Biographical Memoirs Volume 58 (1989) / Chapter Skim
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John Ray Dunning
John Ray Dunning
Pages 162-187
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From page 163... ...
After leaving active research, Dunning served with great distinction as dean of the School of Engineering at Columbia, obtaining financial support for many scientific projects. FAMILY BACKGROUND John Ray Dunning was born in Shelby, Nebraska, the son of Albert Chester ant!
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From page 164... ...
He was sixty-seven years oIcI. Two chilciren, John Ray, fir., and Ann Aclele (the former Mrs.
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From page 165... ...
He became associate professor in 1938 and professor in ~ 946. Granted a Cutting Traveling Fellowship in ~ 936, Dunning traveled extensively in Europe, taking advantage of the opportunity to meet with many distinguishecl physicistsamong them Rutherford, Chadwick, Bohr, Heisenberg, and Fermi to discuss his work on neutrons.
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From page 166... ...
These magnets had been produced by the Federal Telegraph Company cluring World War ~ to be used in Poulsen arc generators, a type of radio transmission that became obsolete after the invention of the vacuum tube. In the 1930s, no government funds were available for such a project and universities measured their budgets for research in the hundreds of dollars.
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From page 167... ...
to detect the large energy release expected from the fission of uranium. Moreover, he had a great deal of experience with neutrons, especially slow neutrons.
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From page 168... ...
Because of his concern about priority, Frisch asked Bohr not to mention these results to the Americans until the paper he was preparing about them appeared in print. We have Dunning's own recollection of what happened at that time in a speech he gave to the American Physical Society some years later: On the morning of Wednesday, January 25, 1939, Willis Lamb, returning from Princeton where Professor Bohr was lecturing, brought further news of Bohr's analysis of Otto Hahn's brilliant chemical identification of lower atomic weight elements like barium in the products resulting from neutron capture by uranium, thus clearly suggesting splitting the uranium-plus-neutron system, rather than the transuranic series postulated before.
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From page 169... ...
Two clays later, Dunning sent a telegram to Fermi in Washington announcing these results. The opening talks by Bohr and Fermi at the Fifth Washington Conference on Theoretical Physics on January 26, 1939, about the implications of the chemical evidence for the fission of uranium obtained by Hahn and Strassmann were sensational.
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From page 170... ...
Anderson decided to try to obtain a chain reaction using natural uranium and a suitable means for slowing down the neutrons. Dunning, Booth, and Slack—believing that the isotope responsible for the slow neutron fission was U235 opted to enrich the uranium with this isotope by the gaseous diffusion method.
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From page 171... ...
The demonstration that uranium splits or fissions, particularly with slow neutrons, with very large energy evolution opens many far-reaching possibilities. It is now quite certain that the recoiling fragments emit some secondary neutrons.
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From page 172... ...
, inevitably, such as capturing elements in the material of construction or in slowing down media such as Hz-containing materials, or in various impurities such as boron or cadmium which will be especially bad. From what we know of the various cross-sections involved now, I believe there is virtually no safety margin left for a successful chain reaction system with ordinary uranium, certainly not unless extreme purity and special slowing down materials are used, possibly deuterium—ordinary water seems out (H absorption)
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From page 173... ...
If U235 can be shown to be the one responsible for the slow neutron fission, then it is very certain that the chain reaction can be produced, particularly if the U235 is concentrated some. Assuming your figures on the relative proportion in ordinary ores of about 1/140, this would raise the effective slow neutron cross-section from about 2 to 5 x 10-24 cm2 for ordinary U
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From page 174... ...
Demonstrated conclusively slow neutron fission due to U235. Atomic energy released now definitely assured at last!
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From page 175... ...
Dunning was of even more value. There was, as he may have told you, a great deal of adverse opinion among many scientists, and even among the group at Columbia as to the possibility of our being able to make the gas diffusion process an operable affair.
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From page 176... ...
The nuclear power industry today assumes even greater importance in the public mind with the realization that fossil fuels will require supplementation in the years ahead. As is well known, the first chain reaction was made with a graphite pile using ordinary uranium.
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From page 177... ...
U235 for their successful economic design and operation. In 1971, the pioneering work of Dunning and his three colleagues on the gaseous diffusion method for U235 separation was recognized by an award of $30,000 each, in lieu of patent royalties, by the Atomic Energy Commission.
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From page 178... ...
He held numerous posts in the world of American science, including: member of the National Academy of Sciences, elected 1948; member of the boarci, American Association for the Advancement of Science; trustee, Fund for Peaceful Atomic Development; chairman, New York City Board of Education Advisory Committee on Science Manpower; member, Scientific Advisory Committee, Department of Defense; chairman, Science Advisory Council to the Legislature of the State of New York; chairman, President's Committee on Super-Sonic Transport. In the 1950s, President Dwight D
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From page 179... ...
It reacts as follows: DR. JOHN RAY DUNNING for exceptionally meritorious conduct in the performance of outstanding service to the War Department, in accomplishments involving great responsibility and scientific distinction in connection with the development of the greatest military weapon of all time, the atomic bomb.
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From page 180... ...
Dunning. ~ WISH TO THANK Professor Dunning's son, John Ray Dunning, Jr., for sending me the Nier letter and the Booth commentary extensively quoted here.
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From page 181... ...
Fink. Thermal equilibrium of slow neutrons.
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From page 182... ...
Segre. Experiments on slow neutrons with velocity selector.
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From page 183... ...
Scattering of slow neutrons by paramagnetic salts.
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From page 184... ...
Fission of uranium and production of delayed emission by slow neutron bombardment.
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From page 185... ...
Wu. Slow neutron velocity spectrometer studies I Cd, Ag, Sb, Ir, and Mn.
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From page 186... ...
Backward-angle electron-proton elastic scattering and proton electromagnetic form factors.
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