The discovery involved three key figures. In late 1938, Otto Hahn and Fritz Strassmann in Berlin experimentally proved uranium could split, producing barium. Exiled in Sweden, Lise Meitner received their data. During a winter walk with her nephew Otto Frisch, she conceived the theory of nuclear fission and calculated its massive energy release, publishing it in 1939. While Hahn, Strassmann, and Meitner collaborated closely, the 1944 Nobel Prize in Chemistry was awarded to Hahn alone. Historians