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EDWIN MATTISON MCMILLAN September ~ 8, ~ 907-September 8, ~ 99 ~ BY J. DAVID JACKSON AND W. K. H. PANOFSKY WITH THE DEATH OF Edwin Mattison McMilIan on Sep- tember 8, 1991, the woric! lost one of its great natural scientists. We acivisecITy use the term "natural scientist" since McMilIan's interests transcenclec! greatly that of his profes- sion of physicist. They encompassed everything natural from rocks through elementary particles to pure mathematics and included an insatiable appetite for understanding ev- erything from funciamental principles. Edwin McMillan spent a large part of his professional life in close association with Ernest 0. Lawrencei ant! succeeclec! Lawrence as director of what is now the Lawrence Berkeley Laboratory in 1958. Yet the two men conic! hardily be more different. Lawrence was a man of great intuition, outgoing, en c! a highly capable organizer of the work of many people. Edwin McMillan was thoroughly analytical in whatever he clic! en c! usually worker! alone or with few associates. He clisTikoc! specialization en c! the division of physics cliviclec! into theory en c! experiment. He remarkoc! at an interna- tional high-energy physics meeting, "Any experimentalist, unless proven a ciamn fool, shouic! be given one half year to interpret his own experiment." McMilIan's first en c! last publications illustrate the un- usual breadth of his interests. While still an undergraduate 215
216 B I O G RA P H I C A L EMOIRS student in 1927, he published a papers on the x-ray study of alloys of lead and thallium, clearly a topic in chemistry. At the time, he took many more courses in chemistry than was customary for a physics major, and this publication was undertaken at the suggestion of Linus Pauling. His last pa- per,3 written together with the mathematician Richard P. Brent, was on an improved algorithm for computing EuTer's constant: the limit of the difference between the sum of the inverse integers from ~ to n and the natural logarithm of n, as nacho. One of us 0.D.~.) recalls an incident that illustrates Ed McMilIan's range in science. When Jackson corresponded at the beginning of 1957 with Luis Alvarez and his col- leagues about muon-catalyzed fusion, he was startled to re- ceive facsimile copies of handwritten notes by McMilIan on a calculation of the mu-mesic molecular formation process! At that time, he knew McMilIan's name as the discoverer of neptunium, the codiscoverer of plutonium, and the inven- tor of phase stability in accelerators but never dreamt that he was a molecular theorist! At the time, Ed was busy as associate director under Lawrence. His molecular physics Ph.D. thesis research with Condon could be the origin of such expertise, but with McMilIan it could just as easily be knowledge acquired for the fun of it. The son of Edwin H. McMillan and Anna Maria Mattison, Edwin M. McMilIan was born on September 18, 1907, in Redondo Beach, California, both parents were Scots. He was brought up in Pasadena, California, beyond age one and a half. His father was a physician, as were the parents of his wife Elsie McMilIan (born Blunter), who incidentally is the sister of E. O. Lawrence's wife, Molly. McMillan is survived by his wife and their three children (Ann Bradford Chaikin, David Mattison McMilIan, and Stephen Walker McMillan). They were a wonderful and harmonious family.
EDWIN MATTISON MCMILLAN 217 As a chiTcI, McMillan built gadgets en c! macle use of the proximity of the California Institute of Technology in at- tencling lectures en c! seminars en c! getting acquainted! with physicists there. After high school McMillan enterer! CalTech, where he hac! a first-rate academic recorc! leacling to both the B.S. en c! M.S. degrees. He completer! his work leacling to the Ph.D. at Princeton University in 1932. McMilIan's work can be separates! into five phases that exhibit a great clear of overlap not surprising considering the universality of McMillan's interests: ~ ~ ~ the early prewar period, (2) studies of the transuranic elements, (3) military work cluring WorIc! War II, (4) accelerator physics, en c! (5) laboratory director. These phases were paralleled! by work on advisory committees en c! other roles as a statesman of science. THE EARLY PREWAR PERIOD McMilIan's Ph.D. thesis, uncler Professor E. U. Conclon, examiner! the generation of a molecular beam of hyciro- gen-chIoricle nuclei in a nonhomogeneous electric fielcI.4 In parallel, McMilIan received a thorough education in ex- perimental nuclear physics at Princeton. He publisher! a papers on the isotopic composition of lithium in the sun from spectroscopic observations immediately after receiv- ing his Ph.D. He then won a highly prizes! National Re- search Council (NRC) fellowship, supporting him at any university of his choice. He accepted! the invitation of E. O. Lawrence to come to Berkeley, where Lawrence was at the time engaged in ex- ploring the experimental potential of the cyclotron. After McMillan accepted! Lawrence's invitation, he cleclicatec! his first two years to activities somewhat separate from the main- stream activities of Lawrence's new Racliation Laboratory. He intenclec! to measure the magnetic moment of the pro
218 B I O G RA P H I C A L EMOIRS ton, but that plan came to naught when Otto Stern en c! collaborators in Germany clic! the measurement. He contin- ucc! to work on hyperfine structure as revealer! in optical spectroscopy en c! publisher! papers on the nuclear magnetic moment of ten talum6 as well as on the hyperfine structure of the solar spectrum.7 But McMilIan became progressively more involves! with the work on Lawrence's cyclotron, which by early 1934 conic! produce a cleflectec! beam of 2.3-MeV cleuterons. His experimental skill was recognizec! by Lawrence en c! his collaborators en c! was put to increasing use on both the cyclotron en c! its instrumentation en c! physical experi- ments with the beam. McMillan user! the extractec! cleuteron beam in collabo- ration with M. Stanley Livingston to irradiate nitrogen to produce the positron emitting i50. Again, McMilIan's skill as a chemist was put to work. He user! a tracer technique in which first nitrogen gas was bombarclec! en c! then mixer! with oxygen en c! an excess of hydrogen. This mixture was catalyzer! to water over heater! platinizec! asbestos, en c! the water was collected! on anhycirous calcium chIoricle. The radioactivity was shown to be localizes! in the calcium chIo- ricle en c! absent elsewhere, proving that oxygen carrier! the activity.8 This work was follower! by funciamental studies on the absorption of gamma rays,9 which revealed the (at that time new) process of electromagnetic pair procluction in the Coulomb field! of a nucleus. The 5.4-MeV gamma ray pro- duced by bombardment of fluorine with protons and also the gamma rays of other isotopes were absorber! by foils of aluminum, copper, tin, en c! leacI, enabling McMilIan to iso- late the components of the absorption process. At 5.4 MeV, electron-positron pair production is about one-half the to- tal absorption cross-section in lead. In 1935, with Lawrence en c! R. L. Thornton, McMillan
EDWIN MATTISON MCMILLAN 219 stucliec! the radioactivity proclucec! when a variety of targets are exposer! to a cleuteron beam.~° At cleuteron energies below 2 MeV, the activity increases rapicIly with energy, as expecter! from the quantum mechanical penetration of the Coulomb barrier, first user! to explain alpha radioactivity lifetimes by George Gamow. The experiments of McMilIan en c! coworkers on (cI,p) reactions with energies up to 3.4 MeV shower! that the yielc! curves flattener! above 2 MeV, even though the Coulomb barrier effects were expecter! to be consiclerably steeper from conventional estimates of the effective nuclear raclli. A cleuteron seemec! to be able to have its neutron captures! by the target nucleus while its proton remainec! relatively far away. These ciata intrigues! l. Robert Oppenheimer en c! his student, Melba Phillips, who then clevelopec! the theoretical explanation of the phenom- enon: the small bincling energy, en c! therefore large size, of the cleuteron permits it to be polarizer! in the nuclear Cou- lomb fielcI, this polarization places the neutron within the cleuteron close to the nucleus, accessible for capture, while the proton is away from it. In essence, the proton becomes a "spectator" of the process. The Oppenheimer-Phillips pro- cess gives a quantitative explanation of the energy indepen- clence of the yielc! curves en c! the predominance of the (cI,p) reactions in cleuteron bombardments. Following this work McMillan investigatec! the properties of i°Be, with its extraordinarily long half-life for a light element (approximately 2.5 million years). He pursued fur- ther details of the properties of i°Be in later publications. During that perioc! McMilIan clic! several aciclitional experi- ments in what tociay has become nuclear chemistry, some of them successful en c! some unsuccessful. At the same pe- riod, he wrote a seminal paperi2 on the production of X rays by the acceleration of very fast electrons, a subject in which he maintainer! a lifelong interest.
220 B I O G RA P H I C A L EMOIRS McMillan macle numerous experimental contributions to the cyclotron, in particular to its beam-focusing properties, to beam extraction, en c! to vacuum gauges. His creep uncler- stancling of the factors that limit the energy attainable by conventional cyclotrons is illustrates! by his correspondence in late 1937 en c! early 1938 with Hans Bethel Bethe hac! worker! with M. E. Rose at Cornell on the energy limit prob- lem, en c! McMilIan was carrying out calculations at Berke- ley with Robert R. Wilson developing orbit-tracing meth- ocis. In 1937 Bethe sent an advance copy of the Bethe-Rose paper to McMilIan. McMilIan fount! some errors in the pa- per en c! shower! that the electrostatic defocusing effect of the cyclotron clee's conic! be counteracted! by the insertion of grids. McMilIan also unclerstooc! clearly the focusing ef- fect of the raclial fall-off of the magnetic field! en c! the mag- nitucle of the deviation from the synchronicity conclition in the cyclotron proclucec! by that raclial fall-off, aciclec! to the relativistic mass increase. Bethe suggester! that McMilIan publish his finclings, but characteristically McMillan felt that an aciclitional paper wouIc! be reclunciant. The correspon- dence demonstrates McMilIan's deep quantitative mastery of the subject while at the same time exhibiting his basic humility. He preferred making an input to the Bethe-Rose paper over cluttering up the literature with controversy. STUDIES ON TRANSURANIC ELEMENTS The discovery of fission of uranium by Hahn ant! Strassmann in 1939 initiates! intense activity woric~wicle. At Berkeley McMilIan first performer! a simple experiment to measure the ranges of the energetic fission fragments by exposing a thin layer of uranium oxide on paper sandwiched between several thin aluminum foils on either side to the neutrons from S-MeV deuterons striking a beryllium target in the 37-inch cyclotron. The amounts of radioactivity in
EDWIN MATTISON MCMILLAN 221 successive foils establishec! the maximum range of the frag- ments as equivalent to approximately 2.2 centimeters in air. He also user! cigarette papers insteac! of the aluminum foils in another sandwich en c! follower! the radioactivity in clif- ferent papers after bombardment, fincling the same time clepenclence in all. In contrast, the activity associates! with the layer of paper on which the uranium oxide hac! been placer! hac! different components. In aciclition to the fission fragment activity, there was one component with a twenty- five-minute half-life and another of roughly two days. McMilIan speculatec! that the twenty-five-minute activity was 239U, iclentifiec! earlier by Hahn en c! co-workers as a procI- uct of resonant neutron capture in uranium.~3 The two-clay nonrecoiling activity intriguer! McMilIan. Accorclingly, he bombarclec! thin ammonium uranate layers clepositec! on a bakelite substrate en c! coverer! with cello- phane (to catch the energetic fission fragments). After ex- posure to the neutrons, the ammonium uranate was scraper! off the bakelite en c! its activity followocI. At Tong times the 2.3-clay activity was dominant, at short times, the twenty- three-minute half-life Of 239U preclominatecI. In contrast, the cellophane shower! the characteristic power law clecay associates! with a mixture of fission fragments of different lifetimes. With the new activity physically separated, it was possible to begin stucly of its chemical properties. As a pu- tative new element next to uranium, the activity seemec! likely to have chemical properties akin to rhenium. McMilIan therefore enTistec! Emilio Segre, who was familiar with the chemistry of rhenium from his discovery of a homolog, technetium, in 1937. Segre found that the 2.3-day activity behaves! like a rare earth, not like rhenium. Since rare earths are prominent among the fission fragments, it appearec! that the 2.3-day activity was one of those. After a gap in his pursuit, McMillan had become persuaded by early 1940 that
222 B I O G RA P H I C A L EMOIRS the nonrecoiling 2.3-day activity just could not be the decay of a fission fragment. He began a set of experiments with the new 60-inch cyclotron en c! its 16-MeV cleuterons. Two observations confirmed! his belief as a certainty. One, using cadmium absorbers to recluce the thermal neutrons, shower! greatly reclucec! fission activity but left the two nonrecoiling activities in the same relative proportion. The other, a fis- sion product experiment with extremely thin colloclion catcher foils, shower! that the range of the 2.3-clay "frag- ments" was less than 0.! millimeter of air equivalent. The 2.3-clay activity conic! not be from fission, the twenty-three- minute en c! 2.3-clay activities almost certainly were geneti- cally relatecI. The beta clecay Of 239U was producing atoms of a new element with Z = 93! McMilIan fount! chemically that the 2.3-clay activity hac! some, but not all, the charac- teristics of a rare earth. Philip H. Abelson was a student at Berkeley in 1939, work- ing on the chemistry of fission products en c! was familiar with McMillan's first observations of the 2.3-clay activity. In 1939-40 at the Carnegie Institution in Washington, D.C., Abelson attempter! (unknown to McMilIan) to separate the 2.3-day activity, initially with rare-earth chemistry, but found his procedures inadequate. In May 1940, as McMilIan was cloing his chemistry, Abelson came to Berkeley en c! they began a collaboration. The key to successful chemistry, as Abelson founcI, was control of the state of oxidation of the material. In the reduced state the activity coprecipitates with rare-earth fluorides, when in an oxiclizec! state it floes not. In fact, the oxiclizec! state behaves similarly to uranium, coprecipitating with sodium urany! acetate. On the other hancI, uranium floes not precipitate in an HE solution with SO2, while the 2.3-clay activity coprecipitates with rare-earth carriers. Abelson and McMilIan were thus able to use an "oxiciation-recluction cycle" to make a series of precipita
EDWIN MATTISON MCMILLAN 223 lions of the 2.3-clay activity from a urany! solution en c! es- tablish its growth from the twenty-three-minute 239U, thus proving it to be an isotope of element 93. They searcher! for alpha activity associates! with the clecay product of the 2.3-clay isotope (an isotope of element 94) en c! notes! that it must be long-livecI. The work was submitter! to the Physi- cal Review on May 27, 1940.~4 The technique of an oxicia tion-recluction cycle former! the basis of all the transuranic chemistry to follow. After Abelson's return to Washington, McMillan turner! to the search for the alpha activity of the daughter of 239Np (as we now denote it). Strong samples of the 2.3-clay activity clic! show some alpha particle emission, clistinguishec! from possible natural uranium activity by greater range. With the hope of producing a different isotope of neptunium en c! so its clecay product, McMillan bombarclec! a uranium target clirectly with 16-MeV cleuterons. A two-clay beta activity, with 1 1 more energetic beta particles than the earlier 2.3-clay cle- cay, was observed, along with a consiclerably more intense 5-MeV alpha activity (now known to be from 238Pu, ninety- two-year half-life). He trier! to separate the alpha activity chemically, eliminating protactinium, uranium, en c! nep tunium as species, while showing that it behaves! similarly to thorium en c! 4-valent uranium. In November 1940 McMillan left Berkeley for military work at MIT. Glenn T. Seaborg, who, with colleague I. W. Kennedy en c! graduate student A. C. Wahl, hac! perfected the oxiciation-recluction technique for isolating neptunium, wrote to McMilIan to say that they wouIc! "be very glac! to carry on in his absence as his collaborators" in the search for element 94.~5 McMillan replier! (in Seaborg's worcis), "informing me that he will not be back soon in Berkeley en c! it wouIc! please him very much if I continue to work on elements 93 en c! 94.~6 McMillan's letter explicates! his own
224 B I O G RA P H I C A L EMOIRS finclings on the physical en c! chemical characteristics of the various activities. Following McMilIan's leacI, by late February 1941 Seaborg, Kennedy, en c! Wah! hac! macle definite the discovery of the ninety-two-year isotope of element 94 (238Pu). A short pa- per on the joint work with McMilIan was submitter! to the Physical Review on January 2S, ~941 (before the final proof of separation from thorium hac! been madly but was volun- tarily withheld from publication until 1946.~7 For his discovery of neptunium with Abelson en c! of plu- tonium with Kennedy, Seaborg, en c! Wahl, McMilIan sharer! with Seaborg the Nobel Prize in chemistry in 1951. MILITARY WORK DURING WORLD WAR II McMilIan's first assignment at MIT in November 1940 was work on airborne microwave racier at the newly estab- lished MIT Radiation Laboratory. The work initially capital- ~zec! on his technical en c! physical ingenuity, but when em- phasis shifter! from incliviclual invention to collaborative engineering, McMilIan mover! to the U.S. Navy Raciar en c! Sounc! Laboratory in San Diego in 1941. There he inventec! en c! clevelopec! a repeater for underwater echoes that greatly extended the detection range of undersea warfare devices. He was then recruited by J. Robert Oppenheimer, who had been appointed director of the Los Alamos weapons labo- ratory to be en c! server! as his principal aciviser on practical technical issues, starting in the fall of 1942. McMillan's nuclear weapons work started with the site selection of Los Alamos. He then led the development of the gun-type weapon, a device in which MU bodies are firer! at one another with a gun to constitute a critical as- sembly. A requirement for such a crevice to work meant the clevelopment at a separate site near Los Alamos of gun bar- rels of Tower weight to propel objects at higher speed than . .
EDWIN MATTISON MCMILLAN 225 was previously consiclerec! feasible. The work then contin- ucc! with McMilIan serving as deputy to William S. (Deak) Parsons, the naval officer who was then in charge of all conventional explosive work at Los Alamos. McMillan's work proceeclec! until it was establishec! that the gun crevice wouIc! work, he clic! not participate in the actual "weaponization." The Hiroshima weapon was baser! on these clevelopments without a nuclear test. The rest is history. Oppenheimer asker! McMilIan to undertake a large num- ber of aciclitional responsibilities. One was to serve as the liaison officer between Los Alamos en c! the California Insti- tute of Technology project known as CAMEL, which among other activities tester! the aerodynamic properties of air- dropped bombs, with McMilIan in charge. Another experi- mental responsibility was clevelopment of diagnostics of the implosion assembly for the plutonium bomb, using a mag- netic detector. McMilIan was an observer cluring the Trinity Test when the first implosion crevice was cletonatecI. He en c! his wife Elsie were mainstays in the evolution of social life in Los Alamos with all its joys en c! heartbreaks. ACCELERATOR PHYSICS By the micicIle of 1945 many scientists at Los Alamos, inclucling McMilIan, were making plans to return home. For the Berkeley physicists, this incluclec! planning new ac- celerator facilities. Before the beginning of the war Lawrence had started to construct a huge conventional cyclotron. It hac! a pole-face diameter of IS4 inches en c! a magnet gap of 5 feet. McMilIan had designed some power supplies for that machine. That large magnet gap was needed because the conventional cyclotron requires! flee voltages in excess of ~ million volts to reach energies close to 100 MeV. This voltage requires! very large clearances between the flee en c! the vacuum chamber walls. Acceleration hac! to be accom
226 B I O G RA P H I C A L EMOIRS plishec! cluring very few turns in order to keep the particles in step with the accelerating rf voltage even with their rela- tivistic increase in mass. McMillan was fully acquainted! with this situation, but he disliked pursuing the plan for completing the IS4-inch cy- clotron. In mulling over this problem, McMilIan, in June 1945, envisioned! the iclea of phase stability, which in a single stroke of invention macle this brute force approach obso- lete. McMilIan recognizes! that when particles are acceler- atec! in a racliofrequency field! not at the crest of the racliofrequency amplitucle but on the sicle of the waveform, the particles wouIc! be locket! stably at a certain phase. The idea had great generality and applied to many types of ac- celerators, inclucling circular heavy particle en c! electron machines en c! heavy particle linear accelerators. For circu- lar accelerators using magnetic fields uniform in azimuth, the phase stability region is during the decreasing part of the racliofrequency amplitucle. If a particle has less than the normal energy, it is bent into a tighter circle in a circular accelerator en c! thus takes less time to complete its orbit. Such a particle thus arrives earlier at the next perioc! en c! therefore is exposer! to a higher accelerating field! cluring the decreasing part of the rf amplitude. It therefore re- ceives a larger energy increase. Conversely, a particle above average energy receives less acceleration. In consequence, the particles execute "phase oscillations" about a stable phase angle cleterminec! by the ratio of the peak acceleration macle possible by the rf amplitucle en c! the actual, lesser, accelera- tion required by the specific accelerator design.~9 McMilIan expresser! these facts in clifferential equations describing a stable "bucket" with particles oscillating about a synchro- nous phase within the bucket at a frequency clefinec! by the accelerator parameters. McMillan, in his discussions at Los Alamos, fully recog
EDWIN MATTISON MCMILLAN 227 nizec! the generality of this new principle en c! its wicle range of application. He published20 his discovery in the Physical Review in September ~ 945. After publication McMilIan learnecI2i that the Russian physicist VIaclimir I. VeksTer hac! conceivec! the same iclea en c! hac! publisher! it previously in a Russian journal that hac! not reacher! the Uniter! States cluring wartime. There follower! an exchange of letters be- tween Veksler en c! McMilIan that will remain an example of gracious interaction between scientists. McMilIan acknowI- ecigecI22 the priority in time of VeksTer's invention. Both parties agrees! that their respective inspirations were incleec! inclepenclent en c! that the iclea of phase stability wouIc! in- evitably have surfaced. In McMilIan's worcis, "It seems to me that this is another case of a phenomenon that has occurrec! before in science- the nearly simultaneous appearance of an iclea in several parts of the worIcI, when the clevelopment of the science concernec! has reacher! such a point that the iclea is neeclec! for its further progress." An c! in VeksTer's words, "You are quite justified in saying that the history of science affords many examples of the simultaneous appearance of similar ideas in several parts of the world, as in our own case." The two physicists became friends en c! mutual admirers. They sharer! the Atoms for Peace Prize for the invention of phase stability in 1963. The concept of phase stability revolutionizec! accelerator design en c! construction throughout the worIcI. It lee! to proposals for new accelerators in France en c! at the new European laboratory at CERN, in the Uniter! Kingdom, en c! in Australia, en c! it lee! to vigorous initiatives in Russia en c! the United States. The original plans for the "classical" IS4-inch cyclotron were scrapped. The magnet was moclifiec! to produce a larger magnetic fielc! over a smaller gap. This conversion macle it
228 B I O G RA P H I C A L EMOIRS into a "synchro-cyclotron." Here the principle of phase sta- bility was user! together with frequency moclulation (pro- viclec! by a rotating capacitor) of the rf accelerating fielcI, neeclec! to compensate for the relativistic change in orbital frequency. The ions, injectec! at the center of the synchro cyclotron magnet, are locket! at stable phases in many or i bits of increasing radius as they gain energy. Since synchro- nization is guarantees! by phase stability, acceleration can occur stably over many turns. Lower flee voltages are there- fore sufficient, en c! a smaller gap en c! a higher magnetic field! can be utilizecI. A moclel was constructed! in recorc! time in the small 37- .nch cyclotron on the Berkeley campus. The success of this moclel lee! to full-speec! conversion of the IS4-inch machine by 1948. That machine supported an impressive series of discoveries, inclucling many important experiments on the first man-macle pi-mesons. McMilIan himself participates! in the mapping of the neutron beam proclucec! by high-en- ergy deuterons on internal targets and was an advisory par- ticipant in innumerable experiments. However, his primary interest shifted to another application of phase stability, a 300-MeV electron synchrotron that became his responsibil- ity for both construction and research supported by Lawrence en c! the Atomic Energy Commission. Prior to the invention of phase stability, the highest en- ergy reached by an electron accelerator was achieved with the betatron with its energy limit about 100 MeV set by that emission of electromagnetic racliation by the electrons. In McMilIan's machine the electrons were confiner! to an annular chamber and accelerated in the traditional beta tron manner to about 2 MeV. Subsequent phase-stable gain in energy was produced by the electric field of an electro- magnetic cavity as the guicling magnetic field! is raised. McMillan's machine hac! a radius of ~ meter en c! attainer!
EDWIN MATTISON MCMILLAN 229 an energy of 300 MeV. McMillan personally clirectec! the builcling of all phases of this pioneering machine en c! con · ~ · · · ~ rem . ~ . ~ ~ ~ try auto engineering sagas. with the vacuum chamber exposed to electromagnetic ra ~ nere were recnn~ca~ problems cliation, the magnets hac! to be clesignec! for proper focus- ing en c! for control of ecicly current effects, special power supplies involving high-current switching hac! to be built to control the time sequence of the magnets, the rf system hac! to be engineered. Nevertheless, the job was clone en c! the machine, like the ~ 84-inch cyclotron, yielclec! important new discoveries. McMilIan personally participates! in the first experiments of production of plans by photons.23 Many other experi- ments were clone, inclucling demonstration of the existence of the neutral pion en c! cletailec! studies of the high-energy electromagnetic cascades. The 300-MeV electron synchro- tron gave McMilIan, for the first time, the opportunity to direct all phases of an accelerator laboratory, he was cle signer en c! buiTcler of the synchrotron en c! also manager of the scientific program associates! with that novel tool, which conic! not have been built prior to the invention of phase stability. The success of the IS4-inch synchro-cyclotron and 300- MeV electron synchrotron proviclec! the impetus for the next stage of accelerator buckling at Berkeley the Bevatron. McMilIan contributes! to the initial concepts of the elusion of that machine, inclucling the calculations that shower! the machine shouic! reach 6 GeV comfortably to produce pro- ton-antiproton pairs. Construction was in the hands of Wil- liam Brobeck, a highly capable engineer long associates! with Lawrence en c! McMillan. Tociay, essentially all high-energy accelerators, be they for electrons, protons, or heavy ions, collie not operate unless they were "phase stable." The explosive development
230 B I O G RA P H I C A L EMOIRS of high-energy accelerators, which lee! to an increase in obtainable energy by roughly a factor of ten per clecacle, is largely a consequence of the invention of McMilIan en c! VeksTer. McMilIan macle other significant contributions to accel- erator physics. He publishecI24 the "McMilIan theorem," a mathematical proof that in a linear accelerator raclial fo- cusing en c! phase stability are mutually incompatible unless external focusing crevices (magnet lenses or gricis) are ap- pliec! to the beam. He also carrier! out calculations on the spin motion in electron linear accelerators, en c! cluring a sabbatical visit to CERN in 1975 he tracer! the puzzling loss of muons in a storage ring to minute machining irregulari- ties in the magnet pole faces. He contributes! extensively to the analysis of orbit dynamics at the Berkeley laboratory. LABORATORY DIRECTOR While in the years after 1945 McMilIan's research focuses! on the design en c! construction of accelerators at the Ra- cliation Laboratory, his interest in other sciences remainec! acute. He was a faculty member in the Department of Phys- ics, University of California at Berkeley, engages! in regular unclergracluate en c! graduate teaching in the perioc! 1946- 54 and supervision of fifteen graduate students to the Ph.D. His classroom teaching antler! with his appointment as as- sociate director of the Racliation Laboratory (1954-58), be- coming deputy director and, later that year after Lawrence's cleath in August 195S, director of the renames! Lawrence Racliation Laboratory. McMilIan server! for fifteen years (1958-73) as director of the Lawrence Racliation Laboratory and, after separation of the Berkeley and Livermore components in ~ 970, the Lawrence Berkeley Laboratory (LBL). In 1958 the labora- tory aireacly hac! 2,000 employees in Berkeley en c! about
EDWIN MATTISON MCMILLAN 23 3,300 at Livermore. The Berkeley part was multiclisciplinary, with the major focus on physics, with numerous accelera- tors, but also hac! divisions of nuclear chemistry, biology en c! medicine, en c! bioorganic chemistry. The vigorous par- ticle physics research program at the Bevatron, with the 72- inch bubble chamber en c! a variety of electronic particle detectors, cirew physicists from arounc! the woric! en c! macle the Berkeley laboratory the center of high-energy physics from the late 1950s to the micI-1960s. Work with the IS4- inch cyclotron en c! McMillan's 300-MeV synchrotron remainec! active. The first half of McMilIan's tenure as director was per- haps the high point of LBL, at least in high-energy physics. The latter part of his term saw changes, both in the scien- tific effort at the laboratory en c! in its funcling from Wash- ington. By the early 1960s accelerators elsewhere achiever! higher energies, en c! so the particle energy frontier began to move away from Berkeley. To McMilIan higher-energy facilities were clesirable en c! inevitable. In fact, he playact an important role in the creation of Fermilab, serving on the boars! of the Universities Research Association in its forma- tive years. McMilIan proviclec! scientific en c! administrative leacler- ship to the laboratory in increasingly complex times, with particle physics funding leveling off en c! Livermore begin- ning to dwarf Berkeley.25 Maintaining a strong and diverse research program in physics and the other fields with lim- itec! resources was clifficult. His tendency was to let the heacis of the scientific divisions have free rein, but he clic! not hesitate to arbitrate conflicting views ant! set the laboratory's course when necessary. He was successful in maintaining a strong multiclisciplinary laboratory, with growth in new fielcis such as energy conservation en c! the environment as oIcler programs leveled off.
232 B I O G RA P H I C A L EMOIRS In the later years, the "Rae! Lab" sufferer! internal en c! external stresses: internal, as some researchers clisagreec! on priorities among existing activities en c! cIamorec! for scarce research clollars for alternative projects less firmly connectec! to the laboratory's mission, external, as the partnership be- tween the laboratory en c! the Atomic Energy Commission (ERDA after 1974) en c! the U.S. Congress began to erocle. Moreover, the Vietnam war raiser! tensions, particularly on university campuses. Lawrence hac! run the Racliation Laboratory from the beginning as a personal empire, en c! this benevolent stew- arciship from the top continues! uncler McMilIan, although he clic! not enjoy the exercise of power. By the late 1960s, protesters against the Vietnam war en c! the military-inclustrial complex hac! tarrec! the Racliation Laboratory as a "bomb factory" en c! worse. The distinction between Livermore en c! Berkeley, while fully unclerstooc! within the scientific community, was lost on the average person. The proximity of the Berkeley part of the Raclia- tion Laboratory to the Berkeley campus macle it an easy target for abuse. Within the laboratory tensions were ris- ing, fuelec! by some faculty en c! graduate students who thought that the war was a legitimate topic for noontime discussion within the laboratory en c! members of the lab staff who clic! not. The issue hinged largely on conflicting views of the laboratory: a part of the academic campus, where free speech shouIc! prevail, or a governmental research enterprise, where politics was inappropriate. Attempts to hoIc! open meetings to discuss the Vietnam war were initially met with heavy-hanclec! prohibition en c! cliscipline. Soon, however, McMillan saw that the protesters were sincere en c! responsible opponents of the war but not of the Berkeley Laboratory. In his quiet, cautious way, he aciciressec! the perceived lack of academic freedoms at the
EDWIN MATTISON MCMILLAN 233 laboratory. In the spring of 1971 he appointed an ad hoc committee of staff en c! faculty to ciraw up rules for incle- penclent open meetings at the laboratory. He promulgates! these rules in September 1971, but the general course! of the regents of the University of California promptly cle- manclec! that the rules be withdrawn. McMilIan clug in his heels because he knew that the committee hac! transmitter! all earlier cirafts of its proposer! rules to the general coun- sel for review. McMilIan en c! the committee rejectee! most of the criticisms as trivial, macle a few cosmetic changes, en c! left the rules in place to see them serve a useful pur- pose, without adverse consequences. McMilIan clic! not like conflict, but he held strong principles. When he saw that something was fair en c! reasonable, he stuck to it over all objections. Another example of McMillan's clear vision was the deci- sion to separate Livermore from Berkeley. The turmoil in the country at large over the Vietnam war, the antimilitary sentiments, en c! the perceives! security issues argucc! for separation. Voices at Livermore urged separation, voices at Berkeley urger! the status quo both for the same reason, money. The Livermore voices believer! that the Berkeley side was riding the Livermore juggernaut, the Berkeley voices fearer! loss of support with separation. McMilIan recom- menclec! separation en c! so became director of the smaller Lawrence Berkeley Laboratory. Funcling clic! change, but not because of the separation en c! not for the worse. The subsequent profounc! changes in the Lawrence Berkeley Laboratory, with particle physics playing an ever-clecreasing role, occurred under subsequent directors. McMilIan stepped clown as laboratory director at the ens! of 1973 en c! retiree! from the Berkeley faculty in June 1974. He continues! to participate in the laboratory's work until he suffered a se- ries of clisabling strokes in 1984.
234 B I O G RA P H I C A L CONCLUSION EMOIRS The above account of the five major phases of McMilIan's contributions fails far short of describing his total contribu- tions as a scholar, teacher, en c! human being. McMillan was an excellent teacher both insicle en c! outside the classroom. His formal courses were extremely well received, with their clarity en c! total absence of preaching from on high. He instiller! in his students an appreciation of physics in its funciamental aspects. He lover! to explain scientific facts as well as gadgets to younger audiences, with his effectiveness resting entirely on creep knowlecige combiner! with an ab- sence of showmanship. McMillan server! on the then General Advisory Commit- tee to the Atomic Energy Commission from 1954 to 1958 en c! participates! as a member of scientific policy commit- tees en c! program advisory committees to several laborato- ries. In committees McMilIan tenclec! to be relatively taci- turn, but when he spoke up his remarks were decisive en c! to the point. When President Eisenhower in 1959 announcer! his decision to built! the Stanforc! Linear Accelerator Cen- ter, he saicI, "I am toIc! by the scientists that this is the most extraordinary thing that has been attempted . . .", the spokes- man referrer! to by the President was Ec! McMilIan. McMilIan's contributions to the progress of science clic! not go unappreciated. As mentioned above, he shared the Nobel Prize with Glenn Seaborg for his discoveries of tran- suranic elements, en c! he sharer! the Atoms for Peace Prize with VIaclimir I. VeksTer for the discovery of phase stability. He was elected to the National Academy of Sciences in 1947. He was awarded the National Medal of Science in 1990. Since by then he was confiner! to a wheelchair, the award was presented to his son, Stephen, by the President. McMilIan receiver! numerous other awards en c! honorary
EDWIN MATTISON MCMILLAN 235 degrees, but none of this recognition affecter! his general humility. He clic! his work quietly, spoke concisely, ant! seemec! to enjoy everything he was cloing. He kept up with evolving knowlecige in a surprisingly large number of fielcis. In his private life McMilIan was a goof! family man en c! was greatly supported in all he did by his wife Elsie. He likes! hiking en c! exploring. His particular love was the Anza Borrego desert region, where he collectec! rocks en c! con- cretions that were spreac! arounc! his office, house, en c! gar- clen. He was interested in plants en c! grew orchids as well as insect-eating Venus Fly Traps. In many of the obituaries Ec! McMilIan was flagger! as an atomic bomb pioneer. Yet while the very discovery of pluto- nium en c! his subsequent work at Los Alamos were major contributions to the nuclear weapons program, his own views on nuclear weapons became increasingly critical after the war. He shunner! all CoIc! War rhetoric en c! remainec! cle tachec! cluring the Korean War from efforts at Berkeley aimec! at replenishing the plutonium supply when it appearec! that the Uniter! States might be cut off from overseas supplies of uranium. The builclup of nuclear weapons cluring the Coic! War lee! him to state publicly, "This country has in its hands some increclibly powerful weapons. The way our gov- ernment clears with the question of nuclear disarmament is shameful a disgrace to our nation." Ec! McMilIan was a humble unassuming person. He en- joyoc! his science, all of nature, his friends, en c! his family. His great contributions seemec! to flow naturally from him without apparent effort but as a simple product of his mincI. The worIc! is richer through Ec! McMilIan's contributions en c! poorer through his cleath. NOTES WE THANK EDWARD J. LOFGREN for opening his files on McMillan
236 BIOGRAPHICAL MEMOIRS to us and Philip H. Abelson for a thoughtful perspective on McMillan's research in the prewar years. 38 1. National Academy of Sciences, Biographical Memoirs, vol. 41, p. 251. Washington, D.C.: National Academy Press, 1970. 2. E. McMillan and L. Pauling. 7. Am. Chem. Soc. 49~1927~:666- 69. 3. R. P. Brent and E. M. McMillan. Math. Comput. 34~1980~:305. 4. E. M. McMillan. Phys. Rev. 42~1932~:905. 5. E. M. McMillan. Phys. Rev. 44~1932~:240. 6. N. S. Grace and E. M. McMillan. Physics Rev. 44~1933~:325. 7. E. M. McMillan. Phys. Rev. 45~1934~:134. 8. M. S. Livingston and E. M. McMillan. Physics Rev. 46~1934~:437 9. E. M. McMillan. Phys. Rev. 46~1934~:325. 10. E. O. Lawrence, E. M. McMillan, and R. L. Thornton. Physics Rev. 48~1935~:493-99. 11. E. M. McMillan and S. Ruben. Phys. Rev. 70~1946~:123-26. 12. E. M. McMillan. Phys. Rev. 47~1935~:801. 13. E. M. McMillan. Phys. Rev. 55~1939~:510. 14. E. M. McMillan and P. H. Abelson. Phys. Rev. 57~1940~:1185. 15. Quotation from The Plutonium Story, The Journals of Professor Glenn T. Seaborg, 1939-46, p. 13. Battelle Press, 1994. 16. Ibid. p. 14. 17. G. T. Seaborg, E. M. McMillan, T. W. Kennedy, and A. C. Wahl. Phys. Rev. 69~1946~:366. 18. Reminiscences of Los Alamos, ed. L. Badash, T. O. Hirschfelder, and H. P. Broida, pp.13-20, 41-48. Holland: Reidel Publishing Company, 1980. 19. In a linear accelerator the situation is reversed. Here the stable phase angle exists at the rising part of the rf amplitude; a particle whose energy and therefore velocity are below the norm arrives late and therefore experiences a larger radiofrequency am- plitude, with the converse being true for a particle whose energy and velocity are above the norm. 20. E. M. McMillan. Phys. Rev. 68~1945~:143-44. 21. V. Veksler. Phys. Rev. 68 ~ 1945 ~ :143. 22. E. M. McMillan. Phys. Rev. 69~1946~:534.
EDWIN MATTISON MCMILLAN 237 23. E. M. McMillan and T. M. Peterson. Science 109~1949~:438-39 and with R. S. White, 110 ~ 1949) :579-83. 24. E. M. McMillan. Phys. Rev. 80~1950~:493. 25. By 1965 Livermore and its ancillary sites had 5,300 employ- ees, and Berkeley had 3,200; the Livermore budget was two and a half times Berkeley's. McMillan was nominally director of the whole laboratory. When the Lawrence Berkeley Laboratory and the Lawrence Livermore Laboratory came into separate existences in 1970, Livermore was more than twice as large, with a budget more than three times that of Berkeley.
238 B I O G RA P H I C A L S E L E C T E D EMOIRS B I B L I O G RAP H Y 1927 With L. Pauling. An X-ray study of the alloys of lead and thallium. 7. Am. Chem. Soc. 49:666-69. 1932 Deflection of a beam of HCL molecules in a non-homogeneous electric field. Phys. Rev. 42:905. 1933 The isotopic constitution of lithium in the sun. Phys. Rev. 44:240. With N. S. Grace. Hyperfine structure in the tantalum arc spec- trum. Phys. Rev. 44:949-50. 1934 Absorption measurements of hard gamma-rays from fluorine bom- barded by protons. Phys. Rev. 46:325. With M. S. Livingston. The production of radioactive oxygen. Phys. Rev. 46:437-38. Some gamma-rays accompanying artificial nuclear disintegrations. Phys. Rev. 46:868-73. 1935 With M. S. Livingston. Artificial radioactivity produced by the deu- teron bombardment of nitrogen. Phys. Rev. 47:452-57. The production of X-radiation by very fast electrons. Phys. Rev. 47:801. With E. O. Lawrence and R. L. Thornton. The transmutation func- tions for some cases of deuteron-induced radioactivity. Phys. Rev. 48:493-99. 1939 Radioactive recoils from uranium activated with neutrons. Phys. Rev. 55:510. 1940 With P. H. Abelson. Radioactive element 93. Phys. Rev. 57:1185-86.
EDWIN MATTISON MCMILLAN 1945 239 The synchrotron a proposed high energy particle accelerator. Phys. Rev. 68: 143-44. 1946 With G. T. Seaborg, J. W. Kennedy, and A. C. Wahl. Radioactive element 94 from deuterons on uranium. Phys. Rev. 69:366-67. 1947 Further remarks on reciprocity. 7. Acous. Soc. Am. 19:922. With A. C. Helmholz and D. C. Sewell. Angular distribution of neu- trons from targets bombarded by 190 Mev deuterons. Phys. Rev. 72: 1003-7. 1949 With J. M. Peterson and R. S. White. Production of mesons by X- rays. Science 110:579-83. 1950 The origin of cosmic rays. Phys. Rev. 79:498-501. The relation between phase stability and first-order focusing in lin- ear accelerators. Phys. Rev. 80:493. 1952 The transuranium elements; early history. In Les Prix Nobel en 1951, pp. 165-73. Stockholm: The Nobel Foundation. 1959 History of the cyclotron, part 2. Phys. Today 12~10~:24-34. 1966 Vladimir Iosifovich Veksler ~ Obituary) . Phys. Today 1 9 (Nov. ): 1 04-5. Correction, ibid 19 (Dec. ~ :14. 1979 Early history of particle accelerators. In Nuclear Physics in Retrospect, Proceedings of a Symposium on the 1930's, ed. R. H. Stuewer, pp. 111-55. Minneapolis: University of Minnesota Press.
240 BIOGRAPHICAL MEMOIRS 1980 With R. P. Brent. Some new algorithms for high-precision computa- tion of Euler's constant. Math. Comput. 34:305-12. 1984 History of the synchrotron. Phys. Today 37~2~:31-37.