 The Los Alamos Laboratory became Los Alamos Scientific Laboratory in 1947.The discovery of the neutron by James Chadwick in 1932, followed by the discovery of nuclear fission by chemists Otto Hahn and Fritz Strassmann in 1938, and its explanation (and naming) by physicists Lise Meitner and Otto Frisch soon after, opened up the possibility of a controlled nuclear chain reaction using uranium.At the time, few scientists in the United States thought that an atomic bomb was practical, but the possibility that a German atomic bomb project would develop atomic weapons concerned refugee scientists from Nazi Germany and other fascist countries, leading to the drafting of the Einstein–Szilard letter to warn President Franklin D. Roosevelt.