The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932. In April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. Then, in December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slowed neutrons, and discovered that barium had been produced. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, explained that the uranium nucleus had been split. By analogy with the division of biological cells, they named the process "fission".