by Trevor Olsen,
PhD candidate at Polytechnique School of Montreal
Certain events in history are forever remembered as breakthrough advancements in humanity: the first lighting of fire, the first smelting of bronze, or turning on the lightbulb in Edison’s lab. However, few such events are shrouded in as much secrecy as Chicago Pile-1.
In 1938, two scientists immigrate to the United States to avoid wartime tensions in Europe. Italian Nobel laureate Enrico Fermi and Hungarian physicist Leó Szilárd meet at Columbia University in New York City. Together, they went on to produce mankind’s first self-sustaining nuclear reaction.
Szilárd had imagined that if chemical chain reactions were feasible, the same process could apply to nuclear reactions. At the time, not enough was known about nuclear physics to test his theory. There weren’t any known reactions that would enable a self-sustaining process. Many scientists, Fermi included, thought that nuclear fission was mathematically impossible. It wasn’t until January 1939 that scientists had experimentally found evidence for the fission reaction. With that discovery, things moved quickly. Szilárd knew the implications on the line; those who could control a nuclear chain reaction would be capable of producing a nuclear weapon.
After hearing the news, Szilárd wanted to test his theory with the help of Fermi, but he was unable to convince him. Instead, he took to the lab with another colleague and was able to show the reaction generated more neutrons than it required. The chain reaction was possible. This time, with the help of Fermi, the experiment was attempted on a much larger scale. The results were undeniable. Szilárd presented his work to Einstein and had him sign a letter to be given to President Roosevelt. This letter warned that “[the] new phenomenon would also lead to the construction of bombs” and that Germany was conducting these experiments in parallel. Roosevelt’s response was the creation of an “Advisory Committee on Uranium”.
The committee did little more than assisting Szilárd and other researchers in obtaining uranium and graphite necessary for the experiments. Szilárd and Einstein sent more letters urging the development of nuclear research programs. Without action, the German regime may be able to produce nuclear weapons and win the war. Then on one fateful day, December 7, 1941, the United States is drawn into World War II through the bombing of Pearl Harbor. Finally, as the need to compete with German scientists arises, the Manhattan Project was set in motion.
Szilárd and Fermi were ordered to move to the University of Chicago and carry on their research in controlling the nuclear fission chain reaction. In their previous experiments, Szilárd and Fermi were able to conclusively show a chain reaction is possible, but they had never achieved “criticality”. Doing so wouldn’t be an easy task. Nothing like this had been attempted before. The question at hand was, “How can we control fission reactions to have neutron multiplication remain controlled; k = 1.000?”
In spring of 1942, they set to work in an underground lab, shrouded in secrecy, located beneath the university’s Stagg Fields spectator stands. Suppliers and builders were told nothing of what was happening. Fermi acquired extremely large amounts of high-quality graphite and uranium bricks, fabricated specifically for this project. The impurities found in standard grade graphite would have ruined the experiment. After slowly building up the pile of uranium, graphite, and a few cadmium “control rods” (consisting of sheet metal nailed to wooden planks), Fermi’s calculations suggested the ad hoc “reactor” would work.
Finally, at 9:45 on December 2nd of that year, a team of scientists working on the project met in the lab to see if they had done it. Tension mounted as the control rods were slowly withdrawn. The sensors used to measure the reactivity were steadily climbing. At last, their makeshift reactor of concrete, wood, and metal had reached criticality, k = 1.00, and with it came the crowning achievement of mankind harnessing the power of nuclear energy. After a moment, the reactor was shut down and they opened a bottle of champagne to celebrate their success and signed the label. The atomic age had begun.
University of Illinois Press, Argonne National Laboratory, 1946-96; Jack M. Holl, Richard G. Hewlett, Ruth R. Harris.
US Office of Science and Information, The Manhatan Project - An Interactive History. https://www.osti.gov/opennet/manhattan-project-history/index.htm
Argonne National Lab. Early Exploration (CP-!); http://www.nc.anl.gov/About/ractors/early-reactors.shtml