Sunday, 4 December 2011

Dec. 2 1942, a double milestone for nuclear research

Dec. 2 1942, a double milestone for nuclear research: first man-made sustained nuclear chain reaction was created this day 69 years ago ( and then 15 years later in 1957, the first full-scale nuclear power plant went online. This is a nice write up about bothe events: ... also see:, see also:
This is also a nice summary of the history of uranium:
As you may know Canada was also putting in efforts to achieve the sustained nuclear chain reaction during the same time period, the reason they lost to the Americans in the race was access to large quantities of high purity graphite. There is a very nice write up by George C. Laurence detailing these efforts: "Experiments in Ottawa
Heavy water was scarce and costly to produce. The 185 kilograms, that the French scientists had obtained from a hydroelectric plant in Norway and brought to England, was most of the world's supply. Rough calculations with the inaccurate data then available suggested that it might be possible to obtain a large release of energy using some form of carbon, instead of heavy water, with the uranium. Carbon would be less suitable for the purpose but was cheaper and easier to obtain. I decided to experiment with carbon and uranium oxide. The experiment would have to be done mostly in overtime because my small section was very busy assisting Canadian industry to become proficient in the radiographic inspection of parts for military aircraft and other equipment. Months later, I learned without surprise that similar experiments with carbon and uranium had been started both in England and the United States at about the same time.
The purpose of the experiment was to determine whether a very large release of nuclear energy would be possible in a large bulk of the kinds of uranium and carbon which I had. It would be possible if at least as many neutrons were released by fission as were captured. That implied that if an independent source of neutrons is surrounded by a small quantity (i.e. a few tonnes) of the combination of uranium and carbon, more neutrons would reach the surrounding walls than if the combination of materials was not present.
In our experiments in Ottawa to test this, the source of neutrons was beryllium mixed with a radium compound in a metal tube about 2.5 centimetres long.   Alpha particles, emitted spontaneously from the radium, bombarded atoms of beryllium and released neutrons from them.   The carbon was in the form of ten tonnes of calcined petroleum coke, a very fine black dust that easily spread over floors, furniture and ourselves.   The uranium was 450 kilograms of black oxide, which was borrowed from Eldorado Gold Mines Limited.   It was in small paper sacks distributed amongst larger paper sacks of the petroleum coke.
The sacks of uranium and coke were held in a wooden bin, so that they occupied a space that was roughly spherical, 2.7 m in diameter.   The wooden bin was lined with paraffin wax about five centimetres thick to reduce the escape of neutrons.   The arrangement is shown above, as a sectional view through the bin and its contents.
A thin wall metal tube supported the neutron source at the centre of the bin, and provided a passage for insertion of a neutron detector which could be placed at different distances from the source.   In the first tests the detector was a silver coin, but in most of the experiments it was a layer of dysprosium oxide on an aluminum disc.
The experimental routine was to expose the detector to the neutrons for a suitable length of time, then remove it quickly from the assembly and place it in front of a Geiger counter to measure the radioactivity produced in it by the neutrons.   The Geiger counter tubes and the associated electrical instruments were homemade because there was very little money to spend on equipment.
The relative rates of neutron capture and neutron release by fission were calculated from the data obtained.   If the release had been greater than the capture it would have been possible to estimate the "critical quantity" of uranium and coke, that is the minimum quantity needed to produce a self-sustained reaction that would release a large amount of nuclear energy.
Prof. B. Sargent of Queen's University joined me in these experiments during the summer university vacations of 1941 and 1942.   Progress was slow because the work was interrupted by other duties and we lacked the better equipment that would be available today.
By late summer in 1942, our measurements had shown that the release of neutrons by fission in our combination of materials was a few percent less than the capture.   Therefore, it would not be possible to obtain a large release of nuclear energy in that combination of materials even if large quantities were used.   There was too much loss of neutrons by capture in impurities in the coke and uranium oxide and in the small quantities of paper and brass that were present.   We did not then realize how a little impurity could lead to failure.
Meanwhile in the United States, E. Fermi, H.L. Anderson, B. Field, G. Weil and W. Zinn, after a first attempt that was also unsuccessful, did succeed in showing that a large release of energy would be possible using purer uranium and very pure carbon in the form of graphite.   Using the necessarily larger quantities, the Americans then built the first nuclear reactor and operated it on December 2, 1942.   They called it an "atomic pile".
In the summer of 1940, R.H. Fowler visited Ottawa, followed soon by J.D. Cockroft.   They had been to the United States to stimulate greater American interest in research of military importance.   They told me about the nuclear energy research in England and that in the United States which they had just seen.
With Prof. Fowler's introduction, I visited L.J. Briggs, who was chairman of the committee that coordinated the American nuclear energy research at that time, and also J.B. Conant, E. Fermi, H.C. Urey and P.H. Abelson and learned of their work.   After my visit, we received in Ottawa copies of reports on the American nuclear energy research for the next two years.   One of them that was particularly helpful was "A Study Concerning Uranium as a Source of Power" by J.B. Fisk and W. Shockly, dated September 17, 1940, a remarkable theoretical discussion of the feasibility of a nuclear reactor to have been written so early.
In response to Cockroft's suggestion when he returned to England we received a gift of $5,000 from Imperial Chemical Industries, which was involved in the nuclear research in England, in support of our experiment.   It was an important addition to our budget, but I valued it most as an expression to Dr. Mackenzie of British confidence in our work." read more:

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