 Fermi's group constructed a nuclear reactor known as Chicago Pile-1 under the stands of Stagg Field, the University's abandoned football stadium, where Woods had once played squash. Walter Zinn did not want a woman involved in the dirty work of placing the graphite blocks, but Woods had plenty of work to do with the detectors and thermocouples, and used a small stack of graphite of her own to measure the effects of a radium-beryllium source on manganese foil to obtain a measure of the neutron cross section in order to calibrate the detectors. Woods was the only woman present when the reactor went critical, asking Fermi "When do we become scared?"
