Tube Alloys
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Tube Alloys was the code-name for the British nuclear weapon programme during World War II, when the very possibility of nuclear weapons was kept at such a high level of secrecy that it had to be referred to by code even in the highest circles of government. The Tube Alloys programme was eventually subsumed into the American Manhattan Project. However the programme had its origins in France and Germany.
[edit] The Paris Group
Otto Hahn in Germany and an exiled Lise Meitner in Sweden had reported nuclear fission in uranium in 1938. In February 1939 a group of scientists in Paris at the Collège de France: Frédéric Joliot-Curie, Hans von Halban, Lew Kowarski and Francis Perrin had shown that when fission occurs in a uranium nucleus, two or three extra neutrons are also given off. This important observation suggested that a self-sustaining chain reaction might be possible. It is immediately apparent to many scientists that, in theory, an extremely powerful explosive could be created, an atomic bomb, but many scientists thought a practical bomb was an impossibility.
Francis Perrin of the Paris Group then defined a critical mass of uranium to be the smallest amount needed to sustain a chain reaction. However it was found that natural uranium cannot sustain a chain reaction without a moderator to slow down the fast-moving neutrons given off by the fission.
Early in 1940 the Paris Group decided on theoretical grounds that heavy water would be an ideal moderator. They asked the French Minister of Armaments to obtain as much heavy water as possible from the only source, a large hydroelectric station in Norway at Vemork. The French then discovered that the Germans had already offered to purchase the entire stock of Norwegian heavy water, indicating that Germany might also be researching an atomic bomb. The French told the Norwegian Government of the possible military significance of heavy water, who then gave the entire stock to a French Secret Service agent who smuggled it into France via England just before Germany invaded Norway in April 1940. However Germany invaded France in May 1940, and so the heavy water inventory of 165 quarts and the Paris Group were shipped to Cambridge. (Joliot remained in France to become an active worker in the resistance movement.)
[edit] Frisch and Peierls
At first British research correctly concluded that an atomic bomb using natural uranium is impossible with fast neutrons, because too many neutrons get lost or captured by the uranium-238 atoms. However in February 1940, Otto Frisch and Rudolf Peierls, two exiled German scientists living in England realised that an atomic bomb could be built and detonated using only a few kilograms of uranium-235, the lighter rare isotope of uranium, using only fast neutrons. Frisch and Peierls reported in their famous Frisch-Peierls memorandum that if uranium-235 is completely separated from uranium-238, there is no need to slow the neutrons down. No moderator is required.
Frisch and Peierls reported to their professor Mark Oliphant who informed Henry Tizard who formed in April 1940, a top-secret committee of experts (later known as the MAUD Committee) to investigate the feasibility of an atomic bomb. The memo prompted the MAUD Report which in turn led to the Tube Alloys project.
[edit] Tizard Mission
The heavy water team from France was invited to continue its slow neutron research at Cambridge; but the project was given a low priority since it was not expected to produce a bomb.
A delegation (the Tizard Mission) was sent in September 1940 to North America to exchange technology in all fields, such as radar, jet engines and nuclear research. They also explored the possibility of relocating the British military research facilities in North America, out of reach of the German bombers.
When the Tizard Mission returned they reported on the slow neutron researches being conducted in Cambridge (by the Paris Group), at Columbia University by Enrico Fermi and in Canada by George Laurence. They concluded that they were irrelevant to the war effort.
[edit] Isotopic separation
The biggest problem faced by the MAUD Committee was to find a way to separate the 0.7% of uranium-235 from the 99.3% of uranium-238. This is difficult because the two types of uranium are chemically identical. However Franz Simon had been commissioned by MAUD to investigate methods. Simon reported in December 1940 that gaseous diffusion was feasible, calculating the size and cost of the industrial plant needed. The MAUD Committee realised that an atomic bomb was "not just feasible; it was inevitable".
The chemical problems of producing gaseous compounds of uranium and pure uranium metal were studied at the University of Birmingham and Imperial Chemical Industries (ICI). Dr Philip Baxter at ICI made the first small batch of gaseous uranium hexafluoride for Professor James Chadwick in 1940. ICI received a formal contract later in 1940 to make 3 kg of this vital material for the future work.
[edit] Plutonium
The breakthrough with plutonium was at the Cavendish Laboratory by Egon Bretscher (1901-1973) and Norman Feather (1904-1978). They realised that a slow neutron reactor fuelled with uranium would in theory produce substantial amounts of plutonium-239 as a by-product. This is because U-238 absorbs slow neutrons so forming a new isotope U-239. The new isotope's nucleus rapidly emits an electron, decaying into new element with a mass of 239 and an atomic number of 93. This element's nucleus then also emits an electron and becomes a new element of mass 239 but with an atomic number 94 and a much greater half-life. Bretscher and Feather showed theoretically feasible grounds that element 94 would be readily 'fissionable' by both slow and fast neutrons, and had the added advantage of being chemically different to uranium and therefore could easily be separated from it.
This new development was also confirmed in independent work by Edwin M. McMillan and Philip Abelson at Berkeley Radiation Laboratory also in 1940. Dr Kemmer of the Cambridge team proposed the names neptunium for the new element 93 and plutonium for 94 by analogy with the outer planets Neptune and Pluto beyond Uranus (uranium being element 92). The Americans fortuitously suggested the same names. The production and identification of the first sample of plutonium in 1941 is generally credited to Glenn Seaborg, who used a cyclotron rather than a reactor.
[edit] Oliphant's visit to the United States
When there was no reaction from America to the reports of the Maud Committee, Mark Oliphant crossed the Atlantic in an unheated bomber in August 1941. He found that Lyman Briggs had merely put the reports in a safe. Oliphant then contacted Ernest Lawrence, James Conant, Enrico Fermi and Arthur Compton and managed to increase the urgency of the Americans research programs. The MAUD Reports finally made a big impression. Overnight the Americans changed their minds about the feasibility of an atomic bomb and suggested a cooperative effort with Britain. Harold C. Urey and George Braxton Pegram were sent to the UK in November 1941, to confer but Britain did not take up the offer of collaboration. The offer lapsed without any action being taken.
[edit] 1942 onwards
The American effort increased rapidly and soon outstripped the British. However separate research continued in each country with some exchange of information. Several of the key British scientists visited the USA early in 1942 and were given full access to all of the information available. They were astounded at the momentum that the American atomic bomb project had then assumed.
The slow neutron research at Cambridge, which the British had thought was not relevant to bomb-making, suddenly acquired military significance, because it provided the route to plutonium. The British Government wanted the Cambridge team to be relocated in Chicago, where the American research was being done but the Americans had became very security-conscious. Only one of the six senior scientists in the Cambridge group, which had originated in Paris, was British. They were therefore sent to Montreal, Canada.
In June 1942 the US Army took over process development, engineering design, procurement of materials and site selection for pilot plants. As a result the information flow to Britain dried up. The Americans stopped sharing any information on heavy water production, the manufacture of uranium hexafluoride, the method of electromagnetic separation, the physical or chemical properties of plutonium, the details of bomb design, or the facts about fast neutron reactions. This was a bombshell to the British and the Canadians who were collaborating on heavy water production and on several other aspects of the research program.
The Montreal team in Canada depended on the Americans for supplies of heavy water from the US heavy water plant in Trail, British Columbia, as well as technical information about plutonium. The Americans said that they would only give heavy water to the Montreal group only if it agreed to direct its research along the limited lines suggested by du Pont. Despite doing much good work, by June 1943 work at the Montreal Lab had come to a complete standstill. Morale was low and the Canadian Government proposed cancelling the project.
Winston Churchill then sought information about building Britain's own diffusion plant, a heavy water plant and an atomic reactor in Britain, despite its immense cost. However in July 1943 in London American officials cleared up some major misunderstandings about British motives, and after many months of negotiations the Quebec Agreement was finally signed by Churchill and President Franklin D. Roosevelt on 19 August 1943. The British then handed over all of their material to the Americans and in return received the copies of all the American progress reports to the President. The British effort was then subsumed into the Manhattan Project until after the war.
In a section of the Quebec Agreement formally entitled "Articles of Agreement governing collaboration between the authorities of the U.S.A. and UK in the matter of Tube Alloys", Britain and the USA agreed to share resources to bring the Tube Alloys [i.e. the Atomic Bomb] project to fruition at the earliest moment.
The leaders agreed that
- we will never use this agency against each other,
- we will not use it against third parties without each other's consent, and
- we will not either of us communicate any information about Tube Alloys to third parties except by mutual consent.
It was also agreed that any post-war advantages of an industrial or commercial nature would be decided at the discretion of the U.S. President.
Later in the war, tube alloy came to refer specifically to the synthetic element plutonium, whose very existence was secret until its use in the atomic bombing of Nagasaki.
[edit] Post-war
One of the people working on Tube Alloys was William George Penney, who was an expert in shock-waves. In June 1944 he went to America to work at Los Alamos as part of the British delegation to the Manhattan Project. His leadership qualities and his ability to work in harmony with others resulted in him being added to the core group of scientists who made all key decisions in the direction of the program.
At the end of the war the British government believed that America would share the technology, which the British saw as a joint discovery. However the passing of the McMahon Act (Atomic Energy Act) by the Truman administration in August 1946 made it clear that Britain would be no longer be allowed access to US atomic research.
Clement Attlee's government decided that Britain required the atomic bomb to maintain its position in world politics. In the words of Foreign Secretary Ernest Bevin - "We've got to have it and it's got to have [a] bloody Union Jack on it." [1], [2], [3] So Dr Penney left the United States and returned to England where he initiated his plans for an Atomics Weapons Section. The project was code-named High Explosive Research (or HER) and in May 1947, Dr Penney was appointed to lead the project. In April 1950 an abandoned WWII airfield, RAF Aldermaston in Berkshire was selected as the permanent home for Britain's nuclear weapons program. On 3 October 1952, under the code-name "Operation Hurricane", the first British nuclear device was successfully detonated off the west coast of Australia in the Monte Bello Islands.
