Product Code Database
The MAUD Committee was a British scientific working group formed during the Second World War. It was established to perform the research required to determine if an atomic bomb was feasible. The name MAUD came from a strange line in a telegram from Danish physicist Niels Bohr referring to his housekeeper, Maud Ray.
The MAUD Committee was founded in response to the Frisch–Peierls memorandum, which was written in March 1940 by Rudolf Peierls and Otto Frisch, two physicists who were refugees from Nazi Germany working at the University of Birmingham under the direction of Mark Oliphant. The memorandum argued that a small sphere of pure uranium-235 could have the explosive power of thousands of tons of TNT.
The chairman of the MAUD Committee was George Thomson. Research was split among four different universities: the University of Birmingham, University of Liverpool, University of Cambridge and the University of Oxford, each having a separate programme director. Various means of uranium enrichment were examined, as was nuclear reactor design, the properties of uranium-235, the use of the then-hypothetical element plutonium, and theoretical aspects of nuclear weapon design.
After fifteen months of work, the research culminated in two reports, "Use of Uranium for a Bomb" and "Use of Uranium as a Source of Power", known collectively as the MAUD Report. The report discussed the feasibility and necessity of an atomic bomb for the war effort. In response, the British created a nuclear weapons project, code named Tube Alloys. The MAUD Report was made available to the United States, where it energised the American effort, which eventually became the Manhattan Project. The report was also revealed to the Soviet Union by its atomic spies, and helped start the Soviet atomic bomb project.
Niels Bohr and John A. Wheeler applied the liquid drop model developed by Bohr and Fritz Kalckar to explain the mechanism of nuclear fission. Bohr had an epiphany that the fission at low energies was principally due to the uranium-235 isotope, while at high energies it was mainly due to the more abundant uranium-238 isotope. The former makes up just 0.7% of natural uranium, while the latter accounts for 99.3%. Frédéric Joliot-Curie and his Paris colleagues Hans von Halban and Lew Kowarski raised the possibility of a nuclear chain reaction in a paper published in Nature in April 1939. It was apparent to many scientists that, in theory at least, an extremely powerful explosive could be created, although most still considered an atomic bomb an impossibility. The term was already familiar to the British public through the writings of H. G. Wells, in his 1913 novel The World Set Free.
Even at such long odds, the danger was sufficiently great to be taken seriously. Lord Chatfield, the Minister for Coordination of Defence, checked with the HM Treasury and Foreign Office, and found that the Belgian Congo uranium was owned by the Union Minière du Haut Katanga company. Its British vice-president, Lord Stonehaven, arranged a meeting with the Belgian president of the company, Edgar Sengier. Since Union Minière management were friendly towards Britain, it was not considered necessary to immediately acquire the uranium, but Tizard's Committee for the Scientific Survey of Air Warfare (CSSAW) was directed to continue the research into the feasibility of atomic bombs. Thomson, at Imperial College London, and Mark Oliphant, an Australian physicist at the University of Birmingham, were each tasked with carrying out a series of experiments on uranium. By February 1940, Thomson's team had failed to create a chain reaction in natural uranium, and he had decided that it was not worth pursuing.
However, Bohr had contended that the uranium-235 isotope was far more likely to capture neutrons and fission even from neutrons with the low energies produced by fission. Frisch began experimenting with uranium enrichment through Thermophoresis. Progress was slow; the required equipment was not available, and the radar project had first call on the available resources. He wondered what would happen if he was able to produce a sphere of pure uranium-235. When he used Peierls' formula to calculate its critical mass, he received a startling answer: less than a kilogram would be required. Frisch and Peierls produced the Frisch–Peierls memorandum in March 1940. In it they reported that a five kilogram bomb would be the equivalent to several thousand tons of dynamite, and even a one kilogram bomb would be impressive. Because of the potential radioactive fallout, they thought that the British might find it morally unacceptable.
Oliphant took the Frisch–Peierls memorandum to Tizard in March 1940. He passed it on to Thomson, who discussed it with Cockcroft and Oliphant. They also heard from Jacques Allier of the French Deuxième Bureau, who had been involved in the removal of the entire stock of heavy water from Norway. He told them of the interest the Germans had shown in the heavy water, and in the activity of the French researchers in Paris. Immediate action was taken: the Ministry of Economic Warfare was asked to secure stocks of uranium oxide in danger of being captured by the Germans; British intelligence agencies were asked to investigate the activities of German nuclear scientists; and A. V. Hill, the British Scientific Attaché in Washington, was asked to find out what the Americans were up to. Hill reported that the Americans had scientists investigating the matter, but they did not think that any military applications would be found.
At first the new committee was named the Thomson Committee after its chairman, but this was soon exchanged for a more unassuming name, the MAUD Committee. MAUD was assumed by many to be an acronym, but it is not. The name MAUD came to be in an unusual way. On 9 April 1940, the day Germany invaded Denmark, Niels Bohr had sent a telegram to Frisch. The telegram ended with a strange line "Tell Cockcroft and Maud Ray Kent". At first it was thought to be code regarding radium or other vital atomic-weapons-related information, hidden in an anagram. One suggestion was to replace the "y" with an "i", producing 'radium taken'. When Bohr returned to England in 1943, it was discovered that the message was addressed to John Cockcroft and Bohr's housekeeper Maud Ray, who was from Kent. Thus the committee was named the MAUD Committee. Although the initials stood for nothing, it was officially the MAUD Committee, not the Maud Committee.
Because of the top secret aspect of the project, only British-born scientists were considered. Even despite their early contributions, Peierls and Frisch were not allowed to participate in the MAUD Committee because, at a time of war, it was considered a security threat to have enemy aliens in charge of a sensitive project. In September 1940, the Technical Sub-Committee was formed, with Peierls and Frisch as members. However, Halban did not take his exclusion from the MAUD Committee in as good grace as Frisch and Peierls. In response, two new committees were created in March 1941 to replace the MAUD Committee and the Technical Sub-Committee, called the MAUD Policy Committee and the MAUD Technical Committee. Unlike the original two committees, they had written terms of reference. The terms of reference of the MAUD Policy Committee were:
The MAUD Policy Committee was kept small and included only one representative from each university laboratory. Its members were: Blackett, Chadwick, Cockcroft, Ellis, Haworth, Franz Simon, Thomson and the Director of Scientific Research at the MAP. The MAUD Technical Committee's members were: Moses Blackman, Egon Bretscher, Norman Feather, Frisch, Halban, C. H. Johnson, Kowarski, Wilfrid Mann, Moon, Nevill Mott, Oliphant, Peierls and Thomson. Its meetings were normally attended by Winston Churchill's scientific advisor, Frederick Lindemann, or his representative, and a representative of Imperial Chemical Industries (ICI). Basil Dickins from the MAP acted as the secretary of the Technical Committee. Thomson chaired both committees.
There were also shortages of manpower, as chemists and physicists had been diverted to war work. Of necessity, the universities employed many aliens or ex-aliens. The MAP was initially opposed to their employment on security grounds, especially as most were from enemy or occupied countries. Their employment was only made possible because they were employed by the universities and not the MAP, which was not allowed to employ enemy aliens. The MAP gradually came around to accepting their employment on the project. It protected some from internment, and provided security clearances. There were restrictions on where enemy aliens could work and live, and they were not allowed to own cars, so dispensations were required to allow them to visit other universities. "And so," wrote historian Margaret Gowing, "the greatest of all the wartime secrets was entrusted to scientists excluded for security reasons from other war work."
This process was based on the fact that when a mixture of two gases passes through a temperature gradient, the heavier gas tends to concentrate at the cold end and the lighter gas at the warm end. That this can be used as a means of isotope separation was first demonstrated by Klaus Clusius and Gerhard Dickel in Germany in 1938, who used it to separate isotopes of neon. They used an apparatus called a "column", consisting of a vertical tube with a hot wire down the centre. The advantage of the technique was that it was simple in design and there were no moving parts. But it could take months to reach equilibrium, required a lot of energy, and needed high temperatures that could cause a problem with the uranium hexafluoride.
Another line of research at Liverpool was measuring the fission cross section of uranium-235, on which Frisch and Peierls' calculations depended. They had assumed that almost every collision between a neutron of any energy and a uranium-235 nucleus would produce a fission. The value they used for the fission cross section was that published by French researchers in 1939, but data published by the Americans in the 15 March and 15 April 1940 issues of the American journal Physical Review indicated that it was much smaller.
No pure uranium-235 was available, so experiments at Liverpool were conducted with natural uranium. The results were inconclusive, but tended to support Frisch and Peierls. By March 1941, Alfred Nier had managed to produce a microscopic amount of pure uranium-235 in the United States, and a team under Merle Tuve at the Carnegie Institution of Washington was measuring the cross section. The uranium-235 was too valuable to send a sample to Britain, so Chadwick sent the Americans a list of measurements he wanted them to carry out. The final result was that the cross section was smaller than Frisch and Peierls had assumed, but the resulting critical mass was still only about eight kilograms.
Meanwhile, Pryce investigated how long a runaway nuclear chain reaction in an atomic bomb would continue before it blew itself apart. He calculated that since the neutrons produced by fission have an energy of about this corresponded to a speed of . The major part of the chain reaction would be completed in the order of (ten "shakes"). From 1 to 10 per cent of the fissile material would fission in this time; but even an atomic bomb with 1 per cent efficiency would release as much energy as 180,000 times its weight in TNT.
This is based on Graham's law, which states that the rate of effusion of a gas through a porous barrier is inversely proportional to the square root of the gas's molecular mass. In a container with a porous barrier containing a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is slightly enriched in the lighter molecules, while the residual gas is slightly depleted. Simon's team conducted experiments with copper gauze as the barrier. Because uranium hexafluoride, the only known gas containing uranium, was both scarce and difficult to handle, a mixture of carbon dioxide and water vapour was used to test it.
The result of this work was a report from Simon on the "Estimate of the Size of an Actual Separation Plant" in December 1940. He described an industrial plant capable of producing a kilogram per day of uranium enriched to 99 per cent uranium-235. The plant would use of membrane barriers, in 18,000 separation units in 20 stages. The plant would cover , the machinery would weigh and consume 60,000 kW of power. He estimated that it would take 12 to 18 months to build at a cost of around £4 million, require 1,200 workers to operate, and cost £1.5 million per annum to run. "We are confident that the separation can be performed in the way described", he concluded, "and we even believe that the scheme is, in view of its object, not unduly expensive of time, money and effort."
In a paper written shortly after they arrived in England, Halban and Kowarski theorised that slow neutrons could be absorbed by uranium-238, forming uranium-239. A letter by Edwin McMillan and Philip Abelson published in the Physical Review on 15 June 1940 stated that this decayed to an element with an atomic number of 93, and then to one with an atomic number of 94 and mass of 239, which, while still radioactive, was fairly long-lived. That a letter on such a sensitive subject could still be published irked Chadwick, and he asked for an official protest to be sent to the Americans, which was done.
Bretscher and Feather argued, on theoretical grounds, that this element might be capable of fission by both fast and slow neutrons like uranium-235. If so, this promised another path to an atomic bomb, as it could be bred from the more abundant uranium-238 in a nuclear reactor, and separation from uranium could be by chemical means, as it was a different element, thereby avoiding the necessity for isotope separation. Kemmer suggested that since uranium was named after the planet Uranus, element 93 could be named neptunium and 94 plutonium after the next two planets. Later it was discovered that the Americans had independently adopted the same names, following the same logic. Bretscher and Feather went further, theorising that irradiation of thorium could produce a new isotope of uranium, uranium-233, which might also be susceptible to fission by both fast and slow neutrons. In addition to this work, Eric Rideal studied isotope separation through centrifugation.
Otherwise, uranium hexafluoride was far from ideal. It solidified at , was corrosive, and reacted with many substances, including water. It was therefore difficult and dangerous to handle. However, a search by the chemists at Birmingham failed to uncover another gaseous compound of uranium. Lindemann used his influence with Lord Melchett, a director of ICI, to get ICI to produce uranium hexafluoride on an industrial scale. ICI's hydrofluoric acid plant was out of commission, and required extensive repairs, so the quote for a kilogram of uranium hexafluoride came to £5,000. Nonetheless, the order was placed in December 1940. ICI also explored methods of producing pure uranium metal.
Peierls and his team worked on the theoretical problems of a nuclear bomb. In essence, they were in charge of finding out the technical features of the bomb. Along with Fuchs, Peierls also interpreted all the experimental data from the other laboratories. He examined the different processes by which they were obtaining isotopes. By the end of the summer in 1940, Peierls preferred gaseous diffusion to thermal diffusion.
A paper was received from the United States in which George Kistiakowsky argued that a nuclear weapon would do very little damage, as most of the energy would be expended heating the surrounding air. A chemical explosive generates very hot gases in a confined space, but a nuclear explosion will not do this. Peierls, Fuchs, Geoffrey Taylor and J. G. Kynch worked out the hydrodynamics to refute Kistiakowsky's argument. Taylor produced a paper on "The Formation of a Blast Wave by a Very Intense Explosion" in June 1941.
The first report concluded that a bomb was feasible. It described it in technical detail, and provided specific proposals for developing it, including cost estimates. A plant to produce one kilogram of uranium-235 per day was estimated to cost £5 million and would require a large skilled labour force that was also needed for other parts of the war effort. It could be available in as little as two years. The amount of damage that it would do was estimated to be similar to that of the Halifax explosion in 1917, which had devastated everything in a radius. The report warned that Germany had shown interest in heavy water, and although this was not considered useful for a bomb, the possibility remained that Germany could also be working on the bomb.
The second report was shorter. It recommended that Halban and Kowarski should move to the US where there were plans to make heavy water on a large scale. Plutonium might be more suitable than uranium-235, and plutonium research should continue in Britain. It concluded that the controlled fission of uranium could be used to generate heat energy for use in machines, and provide large quantities of radioisotopes which could be used as substitutes for radium. Heavy water or possibly graphite might serve as a moderator for the fast neutrons. In conclusion though, while the nuclear reactor had considerable promise for future peaceful uses, the committee felt that it was not worth considering during the present war.
The United Kingdom did not have the manpower or resources of the United States, and despite its early and promising start, Tube Alloys fell behind its American counterpart and was dwarfed by it. The British considered producing an atomic bomb without American help, but the project would have needed overwhelming priority, the projected cost was staggering, disruption to other wartime projects was inevitable, and it was unlikely to be ready in time to affect the outcome of the war in Europe.
At the Quebec Conference in August 1943, Churchill and Roosevelt signed the Quebec Agreement, which merged the two national projects. The Quebec Agreement established the Combined Policy Committee and the Combined Development Trust to co-ordinate their efforts. The 19 September 1944 Hyde Park Agreement extended both commercial and military co-operation into the post-war period.
A British mission led by Akers assisted in the development of gaseous diffusion technology at the SAM Laboratories in New York. Another, headed by Oliphant, assisted with that of the calutron process at the Berkeley Radiation Laboratory. Cockcroft became the director of the joint British-Canadian Montreal Laboratory. A British mission to the Los Alamos Laboratory was led by Chadwick, and later Peierls, which included several of Britain's most eminent scientists. As overall head of the British Mission, Chadwick forged a close and successful partnership, and ensured that British participation was complete and wholehearted.
Bush engaged Arthur Compton, a Nobel Prize winner, and the National Academy of Sciences. His report was issued on 17 May 1941. It endorsed a stronger effort, but did not address the design or manufacture of a bomb in any detail. Information from the MAUD Committee came from British scientists travelling to the United States, notably the Tizard Mission, and from American observers at the MAUD Committee meetings in April and July 1941. Cockcroft, who was part of the Tizard Mission, reported that the American project lagged behind the British one, and was not proceeding as fast.
Britain was at war and felt an atomic bomb was urgent, but the US was not yet at war. It was Oliphant who pushed the American programme into action. He flew to the United States in late August 1941, ostensibly to discuss the radar programme, but actually to find out why the United States was ignoring the MAUD Committee's findings. Oliphant reported: "The minutes and reports had been sent to Lyman Briggs, who was the Director of the Uranium Committee, and we were puzzled to receive virtually no comment. I called on Briggs in Washington, only to find out that this inarticulate and unimpressive man had put the reports in his safe and had not shown them to members of his committee. I was amazed and distressed."
Oliphant met with the S-1 Section. Samuel K. Allison was a new committee member, an experimental physicist and a protégé of Compton at the University of Chicago. Oliphant "came to a meeting", Allison recalled, "and said 'bomb' in no uncertain terms. He told us we must concentrate every effort on the bomb and said we had no right to work on power plants or anything but the bomb. The bomb would cost 25 million dollars, he said, and Britain did not have the money or the manpower, so it was up to us."
Oliphant then visited his friend Ernest Lawrence, an American Nobel Prize winner, to explain the urgency. Lawrence contacted Compton and James B. Conant, who received a copy of the final MAUD Report from Thomson on 3 October 1941. Harold Urey, also a Nobel Prize winner, and George B. Pegram were sent to the UK to obtain more information. In January 1942, the OSRD was empowered to engage in large engineering projects in addition to research. Without the help of the MAUD Committee the Manhattan Project would have started months behind. Instead they were able to begin thinking about how to create a bomb, not whether it was possible. Gowing noted that "events that change a time scale by only a few months can nevertheless change history." On 16 July 1945, the Manhattan Project detonated the first atomic bomb in the Trinity nuclear test.
|
|
