The University of Michigan, an encyclopedic survey ... Wilfred B. Shaw, editor.

DEPARTMENT OF PHYSICS

With the end of World War II and the return to more normal activity, physicists in general found numerous changes in their discipline. The public was now quite aware of the significance of nuclear research. The government, and the scientists themselves, now knew that effective research could be done on a massive scale if it were generously supported. And now technological innovations, particularly in electronics, brought new experiments within reach.

Michigan, with its 42" cyclotron built in the mid-30s, had been active in nuclear research for many years. James Cork, who had had major responsibility for the cyclotron, and H. R. Crane were the senior active nuclear physicists after the war; however the years 1945-50 saw the addition of Wiedenbeck, Pidd, Parkinson, Lennox, and Hough to the faculty. Moreover, since "nuclear physics" at that time included much of what is now called high-energy physics, Hazen, Nierenberg, and Glaser should also be included in that list.

In those years, for what was to prove the last decade of his life, Cork turned from the cyclotron to work with radio-active sources. He used the traditional counters and emulsions for his alpha, beta, and gamma spectroscopy. Wiedenbeck and his numerous students, on the other hand, pressed forward with extensive use of electronic instrumentation for their nuclear structure studies. They undertook coincidence measurements and correlation studies, and they did extensive work on the design and construction of double focusing beta spectrometers.

Direction of the cyclotron project in the postwar years passed from Crane to Wiedenbeck and then, in 1949, to Parkinson. Parkinson and Lennox obtained an Atomic Energy Commission contract to support the Michigan instrument for high-resolution nuclear-structure investigations in a range of energy that was somewhat beyond what Van de Graaff accelerators could reach at that time. This cyclotron remained active with AEC support in the first basement of Randall Laboratory until 1961 when it was moved to the North Campus for a brief period of use as an adjunct to the new, 83" instrument.

In the mid-1940s H. R. Crane, who had much experience with linear accelerators, devised the concept of a cyclic accelerator that had some portions of the particle path being straight, much like the racetrack at a fairground. The advantage of this over a purely circular or spiral trajectory is that the straight line portions are ideal for the insertion of targets, counters, and other instrumentation that are essential for experiments with the accelerated particles. With the assurance provided by detailed orbit stability calculations done by Dennison and T. Berlin, the massive task of constructing a 200 MeV electron synchrotron was undertaken by Crane and his associates in 1946. Beam was obtained in 1950 and a number of high-energy electron-scattering experiments were carried out. The work had been done with a modest budget by faculty and students who also had classroom responsibilities to meet. Meanwhile, the advantages of the synchrotron concept had been widely recognized and a number of other institutions rapidly constructed their own synchrotrons, often with a generously supported staff of full-time engineers and technicians. Thus the Michigan synchrotron did not remain competitive and the project wound down in the mid-1950s.

Another useful by-product of the synchrotron was that the 600 keV electron injector was available for some Mott scattering experiments that Crane had wanted to do for some time. He proposed that the electron injector be used for a thesis experiment on the polarization that should arise from double scattering. For this it seemed advantageous to confine the electron beam between scatterers with the use of a solenoidal magnetic field, and from their intuitive analysis of the electron behavior in that field they concluded that the electron's magnetic moment would precess in a controlled way and that they could even measure the magnetic moment of the free electron. This was confirmed by the experiment of Louisell, Pidd, and Crane in 1953 and put on a solid theoretical basis by Mendlowitz and Case. The reports of these results at the spring meeting of the American Physical Society aroused much controversy because they contradicted a long and widely-held belief that experiments of this sort were impossible in principle. This experiment, however, and its later refinements are now considered a cornerstone of modern quantum electrodynamics.

The number of faculty working actively in infrared spectroscopy was somewhat diminished after the war. Barker had become department chairman and was managing a rapidly-changing department with a minimum of administrative assistance. Randall, who had retired in 1941, had shifted his attention to biophysics. So for a few years Dennison not only did theory but also directed experimental research in the infrared. The number of infrared experimentalists increased when Lincoln Smith came on the faculty for the years 1946-49 and when C. Wilbur Peters arrived in 1948. Among the research pursued was a generalization of the hindered-motion problem that Dennison, Uhlenbeck, Cleeton, and Williams had attacked with the first application of microwave spectroscopy in their study of NH₃ in the early 1930s.

A major impetus to molecular spectroscopy within the department came with the arrival of G.B.B.M. Sutherland in 1949 who quickly built up a large and active group. Their work encompassed studies of relatively simple molecules, including applications of industrial interest; the work also extended to studies of more complicated molecules of biophysical importance. Ernst Katz joined the faculty in 1946 to do experimental work in solid state, particularly studies of reciprocity failure in emulsions and of motion of charge carriers in solids.

Work in atomic spectroscopy was carried on by Ralph Wolfe and Wallace McCormick. Wolfe and his associates had a long-standing interest in industrial applications of atomic spectroscopy. McCormick, who had been a student of Ralph Sawyer's, continued the program of work in ultraviolet spectroscopy. Sawyer, a mainstay of Michigan spectroscopy for many years was at that time (1946) the civilian technical director of the Bikini atomic weapons test. He returned to the University to be Dean of the Graduate School and, later, Vice-President of the University. He also served as chairman of the governing board of the American Institute of Physics from 1959 to 1971.

Otto Laporte, distinguished for his contributions to the theory of spectra, turned to shock-tube research in the early 1950s. His students constructed a series of instruments with which they studied shocks in gases over a temperature range of 80°K to 800°K; the interpretations and theoretical

conclusions that Laporte drew from this work were widely recognized.

The Evolution of Theoretical Physics. George Uhlenbeck, David Dennison, and Otto Laporte were the major figures in theoretical physics at Michigan in the postwar period. Uhlenbeck continued to work on problems in statistical physics, on gamma-gamma correlations in nuclear decay, and on selected aspects of field theory. Dennison continued his work on the theory of molecular structure while branching out to do some nuclear theory and an important series of calculations on particle trajectories in accelerators. Kenneth Case, who joined the department in 1950, had an interest in the more formal aspects of particle theory and did extensive work in mathematical physics.

In the period 1954-62 there were a number of theorists brought on the faculty: J. Luttinger came in 1954 for a three-year period during which time he worked on condensed matter theory, K. T. Hecht in molecular theory but who was later to shift his interests to nuclear physics. Noah Sherman returned as a faculty member in 1957 to do work on electron scattering and on nuclear theory. G. W. Ford worked in statistical physics, in condensed matter physics, and in the theory of the g-2 experiments. R. R. Lewis did an important series of papers on the tests of symmetry, particularly in the weak interaction; he also contributed in a major way to the discovery of level-crossing spectroscopy. Herbert Uberall specialized in high energy electron scattering theory. Peter Fontana worked on the theory of interatomic forces and on the interaction of resonance radiation with atoms. Paul Phillipson did work on molecular theory during 1960-62. A. C. T. Wu, who came in 1962, worked principally in the formal aspects of field theory and in mathematical physics. The research done by these theorists covered a broad spectrum and the work tended to be done in a fairly individual manner; programmatic research and extended collaborations were not common.

In 1964, however, Marc Ross came as a senior high energy theorist from Indiana, and this was followed in short order by the hiring of a number of younger high energy theorists. Their research was characterized by frequent collaborations and by a highly competitive climate in which preprints were

the usual way of disseminating results and in which telephone contact with experimenters at the national laboratories was essential. The work of this group of theorists included the development of phenomenological Regge/adsorption models that proved quite useful for the classification and prediction of experimental results in strong interaction physics. Their work also included detailed calculations in quantum electrodynamics, theories of weak and electromagnetic interactions, and developments in field theories.

The Bubble Chamber. Important to the progress in high energy physics are the advances in particle-detector technology. The best known example is the bubble chamber that was developed by Donald Glaser with the aid of Phoenix funding in the early 1950s and for which he received the Nobel Prize in 1960. Glaser had come to Michigan to work in the general area of nuclear/particle physics; he, along with many others, was keenly aware of the limitations of cloud chambers, nuclear emulsions, and gas-filled counters that were the conventional detectors of that time. He then thought of using a superheated liquid as a target so that bubbles could form around ionization centers. After his theoretical analysis of bubble formation had given encouraging results, he began experiments with small glass bulbs that were filled with liquid ether. The results achieved with these in 1952 encouraged Glaser and his colleagues to construct metal chambers with glass windows from which truly useful photographs could be obtained.

The first bubble chambers were small, only several inches across, and used a variety of liquids for bubble formation. Liquid hydrogen would have been a first choice because protons are the ideal target nucleus, but hydrogen bubble chambers of a useful size are so complicated and dangerous that their construction has usually been left to the national laboratories. All the bubble chambers built at Michigan have used heavy liquids: the first chamber to yield real physics used propane. Glaser and his colleagues subsequently constructed a bubble chamber that used 20 liters (more than $200,000 worth!) of liquid Xenon. And in 1960-64 the group headed by Sinclair, Roe, and Vander Velde constructed a 40-inch chamber that used freon as the working liquid; the design and construction was done at Randall and at an assembly area in a hanger at the Willow Run Airport. During the

construction time, the group kept active in research physics by becoming users of bubble chambers already in place at the Brookhaven National Laboratory. In 1964 the freon chamber was moved to its destination at the Argonne Zero Gradient Proton Synchrotron where it was used until 1971.

High Energy Physics. The bubble chamber was the most productive particle detector of the 1955-65 decade but it had the limitation that each of the photographs taken had to be scanned individually for events of interest; each event then required painstaking measurement. Since a single experiment could require the scanning of hundreds of thousands of photographs, there was an obvious need for automation in the scanning process. Rooms on the third and fourth floors of Randall were given over to the scanning machines. Considerable work was done toward the construction of completely automated scan-and-measure systems that would not require a human observer, but these were not available until rather late in the era of the bubble chamber work.

It was recognized from the very beginning that other particle detectors would be of interest, particularly if they could be triggered only in coincidence with several signatures of the event of interest in a given experiment. Perl and Meyer, who had initially been with the bubble chamber effort, turned to the development of alternative detectors. Perl, with Jones, worked on luminescent chambers and image intensifiers. Meyer and his colleagues did work with spark chambers. Initially these detectors had photographic readouts that required scanning and measurement, but the next step was to use wire chambers so that the events could be detected and measured electronically. In this way it was possible to analyze results even while the experiment was in progress. In recent years, developments with spark, streamer, and wire techniques have made it possible to construct large volume detectors with completely electronic readout.

Experiments in high energy physics continued to form a large fraction of the department's effort during the 1970s. The experiments were done at accelerators both in the U.S. and abroad; indeed Michigan groups had participated in many of the first experiments done with the Fermilab accelerator

and they will be among the first users of the colliding beam facility at Stanford. An extensive series of p-p scattering experiments were done at the Argonne ZGS; when the experiments were done with a polarized beam and a polarized target, a surprising spin-dependence of the p-p cross section was found.

Cosmic rays offer the physicist an opportunity to do experiments at energies far higher than are available from accelerators. Such experiments have been carried out since the mid-1940s by Wayne Hazen, briefly in 1948-50 by William Nierenberg, and by Alfred Hendel as a collaborator of Hazen's since 1958. Hazen and Hendel have worked with cloud chambers, spark chambers, nuclear emulsions, and also with directional UHF/VHF antennas to study showers and radio pulses that are associated with the arrival of very energetic primaries. Lawrence Jones did considerable cosmic ray work in the 1960s with one of the findings being a growth in the cross-section for proton interaction with increasing energy.

Nuclear Physics. It had been increasingly evident throughout the 1950s that a new accelerator would be required if the experimental program on nuclear structure were to be continued. A proposal for a new 83" spiral ridge cyclotron, together with the analyzing magnets needed to do high resolution work with 45 MeV protons, was accepted by the Atomic Energy Commission, and the State of Michigan agreed to provide a new building on North Campus. (The building was constructed to house the new cyclotron on one side and the electron synchrotron on the other, but with the phase-out of the synchrotron project it was decided to move the old cyclotron to the new building, a process during which it was upgraded from 42" to 50".) Construction of the 83" cyclotron required about four years, with the first circulating beam being obtained in 1962. The good energy resolution of the instrument permitted detailed studies of elastic, inelastic, and particle transfer reactions with p,d,T, and α projectiles incident on relatively heavy nuclei.

Nuclear research with activated sources continued with increasingly sophisticated instrumentation. Ever larger multichannel analyzers and higher resolution particle detectors were used for the nuclear spectroscopy program. In 1962 a

high precision bent crystal gamma ray spectrometer was an important addition to their facilities. The nuclear spectroscopy work continued for a number of years during which time investigations with correlation methods and precision energy determinations were used to elucidate the decay schemes of medium mass radioactive nuclei.

In the 1970s, it became a matter of national science policy to concentrate the resources for medium energy nuclear physics in a few regional facilities, much as had been done in high-energy physics two decades previously. Federal funding of the nuclear laboratories at dozens of universities, including Michigan, was sharply curtailed. The result was the phase-out in the mid-1970s of the cyclotron facility on North Campus and also of the nuclear spectroscopy laboratory that had been on the 6th floor of the Dennison building. The nuclear experimentalists from Michigan then became users of more distant accelerators, again following the high energy example. A laboratory for radiocarbon dating was run by Crane from 1953 until 1972 in which hundreds of samples were run.

g-factor. It was clear from the results of the first electron g-factor experiment in 1953 that substantially better results could be obtained. Crane and Pidd together with students Schupp and Wilkinson made the refinements necessary to get a g-factor result that was of major importance to the theorists. Then in the early 1960s Rich measured the g-factor of the positron for his dissertation. In 1965 Crane was chosen to be the new department chairman, and Rich was named to the faculty and gradually assumed leadership of the group. Gilleland did an improved version of the positron experiment, and Wesley did a fourth generation electron experiment to achieve 3 parts per million precision for the measurement. Rich and his students then moved with their expertise in positon/positronium physics to do a test for TCP invariance, a redetermination of the lifetime of positronium, and other experiments with polarized positrons.

Astrophysics/Geophysics. Research related to astrophysical problems has been carried out by many members of the department, but often concurrently with the pursuit of

other problems. Sander has done work on the theory of neutron stars, and Rich and Williams have done measurements on the circular polarization of radiation from white dwarfs. Crane devoted considerable time in the years after his chairmanship to laboratory experiments on geomagnetism, and Meyer worked on the application of counter physics methods to geophysical questions. It was with the arrival of Dennis Hegyi in the mid-70s, however, that the department had a faculty member with a principal commitment to experimental/observational astrophysics; Hegyi's research is on the distribution of mass in galactic halos.

Low Energy Physics. In the years following 1955, many of the physicists working in the three basements of Randall laboratory began an affiliation in what became known as the "resonance group." The affiliation arose from the circumstance of adjacent laboratory space and a common research interest in atomic, molecular, and condensed-matter phenomena that occurred at energies below 50 eV; the affiliation was later formalized by common financial support under a large umbrella contract from the Atomic Energy Commission. Not all of the funding was from the AEC, but there was a strong communal spirit that pervaded the basements at that time.

The resonance group had its origins with Peter Franken and Richard Sands who had come to Michigan, in 1956 and 1957 respectively, from postdoctoral experience at Stanford. Franken had been involved in cyclotron resonance studies of the proton and Sands had been doing EPR work and this work continued, but they initiated a new, common effort on the interaction of light with dilute atomic vapors that led to studies of spin exchange, optical pumping, and to the discovery and application of the level crossing method of fine structure spectroscopy; they hosted an international conference on optical pumping in 1959.

When lasers became available in the early 1960s, a collaboration from the resonance group published the first report of the generation of optical harmonics. Franken undertook a number of other experiments, including tests of the absolute neutrality of un-ionized matter and a search for fractionally charged particles, tests for the deviation of the electrostatic force laser from pure 1/r² form, and an attempt to use laser ranging as a detector of clear air turbulence.

Atomic and molecular beam research was started in the department when Jens Zorn came in 1962 to begin a program for the measurement of molecular hyperfine structure and of atomic polarizability. In 1969, he and his students turned to research in collision physics; they developed the time-of-flight method for determination of electron atom cross sections and for the study of molecular dissociation.

Peters continued the Michigan tradition of high precision infrared spectroscopy of small molecules with the spectrometers in the second and third basements of Randall. He also supervised the operation of the ruling engine until the ruling engine was sold. An interesting and useful result emerged in the mid-1950s when Peters, with H. M. Pollard and B. Hirschowitz of the medical school, wanted to make a coherent fiber optic bundle for use as a gastroscope. The first bundles were made from simple glass fibers and were completely unsatisfactory. Peters then suggested varnishing the individual fibers to reduce the crosstalk and this did give some improvement but the overall result was still inadequate. Curtis, after suggesting that the fibers be drawn with an outer sheath of low index glass, was able to draw composite fibers and form them into a fiber optic bundle that gave a satisfactory image; this is the principle behind almost all coherent fiber optics that are in use today.

W. L. Williams joined the faculty in 1965 and began his research program with excited state lifetime studies and with some experiments on electronic and ionic collisions. When R. T. Robiscoe came for the 1966-69 period, he and Williams embarked on a redetermination of the hydrogen fine structure, a subject that has also been investigated, using level crossing spectroscopy. Williams then began an extended collaboration with R. R. Lewis to search for parityviolating effects in atomic hydrogen.

Work in condensed-matter physics had been done in the pre-1963 resonance group with Sands doing EPR on solids at high pressure and with Weinreich doing experiments on the acousto-electric effect. In 1964, T. Michael Sanders began liquid helium work in the department. From measurements of the photoejection of electrons from bubbles in liquid helium, Sanders was able to deduce the radius and effective potential of the bubble. From measurements of the charge trapped in

the vortex lines in rotating liquid helium, he was able to observe the creation and destruction of quantized vortex lines as the angular velocity of the helium changed. He also worked on surface tension in helium and on the magnetic properties of microcrystals at low temperature. Work on the mobility of charges in liquid helium was done by Springett during his time in the department. Then, in the early 1970s, Michael Bretz and his group started extensive studies of the thermodynamic behaviors of two-dimensional helium films that arise when the gas condenses on a prepared substrate and undergoes phase changes.

Biophysics and Macromolecules. The optical and infrared methods used for biophysical and macromolecular studies in the early postwar years were augmented by x-ray and neutron diffraction, microwave and double resonance spectroscopy, and Raman spectroscopy in the times that followed. In the later '60s and early '70s Samuel Krimm and his colleagues have done both experimental and theoretical studies on vibrations of polypeptides, on chain organization in crystalline polyethylene and in collagen, and on the structure of biopolymers and membranes. The research is done in close collaboration with members of other university departments with facilitation from the Macromolecular Research Institute.

Examination of electron transfer mechanisms in biological processes and general studies of the structure and function of proteins have been pursued by Richard Sands and his colleagues since the late 1950s. This work was innovative in its use of ESR in its early days, and since that time a much broader range of spectroscopies have been brought to bear on the questions of interest: electron-nuclear double resonance, electron-electron double resonance, and Mossbauer techniques have all found application.

Buildings and Shops. The two buildings available to the department after the war were West Physics and Randall Laboratory. In West Physics there were classrooms, a few small workspaces, and the instrument shop. Randall housed everything else including the 43" cyclotron, the synchrotron, and the library. It was clear that more space was required and the state agreed to supply it.

A large, ten-story building with a long, low extension was then built to house physics classrooms, laboratories for teaching and research, faculty offices, and the entire astronomy department. The Physics/Astronomy Library, a colloquium room, and two large lecture halls occupied the low portion of the building. It was completed in 1962-63 and provided considerable relief from the earlier space constraints. At about the same time, the North Campus cyclotron building was also nearing completion and most of the nuclear research facilities, including the 43" cyclotron, moved to the North Campus; this opened up still more space in Randall.

With the opening of the new buildings, physics was obligated to turn West Physics over to the psychologists; the main complication was the transfer of the instrument shop to the first basement of Randall, a move that required extensive renovation of that basement.

The glassblower Guenther Kessler and the shop foreman Hermann Roemer retired in the early 1960s; August Wagner then became foreman of the instrument shop for four years before his own retirement. All three of them had been recruited abroad in the mid-1920s and were an integral part of the Michigan physics tradition.

West Physics burned to the ground in a spectacular fire about one year after the physics department had moved out.

Jens C. Zorn