MORE 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.
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 of Cleveland to produce
hexafluoride on a scale sufficient to keep the vital isotope separation
research going.
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."
In
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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