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
the codenamed SAM (Substitute or Special Alloy Metals) Laboratory. At
Berkeley, Ernest Lawrence
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
Laboratory, continued his work on liquid
thermal diffusion but with few positive results, and he had
contact with the S-1 Section of
the Office of Scientific Research and
Development. Meanwhile Eger Murphree’s group hurriedly studied
move from laboratory experiments to production facilities.
Research 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
Cleveland to produce hexafluoride on a scale sufficient to keep the
vital isotope separation research going.
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
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
expressed more confidence that it could be detonated
thought that if matters were expedited a bomb was possible in
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."
contrast, the centrifuge and gaseous diffusion work at Columbia was
confronting serious engineering difficulties. The production of
centrifuges was proving to be a very difficult task, and it looked like
take tens of thousands of centrifuges to produce enough uranium-235 to
value. Building an effective, corrosion-proof barrier for gaseous
diffusion systems was even more problematic. Both separation
demanded the design and construction of new technologies and required
parts, many of them never before produced, be finished to tolerances
not previously imposed on American industry.
Despite the difficulties encountered with the centrifuge
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
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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