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KENNETH TOMPKINS BAINBRIDGE July 27, 1904-July 14, 1996 BY ROBERT V. POUND AND NORMAN F. RAMSEY KENNETH TOMPKINS BAINB~DGE was recognized early in his scientific career for his design en c! applications of mass spectrographs as research tools for nuclear mass measure- ments. His precise measurements of mass differences be- tween nuclear isotopes, when comparer! to the energies of clecay racliations, allowed! him to confirm the mass-energy equivalency of A. Einstein. In collaboration with the late l. Curry Streeti he clesignec! en c! built the cyclotron at Harvarc! University that was sent to Los Alamos, New Mexico, cluring Woric! War II. Bainbricige participates! in the formation of the wartime Racliation Laboratory at MIT, where he spent more than two en c! one-half years cleveloping microwave racier, particularly high-powerec! systems. In the spring of 1943 he transferred to the nuclear weapons project at Los Alamos, where he oversaw the test explosion of the first nuclear bomb at Alamogorclo. Returning to Harvarc! after . a the war, he renewer! his work with mass spectrographs, be- gan the construction of a new cyclotron, en c! was able to measure changes in the clecay rates of some radioactive nuclei resulting from differing molecular boncling en c! from physical compression. 19

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20 BIOGRAPHICAL MEMOIRS FAMILY BACKGROUND Kenneth Bainbricige was born on July 27, ~ 904, in Cooperstown, New York, the seconc! of three brothers. He grew up in New York City, attending the Horace Mann School en c! the Horace Mann High School. He attributer! his early interest in technology to the influence of two uncles who were engineers. His Uncle George worker! on switching en c! safety crevices for the New York subway en c! conceivec! a form of safety braking, but he was beaten out by Westinghouse, which hac! clevelopec! a better system. The Bainbricige family five c! on Riverside Drive near 15Sth Street en c! the Hucison River, where just after WorIc! War I return- ing naval vessels clockocI. As a high schooler, Ken became interested in radio, on the famiTy's rooftop he put an an- tenna that came to the attention of ship raclio operators, who wouIc! knock on his floor to investigate. These contacts enablec! him to acquire rare 5-watt vacuum tubes from his callers for a couple of clolIars. With those tubes he was able to set up a racliotelephone, obtainer! a raclio amateur li- cense, en c! operates! a "ham" station with call letters 2WN (this was before the national prefix letter "W" was usecI.) COLLEGE YEARS Ken gave up his activities in raclio en c! schoolboy chemis- try, when in 1921 he enterer! MIT to study electrical engi- neering in a cooperative program with the General Electric Company. In that five-year program he was able to receive both an S.B. en c! an S.M. degree en c! to work summers at one of the General Electric facilities. In Ken's case this was at first in Lynn, Massachusetts, en c! then mostly at the Re- search Laboratories in Schenectady, New York. After comple- tion, a natural consequence of his participation in the co- operative program with GE wouIc! have been for him to

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KENNETH TOMPKINS BAINBRIDGE 21 continue as an engineer at General Electric. As an out- growth of his work there, Ken obtainer! patents on photo- cathocle materials for photocelIs2 en c! on amplification of photocurrents by secondary emission cathocles3. His work at the GE laboratories hacI, however, brought him to realize that his strong interest was in physics, en c! his colleagues there acivisec! him to Took to Princeton University for graduate work. Among those Divisors was Karl T. Compton, who servec! as a consultant to GE en c! was then heat! of the physics department at Princeton. With Tom Killian, his frienc! from his years at MIT, Ken applier! to Princeton, en c! they were acimittec! in 1926. He clescribec! the two young men's interview with Dean West soon after their arrival, en c! creclitec! West with saying, "You're nice boys, but it's too bac! you never went to college." After repeating that story, Ken usually inclicatec! that, with his immersion into the collegiate Princeton atmosphere, he hac! soon somewhat macle up for that lack in his background. As a graduate student in physics at Princeton, he became in- terestec! primarily in the cleveloping study of nuclei, which hac! not yet become well coverer! in formal course work. Ken's initial attraction to mass spectroscopy was exciter! by his desire to search for the then uncletectec! element 87 of the periodic table, an element that shouIc! behave chemi- cally as a heavy alkali, en c! which he therefore wouic! call eka-cesium. He searcher! for it mainly in materials extractec! from ores that were rich in the lighter alkalis lithium, so- clium, potassium, rubidium, en c! cesium without success. Element-87 turns out to exist naturally only as short-livec! isotopes resulting from the clecay of actinium, the longest- livec! having a half-life of 22 minutes. It was finally fount! in 1939 by Marguerite Percy at the Curie Laboratory of the Radium Institute of Paris, en c! hence has become known as "francium. "

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22 BIOGRAPHICAL MEMOIRS THE YEARS BEFORE WORLD WAR II After completing his Ph.D. program at Princeton, Ken Bainbricige spent four years, first as a National Research Council fellow en c! then as a Barto! Research Foundation fellow, at the Franklin Institute's Barto! Research Founcia- tion. The "Bartol" was then locater! on the campus of Swarthmore College in Pennsylvania, en c! was clirectec! by the eccentric Englishman, W. F. G. Swann, who was espe- cially interested! in research on cosmic rays en c! nuclear physics. (I use the term "eccentric" in recalling his frequent participation in the meetings of the American Physical So- ciety with comments from the front row seats. He often carrier! his cello along en c! his Tong white hair, perhaps even then less remarkable for a musician, was quite uncon- ventional at that time for a physicist.) It was there that Ken continues! to clevelop his mass spectrographs en c! to uncler- take precise nuclear mass measurements, which he user! to confirm the mass-energy equivalence, E = Mc2. In September 1931 Ken en c! Margaret ("Peg") Pitkin, then a member of the Swarthmore teaching faculty, were mar- riecI. In the summer of 1933 they traveler! to Cambridge, EnglancI, where, as a John Simon Guggenheim fellow, Ken joiner! Lorc! Ernest Rutherforcl's Cavenclish Laboratory, then a worIc! leacler in experimental nuclear physics. Ken cle- scribec! (1975) his first encounter there with the iclea of a nuclear chain reaction when Rutherforc! stopper! him in passing in a corridor to ridicule as obviously impractical a suggestion just macle to him by a visitor, Leo SzilarcI, for such a process based on protons. Szilard went on to envis- age a much more practical process involving neutrons, which, of course, only became reality after neutron-induced ura- nium fission was discovered. At Cambridge Ken continued to pursue mass spectroscopy and began a continuing close

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KENNETH TOMPKINS BAINBRIDGE 23 friendship with John D. Cockroft (later to become Sir John). Martin K. Bainbridge, the first child of Ken and Peg was born in Cambridge, England, in 1933. In September of 1934 Ken returned to the United States and began his long association with the physics department at Harvard University. He built and employed the improved mass spectrograph he had designed during his sojourn at the Cavendish Laboratory. With the collaboration of I. Curry Street he also undertook to build a cyclotron. He was grate- fuT to E. O. Lawrence of the University of California at Berkeley for assisting them in the design by sending details of his new 37-inch cyclotron. It was a lifelong characteristic of Ken's style that he thoroughly documented all of his projects and, to emphasize that point, he said (1975), "In the event the cyclotron was ever mislaid, stolen, or bor- rowed, I knew I could identify it and later did at Los Alamos." The operational cyclotron was requisitioned in 1943 by the U. S. Army, dismantled, and rebuilt at the weapons laboratory. It remained there after the war, never to return to Harvard. Bainbridge's interest in mass spectroscopy of nuclei led him to modify the naturally occurring abundances of nuclear isotopes, and he proposed a method using gaseous counterflow in a Holwock molecular vacuum pump. With the discovery of uranium fission he recognized the impor- tance of enrichment Of MU and enlisted colleagues from the Harvard chemistry department George B. Kistiakowsky and E. Bright Wilson in pursuing such a project. A trial experiment with argon gas confirmed their expectations, but when they sought to gain the interest of officials in Washington in 1940, they were told to forget it, that ciassi- fied work was going on, and "the situation kwas] well in hand."

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24 BIOGRAPHICAL MEMOIRS THE WAR YEARS As Europe became embroilec! in WorIc! War II en c! with the resulting recognition of a new! for increaser! military preparations in the Uniter! States, an exchange of military technical secrets with the beleaguered! British was uncler- taken. This was the subject of the Tizarc! Mission from Brit- ain in September of 1940. A major element of the exchange turner! out to be a demonstration by the British of the newly developed puIsed-cavity magnetron, which produced many kilowatts of peak power at a microwave frequency near the 10-cm wavelength. The members of the microwave subcommittee, chairec! by Alfrec! Loomis of the National Defense Research Committee, were so exciter! by the clem- onstratec! performance that they undertook almost over- night to establish a special laboratory to develop microwave "radar" around it. Kenneth Bainbridge was the first scien- tist not aIreacly involves! with the committee to be recruiter! (by E. O. Lawrence) to the laboratory, which became the Racliation Laboratory at the Massachusetts Institute of Tech- nology. On a leave of absence from Harvard, he spent more than two en c! one-half years on that project, cluring a part of which, in the spring of 1941, he participates! in a mission to Britain. In wartime activities that involved close collaboration with parallel projects in Britain, Ken's friendship with British physicists, especially with Cockroft, who hac! been a scien- tist member of the Tizard Mission, was an asset. On his visit he gainer! information about not only the racier program but also learner! of British progress towarc! releasing nuclear energy while attending a meeting of the Maul! Committee, which was overseeing that effort in Britain. Ken's particular project at the Racliation Laboratory was the push towarc! higher-powered radars, especially for the Navy. He found the Navy at that time the most technically oriented! of the

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KENNETH TOMPKINS BAINBRIDGE 25 U. S. military services en c! the least hanclicappec! by proto- cols relater! to military rank. This experience was reflected! in his concern about the organization of Los Alamos, where he was recruitec! in May of 1943, which operates! uncler the Manhattan District of the U. S. Army en c! General Leslie R. Groves. The Bainbricige's two daughters loan (Bainbricige) Safforc! en c! Margaret Tomkins (Bainbricige) Robinson were born in Cambridge, Massachusetts, well before the family mover! to Los Alamos. At Los Alamos early in 1944, at the request of George Kistiakowsky en c! Director I. Robert Oppenheimer, Ken un- clertook the oversight of the design of high explosive as- semblies en c! preparations for a full-scare test of a nuclear bomb. In articles in the Bulletin of the Atomic Scientists (1975), he lucicIly clescribec! the search for an appropriate site, the preparations, en c! the successful carrying out of the test early in the morning of July 16, 1945. He titles! the seconc! of those stories "A Foul en c! Awesome Display." His remark to l. Robert Oppenheimer immecliately after the event "Now we are all sons of bitches" marked the beginning of his cleclication to encling the testing of nuclear weapons en c! to efforts to maintain civilian control of future clevel- opments in that fielcI. RETURN TO ACADEMIC LIFE In the fall of 1945 Ken was at last free to return to aca- clemic science at Harvard. He undertook then to built! a large mass spectrograph, clesignec! for high resolution of masses en c! to replace the prewar cyclotron with a much more powerful one utilizing the then newly inventec! con- cept of synchronous acceleration. The relativistic increase of effective mass as the protons gainer! energy was compen- sated by sweeping the radio frequency down appropriately cluring an acceleration cycle. The latter project was hanclec!

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26 BIOGRAPHICAL MEMOIRS over to Robert R. Wilson, who hac! joiner! the physics cle- partment at Harvarc! after the enc! of the war. Wilson, how- ever, was recruitec! to heat! the large nuclear physics group at Cornell after residence at Harvarc! for just one semester. Norman F. Ramsey was then recruitec! to the Harvarc! cle- partment en c! assumer! responsibility for managing the con- struction of the new cyclotron. Its design hac! been com- pleted before discovery of the pi meson as the particle mediating nuclear forces. The energy of the new synchrocy- clotron turner! out to be just less than requires! for plan procluction. For about a clozen years the new Harvarc! cy- clotron was employoc! for many scattering experiments en c! other studies of nucleon-nucleon forces en c! of nuclear struc- ture. The operating life of the cyclotron was greatly ex- tenclec! when it became a facility for research on the use and clinical applications of the highly focused proton beam in collaborative projects with staff members from the Mas- sachusetts General Hospital. It will be shut clown finally in the late 199Os, when its role will be taken over by an even more powerful cleclicatec! machine at the hospital, enabling further expansion of the important clinical applications clevelopec! using the physics cyclotron. Ken clevotec! much of his energy just after the war to designing for the Harvarc! physics department an acivancec! laboratory in nuclear physics intenclec! as a course of study for graduate students. Because of the many new students underwritten by the GI Bill, the number of graduate stu- clents in physics was far greater than hac! been the norm before the war. Nuclear physics had gained new visibility en c! popularity from its contributions to winning the war. Students gainer! their first experience in activities prepar- ing them for research in experimental physics in Ken's me- ticulously clesignec! en c! clocumentec! laboratory. The ex- periments ranger! from a replica of l. l. Thompson's positive

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KENNETH TOMPKINS BAINBRIDGE 27 ray apparatus (a precursor of mass spectrographs) through a bent crystal X-ray spectrograph, a IS0 beta-ray spectrograph using the then new technique of NMR for fielc! calibration, to analysis of tracks in photographic emulsions to identify muons. As a part of Ken's clislike of the clevelopment en c! testing of nuclear weapons, he set up a facility associates! with his laboratory of nuclear physics to collect en c! mea- sure radioactive fallout. In his own research he built bal- ancec! ionization chambers with which he was able to cleter- mine changes in lifetimes of several Tong-livec! isomers, which clecay by internal electron conversion when their atoms are clifferently bonclec! chemically or are subjectec! to physical compression. In aciclition to constructing his large mass spec- trograph to make precise measurements of mass differences among pairs, he built an elegant clouble-focusing electron spectrograph. In the years before his retirement in 1975, Ken clevotec! much of his time to improving the graduate student acivancec! laboratory en c! to cleveloping a similar version for acivancec! unclergracluates. Among his other con- tributions to teaching were lecture courses on nuclear physics, mainly for graduate students. From 1950 to 1954 Ken server! as chairman of the physics department at Harvard. This was a time market! by the vicious attacks on certain members of academia, en c! espe- cially at Harvard, by the House Un-American Activities Com- mittee en c! a committee of the Senate clominatec! by Sena- tor Joseph McCarthy. Ken gave generously of his time en c! energy overseeing the relationship between the university administration en c! one of our colleagues who became a prime target of these attacks. Two legacies of Ken's years as chairman were a renova- tion of a part of the then seventy-year-oIc! Jefferson Physical Laboratory en c! the establishment of the Morris Loeb Lec- tures in Physics. Both were enabler! by use of a part of a

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28 BIOGRAPHICAL MEMOIRS newly available endowment funcI, which hac! been hell! in trust for many years. Thus the Morris Loeb endowment was sharer! between the chemistry en c! physics departments. A characteristic of Ken's style of work in his cleveloping of instruments, lecturing in courses, research, en c! aciministra- tive activities was a meticulous documentation en c! keeping of records, habits of enormous help to his successors in all those projects. In the late 1950s Ken was one of the first members of the Harvarc! faculty to participate in a new academic exchange program with the Soviet Union. Harvarcl's sister university was clesignatec! to be the University of Leningrad. Almost concurrent with his arrival in Leningrac! there occurrec! the incident of the crash of the RB72 reconnaissance plane somewhere off Murmansk, which threw a clifficult shallow over his relationship with his Soviet hosts, but the tension relaxer! cluring the course of his stay. In June 1975 in his last year before his retirement, Bainbricige was enTistec! to serve on a joint Iran-Harvarc! planning commission to design Reza Shah Kabir University for Iran. Ken en c! his Harvarc! colleagues macle visits to Iran, however this project was short liver! because of the political upheaval en c! expulsion of the Shah from Iran. Ken's years in Los Alamos and Alamogordo, New Mexico, proviclec! him an opportunity to inclulge in his Tong estab- lished amateur interest in mineral crystallography, a source of great pleasure. He hac! always enjoyoc! outings in the mountains, even in New England, to collect specimens, and New Mexico brought a much expanclec! dimension to that interest. In January 1967 Ken sufferer! a tragic Toss when his wife Margaret (Pitkin) Bainbricige, the mother of his three chil- dren, died suddenly at their home in Watertown, Massachu- setts, from a blooc! clot associates! with a recently fractures!

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KENNETH TOMPKINS BAINBRIDGE 29 wrist. Ken, Peg, en c! their chiTciren hac! former! a great at- tachment to the islanc! of Martha's Vineyard, where they hac! spent many of their summers as tenants in a cottage in Chilmark overlooking Chilmark Ponc! just below Abel's Hill. They hac! finally been able to buy a piece of lane! there en c! hac! just completec! their own summerhouse the year before Peg's suciclen cleath. That beautifully situates! house was cle- signec! en c! constructor! with the same careful attention to cletail that exemplifiec! all of Ken's personal en c! profes- sional activities. His daughters have clescribec! instructions he left for the continues! upkeep of the house, especially its extensive cleck, willing that a supply of the neeclec! materi- als was storm! in the basement. Peg, their son Martin, en c! finally Ken were all buries! in a plot in the small historic cemetery on Abel's Hill overlooking their house below. I (R.V.P.) am grateful to Ken for also introducing my wife en c! me to the beauties of the islanc! as long ago as 1950, where we, too, were able to spenc! several happy holiciays. In October 1969 Ken marries! Helen Brinkley King, an oIc! frienc! then serving as an editor for the William Mor- row publishing house in New York City. She, as well as his son Martin Keeler Bainbricige, precleceasec! him. He is sur- vivec! by his two daughters loan Bainbricige Safforc! of Evanston, Illinois, who is deputy Uniter! States attorney for the northern district of Illinois, en c! Margaret Bainbricige Robinson of Clevelanc! Heights, Ohio, who is clean of un- clergracluate studies at Case Western Reserve University, en c! five grancichiTciren. CONCLUSION Kenneth Bainbricige contributes! extensively to the clevel- opment of the field! of nuclear physics cluring his many active years. Especially notable were his several designs of mass spectrographs en c! their many applications to the stucly

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30 BIOGRAPHICAL MEMOIRS of nuclear isotopic masses en c! energy-mass equivalence. Other important contributions to nuclear physics were his early construction of cyclotrons en c! his discovery of the effect of chemical states on nuclear clecay rates. During Woric! War II, as the first recruit to the MIT Racliation Laboratory, he macle major contributions to the microwave racier program of the Allies en c! then mover! on to Los Alamos, where he oversaw the preparations en c! carrying out of the first test nuclear explosion. He was a strong acivocate of civilian con- tro! of nuclear clevelopments en c! clevotec! time en c! energy to efforts to restrict any first use of nuclear weapons by the Uniter! States. Bainbricige, as a teacher, introclucec! many students to the science of physics, especially nuclear phys- ics, through his lecture courses en c! his acivancec! labora- tory. He was a careful designer and painstaking keeper of records. The work of his colleagues en c! his successors in the enterprises he hac! clevelopec! gainer! enormously from his pioneering contributions, detailed designs, and meticu- Tous recorc! keeping. He was a mocle! of personal en c! scien- tific integrity en c! a personal frienc! who is much missecI. Kenneth Bainbricige was awarclec! the Levy Mecial of the Franklin Institute in 1934. He was electec! a fellow of the American Academy of Arts en c! Sciences in 1937 en c! a mem- ber of the National Academy of Sciences in 1946. He was the recipient of two letters of commendation from General Leslie R. Groves for his work on the Manhattan Project and the Presidential Certificate of Merit for his services as staff member of the MIT Racliation Laboratory, ESPECIALLY HELPFUL sources for this memoir were an interview of K. T. Bainbridge by John Bryant published as "Rad Lab: Oral Histories Documenting World War II Activities at the MIT Radiation Laboratory" published by the IEEE in 1993 and the Bainbridge articles in the Bulletin of the Atomic Scientists cited in the bibliography (1975~.

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KENNETH TOMPKINS BAINBRIDGE NOTES 31 1. K. T. Bainbridge and others. Jabez Curry Street 1906-1989. In Biographical Memoirs, vol. 71, pp. 346-55. Washington, D. C.: Na- tional Academy Press, 1997. 2. Photo-electric tubes, patent no. 1,901,577; method of prepar- ing photo-electric tubes, patent no. 1,901,578 (British patent no. 303,476~. 3. A method of amplifying photo-electric currents by means of secondary emission from an auxiliary cathode, patent no. 2,206,713.

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32 BIOGRAPHICAL MEMOIRS SELECTED BIBLIOGRAPHY 1929 A search for element 87 by analysis of positive rays. Phys. Rev. 34:752- 62. 1930 Simple isotopic constitution of caesium. Phys. Rev. 36:1668. 1931 The isotopes of lithium, sodium, and potassium. 7. Franklin Inst. 212:317-39. 1932 A mass spectrograph. Phys. Rev. 40:130A. 1933 Comparison of the masses of He and Hi on a mass spectrograph. Phys. Rev. 43:103-105. The equivalence of mass and energy. Phys. Rev. 44:123. Atomic masses and structure of atomic nuclei.7. Franklin Inst. 215:509- 34. 1936 With E. B. Jordan. Mass spectrum analysis.]. The mass spectrograph. 2. The existence of isobars of adjacent elements. Phys. Rev. 50:282 96. 1940 The Harvard cyclotron. Harv. Alumni Bull. May 17. 1941 With R. Sherr and H. H. Anderson, Transmutation of mercury by fast neutrons. Phys. Rev. 60:473-79. 1951 With A. A. Bartlett. High resolution two-directional focussing beta- ray spectrometer. Rev. Sci. Instrum. 22:517-23.

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KENNETH TOMPKINS BAINBRIDGE 1951 33 With M. Goldhaber and E. Wilson. Influence of the chemical state on the lifetime of an isomer. Phys. Rev. 84:1260-61. 1953 With M. Goldhaber and E. D. Wilson. Influence of the chemical state on the lifetime of a nuclear isomer, Tc99m. Phys. Rev.90:430- 39. Charged particle dynamics and optics, relative isotopic abundances of the elements, atomic masses. In Experimental Nuclear Physics, vol. I, ed. E. Segre. New York: Wiley and Sons. With J. J. Kraushaar and E. D. Wilson. Comparison of the values of the disintegration constant of Be7 in Be, BeO, and BeF2. Phys. Rev. 90:610-14. 1957 With T. L Collins. A large mass spectrograph. In Proceedings of the Conference on Nuclear Masses and Their Determination, MAINZ, 1956. Pergamon Press. 1960 With P. E. Moreland. The mass spectrometer at Harvard University. In Proceedings of the International Conference on Nuclidic Masses. Toronto: University of Toronto Press. 1966 With A. C. Malliaris. Alteration of the decay constant of Tei25M by chemical means. Phys. Rev.149:958-64. 1967 With J. W. Dewdney. Use of a lock-in amplifier for mass doublet measurements by the coincidence method. In Proceedings of the 3rd International Conference on Atomic Masses, Winnipeg, Manitoba, Canada, 28 Aug. -1 Sept. 1967, pp. 758-76. Winnipeg: University of Manitoba Press. 1969 With A. Olin. Influence of superconductivity on the half-life of nio- bium-9Om. Phys. Rev. 179:450-52.

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34 BIOGRAPHICAL MEMOIRS 1971 With D P. Kerr The 235U-207Pb and 238U-208Pb mass differences. Canad. J. Phys. 49:756-60. With D. P. Kerr. The i4ND-~5NH mass differences. Canad. i. Phys. 49:1950-51. 1975 All in our time Prelude to Trinity. Bull. At. Sci. 31~4~:42-46. All in our time Afoul and awesome display. Bull. At. Sci. 31~5~:40- 46.

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