Neutron discovery (1932)

James Chadwick F.R.S. worked under Rutherford. He announced the existence of the neutron in 1932, in a paper published by the Royal Society. Chadwick, J.; The Existence of a Neutron, Proc. Roy. Soc. A136 (1932) p. 692.

"The properties of the penetrating radiation emitted from beryllium (and boron) when bombarded by the a-particles of polonium are examined. It is concluded that the radiation consists of neutrons, particles of mass number 1, and charge zero." 

Chadwick estimated the mass of the neutron to be ~1.0067 times the mass of the proton by adding the masses and mass equivalents of the known kinetic energies of the reactants, products, and the KE's of nitrogen atoms and neutrons after a subsequent collision for the reaction....

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