Crawford Greenewalt managed the plutonium production operations in Hanford, WA, for the DuPont Company. Greenewalt witnessed the first critical nuclear reaction of the Chicago Pile-I, or CP-1, and kept a diary in which he recorded his experience, noting that during the experiment Enrico Fermi was "cool as a cucumber."
On Wednesday afternoon, 12/2/42, Compton took me over to West Stands to see the crucial experiment on Pile #1. When we got there, the control rod had been pulled out to within 3 inch of the point where K would be 1.0. The rod had been pulled out about 12 inch to reach this point. The resultant effects were being observed 1) by counting the neutrons as recorded on an indium strip inside the pile (see previous notes) and 2) on a recorder connected to an ionization chamber placed about 24 inch from the pile wall. The pile itself was encased in a balloon cloth envelope. The neutron counter was not a good index of what was going on since the number striking the indium strip was near and above the number which could be counted with accuracy. Hence the best index was the recorder attached to the ionization chamber. This had two ranges, one about twenty times as sensitive as the other. Fermi was cool as a cucumber—much more so than his associates who were excited or a bit scared.