 For a practical reactor configuration, it needed to be at least 3 or 4 percent more; but in August 1941 Zinn's initial experiments indicated a disappointing value of 0.87.Fermi pinned his hopes of a better result on an improved configuration, and purer uranium and graphite.In early 1942, with the United States now embroiled World War II, Arthur Compton concentrated the Manhattan Project's various teams working on plutonium at the Metallurgical Laboratory at the University of Chicago.