Seventy-five years ago the brightest minds in the world came to the University of Chicago to embark on the greatest scientific experiment of the century.
As the Western world anxiously watched Hitler’s rise, Prof. Arthur Holly Compton, a Nobel laureate and dean of the physical sciences, recruited physicists, chemists and engineers including Enrico Fermi, Leo Szilard and Eugene Wigner to work on a secret government project in a squash racquets court under the west stands of Stagg Field.
Their goal: Conduct the first, self-sustaining nuclear chain reaction, providing the experimental basis for development of a powerful weapon. And do it before the Germans, who were working to pioneer a similar breakthrough. “Our project became to us more vital than life or death,” Compton later wrote.
Scholars discuss the ‘monumental physics achievement’ of the first controlled, self-sustaining nuclear chain reaction and the immense wartime pressures facing UChicago scientists.
Video by UChicago Creative
Beginning in October 1942, members of the classified Metallurgical Laboratory project worked as many as 90 hours a week, often smoking cigarettes in place of eating. UChicago students as well as local laborers worked side by side with the scientists to build a lattice of graphite bricks and uranium into a 20-foot-tall, beehive-shaped structure known as Chicago Pile-1—hoping it would create a chain reaction that would grow from the splitting of a single uranium nucleus.
Graduate student Albert Wattenberg, PhD’47, recalled one morning when physicist Alvin Graves came into work unexpectedly, complaining he couldn’t sleep. “He felt the Nazis were working, that they were pushing ahead to get there before us,” Wattenberg wrote in 1982 in the Bulletin of the Atomic Scientists. “We were in a real race, and he felt he shouldn’t be taking a day off.”
As UChicago spends the fall commemorating the Dec. 2, 1942 breakthrough, a look back at the months leading up to the experiment recalls the intense pressures and pioneering science that produced the first nuclear chain reaction.
In early 1942, President Robert Maynard Hutchins told the Board of Trustees: ‘This war will be won in the laboratories,’ adding that ‘research designed to win the war is our first scientific obligation.’ During World War II the military often held drills at Stagg Field, but the secret nuclear pile project beneath the West Stands was well hidden from view.
Photo courtesy of the University of Chicago's Special Collections Research Center
The Plan B decision to build at UChicago
The University wasn’t the original site for the historic experiment though. In early 1942, Compton identified a promising plot of land while on a horseback ride in a forest preserve about 25 miles southwest of Chicago. But by late October, workers constructing the buildings in the so-called Argonne Forest went on strike, and it soon became clear that the site wouldn’t be ready until year’s end.
Fermi suggested to Compton that he could demonstrate the controlled chain reaction safely on campus—under Stagg Field, the long-abandoned, crumbling home of the former Big Ten football powerhouse. And if something were to go wrong, “I will walk away—leisurely,” Fermi once wrote. As a safeguard, a series of control rods would be installed to prevent a runaway reaction.
“Based on considerations of the University’s welfare, the only answer he could have given would have been—no.”
—Prof. Arthur Holly Compton, on whether to inform President Robert Hutchins about building under Stagg Field
“According to Fermi’s calculations, which I carefully checked…it should take some minutes for the reaction to double its power," Compton wrote in his memoir. “If this proved correct, there would be ample time for adjustments, and the reaction would be under full control.”
Compton at the outset had predicted a nuclear chain reaction would be achieved by Jan. 1, 1943. With time of the essence, Compton told Fermi to proceed without informing UChicago President Robert Maynard Hutchins. Compton felt Hutchins, a trained jurist and former Law School dean, “was in no position to make an independent judgment of the hazards involved.”
“As a responsible officer of the University, according to every rule of organizational protocol, I should have taken the matter to my superior. But that would have been unfair,” wrote Compton. “Based on considerations of the University’s welfare, the only answer he could have given would have been—no. And this answer would have been wrong. So I assumed the responsibility myself.”
Chicago Pile-1 was built in a squash racquets court under Stagg Field, which once was home to a Big Ten powerhouse. President Hutchins eliminated the football program in 1939, calling it an ‘infernal nuisance’ that detracted from academics.
Photo courtesy of the University of Chicago's Special Collections Research Center
Path to criticality
The self-assured Fermi gave Compton little cause for concern. In September, Fermi began a series of multi-hour weekly lectures at Eckhart Hall on the UChicago campus, where he described the measurements that would determine when the pile would go critical.
When he started building chain-reacting piles at Columbia University after his arrival in January 1939, Fermi would don a lab coat and worked alongside football players enlisted to move the 50- to 100-pound bricks of graphite. “With Fermi, it was the work that made the physics worthwhile. He wanted to wrestle with nature himself, with his own hands,” wrote physicist Herbert Anderson, who ran the night shift in Chicago’s pile program, in a 1974 Bulletin essay. “He liked to have someone to work with. He liked the companionship; the work went faster that way.”
This artist's conception shows the UChicago students, scientists and day laborers working on Chicago Pile-1.
Photo courtesy of National Archives and Records Administration
There were no blueprints for the Chicago pile. Instead, machinists and scientists reported on the daily progress of construction to Fermi. Two crews formed: One pressed uranium oxide power into 22,000 spheres the size of baseballs. The other used a wood planer to mill about 400 tons of graphite into rectangles, which were then drilled to create holes to hold the uranium.
“We found out how coal miners feel,” wrote Wattenberg in the Bulletin. “One shower would remove only the surface graphite dust. About a half-hour after the first shower, the dust in the pores of your skin would start oozing.”
By late fall, dozens of smaller test piles had provided proof-of-concept for Fermi’s larger experiment. But CP-1, 20 times larger than its predecessors, would require even larger amounts of uranium and graphite in purer forms.
On Nov. 16, two 12-hour shifts began to construct the pile—work that would continue non-stop over the next 15 days. By the evening of Dec. 1, they had constructed the reactor, which resembled a 57-layer graphite cake, wrapped in wood and studded with hundreds of uranium raisins toward the center that would serve as the nuclear fuel for the reaction.
By the morning of Dec. 2, Chicago Pile-1 was ready.
Photograph taken in November 1942 during construction of the first nuclear reactor. Chicago Pile-1 consisted of 57 layers cost an estimated $2.7 million and contained 380 tons of graphite, 40 tons of uranium oxide and six tons of uranium metal.
Photo courtesy of Argonne National Laboratory
Unlocking a giant
Nearly a year of hard work culminated on a cold, snowy Wednesday, when at 3:25 p.m. on Dec. 2, the feverish clickety-clack of Geiger counters proved to the 49 people huddled inside the balcony of the squash racquets courts that they had sustained and controlled a nuclear chain reaction for the first time in history.
Although at full strength it produced only enough energy to power a lightbulb, the discovery marked the dawn of the Atomic Age—forever changing the world. “The event was not spectacular: No fuses burned, no lights flashed,” Fermi later conceded. But the UChicago scientists had succeeded, beating Compton’s original prediction by nearly a month.
Scientists huddle inside the crowded balcony of a squash racquets court under Stagg Field to witness the first chain reaction, which occurred at 3:25 p.m. Dec. 2, 1942.
Illustration by John Cadel/courtesy of the Chicago History Museum
To mark the occasion, scientist Eugene Wigner presented Fermi with a small bottle of Chianti wine. “No toast, nothing, and everyone had a few memorable sips,” wrote Leona Woods, a 23-year-old UChicago graduate student, in her memoir.
“There was a greater drama in the silence than if the words had been spoken. Everyone was thinking—if we did it, haven’t the Germans already achieved the chain reaction?”
“[W]e had known that we were about to unlock a giant; still, we could not escape an eerie feeling when we knew we had actually done it.”
—Eugene Wigner, CP-1 scientist
For Wigner, one of the lead scientists on the project who would later win a Nobel in physics, the experiment was the culmination of years of scientific work, which began when he and fellow Hungarian physicist Szilard convinced Albert Einstein to sign a letter to President Roosevelt in 1939, urging the United States to fund nuclear research before the Nazis developed a bomb.
“For some time, we had known that we were about to unlock a giant; still, we could not escape an eerie feeling when we knew we had actually done it,” Wigner wrote in The New York Times Magazine in 1963. “We felt as, I presume, everyone feels who had done something he knows will have very far-reaching consequences which he cannot foresee.”
President Robert Maynard Hutchins (right) with Enrico Fermi (immediate right) and Met Lab scientists in 1947, the fifth anniversary of the first nuclear chain reaction.
Photo courtesy of the University of Chicago's Special Collections Research Center
—UChicago doctoral candidate Gregory Montoya-Mora contributed archival research to this report.
