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J.R. Oppenheimer and General Groves
Events People Places Processes Science Resources

Time Periods

1890s-1939:
Atomic Discoveries

1939-1942:
Early
Government Support

1942:
Difficult
Choices

1942-1944:
The Uranium
Path to
the Bomb

1942-1944:
The Plutonium
Path to
the Bomb

1942-1945:
Bringing It All Together

1945:
Dawn of the
Atomic Era

1945-present:
Postscript --
The Nuclear Age


Cubes of uranium metal, Los Alamos, 1945MORE URANIUM RESEARCH
(1942)
Events > Difficult Choices, 1942

During the first half of 1942, several routes to a bomb via uranium continued to be explored. At Columbia University, Harold Urey worked on the gaseous diffusion and centrifuge systems for isotope separation in the codenamed SAM (Substitute or Special Alloy Metals) Laboratory. At Berkeley, Ernest Lawrence continued his investigations on electromagnetic separation using the "calutron" he had converted from his thirty-seven-inch cyclotron. Phillip Abelson, who had moved from the Carnegie Institution and the National Bureau of Standards to the Naval Research Laboratory, continued his work on liquid thermal diffusion but with few positive results, and he had lost all contact with the S-1 Section of the Office of Scientific Research and Development.   Meanwhile Eger Murphree’s group hurriedly studied ways to move from laboratory experiments to production facilities.

Manhattan Project facilitiesResearch on uranium required uranium ore, and obtaining sufficient supplies was the responsibility of Murphree and his group.  Fortunately, enough ore was on hand to meet the projected need of 150 tons through mid-1944.  Twelve hundred tons of high-grade ore were stored on Staten Island, and Murphree made arrangements to obtain additional supplies from Canada and the Colorado Plateau, the only American source.  Uranium in the form of hexafluoride was also needed as feed material for the centrifuge and the gaseous and thermal diffusion processes. Abelson was producing small quantities, and Murphree made arrangements with E. I. du Pont de Nemours and Company and the Harshaw Chemical Company of Cleveland to produce hexafluoride on a scale sufficient to keep the vital isotope separation research going.

60-inch cyclotron at Berkeley's Rad Lab. Ernest Lawrence is second from the left, and Edwin McMillan is on the cyclotron to the right.Lawrence was so successful in producing enriched samples of uranium-235 electromagnetically with his converted cyclotron that Vannevar Bush sent a special progress report to President Roosevelt on March 9, 1942.  Bush told the President that Lawrence's work might lead to a short cut to the bomb, especially in light of new calculations indicating that the critical mass required might well be smaller than previously predicted.  Bush also emphasized that the efficiency of the weapon would probably be greater than earlier estimated and expressed more confidence that it could be detonated successfully.  Bush thought that if matters were expedited a bomb was possible in 1944.  Two days later the President responded: "I think the whole thing should be pushed not only in regard to development, but also with due regard to time.  This is very much of the essence."  

Columbia UniversityIn contrast, the centrifuge and gaseous diffusion work at Columbia was confronting serious engineering difficulties.  The production of adequate centrifuges was proving to be a very difficult task, and it looked like it might take tens of thousands of centrifuges to produce enough uranium-235 to be of value.  Building an effective, corrosion-proof barrier for gaseous diffusion systems was even more problematic.  Both separation methods demanded the design and construction of new technologies and required that parts, many of them never before produced, be finished to tolerances not previously imposed on American industry.

Despite the difficulties encountered with the centrifuge and gaseous diffusion methods, and even with Lawrence's successes at Berkeley, no clear-cut victor had yet emerged. The question of which method of uranium enrichment would prove most effective remained wide open.

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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), 10-11, 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), 168-69. President Franklin Roosevelt's reply to Vannevar Bush is cited in Hewlett and Anderson, Jr., The New World, 1939-1946, 406. The photograph of the blocks of uranium is courtesy Los Alamos National Laboratory; it is reprinted in Rachel Fermi and Esther Samra, Picturing the Bomb: Photographs from the Secret World of the Manhattan Project (New York: Harry N. Abrams, Inc., Publishers, 1995), 99.  The map of Manhattan Project facilities in North America is reproduced from Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 463.  The photograph of Ernest Lawrence (and others) in front of a cyclotron is courtesy the Lawrence Berkeley National Laboratory.  The photograph of Columbia University is courtesy the Library of Congress; it originated from the Detroit Publishing Company, and it was a 1949 gift to the Library of Congress from the State Historical Society of Colorado.

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