James Chadwick

James Chadwick 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 were examined. It was concluded that the radiation consisted of neutrons, particles of mass 1, and charge zero."

"Chadwick inferred that neutrons had come into being when a boron nucleus absorbed an alpha particle in the reaction B11+a -> n+N14. He computed the neutron mass by subtracting the kinetic energy of the neutron and the rest energy of N14 from the total energies of the incident particle and the target atom." Rutherford, with Chadwick at extreme right.