Prior to World War II , Langsdorf co-developed a cyclotron for splitting atomic particles at Washington University in St. Louis . It was designed for use in medical research . During World War II , he worked with Enrico Fermi at the University of Chicago on the Manhattan Project . Langsdorf was one of the designers of the first two nuclear reactors after Fermi completed the first sustained nuclear chain reaction in 1942 . Langsdorf was able to produce a tiny usable sample of plutonium using his device . That sample was then used in the Trinity nuclear test on July 16 , 1945 . Langsdorf urged President Harry S Truman not to use the bomb against the Japanese , but a plutonium-based bomb was dropped on Nagasaki soon after
Trinity nuclear test
Trinity (nuclear test)
Alexander Langsdorf Jr.