 In 1942 Graves was invited back to the University of Chicago by Arthur H. Compton . Graves had already received a request from the MIT Radiation Laboratory to work on radar , and he asked if he could contribute more to Compton 's project . Compton replied that he could . He joined the Manhattan Project 's Metallurgical Laboratory , and helped build the first nuclear reactor , the Chicago Pile @-@ 1 . Graves , Harold V. <unk> and Warren <unk> formed Enrico Fermi 's " suicide squad " or " liquid @-@ control squad " , assigned to smash 5 @-@ US @-@ gallon ( 19 l ; 4 @.@ 2 imp gal ) glass bottles containing a solution of cadmium sulfate over the reactor with hammers if something went wrong . Cadmium is a strong neutron absorber and Fermi hoped that this would halt a runaway nuclear chain reaction , if the reactor control rods proved to be incapable of halting it in the first place . 
