary developments in atomic physics that occurred in the first half of the 20th century. The century began with
Ernest Rutherford and
Thomas Royds proving that
alpha radiation is
helium ions in 1908 and
Rutherford's model for the atom in 1911, in which atoms have their mass and positive charge concentrated in a very small
nucleus. The essential nature of the atomic nucleus was established with the discovery of the neutron by
James Chadwick in 1932.