 Graves and Elizabeth moved to work at Los Alamos Laboratory in New Mexico when it opened in 1943 . He made it a condition of his going to Los Alamos that a job be found there for her . This was probably unnecessary , as someone with her skills — she was one of the few physicists who had experience with a Cockcroft @-@ Walton accelerator — would have been quickly snapped up at Los Alamos . At the time of the Trinity nuclear test in 1945 , Elizabeth was seven months pregnant with her first child . Graves therefore requested that they be assigned to a post far from the blast . They listened to Samuel K. Allison 's countdown to the explosion on the radio , and monitored the radioactive fallout from the test , which took until the afternoon to reach them , with Geiger counters . The child was a healthy daughter , Marilyn Edith . 
