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Enrico Fermi: Atomic Energy, 9147

Atomic Pile

At Columbia, Fermi and his team continued investigations into the feasibility of controlled chain reactions from nuclear fission. Experimentation led them to build an "atomic pile," beginning as a stack of pure graphite brick surrounding a neutron source. This first step enabled the examination of graphite's effect on neutron activity: absorption and re-emission, quantities, fissions. Step two was the addition of uranium to the experiment. The original stack was rebuilt with some of the graphite bricks being seeded with pieces of uranium. Observations on the effect of graphite resumed. Results showed Fermi that a stack larger than the current "pilot" version was needed to produce a measurable nuclear chain reaction, and a search for larger facilities began.

The expansion at Columbia was slowed by the U.S. government's decision to accelerate and centralize atomic research. Fermi's work eventually relocated to the University of Chicago in 1942. Secrecy covered all endeavors at this location, divertingly labeled the Metallurgical Laboratory. The physicists who gathered at the new facility concentrated on fundamental atomic research as an arm of the newly-named Manhattan Project, the first instance of "big science" with the research, materials production, and support personnel consolidated and directed to a single goal.

Now Fermi had the space needed for his enlarged atomic pile. That space—about 200 sq. ft. in area and more than 26 ft. high in the unused squash court under the West Stands of Stagg Field Stadium in the middle of a city of over 3 million people—was destined for lasting fame.

The Fermi group in Chicago built and examined small piles, becoming confident that all parameters to create a pile of the critical size and composition for sustained chain reaction were known. In a period of just six weeks the final pile, standing less 26 feet high and completely encased in an enormous square balloon of rubberized cloth, was built. On December 2, 1942, Fermi managed the historic operation, directing the gradual removal of the control rods and monitoring the consequent increases in radioactivity. As everything went according to plan, Fermi, a creature of habit, declared a break for lunch. Work resumed after lunch and at 3:20 in the afternoon the last control rod had been carefully withdrawn in one-foot increments when Fermi gave the final instruction to remove it completely. All monitoring instruments showed rising radioactivity—the controlled nuclear fission chain reaction had been achieved!

The message reporting success sent by the director, Arthur Compton, to the Office of Scientific research and Development said, "The Italian Navigator has reached the New World." A toast of Chianti was raised in celebration.

Meanwhile the crash program to develop weapons incorporating this achievement had been proceeding. An atomic bomb, with an uncontrolled nuclear explosion, was envisioned.