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Dec. 2 1942, a double milestone for nuclear research
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: http://media.cns-snc.ca/history/early_years/earlyyears.html
 
 
 
          
      
 
  
 
 
  
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