James Chadwick (1891-1974), British physicist. Educated in Manchester, Chadwick's research under Rutherford was mainly with alpha particles (helium nuclei). He used data gained in these experiments to show that the positive charge of a nucleus (model nucleus held in his hand) is the same as its atomic number. In 1932, he re-interpreted an experiment by the Joliot-Curies as evidence for the existence of the neutron. Chadwick's own experiments confirmed this. This discovery was key to the advance of nuclear physics, with neutrons used to initiate nuclear reactions. In 1935, Chadwick was awarded the Nobel Prize in Physics.