Sir James Chadwick (1891-1974), English physicist. Educated in Manchester, Chadwick then worked under Rutherford on research mainly with alpha particles (helium nuclei). He used data gained in these experiments to show that the positive charge of a nucleus is the same as its atomic number. In 1932, he was able to re-interpret an experiment by the Joliot-Curies, which he saw as evidence for the existence of the neutron. Chadwick's own experiments confirmed this. This discovery of the neutron allowed a massive advance in knowledge of atomic nuclei. Neutrons are the most useful particle for initiating nuclear reactions. In 1935 he received the Nobel Prize in Physics for his discovery.