Tube Alloys was the codename for the British Nuclear Program, which commenced in May 1940 with the worsening of the war. A committee was set up, the MAUD Committee, which recommended that research into the creation of a nuclear bomb should begin immediately, leading to the creation of a facility in Canada. However, collaboration with the US nuclear program was patchy, with both sides refusing to share vital secrets. As a result, while the British program had originally had a substantial lead over the American Manhattan Project, due to the diversion of all available materials to the immediate war effort, and the crippling German blockade, Tube Alloys began to fall behind its counterpart, eventually merging with the Manhattan Project in 1943 under the Quebec Act. The UK would not have its own nuclear weapons program until the McMahon Act of 1946, which barred the UK from accessing nuclear secrets, in spite of its significant wartime contribution to research, leading to the creation of a separate British program, and the first successful British Nuclear Program
While the use of nuclear energy for electricity and for war had been predicted, no serious government attention was drawn until the discovery of nuclear fission on 17th December 1938, by Otto Hahn and Lise Meitner. Further interest arose after the discovery, in February 1939, that the splitting of one uranium-235 atom produced on average more than one neutron, leading to the possibility of a self-sustaining fission reaction, and therefore the ability to create a nuclear bomb.
The Frisch-Peierls memorandum was published in March 1940. In it, estimates were given as to the critical mass of uranium-235, which was small enough to be transportable by air, indicating the potential to create a nuclear bomb out of uranium which could be dropped from a bomber. As a direct result of the conclusion of the memorandum on the viability of nuclear weapons, both the US and the UK began nuclear projects, with Winston Churchill personally authorising the creation of the MAUD Committee.
Due to the intense need for secrecy, 'aliens' were prevented from becoming part of the MAUD Committee. The extent of government paranoia was such that even Frisch and Peierls were banned from taking part, as neither of them was born in the UK (Frisch was born in Austria, while Peierls was born in Germany). The MAUD Committee released a report in 1941, which stated that it would be possible to create an effective uranium bomb, using 25lbs of active material (uranium-235), with a destructive effect equivalent to 1,800lbs of TNT. The report also highlighted the adverse effects of radioactive fallout, stating that places near to where the bomb exploded would be "dangerous to human life for a long period"
The report also outlined the significant cost of such a nuclear bomb, explaining that a plant which produced 2.25lbs of U-235 per day(the equivalent of three bombs worth per month) would cost approximately £5 million(approximately £250 million today), and would require highly skilled labour, difficult to acquire. In spite of the significant difficulties outlined in the MAUD report, it nevertheless led to the creation of the Tube Alloys project in 1942, in part because the Committee state that an atomic bomb was "not just feasible; it was inevitable", urging the government to start work before other governments developed weapons, depriving Britain of its superpower status.
The greatest problem faced by the project was the separation of U-235, which made up 0.7% of uranium, from U-238, which made up the remaining 99.3%. This problem was solved by Sir Francis Simon(originally Franz Simon), who devised the method of gaseous diffusion. In the first step, yellowcake (powdered uranium oxide) is reacted with hydrogen fluoride and fluorine gas to produce uranium hexafluoride. The gaseous uranium hexafluoride is then pressurised and pumped past semi-permeable membranes, where some of it diffuses through the membranes into a lower pressure area. As U-235 has a slightly lower mass than U-238, more of it diffuses through the membranes. At the end, two streams, one connected to the high-pressure area, and one to the low-pressure area, remove the uranium hexafluoride. The stream from the low-pressure area has a higher concentration of U-235 and is fed past more membranes, each time increasing the concentration of U-235, to eventually produce a very highly concentrated sample of U-235, suitable for creating nuclear weapons.
At the Cavendish Laboratory, it was also theorised that plutonium could be created in a nuclear reactor. Bretscher and Feather stated that a U-238 nucleus, if hit by a slow-moving neutron, would not split, would instead form a highly unstable U-239 atom, which would decay by beta decay into an atom with an atomic number of 93, dubbed neptunium. This atom would then rapidly decay into an atom with an atomic number of 94, dubbed plutonium. Bretscher and Feather postulated, correctly, that plutonium had the potential to be used in a nuclear bomb and had the advantage of being much more easily separatable from uranium, as they weren't isotopes, and so were chemically different.
Due to greater funding, the Manhattan Project quickly eclipsed Tube Alloys. Despite this, the British limited co-operation with the Americans, refusing their offers to collaborate in 1941. As a result, Tube Alloys fell even further behind its American counterpart. After the US Army took over the Manhattan Project in 1942, the Americans ceased co-operation with the British and tightened security, and keeping secret details of heavy water production, uranium hexafluoride production, or of the properties of plutonium. This antagonised the British, who had still been co-operating over these matters, leading to a British boycott of the American program, severely hindering the Americans. This in part led to the rapprochement of the British and American governments in 1943 and the Quebec Act, in which the British agreed to hand over all materials relating to the project, as a result of which Tube Alloys was subsumed into the Manhattan Project, with a British Mission comprised of scientists of multiple nationalities sent to Los Alamos.
Despite the significant assistance given by the British to the Manhattan Project, the McMahon Act of 1946 limited nuclear secrets to the US, in effect forcing the UK to restart their nuclear program from scratch. As a result, the UK would not have nuclear weapons until 1952, being the 3rd country to achieve this, after the US and the USSR.
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