Building the Bomb: Vanderbilt Physicists Played a Key Role in Developing the First Nuclear Weapons

By GayNelle Doll
“Fat Man,” the second atomic bomb developed by Manhattan Project physicists, is dropped on Nagasaki, Japan, on Aug. 9, 1945, prompting the end of World War II. (LIBRARY OF CONGRESS ARCHIVES)
“Fat Man,” the second atomic bomb developed by Manhattan Project physicists, is dropped on Nagasaki, Japan, on Aug. 9, 1945, prompting the end of World War II. (LIBRARY OF CONGRESS ARCHIVES)


Fat Man. Little Boy. Los Alamos. Robert Oppenheimer. Enrico Fermi. Oak Ridge.

Most Americans, if asked for words they associate with the atomic bomb and nuclear energy, could more readily recite these names and places than those of Francis Slack, Ernest Jones, Newton Underwood—or Vanderbilt University.

In part because much of their work remains classified even after 70 years, the contributions of a group of young Vanderbilt physicists to the Manhattan Project have never received the level of recognition they deserve.

The story of Vanderbilt’s role in the U.S.-led research and development project that produced the first nuclear weapons begins with Francis Slack. A Columbia University-trained theoretical physicist, Slack joined the Vanderbilt faculty in 1928. Vanderbilt, the fifth university in the country to offer graduate degrees in physics, already enjoyed a tradition of training top physicists; its first chancellor, Landon Garland, was chair of physics for 20 years.

After a decade at Vanderbilt, Francis Slack embarked on an unpaid sabbatical, envisioning a year of visiting other universities, reconnecting with Columbia colleagues and touring Europe. Slack arrived in New York City during the winter of 1938–39 just as news reached Columbia physicists that German scientists Otto Hahn and Fritz Strassmann had succeeded in splitting uranium atoms.
Nuclear fission made the development of an atomic bomb possible, at least theoretically. Uranium offered a potential source of bombs with an unprecedented ability to destroy.

At Columbia, which had the country’s largest physics department, a group led by John R. Dunning was working on a process to enrich uranium for use in high-energy weapons. Slack found himself in the right place at precisely the right moment. On Jan. 25, 1939, he was part of a small team of physicists—which included Fermi, who had won the Nobel Prize a year earlier for his work in nuclear physics—to conduct the first U.S. experiment demonstrating the separation of uranium atoms using nuclear fission.

News coming out of Germany that spring grew ever more ominous, and with it fear that the Nazis would develop a nuclear bomb. Slack and his wife, Belle, nevertheless proceeded with plans to visit Europe.

“From Munich [the Slacks] went to Göttingen, where all was in disarray, because the National Socialists had taken over both physics institutes, and then to Berlin, where Francis met several scientists, including Otto Hahn,” wrote Robert T. Lagemann, who taught at Vanderbilt from 1951 to 1977, in his history of Vanderbilt’s Department of Physics, To Quarks and Quasars.

Talking to professional acquaintances in Germany about developments in nuclear research—conversations that usually took place on long streetcar rides to avoid being overheard—Slack determined that they were unaware of the head start that Danish physicist Niels Bohr had made, and that he was sharing his work with American scientists.

Back in the U.S. later that year, Slack again visited Columbia before returning to Vanderbilt for the start of fall classes. That same semester he was named department chair and the Landon C. Garland Professor of Physics.

The spread of war, meanwhile, heightened the American government’s sense of urgency about nuclear defense, and efforts accelerated at research facilities across the country. Researchers needed more help quickly, and they looked to known entities they could trust. Columbia physicists tasked with developing the barrier used to separate the U235 and U238 isotopes entreated Slack to join them.

In the spring of 1941, as soon as classes ended, Slack went to New York. He and Vanderbilt physicist Newton Underwood were among the dozen senior scientists to join what is now known as the Manhattan Project, which was responsible for developing nuclear fuel. (The actual bombs were being developed in Los Alamos, New Mexico.) Slack was 43 years old, Underwood 34.

To aid them in the Special Alloys Material (SAM) project—one part of the larger effort—they recruited Vanderbilt physicists Ernest A. Jones, age 22, with a freshly minted master’s in physics; Lagemann, age 28; William C. Skinner, age 20; Clifford K. Beck, age 27; Edward B. Nelson, age 24; and Elizabeth Briggs Johnson, age 23.

Slack assumed chief responsibility for development of the barrier used to separate uranium isotopes and finding ways to test it with inert gases to avoid causing any catastrophic reactions. Lagemann was put in charge of measuring the quality of the separation barrier made by other groups. Jones wrote the first paper describing technical details of the separation barrier; today it still remains among the most highly classified files at the Oak Ridge National Laboratory in East Tennessee.

Ultimately, this separation barrier made possible the enormous uranium separator plants in Oak Ridge, staffed by 75,000 Manhattan Project workers, that were integral in developing the atomic weapons used in the bombings of Hiroshima and Nagasaki, which led to the end of World War II.

When Slack returned to Vanderbilt near the end of the war, he faced a department depleted by the country’s increased demand for physicists. He worked to rebuild the department and remained at Vanderbilt until 1951.

Underwood went on to invent a radically new method of separating uranium isotopes that improved quality and cost less. He left Vanderbilt for North Carolina State University in 1950.
Lagemann became chair of Vanderbilt’s Department of Physics in 1951 and later served as dean of the Graduate School.

Jones received his doctorate from Ohio State University in 1948 and worked for two years at Oak Ridge National Laboratory before joining the Vanderbilt faculty, where he was to remain for 37 years.

“He can undoubtedly point to more physics majors who were led into their field through his own personal efforts than anyone in the Southeast,” noted Landon C. Garland Professor of Physics Joseph H. Hamilton in a letter nominating Jones for the 1977 George B. Pegram Award for Excellence in Physics Education in the Southeast.

Jones was 97 when he died Dec. 19, 2015, the last of an elite group of brilliant young Vanderbilt physicists who secured a place in history.

“Perhaps more than any other group in the project, those who have worked on gaseous diffusion deserve credit for courage and persistence as well as scientific and technical ability,” Jones noted in a contribution to Lagemann’s book. “For security reasons, we have not been able to tell how they solved their problems.”

GayNelle Doll, a native Iowan, is former editor of Vanderbilt Magazine. She retired in 2015 and lives in Nashville.