sentences:  In 1939, John Archibald Wheeler and Niels Bohr proposed the liquid-drop model of nuclear fission.Their work suggested that uranium 235 was responsible for thermal neutron fission.This was borne out by the work of Eugene T. Booth, John R. Dunning, A. V. Grosse, and Alfred O. C. Nier, which was submitted for publication in the spring of 1940.