On December 2, 1942, in a squash court beneath the football stadium, Enrico Fermi's team created humanity's first controlled nuclear chain reaction. A Henry Moore sculpture is at the spot.
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The Pile in the Squash Court
Beneath the abandoned west viewing stands of Stagg Field at the University of Chicago, a team of scientists assembled what Enrico Fermi called a "crude pile of black bricks and wooden timbers". This was Chicago Pile-1 (CP-1), the world's first artificial nuclear reactor. Construction finished on December 1, 1942. The structure was a 20-foot-tall, flattened ellipsoid of stacked graphite blocks, built in 57 layers.
The pile contained 45,000 graphite blocks with a total weight of 360 short tons (330 tonnes). Embedded within this graphite moderator were 5.4 short tons (4.9 tonnes) of uranium metal and 45 short tons (41 tonnes) of uranium oxide. The total cost of these materials was approximately $1 million. The ultra-pure, low-boron "AGOT graphite" was supplied by National Carbon Company. The entire assembly was built without radiation shielding or a cooling system, as it was only intended to operate at a very low power.
The 28-Minute Experiment
On December 2, 1942, a group of 49 scientists gathered to witness the experiment. From a balcony overlooking the squash court, Fermi directed physicist George Weil, who was on the floor, to slowly withdraw the cadmium-coated control rods. These rods absorbed neutrons and prevented a chain reaction.
The process was deliberate. Weil moved the final rod mere inches at a time while Fermi monitored the neutron activity with a slide rule. The experiment was paused for lunch after an automatic safety rod slammed back into the pile because its trip level was set too low. The test resumed at 2:00 PM. At 3:25 PM, Fermi announced that the pile had "gone critical," sustaining a nuclear chain reaction. The reaction was allowed to continue for 28 minutes, producing about half a watt of thermal power, before being shut down. To celebrate, physicist Eugene Wigner produced a bottle of Chianti, and the team drank from paper cups. Many of them signed the bottle's straw wrapper as a memento.
The site is now a National Historic Landmark, marked by a 12-foot-tall bronze sculpture by Henry Moore titled "Nuclear Energy," which was unveiled on December 2, 1967.
💡Fun Facts
The experiment's success was relayed in a coded phone call: "The Italian navigator has landed in the new world."
Safety measures were primitive: a man, Norman Hilberry, stood by with an axe to cut a rope attached to an emergency safety rod.
A "liquid control squad" of three graduate students was positioned above the pile with buckets of cadmium salt solution to douse the reactor in case of a runaway reaction.
After the experiment, CP-1 was dismantled in early 1943 and rebuilt with shielding at a more remote site, where it was renamed Chicago Pile-2.
