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JOHN RAY DUNNING September24, 1907-August25, 1975 BY HERBERT L. ANDERSON JO H N RA Y D U N N I N G. professor of physics at Columbia Uni- versity, was a pioneer in the development of nuclear en- ergy. From 1932, when he was twenty-five, he worked almost exclusively on the stucly of the then newly discovered neu- tron. His work led naturally to the demonstration the first in the United States of the large release of energy in the fission of uranium by slow neutron bombardment. Dunning realizect that by enriching uranium in the light isotope, he could make a nuclear chain reaction a practicality. His work to adapt the gaseous diffusion process for this pur- pose macle possible the nuclear power industry as we know it today. This achievement, pursuccl with unique vigor and single-mindedness, places him in the ranks of outstanding . . ~ . . scientists ot this century. 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! Josephine (Thelen) Dunning, on Sep- tember 24, 1907. His father was according to Dunning himself, quoted in Current Biography, 1948- a "congenial, en- 163

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64 BIOGRAPHICAL MEMOIRS ergetic, ant] hearty grain dealer." He was also an amateur radio engineer. tohn's early conviction that it was "easier to make equipment work . . . than to save souls or prepare legal briefs" turner! him away from the ministry anc} the law and lee] him to science. He was only twelve years oIct when he built and then operated a ractio sending set, the first in his section of the country. After graduating from Shelby High School in 1925, he entered Nebraska Wesleyan University, and, in 1929, receiver! a B.A. clegree with highest honors. Between 1926 and 1929, he and his father, with the encouragement and assistance of one of his professors, built the radio stations WCA} and KGBY, which operated on the regular broadcast bancts and were later soIct. Immecliately after graduation, Dunning went to Columbia University, where he was an as- sistant in the physics department for three years and a uni- versity fellow from ~ 932 to ~ 933. Dunning was married in 1930 to Esther Laura Blevins, now clead, who was his clevotecI companion throughout his lifetime. He was elected to the National Academy of Sciences in 1948. He diec! of a heart attack at his home in Key Bis- cayne, Florida, on August 23, 1975. He was sixty-seven years oIcI. Two chilciren, John Ray, fir., and Ann Aclele (the former Mrs. Ec~warc! Coyle), and a grandchild survive. NEUTRON RESEARCH The neutron, cliscovered shortly after Dunning arrived at Columbia, became his principal subject of research. This work was supported enthusiastically by George B. Pegram, who had resigned his post as dean of engineering to do re- search. Their collaboration was both close and productive, and they published twenty-four papers together on neutrons between 1933 and 1936. Dunning's drive and exceptional skill "in making things work" contributed greatly to their

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JOHN RAY DUNNING 165 joint success. One 1934 paper, "The Emission and Scattering of Neutrons," became the basis of his Ph.D. dissertation. Dunning spent his entire career at Columbia. He was ap- pointed to the faculty as an instructor in 1933, received his Ph.D. in 1934, and acivancect to assistant professor in the following year. 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 physicists- among them Rutherford, Chadwick, Bohr, Heisenberg, and Fermi to discuss his work on neutrons. After his 1935 promotion to assistant professor, Dunning became the central figure in neutron research at Columbia. His was the leading laboratory for neutron research in the Unitec! States, complementing Fermi's laboratory in Rome. Segre, Amalcli, Rasetti, anct Fermi himself came to Columbia to work with Dunning and his colleagues. He also worked with a procession of graduate students and younger faculty members, studying, among other topics, the magnetic prop- erties and magnetic moment of the neutron. One experiment of fundamental importance, the scattering of neutrons by ortho- and para-hy(lrogen, was clone in collaboration with a group from the National Bureau of Standarcts. PERSONALITY What kinc! of a man was John Dunning? As one of his former graduate students, William W. Havens, fir., put it: Dunning was a man of contagious optimism, boundless enthusiasm, and almost infinite energy. He was also an inspired experimentalist who knew intuitively the critical factors in a scientific problem. He had a real flair for getting apparatus to work. On many occasions, his graduate students would give up in despair when one of Dunning's electronic devices would not function. Dunning could then be found in the laboratory at 2:00 or

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166 BIOGRAPHICAL MEMOIRS 3:00 A.M. fiddling with the apparatus and by dawn it was usually working perfectly. His colleagues jokingly referred to the 'DOF' or 'Dunning Op- timism Factor' when planning any project because Dunning always mini- mized the difficulties and emphasized the accomplishments. However, all admired the ingenuity, enthusiasm, and inspiration he contributed to any project. . My own view is very much in accord with this. Dunning had a creep conviction that, unless fundamental principles were being violated, the apparatus had to work. It was just a matter of getting it to clo what it was supposed to do anyway. CYCLOTRON . In the early days, before accelerators were common, a mixture of beryllium powder anc! radon gas contained in a small glass bulb was used as a neutron source. Such sources had a yielc} of io6 neutrons per second. The radon was ob- taine(1 from Memorial Hospital by "milking" four grams of raclium every few days for this decay product (half-life = 3.8 clays). The radon was used primarily in goIc! seects for im- plantation in cancerous tumors, but there was plenty avail- able for the neutron work. Still, Dunning followed the news of Ernest Lawrence's suc- cessfut clevelopment of the cyclotron at Berkeley with great interest. He wanted a much more powerful neutron source than he had at his clisposal, and the cyclotron was the way to go. When he heard of an SO-ton magnet like that Lawrence had used in the construction of his 37-inch cyclotron, he went after it. These magnets had been produced by the Federal Telegraph Company cluring World War ~ to be used in Poul- sen 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. But Dunning was un-

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JOHN RAY DUNNING 167 ciauntecl. His energy, enthusiasm, and self-conficlence were persuasive, anc! he went around raising money from foun- dations and obtaining gifts of equipment from industry until the magnet was shipped and installed and a cyclotron built in the basement of the Pupin Physics Laboratory at Co- lumbia. Dunning worked with a small staff. Dr. E. T. Booth, his long-time collaborator and a postdoctoral fellow at the time, worker! full time constructing the cyclotron and getting it to work. My own recollections are vivid of Booth, infinitely pa- tient, looking for leaks. As a graduate student hoping to do my thesis experiment with the cyclotron, ~ was assigned a variety of tasks. Hugh Glassforcl, an engineer, looked after the more conventional engineering needs. Three junior members of the faculty, G. N. Glasoe, D. P. Mitchell, and Hugh Paxton worked on the cyclotron part time. Once built, the cyclotron was a huge success. It playecl a crucial role in the clevelopment of nuclear energy and is now on permanent exhibit at the Smithsonian Institution in Wash- ington, D.C. FISSION OF URANIUM When fission was cliscovered in 193S, Dunning was the right man at the right place at the right time. He had a strong source of neutrons from his cyclotron. He hac! constructed a linear amplifier-ionization combination that could be readily aciaptec] to detect the large energy release expected from the fission of uranium. Moreover, he had a great deal of expe- rience with neutrons, especially slow neutrons. It is important to point out that the idea of looking for the energy release in fission was attributable to Otto Frisch and his aunt, Lise Meitner. Frisch was the first to realize that the fast-moving nuclei from the splitting of uranium wouIcl produce a huge amount of ionization compared with the

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168 BIOGRAPHICAL MEMOIRS background from the alpha particles of uranium decay. Frisch also had a uranium-lined ionization chamber con- nected to a linear amplifier and he readily saw huge pulses of ionization on an oscilloscope when a neutron source 300 milligrams of radium mixed with beryllium was brought up to the ionization chamber. It was a historic occasion. Niels Bohr was at the point of leaving for the United States when Frisch came to report these results. 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, re- turning from Princeton where Professor Bohr was lecturing, brought fur- ther 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 ura- nium-plus-neutron system, rather than the transuranic series postulated before. In discussions around the EColumbia] faculty club lunch table it was clear that large kinetic energy release should accompany such splitting. Fermi, Rabi and others left for the Fifth Annual Washington Theoretical Physics Conference. After returning to the Pupin cyclotron laboratory, it seemed clear we should try to detect the energy, which on elementary mass-defect reasoning ought to be in 100 or 200 MEV range. Unfortunately, the new cyclotron in the Pupin basement was behaving poorly, and chamber modifications were being made by Dr. E. T. Booth, Dr. F. G. Slack, and Herbert Anderson, but I hoped it could get working that afternoon. A flexible new linear amplifier-ionization chamber- oscillograph system was already installed next to the cyclotron being used largely as a neutron detector with the cyclotron. After several at- tempts a small metal disk was finally coated with uranium oxide and in- stalled in the ion chamber as one electrode. The alpha-particle pulses around 4.5 MEV were clearly visible. That evening, while my colleagues still worked on the cyclotron, I fi-

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JOHN RAY DUNNING 169 natty brought from the thirteenth-floor laboratory a radon + beryllium fast neutron source the type used for most of our previous work and placed it next to the U-containing ion chamber. In great excitement, we saw about one big pulse on the oscilloscope every minute. The rate was so slow we had doubts at first whether it was real or maybe a poor electrical connection. But when I put the neutron source in a paraffin vessel, usually called a slow-neutron "howitzer," my notebooks indicate that the rate went up to seven or so huge pulses per minute. With a cadmium, slow-neutron- absorber screen interposed, the rate dropped to around one or two a min- ute. Clearly the main effect was due to slow neutrons. A rough calibration of the pulse height versus the 4.5 MEV alpha-particle pulse height indi- cated around 65 to 100 MEV peak energy. Since in fission, one of the two fragments goes backwards into the electrode plate, the total energy per splitting should be in the 130 to 200 MEV range. Fission energy was clearly a new order of magnitude! We quit about eleven P.M. My diary that night says cryptically: "Believe we have observed new phenomena of far-reaching consequences," and re- lates what I have just described. In aciclition to Dunning's recollections, the archives of The University of Chicago library preserves a notebook contain- ing my own first observations, as Dunning's graduate student, of fission pulses. Two clays later, Dunning sent a telegram to Fermi in Wash- ington announcing these results. The opening talks by Bohr and Fermi at the Fifth Washington Conference on Theoret- ical Physics on January 26, 1939, about the implications of the chemical evidence for the fission of uranium obtained by Hahn and Strassmann were sensational. The physical evi- clence obtainer! by Frisch a few weeks earlier using the ioni- zation method clemonstrated the energy release. Dunning's result confirmed! it and was quickly repeater! in three other American laboratories. The implications for nuclear power and possibly nuclear explosives were immediately recognized and given wide media coverage. Dunning hac! helpec! open the nuclear age. These results of the Columbia group plus some additional

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170 BIOGRAPHICAL MEMOIRS observations on the nature of the fission process were promptly reported in a classic paper in the March I, 1939, issue of the Physical Review, "The Fission of Uranium," by H. L. Anderson, E. T. Booth, I. R. Dunning, E. Fermi, G. N. Glasoe, and F. G. Slack. Words alone cannot recapture the excitement of those times. THE CHAIN REACTION To make nuclear power and nuclear explosives practical, it was recognized that it would be necessary to induce large numbers of fissions using large quantities of uranium. This coup be clone if neutrons were emitted in the fission process. In this case, it would be necessary to arrange matters so that the new neutrons would cause aciclitional fissions, with fur- ther additions from the neutrons from these in turn. With more neutrons procluced than absorbed in each generation, there would be a rapid builclup in their number a chain reaction. In the late 1930s, there was, as yet, no evidence for the neutron emission. Moreover, the cross-section for fission by slow neutrons in natural uranium was rather small, raising the question of excessive loss of reproduction factor clue to ~ parasitic processes. The question was how to proceed from there. The Co- lumbia team split up. Fermi ant! Anderson decided to try to obtain a chain reaction using natural uranium and a suitable means for slowing down the neutrons. Dunning, Booth, and Slackbelieving that the isotope responsible for the slow neutron fission was U235 opted to enrich the uranium with this isotope by the gaseous diffusion method. This was the surest way to proceed provided the problem of isotope sepa- ration could be solvecl in a practical way. Dunning had no doubt it could be clone.

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J JOHN RAY DUNNING LETTER TO NIER 171 He lost no time. If he could demonstrate experimentally what seemed plausible from the arguments of Bohr and Wheeler, then the proper course for nuclear energy was by enrichment of the light isotope U235. On April 6, 1939, Dun- ning dispatched a letter to Alfred O. Nier, then a professor of physics at the University of Minnesota, to enlist his support in making this test. The letter shows how clearly Dunning understood what was involved. Because of its historic impor- tance, ~ have reproclucect the letter here in its entirety: Dear Professor Nier: There are a number of things which I hope to be able to discuss with you during the Physical Society meeting in Washington, April 27-29. I trust you will be there as usual as I understand you have a paper. In order that you will be acquainted with the situation from my point of view so that you can consider the possibilities before we meet, perhaps the following should be outlined. 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. The fragments have too little positive nuclear charge for their atomic weight, i.e., they have a neutron excess and are unstable. They therefore achieve stability by emitting betas or neutrons or both. This is almost obvious. As a matter of fact Dr. Booth and I started looking for secondary neutrons almost immediately after demonstrating that U fissions the last part of January, although the first experiments were not very conclusive. Later experiments by a number of people here and abroad all indicate the existence of secondary neutrons. There are likely to be somewhere between 1 and 5 secondary neutrons per fission. Fermi is going into that phase of the problem particularly. If there is on the average at least more than one secondary neutron for each "primary" neutron, so that the net effect of the absorption of neutrons through non-fission processes is more than counterbalanced, then we have the possibility of setting up a self-perpetuating, cascade type of reaction analogous to ionization by impact build-up. The development

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172 BIOGRAPHICAL MEMOIRS of enormous energy through the release of nuclear energy on a large scale is coming closer to realization than most people realize. From simple physical reasoning, it seems clear, crudely speaking, that the following factors must be considered: On the one hand we have (A). Neutron fission processes: Concentration of fissioning U. together with the effective fission cross-section of the U; on the other hand (B). The summation of the non-fission capture processes: i.e., summation of the concentrations of the various capturing elements or isotopes in the system (including the U), each with its appropriate cross-section. In addition we have (C). The effective number of neutrons liberated per fission; and fi- nally (D). The effective probability of a neutron to stay in the system, i.e., not to escape. (This is always less than 1~. Of course, this must be summed or integrated and the variables con- sidered as functions of the neutron energies. So far as I know, no one has dealt with this problem on any thorough basis, and it is obvious that the exact calculations are going to be quite involved. However the essential physics is fairly simple and it seems that if (A/B)CD is effectively greater than unity, then a chain reaction will occur. (Ed note: The quantity (A/B) should be the fraction of neutron captures that lead to fission; thus, B should include the neutron capture processes that lead to fission.) There are some very serious problems yet remaining however. The actual cross-section for fission with slow neutrons of uranium is not very largeonly about 2 to 5 x 10-24 cm2 at most, so the numerator A above is not large. Unfortunately, there is also a strong resonance capture of neutrons by U which almost certainly does not give fissions, and this gives a fairly high cross-section all through the slow neutron region as well as the sharp peak at resonance (or resonances). This competing process thus contributes to (B) above. In addition, there are other contributions to (B), inevitably, such as capturing elements in the material of construction or in slowing down media such as Hz-containing materials, or in various impur- ities 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 vir- tually 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 deuteriumordinary water seems out (H absorption). Very large amounts of material will be required or else the neutron escape factor (D) will be serious. It is clear that making a chain reaction "go" is not going to be easy. There is one line of attack that deserves strong effort, and that is where

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JOHN RAY DUNNING 177 was carried out in this laboratory, but the large-scale engi- neering research and development was done by the M. W. Kellogg Company uncler the direction of Percival ("Dobie") C. Keith. For the construction of the huge plants at Oak Ridge, a new company, the Kellex Company, was establishecl. It was completely owned by Kellogg, and staffed with virtually the same officers. The Oak Ridge gaseous diffusion plant, K-25, was built and began operating in ~ 945. Subsequently, the Oak Ridge complex expanded through several major plant addi- tions. During the Korean War, two aclclitional gas (Effusion plants were built at Paclucah, Kentucky, and Portsmouth, Ohio. The Union Carbide Company was selected to operate the first two, and the Goodyear Group the third. Dunning maintained close contact with all these entities until the whole enterprise was successfully launched. At the peak of their operations, these plants consumed about 15 percent of the total electrical power proclucec! in the United States. Dunning could, quite rightfully, take pride in the fact that, increasingly, nuclear power plants were being built using en- richec! U235 for their successful economic design and opera- tion. In 1971, the pioneering work of Dunning and his three colleagues on the gaseous diffusion method for U235 separa- tion was recognized by an award of $30,000 each, in lieu of patent royalties, by the Atomic Energy Commission. The work hac! been recognized as patentable by the U.S. Patent Office, but a patent collie not be issued because of the secrecy . restrictions. NEV I S C Y C LO TRO N After the end of WorI(1 War IT, Dunning served as scien- tific director for construction of Columbia's Nevis Laborato- ries, a cooperative endeavor of Columbia University, the Atomic Energy Commission, and the Office of Naval Re-

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178 . BIOGRAPHICAL MEMOIRS search. The principal activity was the construction and op- eration of the 385 MEV synchrocyclotron. The detailed de- s~gn and construction as well as much of the initial operation was carried out by Dunning's close collaborator, Eugene T. Booth. DEAN OF ENGINEERING In 1946, Dunning was appointed Thayer Lindsley Pro- fessor of Applied Science, and in 1950, dean of the School of Engineering and Applied Science appointments which marked the end of his active participation in research. After his appointment as dean, Dunning threw himself Into a fund-raising campaign that resulted in the construc- tion of the Seeley Wintersmith Mudd and Terrace Engineer- ing Center at Columbia. When he resigned his deanship in 1969, he had raised more than $50 million for the school. He held numerous posts in the world of American sci- ence, including: member of the National Academy of Sci- ences, elected 1948; member of the boarci, American As- sociation for the Advancement of Science; trustee, Fund for Peaceful Atomic Development; chairman, New York City Board of Education Advisory Committee on Science Man- power; member, Scientific Advisory Committee, Department of Defense; chairman, Science Advisory Council to the Leg- islature of the State of New York; chairman, President's Com- mittee on Super-Sonic Transport. In the 1950s, President Dwight D. Eisenhower and Ad- miral Hyman G. Rickover consulted him frequently on mili- tary matters and on the development of nuclear-powered submarines. He was a member of the board of directors of a number of corporations and chairman of several. He received nine honorary degrees and eight awards.

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1 JOHN RAY DUNNING MEDAL OF MERIT 179 President Harry S. Truman signed the citation accompa- nying the 1946 Mecial of Merit. It reacts as follows: DR. JOHN RAY DUNNING for exceptionally meritorious conduct in the per- formance of outstanding service to the War Department, in accomplish- ments involving great responsibility and scientific distinction in connection with the development of the greatest military weapon of all time, the atomic bomb. As a physical researcher, he took a leading part in the initia- tion of the early phases of the project; then he was in charge of essential research in the SAM Laboratories for the Manhattan Engineer District, Army Service Forces, and then he served as advisor to the contractor for full scale operation of his process. A physicist of national distinction, Dr. Dunning's unselfish and unswerving devotion to duty have contributed significantly to the success of the Atomic Bomb project. PUBLIC SERVICE A strong believer in informing the public more fully about the nature ant! implications of atomic energy, Dunning spoke often across the nation before teachers' associations, business conferences, civic clubs, town meetings, as well as on radio and TV programs. These talks ranged over a broad spectrum of subjects: "Education for the Atomic Age," "On the Ecige of Disaster Technological Challenge to America," "On Sci- ence Teaching," "The What ant! How of Nuclear Power," "Sputniks Are Not Enough," "Breakthroughs in Science," "The Next 100 Years," and "Impact Government Support and Engineering Education." He took a special interest in explaining abstruse subjects such as nuclear fission to nontechnical audiences, with the aid of contemporary "props" whenever possible. For ex- ample, to help explain the principles of nuclear fission to youngsters of school age, he assisted in the production of a "Blondie anct Dagwood" comic book that reduced the story of atomic energy to its simplest terms.

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180 BIOGRAPHICAL MEMOIRS Similarly, he enlivened the Columbia Engineering clean's platform talks with a variety of mechanical and electronic gadgets he used to illustrate or dramatize his remarks. These incluclecl a radioactive "atomic ray gun" inspired by Buck Rocigers's famous "disintegrator pistol" Geiger counters, oscillographs, and various combinations of bells and colored lights that culminated in an "atomic pinball machine" a miniature atomic power system that demonstrated actual atomic fission energy release. For Dunning, the phenomenon of radioactivity never lost its fascination. ~ remember vividly the way he demonstrated the circulation of the bloo(1 using radioactivity. He prepared a sample of Na24 (15-hour half-life) by irradiating a glass of salt water with the cyclotron. Using a Geiger counter, he first showed that the radioactivity was in the glass. He then stretched out his banal with the Geiger counter at his finger tips: no activity. He then drank the glass of irradiated water. After some anxious minutes, the Geiger counter at the finger tips began to respond at first weakly then increasingly, as the circulating bloocl brought more and more of the raclio- active salt to the finger tips. It was a great show. The audience lovecl it, and so die! Dunning. ~ WISH TO THANK Professor Dunning's son, John Ray Dunning, Jr., for sending me the Nier letter and the Booth commentary ex- tensively quoted here. .

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JOHN RAY DUNNING SELECTED BIBLIOGRAPHY 1933 181 Detection of corpuscular radiation by vacuum tube. Phys. Rev.? 43:380. With G. B. Pegram. Scattering and absorption of neutrons. Phys. Rev., 43:497-98. With G. B. Pegram. On neutrons from a beryllium-radon source. Phys. Rev., 44:317. 1934 With G. B. Pegram. Neutron emission. Phys. Rev., 45:295. The emission and scattering of neutrons. Phys. Rev., 45:586-600. With G. B. Pegram. The scattering of neutrons by Hl2O, H22O, paraffin, Li, B. and C and the production of radioactive nuclei by neutrons found by Fermi. Phys. Rev., 45:768-69. Amplifier systems for the measurement of single particles. Rev. Sci. Instrum., 5:387 - 94. 1935 With G. B. Pegram. Electrolytic separation of polonium and Ra D. Phys. Rev., 47:325. With G. B. Pegram and G. A. Fink. The capture, stability, and ra- dioactive emission of neutrons. Phys. Rev., 47. With G. B. Pegram, G. A. Fink, and D. P. Mitchell. Interaction of low energy neutrons with atomic nuclei. Phys. Rev.,47:416-17. With G. B. Pegram. Absorption and scattering of slow neutrons. Phys. Rev., 47:640. With G. B. Pegram, G. A. Fink, and D. P. Mitchell. Absorption and velocity of slow neutrons. Phys. Rev., 47:796. With G. B. Pegram, D. P. Mitchell, and G. A. Fink. Thermal equi- librium of slow neutrons. Phys. Rev., 47:888-89. With G. B. Pegram, G. A. Fink, and D. P. Mitchell. Slow neutrons. Phys. Rev., 47:970. With G. B. Pegram, G. A. Fink, and D. P. Mitchell. Interaction of neutrons with matter. Phys. Rev., 48:265-80. With Selby M. Skinner. Ionizing particle counters. Rev. Sci. In- strum, 6:243. With G. B. Pegram, G. A. Fink, D. P. Mitchell, and E. Segre. Veloc-

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182 BIOGRAPHICAL MEMOIRS ity of slow neutrons by mechanical velocity selector. Phys. Rev. 48:704. With D. P. Mitchell, E. Segre, and G. B. Pegram. Absorption and detection of slow neutrons. Phys. Rev., 48:774-75. 1936 With G. A. Fink, G. B. Pegram, and D. P. Mitchell. The velocities of slow neutrons. Phys. Rev., 49: 103. With F. Rasetti, E. Segre, G. A. Fink, and G. B. Pegram. On the absorption law for slow neutrons. Phys. Rev., 49:104. With G. A. Fink, G. B. Pegram, and E. Segre. Experiments on slow neutrons with velocity selector. Phys. Rev., 49: 198. With G. B. Pegram, D. P. Mitchell, G. A. Fink, and E. Segre. Sulla velocita dei neutron) lent). Atti. Accad. Naz. Lincei C1. Sci. Fis. Mat. Nat. Rend., 23:340-42. With F. Rasetti, E. Segre, G. A. Fink, and G. B. Pegram. Sulla legge di assorbimento dei neutron) lent). Atti. Accad. Naz. Lincei C1. Sci. Fis. Mat. Nat. Rend., 23:343-45. With G. A. Fink, G. B. Pe~ram. and E. Severe. Production and ab- ~ , ~ sorption of slow neutrons in hydrogenic materials. Phys. Rev. 49:199. With D. P. Mitchell and G. B. Pegram. Absorption of slow neutrons with lithium and boron as detectors. Phys. Rev., 49: 199. With G. A. Fink and G. B. Pegram. The absorption of slow neu- trons in carbon. Phys. Rev., 49:340. With G. A. Fink and G. B. Pegram. Slow neutron production and absorption. Phys. Rev., 49:642. 1937 With P. N. Powers and H. G. Beyer. Experiments on the magnetic properties of the neutron. Phys. Rev., 51:51. With P. N. Powers and H. G. Beyer. Experiments on the magnetic moment of the neutron. Phys. Rev., 51:371-72. With P. N. Powers and H. G. Beyer. Experiments on the magnetic properties of the neutron. Phys. Rev., 51 :382-83. With H. L. Anderson. High frequency filament supply for ion sources. Rev. Sci. Instrum., 8:158-59.

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JOHN RAY DUNNING 183 With H. Carroll and P. N. Powers. Experiments on the magnetic moment of the neutron. Phys. Rev., 51:1022. With P. N. Powers and H. Carroll. Experiments on the magnetic moment of the neutron. Phys. Rev., 51: 1112-13. With P. N. Powers, H. Carroll, and H. G. Beyer. The sign of the magnetic moment of the neutron. Phys. Rev., 52:38-39. With H. W. Farwell. The two-year science program at Columbia College. Am. Phys. Teach., 5:150-56. With I. H. Manley, H. I. Hoge, and F. G. Brickwedde. The inter- action of neutrons with normal and parahydrogen. Phys. Rev., 52: 1076-77. With Edith Haggstrom. A horizontal projection cloud chamber. Am. Phys. Teach., 5:274-75. With H. L. Anderson and D. P. Mitchell. Regulator systems for electromagnets. Rev. Sci. Instrum., 8:497-501. 1938 With H. I. Hoge, J. H. Manley, and F. G. Brickwedde. The inter- action of neutrons with normal and parahydrogen. Phys. Rev., 53:205. With H. L. Anderson. High frequency systems for the cyclotron. Phys. Rev., 53:334. With H. Carroll, P. N. Powers, and H. G. Beyer. The scattering of neutrons by gases. Phys. Rev., 53:680. With P. N. Powers, H. H. Goldsmith, and H. G. Beyer. Dependence of neutron interaction with nuclei on neutron energy. Phys. Rev., 53:947A. With H. G. Beyer, H. Carroll, and C. Witcher. Dependence of mag- netic scattering of neutrons on magnetization of iron. Phys. Rev., 53:947A. With H. Carroll, H. G. Beyer, and K. Wilhelm. Scattering of neu- trons by gases. Phys. Rev., 53:947A. With F. G. Brickwedde, H. J. Hoge, and J. H. Manley. Neutron scattering cross-sections for para- and orthohydrogen, and of N2, O2, and H2O. Phys. Rev., 54:266-75. With Henry Carroll. The interaction of slow neutrons with gases. Phys. Rev., 54:541. With M. D. Whitaker and H. G. Beyer. Scattering of slow neutrons by paramagnetic salts. Phys. Rev., 54:771.

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184 BIOGRAPHICAL MEMOIRS 1939 With H. L. Anderson, E. T. Booth, E. Fermi, G. N. Glasoe, and F. G. Slack. The fission of uranium. Phys. Rev., 55:511-12. With E. T. Booth and F. G. Slack. Delayed neutron emission from uranium. Phys. Rev., 55:876. With E. T. Booth and F. G. Slack. Energy distribution of uranium fission fragments. Phys. Rev., 55:980. With E. T. Booth and F. G. Slack. Range distribution of the ura- nium fission fragments. Phys. Rev., 55:982. With H. H. Goldsmith and V. W. Cohen. Scattering of slow neu- trons by uranium. Phys. Rev., 55: 1124. With E. T. Booth and F. G. Slack. Fission of uranium and produc- tion of delayed emission by slow neutron bombardment. Phys. Rev.,55:1124. With I. S. O'Connor, C. Witcher, and E. Haggstrom. An electron lens type of beta-ray spectrometer. Phys. Rev., 55: 1132. With E. T. Booth and F. G. Slack. Erratum: range distribution of the uranium fission fragments. Phys. Rev., 55:1273. With A. V. Grosse and E. T. Booth. The fission of protoactinium. Phys. Rev., 56:382. 1940 With Alfred O. Nier, E. T. Booth, and A. V. Grosse. Nuclear fission of separated uranium isotopes. Phys. Rev., 57:546. With H. B. Hanstein. Transmission measurements with indium resonance neutrons (1 ev to 0.5 ev). Phys. Rev., 57:565-66. With F. C. Nix and H. G. Beyer. Neutron transmission studies in Fe-Ni alloys. Phys. Rev., 57:566. With F. C. Nix and H. G. Beyer. Neutron studies of order in Fe-Ni alloys. Bell Telephone System Monogr. B-1267. With A. O. Nier, E. T. Booth, and A. V. Grosse. Further experi- ments on fission of separated uranium isotopes. Phys. Rev., 57:746. With K. H. Kingdon, H. C. Pollack, E. T. Booth, and A. O. Nier. Fission of the separated isotopes of uranium. Phys. Rev., 57:749. With E. T. Booth, A. V. Grosse, and A. O. Nier. Neutron capture by uranium 238. Phys. Rev., 58:475-76.

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JOHN RAY DUNNING 185 With Paul A. Zahl and S. Cooper. Some in viva effects of localized nuclear disintegration products on a transplanted mouse sar- coma. Proc. Natl. Acad. Sci. USA, 26:289. With F. C. Nix and H. G. Beyer. Neutron studies of order in Fe-Ni alloys. Phys. Rev., 57:1031 - 34. 1941 With H. C. Paxton. Matter, Energy, and Radiation. New York: Mc- Graw-Hill. With A. V. Grosse and E. T. Booth. The fourth (4n + 1) radioactive series. Phys. Rev., 58:322 - 23. Commentary. In: Molecular Films, the Cyclotron and the New Biology. New Brunswick: Rutgers University Press. Science in war. Am. Sci., 30:301-3. 1946 With Allen F. Reid. Half-life of Cl4. Phys. Rev., 70:431. Background to atomic energy. Introduction in: Molecular Films, the Cyclotron, and the New Biology. New Brunswick: Rutgers Univer- sity Press. 1947 With L. J. Rainwater, W. W. Havens, Jr., and C. S. Wu. Slow neu- tron velocity spectrometer studies I Cd, Ag, Sb, Ir, and Mn. Phys. Rev., 71:65-79. With A. S. Well and A. F. Reid. Metaborate compounds for internal cyclotron targets. Rev. Sci. Instrum., 18:556-58. With A. F. Reid and A. S. Weil. Properties and measurement of carbon 14. Anal. Chem., 19:824. 1948 With L. J. Rainwater, W. W. Havens, Jr., and C. S. Wu. Slow neu- tron velocity spectrometer studies of H. D, F. Mg, S. Si, and quartz. Phys. Rev., 73:733-41. With L. I. Rainwater, W. W. Havens, fir. and C. S. Wu. Slow neutron velocity spectrometer studies of Cu. Ni, Bi, Fe, Sn, and calcite. Phys. Rev., 73:963-72. With E. Melkonian, L. i. Rainwater, and W. W. Havens, fir Slow

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186 BIOGRAPHICAL MEMOIRS neutron spectrometer studies of oxygen, nitrogen, and argon. Phys. Rev., 73:1399-1400. 1968 With R. J. Budnitz, J. Appel, L. Carroll, J. Chen, and M. Goitein et al. Neutron form factors from quasi-elastic electron-deutron scattering. Phys. Rev., 173~5~:1357-90. With J. L. Alberi, J. A. Appel, R. J. Budnitz, J. Chen, and M. Go- itein et al. Search for the electroproduction of the N minutes 1470) resonance from deuterium. Phys. Rev., 176~5~: 1631-34. 1969 With C. Mistretta, I. A. Appel, R. I. Budnitz, L. Carroll, and I. Chen et al. Coincidence measurements of single-pion electro- production near the delta ~ 1236) resonance. Phys. Rev., 184~5~: 1487-507. 1970 With M. Goitein, R. I. Budnitz, L. Carroll, I. R. Chen, and K. Han- son et al. Elastic electron-proton scattering cross sections mea- sured by a coincidence technique. Phys. Rev., 1~91:2449-76. 1971 With L. E. Price, M. Goitein, K. Hanson, T. Kirk, and R. Wilson. Backward-angle electron-proton elastic scattering and proton electromagnetic form factors. Phys. Rev., 4(1 ~ :45 -53. 1972 With K. Hanson, M. Goitein, T. Kirk, L. E. Price, and R. Wilson. Large-angle quasi-elastic electron-deuteron scattering. Inter- national Symposium on Electron and Photon Interactions at High Energies, Ithaca, New York, ed. N. B. Mistry. Ithaca: Cor- nell University Press. 1973 With K. M. Hanson, M. Goitein, T. Kirk, L. E. Price, and R. Wilson. Large-angle quasielastic electron-deuteron scattering. Phys. Rev., 8~3~:753-78.

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