 At Columbia University in the United States, Enrico Fermi and Leó Szilárd attempted to use graphite as a moderator instead.This turned out to be possible, but the graphite had to be very pure, as impurities, particularly boron, tended to absorb neutrons.On 2 December 1942, Fermi's team initiated the first artificial self-sustaining nuclear chain reaction in an experimental reactor known as Chicago Pile-1.