Manhattan Project: Early Uranium Research, 1939-1941

EARLY URANIUM RESEARCH
(1939-1941)
Events > Early Government Support, 1939-1942

President Franklin D. Roosevelt responded to the call for government support of uranium research quickly but cautiously. He appointed Lyman J. Briggs, director of the National Bureau of Standards, head of the Advisory Committee on Uranium, which met for the first time on October 21, 1939. The committee, including both civilian and military representation, was to coordinate its activities with Alexander Sachs and look into the current state of research on uranium to recommend an appropriate role for the federal government. In early 1940, only months after the outbreak of war in Europe, the Uranium Committee recommended that the government fund limited research on isotope separation as well as Enrico Fermi's and Leo Szilard's work on fission chain reactions at Columbia University (below).

Scientists had concluded that enriched samples of uranium-235 were necessary for further research and that the isotope might serve as a fuel source for an explosive device. Finding the most effective method of isotope separation thus was a high priority. Since uranium-235 and uranium-238 were chemically identical, they could not be separated by chemical means. And with their masses differing by less than one percent, separation by physical means would be extremely difficult and expensive. Nonetheless, scientists pressed forward on several complicated techniques of physical separation, all based on the small difference in atomic weight between the uranium isotopes.

Many scientists initially thought the best hope for isotope separation was the high-speed centrifuge, a device based on the same principle as the cream separator. Centrifugal force in a cylinder spinning rapidly on its vertical axis would separate a gaseous mixture of two isotopes since the lighter isotope would be less affected by the action and could be drawn off at the center and top of the cylinder. A cascade system composed of hundreds, perhaps thousands, of centrifuges could produce a rich mixture. Centrifuge research, being pursued primarily by Jesse W. Beams at the University of Virginia and Harold Urey at Columbia University, received much of the early isotope separation funding.

Another possible method of separating the uranium isotopes was gaseous diffusion. Based on the well-known principle that molecules of a lighter isotope would pass through a porous barrier more readily than molecules of a heavier one, this approach proposed to produce by myriad repetitions a gas increasingly rich in uranium-235 as the heavier uranium-238 was separated out in a system of cascades. Theoretically, this process could achieve high concentrations of uranium-235 but would be extremely costly. British researchers led the way on gaseous diffusion, with John R. Dunning, Urey, and their colleagues at Columbia University joining the effort in late 1940.

Of several other separation methods that scientists considered in the spring and summer of 1940, liquid thermal diffusion was the most significant. This process was being investigated by the Carnegie Institution's Philip Abelson, working at the National Bureau of Standards where the facilities were better. Into the space between two concentric vertical pipes, Abelson placed pressurized liquid uranium hexafluoride. With the outer wall cooled by a circulating water jacket and the inner heated by high-pressure steam, the lighter isotope tended to concentrate near the hot wall and the heavier near the cold. Convection would in time carry the lighter isotope to the top of the column.

In June 1940, the President transferred the Uranium Committee to the newly-created National Defense Research Committee (NDRC). Roosevelt appointed Vannevar Bush (right), president of the Carnegie Foundaton, to head the NDRC. Bush reorganized the Uranium Committee into a scientific body and eliminated military membership. Not dependent on the military for funds, as the Uranium Committee had been, the NDRC would have more influence and more direct access to money for nuclear research. In the interest of security, Bush barred foreign-born scientists from committee membership and blocked the further publication of articles on uranium research. Retaining programmatic responsibilities for uranium research in the new organizational setup, the Uranium Committee recommended that all four isotope separation methods and the chain reaction work continue to receive funding for the remainder of 1940. Bush approved the plan and allocated the funds. All possible paths to the bomb would continue to be pursued until the best route was found.

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Sources and notes for this page.

The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources, publications: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 5-7, and Richard G. Hewlett and Oscar E. Anderson, Jr., The New World, 1939-1946: Volume I, A History of the United States Atomic Energy Commission (Washington: U.S. Atomic Energy Commission, 1972), 29-32. Click here for information on the photograph of Ernest Lawrence, Arthur Compton, Vannevar Bush, and James Conant. The photograph of Columbia University ca. 1903 is courtesy the Library of Congress; it originated from the Detroit Publishing Company and was a 1949 gift to the Library of Congress from the State Historical Society of Colorado. The photograph of Vannevar Bush and Arthur Compton is courtesy the Lawrence Berkeley National Laboratory.

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