Arthur Compton put the first nuclear reactor in an abandoned squash court under Stagg Field’s football stands because the site he had actually planned for it, west of Chicago, ran into construction delays. Rather than wait, he moved the project to the University of Chicago court where his team’s earlier experiments had already been running.
more
That put an untested chain reaction in a city of more than three million people, with no shielding and no way to cool the pile if it ran away. Compton later said he never told the university’s president, Robert Maynard Hutchins, what his team was building under the stands, and Chicago’s mayor was not told either.
Why the work landed at Chicago
The Manhattan Project needed one place to settle whether a controlled chain reaction was possible at all, before it could try to build a weapon from one. The urgency traced back to late 1938, when chemists Otto Hahn and Fritz Strassmann, working with the physicist Lise Meitner, found that bombarding uranium with neutrons could split its nucleus. By August 1939, Albert Einstein and Leo Szilard had written to President Franklin Roosevelt, warning that Nazi Germany might already have the tools to build a weapon from that discovery. The University of Chicago got the job under the deliberately bland code name Metallurgical Laboratory, because the city already held a strong community of physicists and chemists, sat far from both coasts, and had space and housing ready.
Arthur Holly Compton, a Nobel laureate and dean of the university’s physical sciences, led the effort. His recruits included Enrico Fermi, Szilard, and Eugene Wigner, plus one woman, Leona Woods Marshall Libby, who was also the youngest scientist on the team. Hundreds more joined to “help the war effort”, most of them told little about the work.
What the crew built
Chicago Pile-1, nicknamed CP-1, was a roughly 20-foot stack of graphite blocks studded with hundreds of smaller blocks of uranium. One tally of the ingredients, reported separately, put the load at about 360 tonnes of graphite and 45 tonnes of uranium oxide. Crews worked around the clock for two weeks, purifying the graphite and uranium, stacking 57 precise layers, and boring holes for cadmium control rods that could soak up stray neutrons and hold the reaction in check. They finished on the evening of December 1, 1942.
The physics was straightforward to state and difficult to build: a uranium atom throws off neutrons as it decays, and arranging enough uranium in the right geometry lets those neutrons split further atoms, which throw off more neutrons in turn. Get the spacing and purity right, and the reaction sustains itself. The cadmium rods existed to stop that from happening until the team was ready.
The lunch break in the middle of history
On December 2, 1942, 49 scientists gathered to run the criticality test. Fermi had George Weil ease the last control rod out foot by foot while he tracked the neutron count against predictions he worked out on a slide rule. By late morning the trend was unmistakable, and Fermi sent the entire team to lunch anyway. Nobody discussed the experiment at the table, according to Cindy Kelly of the Atomic Heritage Foundation, even though it was all anyone was thinking about.
When the crew returned, Weil pulled the rod out another notch, and at 3:53pm the pile went critical: a self-sustaining chain reaction, the first one anybody had ever built. Fermi later described the moment as unspectacular. No fuses burned, no lights flashed. Compton phoned James Conant at the National Defense Research Committee in coded language: “The Italian navigator has just landed in the new world,” he said, meaning Fermi’s experiment had worked. “Everyone landed safe and happy,” he added, when Conant asked whether the natives were friendly.
Eugene Wigner had brought a bottle of Chianti for the occasion, and the scientists present drank it from paper cups. Fermi’s own account of the danger was calmer than the setting deserved: he had told Compton beforehand that a catastrophic failure was unlikely, though the outcome was never certain going in.
Why a football team’s old court, of all places
Part of the answer is mundane. The university’s football programme had shut down in 1939, so the Stagg Field stands and the disused court beneath them sat empty, and the former players who once used the facility had time on their hands to help assemble the pile.
The secrecy held. Even the mayor went unnotified, on the reasoning, as Kelly put it, that officials outside the project “wouldn’t have understood if they’d told him.”
What the pile proved, and what came after
CP-1 answered the one question the Manhattan Project needed answered before it could go further: a chain reaction could be started, controlled, and stopped. That cleared the way for a bigger version, the X-10 Graphite Reactor at Oak Ridge, built a few months later and used as the model for the plutonium-producing reactors at Hanford, Washington.
CP-1 itself did not last where it was built. Workers dismantled it and moved it to a forest preserve outside the city, where it was rebuilt with the shielding the original had lacked. The Metallurgical Laboratory itself outlived the war, reorganised afterward into Argonne National Laboratory, the country’s first national laboratory, to study peaceful uses for the atomic energy the team under Stagg Field had first coaxed into being.
The site of the original squash court has carried National Historic Landmark status since 1967, marking the spot under the football stands where the team first proved a chain reaction could be built and stopped on command.
