James Chadwick

In 1907, while enrolling at the University of Manchester, James Chadwick accidentally found himself in the line for those hoping to major in physics. Chadwick, who had intended to be a mathematician, was too shy to admit he was mistaken and stayed in line. Thus began the career of one of this century's most distinguished physicists. In 1913 he received his master's degree and left for Germany to work with Hans Geiger. There, Chadwick was the first to show that beta particles possess a range of energies up to some maximum value. Trapped in Germany when WW I broke out, Chadwick was imprisoned in a horse stall at a racetrack that served as an internment camp. As soon as the war ended and he gained his freedom, Chadwick returned to England and joined forces with Ernest Rutherford. Intrigued by Rutherford's speculation about a subatomic particle with no charge, Chadwick began a series of experiments to demonstrate the existence of such a particle. Initially, none of the experiments succeeded. Then, in 1930, Walther Bothe and Herbert Becker described an unusual type of gamma ray produced by bombarding the metal beryllium with alpha particles. Chadwick recognized that the properties of this radiation were more consistent with what would be expected from Rutherford's neutral particle. When Frédéric and Irène Joliot-Curie subsequently claimed that Bothe and Becker's "gamma rays" could eject high energy protons from paraffin, Chadwick knew these were not gamma rays. The subsequent experiments by which Chadwick proved the existence of the neutron earned him the 1935 Nobel Prize in physics. Not only did this singular particle provide physicists with a superlative tool for investigating the atom, it was also used to produce a wide variety of new radioisotopes and permitted the initiation of nuclear chain reactions. Hans Bethe has referred to Chadwick's discovery as the historical beginning of nuclear physics.

Thanks to the following group for allowing us to reprint this information:

The Health Physics Society
1313 Dolley Madison Blvd., Suite 402
Mclean, Virginia 22101

Tel: 703-790-1745
Fax: 703-790-2672