The 1949 detonation of Joe-1 by the Soviet Union prompted an all-out effort by the United States, led by Teller, to develop the more powerful hydrogen bomb in response. Henry D. Smyth , Wheeler's department head at Princeton, asked him to join the effort. Most physicists were, like Wheeler, trying to re-establish careers interrupted by the war and were reluctant to face more disruption. Others had moral objections.  Those who agreed to participate included Emil Konopinski , Marshall Rosenbluth , Lothar Nordheim and Charles Critchfield , but there was also now a body of experienced weapons physicists at the Los Alamos Laboratory , led by Norris Bradbury .   Wheeler agreed to go to Los Alamos after a conversation with Bohr.  Two of his graduate students from Princeton, Ken Ford and John Toll , joined him there.