Chicago Pile-1 — The First Controlled Chain Reaction
The first self-sustaining nuclear chain reaction took place at 3:25 in the afternoon of 2 December 1942, in a squash court under the west stands of Stagg Field at the University of Chicago. Chicago Pile-1 was built by Enrico Fermi's team in seventeen days from about 45,000 graphite blocks, 19,000 pieces of uranium metal and oxide, and cadmium control rods. The graphite moderated the neutrons — slowed them enough to be captured by uranium-235 — and the purity of it mattered enormously, since boron impurities in ordinary graphite absorb neutrons and had misled German researchers into abandoning the approach. It had no radiation shielding and no cooling. The safety arrangements were a rod suspended by a rope with an axe beside it, a man designated to cut it, and three physicists on a platform with buckets of cadmium salt solution, called the suicide squad. Fermi ran the approach in steps, calculating on a slide rule, withdrawing the control rod inch by inch and checking that the neutron count matched his prediction, and broke for lunch at the point of criticality because it was lunchtime. The pile went critical at half a watt and ran for about twenty-eight minutes. Arthur Compton telephoned James Conant at Harvard and said, in an improvised code, that the Italian navigator had landed in the New World and that the natives were friendly. It proved that a bomb was possible and made the reactors at Hanford, and plutonium, an engineering problem rather than a theoretical one. The reactor was dismantled the following year and rebuilt outside the city, where the university had originally been told to build it. A Henry Moore sculpture now stands on the site.
- Year: 1942 CE
- Category: Technology
