Editing Manhattan Project (section)

==== Centrifuges ====
The centrifuge process was regarded as the only promising separation method in April 1942.<ref>{{harvnb|Hewlett|Anderson|1962|pp=22–23}}.</ref> [[Jesse Beams]] had developed such a process in the 1930s, but had encountered technical difficulties. In 1941 he began working with [[uranium hexafluoride]], the only known gaseous compound of uranium, and was able to separate uranium-235. At Columbia, [[Karl P. Cohen]] produced a body of mathematical theory making it possible to design a centrifugal separation unit, which Westinghouse undertook to construct.<ref>{{harvnb|Hewlett|Anderson|1962|p=30}}.</ref>

Scaling this up to a production plant presented a formidable technical challenge. Urey and Cohen estimated that producing a kilogram (2.2&nbsp;lb) of uranium-235 per day would require up to 50,000 centrifuges with {{convert|1|m|adj=on|sp=us}} rotors, or 10,000 centrifuges with {{convert|4|m|adj=on|sp=us}} rotors, assuming that 4-meter rotors could be built. The prospect of keeping so many rotors operating continuously at high speed appeared daunting,<ref>{{harvnb|Hewlett|Anderson|1962|p=64}}.</ref> and when Beams ran his experimental apparatus, he obtained only 60% of the predicted yield, indicating that more centrifuges were required. Beams, Urey and Cohen then began work on a series of improvements which promised to increase efficiency. However, frequent failures of motors, shafts and bearings at high speeds delayed work on the pilot plant.<ref>{{harvnb|Hewlett|Anderson|1962|pp=96–97}}.</ref>

In November 1942 the centrifuge process was abandoned by the Military Policy Committee.<ref>{{harvnb|Nichols|1987|p=64}}.</ref> Successful gas centrifuges of the [[Zippe-type centrifuge|Zippe-type]] design were instead developed in the Soviet Union after the war. It eventually became the preferred method of uranium isotope separation, being far more economical.<ref>{{harvnb|Kemp|2012|pp=281–287, 291–297}}.</ref>