A momentous step into the atomic age happened around 3:20 p.m. Central War Time on Dec. 2, 1942, seventy-five years ago, in a vast, unheated space (a former squash doubles court) under the abandoned University of Chicago football stands at Stagg Field. A cadmium control rod was pulled out from a huge, painstakingly assembled cube of ultra-pure rods of uranium metal and oxide and 40,000 graphite bricks, prosaically called a “pile.” The whole mass was “canned” in strips of metal soldered together to keep out moisture that would have interfered with the nuclear reactions inside. The rod came out just far enough out to trigger, for the very first time, the harbinger of an immense new force—a controlled, sustained nuclear chain reaction that, in this first test, released less than one watt of energy.
The official history of the U.S. Atomic Energy Commission called the pile “a bizarre structure” with wooden supports that had been completed only the night before by Martin D. Whitaker and Walter H. Zinn of the Metallurgical Laboratory at the university. The cost was estimated at about $1 million. Construction by 12-hour day and night crews had begun Nov. 16 as Chicago slipped into sub-zero winter weather. It contained almost 400 tons of the graphite (arranged to slow down the neutrons emerging from the uranium), six tons of uranium metal, and 50 tons of uranium oxide.
Directing the work of a team of about 20 was the Italian refugee physicist Enrico Fermi, who began ordering the removal of control rods, one by one, around 9:45 a.m. As each rod was pulled out, usually about six inches at a time, Fermi and his associates on the squash court balcony scanned instruments to see whether the chain reaction had begun. Before noon, he sent word to Arthur Compton, head of the Metallurgical Lab, to witness the progress. After the crew finished a pause for lunch, Compton brought along one member of a high-level review committee visiting the lab that day, Crawford H. Greenewalt of DuPont. Finally, around 3:20, the galvanometer recorded the “self-sustaining” reaction.
An eyewitness, Herbert Anderson recalled: “At first, you could hear the sound of the neutron counter, clickety-clack, clickety-clack. Then the clicks came more and more rapidly, and after a while they began to merge into a roar; the counter couldn’t follow any more.” The crew switched over to a chart recorder and fell silent as they watched as the pen kept deflecting upward. “It was an awesome silence,” according to Anderson, as the recorder scale was increased again and again. “Suddenly Fermi raised his hand. ‘The pile has gone critical,’ he announced. No one had any doubt about it.” By then, the neutron intensity was doubling every two minutes. Fermi grinned.
In only four and a half minutes, the level of radioactivity in the room rose to the point where the reaction needed to be shut down again. Longer operations would be delayed until the pile could be shifted to Argonne, well away from the city. But those present knew, in the words of the official history, that “the long quest was over.” A “glow of success” lit up Greenewalt’s face.
In his notable history, The Making of the Atomic Bomb, Richard Rhodes reports Hungarian refugee physicist Eugene Wigner’s reaction, published in 1967: “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.”
Back at his office, Compton placed a long-distance call to Harvard’s President, James B. Conant, the overall scientific boss of the U.S. atomic bomb effort, in Cambridge, MA. In a makeshift code, Compton told Conant, “You’ll be interested to know that the Italian navigator has just landed in the new world.”
This famous experiment, showing that the long-anticipated chain reaction really worked, was not, as the official history of 1962 notes, “an unexpected burst of knowledge which staggered man’s comprehension. It was rather the capstone of a structure which Fermi and others had been patiently building since the first weeks of 1939.” Eugene Wigner had bought the celebratory bottle of Chianti for the occasion almost a year earlier.
Nonetheless, the success opened a possibility that had looked dubious only a short while before. This was the secret creation of an industry of giga-piles (reactors) and giant chemical separation “canyons” to make and purify a recently named element called plutonium. Number 94 in the periodic table and long disappeared from nature, plutonium “was beheld by the eye of man” for the first time on Aug. 20, 1942, according to Glenn Seaborg of Berkeley. It could be used in an atomic bomb (which, it was feared, Germany might achieve first). In the immense nuclear reactors, atoms of uranium 238 would be slightly “fattened” with neutrons, transforming them into atoms of plutonium 239.
This plutonium industry in turn gave the United States a second avenue to an atomic bomb, alongside the feverish parallel enterprise for isolating a rare form of element 92, uranium 235 (which constituted less than 1 percent of the uranium in nature). The latter effort, also part of the U.S. Army’s vaguely code-named Manhattan Engineer District, would take a noxious compound of uranium and fluorine and pump it as a gas through one of three separation processes: magnetic, thermal, or filters. By the summer of 1945, at a total cost around $2 billion in money of the time, the twin industries were cranking out enough to make a few uranium or plutonium bombs a month. “Little Boy,” a uranium bomb, destroyed Hiroshima, and “Fat Man, a plutonium bomb, destroyed Nagasaki.
These momentous achievements were going into high gear only four years after the phenomenon of nuclear fission had been discovered by Otto Hahn and Fritz Strassmann on a tabletop in Berlin, Germany, and interpreted days later at a hotel on the coast of Sweden by the exiled Lise Meitner (Hahn’s former colleague) and her exiled nephew Otto Frisch. And only in the summer of 1941 had the United States belatedly accepted findings from Britain showing that utterly new nuclear explosives could be developed and used in the present cataclysmic war against the Axis dictatorships.
And now, on the same day as Fermi’s successful demonstration, the committee reviewing the technologies of the enormous nuclear effort, headed by the famous MIT chemist Warren K. Lewis, was meeting at the University of Chicago with top industrial engineers from firms like DuPont and Stone and Webster to map what would become the immense plutonium factory at Hanford along the Columbia River, in desert country in the state of Washington.
The work of Fermi and his colleagues on the “pile” under the Stagg Field stands was happening at a turning point in the Second, and far bloodier, World War. In the fall of 1942, less than a year after Pearl Harbor, American soldiers were blocking the Japanese onslaught toward Australia on Guadalcanal, Russian soldiers were surrounding an entire German army at Stalingrad, and American and British troops were pushing both east and west across northern Africa to Tunisia. To be sure, wolf packs of German submarines continued their costly attacks on transatlantic convoys and swarms of German fighters were ripping away at Allied bombers over their homeland. Victory for the western democracies was far from assured, and the products of science looked like the equalizer.
[Editor’s note: This is the fifteenth of a series of notes about major anniversaries in innovation and what they teach us. Earlier notes have highlighted the 1940 memo by two refugee scientists in Britain that energized the drive toward the atomic bomb, and the first U-2 overflights of the Soviet Union in 1956. You’re invited to suggest other Milestones of Innovation for the Xconomy Forum.]
Further reading:
Richard G. Hewlett and Oscar E. Anderson, The New World 1939/1946, Pennsylvania State University Press, 1962.
Richard Rhodes, The Making of the Atomic Bomb, Simon and Schuster, 1986.
