Lawrence Litz was a young physicist when he began working on radioactivity at the Metallurgical Laboratory at the University of Chicago. From there he was transferred to Los Alamos, where he worked on casting the plutonium hemispheres for the atomic bombs and became the first person to see metallic plutonium.
He cast a third plutonium core in 24 hours in August 1945. This core was to be used if Japan refused to surrender after the bombing of Nagasaki. It was not used in World War II, but continued to be used in experiments, becoming known as the "demon core" for its role in the deaths of Manhattan Project scientists Harry Daghlian in 1945 and Louis Slotin in 1946.
His wife, Evelyne Litz, also worked on the Manhattan Project at Chicago and Los Alamos.