Two months later, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. In December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slow neutrons, and discovered that barium had been produced. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, proved that the uranium nucleus had been split. They published their finding in "Nature" in 1939. This phenomenon was a new type of nuclear disintegration, and was more powerful than any seen before. Frisch and Meitner calculated that the energy released by each disintegration was approximately . By analogy with the division of biological cells, they named the process "fission".