Atomic bomb test explosion in Alamagordo, New Mexico, July 16, 1945. AP/Wide World Photos In 1932, James Chadwick discovered the neutron, a small atomic particle with mass but no charge.

Robert Oppenheimer's name has become almost synonymous with the atomic bomb, and also with the dilemma facing scientists when the interests of the nation and their own conscience collide.

Today is the anniversary of Hiroshima – when an atomic bomb nicknamed Little Boy was dropped on Japan. On August 6, 1945, Hiroshima was left devastated, with up to 166,00 dying in the blast ...