 In 1944 Richard Feynman recruited Reines to work in the Theoretical Division at the Manhattan Project 's Los Alamos Laboratory , where he would remain for the next fifteen years . He joined Feynman 's T @-@ 4 ( <unk> Problems ) Group , which was part of Hans Bethe 's T ( Theoretical ) Division . <unk> was an important aspect of critical mass calculations . In June 1946 , he became a group leader , heading the T @-@ 1 ( Theory of Dragon ) Group . An outgrowth of the " <unk> the Dragon 's tail " experiment , the Dragon was a machine that could attain a critical state for short bursts of time , which could be used as a research tool or power source . 
