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National Museum of Nuclear Science & History

Columbia University

Important Manhattan Project research was conducted at Columbia University’s Schermerhorn Hall (pictured) and Pupin Hall. World-class physicists, including Nobel Prize winners Isidor I. Rabi and Enrico Fermi, joined Columbia’s research team to investigate the relatively new science of atomic particles. Hungarian physicist Leo Szilard first realized the possibility of a nuclear chain reaction in 1933, and against the backdrop of escalating hostilities in Europe, the race began to harness the enormous energy within the atom.

The basement laboratory of Pupin Hall became home to a cyclotron, a type of particle accelerator first invented in the early 1930s by Ernest O. Lawrence of the University of California. Known as “atom smashers,” cyclotrons accelerate atoms through a vaccuum and use electromagnets to induce collisions at speeds up to 25,000 miles per second. The results of such experiments provided valuable clues about the behavior of atoms. The cyclotron in Pupin Hall’s basement was built by Dr. John R. Dunning, an associate professor of physics, and Dr. George Pegram.

In January 1939, Columbia’s cyclotron made history. Physicists in the United States had just received word that German scientists Otto Hahn and Fritz Strassmann had bombarded uranium atoms with neutrons and observed that the uranium seemed to split into atoms of smaller elements. They shared their results with Austrian physicists Otto Frisch and Lise Meitner, who termed the phenomenon “nuclear fission.”

Fermi, Dunning, and Mitchell converse in front of the Columbia CyclotronColumbia physicists rushed to replicate the experiment using the cyclotron in Pupin Hall. A team of scientists including Dunning, Herbert Anderson, Eugene Booth, and Francis Slack were the first Americans to split the uranium atom and demonstrate the enormous release of energy that resulted. Fermi helped to plan the experiment, but was in Washington, DC, for a physics conference. On the night of January 25, 1939 Dunning recorded the monumental event in his diary: “Believe we have observed new phenomenon of far-reaching consequences.” The work at Columbia confirmed “nuclear fission” and provided further evidence for the possibility of creating a nuclear chain reaction.

The following year, Columbia scientists first proved that the fissionable material in uranium that released energy when bombarded with neutrons was the isotope uranium-235. However, uranium-235 is a rare isotope, comprising about 0.7 percent of naturally-occurring uranium ore. Uranium-235 isotopes needed to be separated from the more prevalent uranium-238 isotopes and concentrated to about 90 percent for use in a nuclear weapon.

A scientific team at Columbia, including Dunning and chemist Harold Urey, invented and perfected the “gaseous diffusion” method of separating uranium isotopes. During the Manhattan Project, a gaseous diffusion plant known as K-25 was built and operated at Oak Ridge, Tennessee. Until recent years, gaseous diffusion was the primary method used to obtain uranium-235. The Columbia cyclotron was used for experiments until 1965.

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