Splitting the atom

On this day in 1932, physicists John Cockcroft and Ernest Walton split the atom for the first time. The physicists worked at the University of Cambridge’s Cavendish Laboratory, then headed by Ernest Rutherford (center in photo, flanked by Cockcroft on the left and Walton on the right). In the preceding years Cockcroft and Walton had designed and built a machine that could produce protons and accelerate them through 300,000 volts. According to calculations by theoretical physicist George Gamow, that voltage would speed protons up enough to penetrate some atomic nuclei. On April 14, 1932, Cockcroft and Walton bombarded lithium nuclei with energetic protons. Observing from a lead-lined room, the scientists saw glowing spots on a zinc sulfide screen, indicating interactions with alpha particles. Individual lithium nuclei had been split to form two alpha particles. The year 1932 proved to be a big one for physics: In addition to splitting the atom, researchers discovered the neutron as well as the positron, the first particle of antimatter. (Image credit: UK Atomic Energy Authority, courtesy AIP Emilio Segre Visual Archives)

Date in History: 14 April 1932