<P> The September 1944 Hyde Park Agreement extended both commercial and military cooperation into the post-war period . The Quebec Agreement specified that nuclear weapons would not be used against another country without mutual consent . On 4 July 1945, Wilson agreed that the use of nuclear weapons against Japan would be recorded as a decision of the Combined Policy Committee . </P> <P> Tube Alloys made its greatest advances in gaseous diffusion technology, and Chadwick had originally hoped that the pilot plant at least would be built in Britain . Gaseous diffusion technology was devised by Simon and three expatriates, Nicholas Kurti from Hungary, Heinrich Kuhn from Germany, and Henry Arms from the United States, at the Clarendon Laboratory in 1940 . The prototype gaseous diffusion equipment, two two - stage models and two ten - stage models, was manufactured by Metropolitan - Vickers at a cost of £ 150,000 for the four units . Two single - stage machines were later added . Delays in delivery meant that experiments with the single - stage machine did not commence until June 1943, and with the two - stage machine until August 1943 . The two ten - stage machines were delivered in August and November 1943, but by this time the research programme they had been built for had been overtaken by events . </P> <P> The Quebec Agreement allowed Simon and Peierls to meet with representatives of Kellex, who were designing and building the American gaseous diffusion plant, Union Carbide and Carbon, who would operate it, and Harold Urey's Substitute Alloy Materials (SAM) Laboratories at Columbia University, the Manhattan Project's centre tasked with research and development of the process . The year's loss of cooperation cost the Manhattan Project dearly . The corporations were committed to tight schedules, and the engineers were unable to incorporate British proposals that would involve major changes . Nor would it be possible to build a second plant . Nonetheless, the Americans were still eager for British assistance, and Groves asked for a British mission to be sent to assist the gaseous diffusion project . In the meantime, Simon and Peierls were attached to Kellex . </P> <P> The British mission consisting of Akers and fifteen British experts arrived in December 1943 . This was a critical time . Severe problems had been encountered with the Norris - Adler barrier . Nickel powder and electro - deposited nickel mesh diffusion barriers were pioneered by American chemist Edward Adler and British interior decorator Edward Norris at the SAM Laboratories . A decision had to be made whether to persevere with it or switch to a powdered nickel barrier based upon British technology that had been developed by Kellex . Up to this point, both were under development . The SAM Laboratory had 700 people working on gaseous diffusion and Kellex had about 900 . The British experts conducted a thorough review, and agreed that the Kellex barrier was superior, but felt that it would be unlikely to be ready in time . Kellex's technical director, Percival C. Keith, disagreed, arguing that his company could get it ready and produce it more quickly than the Norris - Adler barrier . Groves listened to the British experts before he formally adopted the Kellex barrier on 5 January 1944 . </P>

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