Associated with Oak Ridge as a consultant since 1948, Eugene Guth is currently technical advisor to ORNL Director Alvin Weinberg. A native of Budapest, Guth was educated at the University of Vienna, and was later a postdoc with Wolfgang Pauli in Zurich, and with Werner Heisenberg in Leipzig. In 1937 he joined the University of Notre Dame where he became Research Professor of Physics and established the Polymer Physics Laboratory, which he directed. He is one of the founders and chief developers of the fields of both the physics and physical chemistry of polymers. In 1965 he received the Bingham Medal, the highest honor of the Society of Rheology. He initiated the statistical treatment of flexible randomly linked polymer molecules in Brownian motion and applied it to the explanation of rubberlike elasticity. Guth's article reaches back through a thirty-year collegial acquaintance with Oppenheimer and many of his students and associates.

Julius Robert Oppenheimer (1904-1967)

A Fellow Physicist's Tribute to a Pioneer of the Nuclear Age

By Eugene Guth

Reprinted from The ORNL Review (Winter 1968)

With the death of J. Robert Oppenheimer on February 18, 1967, the scientific world in general and American science in particular suffered a great loss. Though the world may remember him longest for his instrumental role in the development of the atomic bomb, Oppenheimer excelled as a creative scientist, an inspiring teacher, a public servant and a great leader within the scientific community.

He was also a great wartime leader and dedicated post-war public figure. In both of these capacities Oppie (as he was usually called by his friends) had some influence on Oak Ridge.

Born in New York on April 22, 1904, Oppenheimer was a sensitive son of highly cultured parents, members of an "Ethical Community." His father was a textile importer. Already in his early years, his family provided him with an environment where his lively mind was given every opportunity and encouragement to develop. He was surrounded by books and paintings and had a small chemical laboratory built for him when he was still very young. At the age of five he started a rock collection and was admitted to the New York Mineralogical Club when he was only eleven years old- all this in spite of the fact that he suffered from tuberculosis in his youth.

In 1922, he went to Harvard, with the initial intention of becoming a chemist. In addition to chemistry, physics and mathematics, he also learned Latin, Greek, German and Dutch, finally graduating "summa cum laude" in 1925, completing four years of work in three and shifting from chemistry to theoretical physics. He went to Europe, at that time the center for red-hot atomic and nuclear physics. In nuclear physics, Rutherford, at Cambridge, was the leader. In theoretical atomic physics, Born had created a center at GOttingen. Oppenheimer first worked under Rutherford then at Born's invitation went to Gottingen, where he received his Doctorate in 1927. He returned in 1928 to the United States as a research fellow at Harvard and at the California Institute of Technology. In 1929 he took his first teaching positions, concurrent appointments as assistant professor at Caltech and at the University of California at Berkeley, advancing to full professor in 1936. Hemarried Katherine Harrison in 1940 and is survived by her and their two children, Peter and Katherine.

Beginning in the fall of 1941, Oppenheimer, by then the chief theorist at Berkeley, became more and more involved in the United States' effort to manufacture atomic weapons. In 1943 he was chosen director of the Los Alamos Laboratory, established at a site of a fashionable boys' school, near the Oppenheimer family summer ranch in northern New Mexico. He remained at Los Alamos until the fall of 1945 when he returned to Berkeley.

Accelerated Developments at Oak Ridge

Oppenheimer's great wartime leadership as director of the Los Alamos Scientific Laboratory is well known. It is, perhaps, lesser known that, at least on two occasions, he directly accelerated developments at Oak Ridge also. Oppenheimer's first contact with the uranium project arose when, in 1941, Lawrence asked him to help on the electromagnetic separation process for the production of U²³⁵.

Oppenheimer as the wartime director of Los Alamos Scientific Laboratory.

Oppenheimer's suggestions led to a considerable increase in the efficiency of the process. Of course, it was natural that Lawrence ask Oppenheimer to participate in his project, since Oppenheimer was in close touch with the experimental work of Lawrence's group. In the fall of 1941, at Lawrence's recommendation, Oppenheimer was invited to the first comprehensive discussion of the physics of the bomb. Oppenheimer made preliminary estimates of the critical mass needed for a U²³⁵-bomb (between 2 and 100 kilograms). In 1942, Oppenheimer organized a group for weapon study. New crosssection data led to a critical mass for a sphere of U²³⁵ between 2.5 and 5 kg. In the middle of 1942, Oppenheimer was chosen by A. H. Compton to head a fast neutron theoretical research group. This group estimated the U2a5 critical mass to be between 5 and 10 kg. Incidentally, already at this early time, the group envisaged the possibility of an H-bomb! In the beginning of 1943, construction of Alpha and Beta tracks was initiated at Y-12 at Oak Ridge. Somewhat later, the Oak Ridge Gaseous Diffusion Plant, K-25 , got started. It was thought that Y-12 and K-25 together could produce enough U²³⁵ for a bomb.

In the meantime, Los Alamos had been established, with Oppenheimer as director. It is to the great credit of General Groves that he fully approved the selection of Oppenheimer as director in spite of Oppie's lack of previous administrative experience. Moreover, General Groves always emphasized that Oppenheimer was a magnificent director. This was the beginning of a dramatic story. The estimates for the critical mass had their "ups" and "downs" or rather "downs" and "ups". First they were more optimistic. This led to the visualization of smaller production plants, than the later, more pessimistic, estimates necessitated. His theoretical group made new estimates of the critical mass, roughly tripling the previous estimate. This led to plans to enlarge Y-12, inasmuch as some barrier troubles developed at K-25. In March 1944, the Military Policy Committee called an important meeting in Chicago; General Groves, Oppenheimer, and Lawrence all expected the expansion of Y-12 to be the chief issue. However, for some reason, the Y-12 expansion was not discussed.

In a roundabout way, through a letter from Oliphant, Lawrence heard rumors that U²³⁵ would be abandoned in favor of Pu239 from Hanford. Receiving a wire from Lawrence about this matter, Oppenheimer reassured him that he still favored the Y-12 expansion. Lawrence went immediately to Oak Ridge to accelerate developments. Still, it looked as though even the combined capabilities of Y-12 and K-25 would not suffice to produce enough U²³⁵. Here, again, Oppenheimer came up with the suggestion to push the liquid thermal diffusion method. His suggestion led to the construction of the S-50 plant in Oak Ridge. The combination of S-50, K-25, and Y-12 finally produced U²³⁵ in sufficient quantity.

Oppenheimer traveled to wartime Oak Ridge several times, first in the fall of 1943, and on at least one occasion visited his brother, Frank Oppenheimer, who worked at the Y-12 plant from 1943 to 1944.

After the war, in February 1946, Oppenheimer revisited Oak Ridge as a member of the Lilienthal Board of Consultants connected with the Acheson-Lilienthal report. As a matter of fact, Oppenheimer was the guiding spirit of this Board. The report asked for an international authority for the control of atomic energy in all its ramifications. The job of the authority would have been dual: development of atomic reactors for peaceful uses and also of atomic weapons, if needed. This remarkable plan was endorsed by a State Department committee chaired by Dean Acheson and was declared official U.S. policy. Baruch presented it to the United Nations but there, unfortunately, the U.S.S.R. rejected it. Oppenheimer as a wartime leader and as a postwar public figure was a "realist" and one of the first to see that the American plan would be rejected by Russia.

After creation of the AEC early in 194 7, Oppenheimer was appointed chairman of its General Advisory Committee (GAC). He was also a consultant to DOD on atomic weapons and on the general strategic policy of U.S. The GAC, under Oppenheimer, recommended extensive basic research which gave U. S. its present leadership in nuclear and high energy physics. The national laboratories at Oak Ridge, Brookhaven, and Argonne were either established or strengthened during this period. The AEC and its GAC took care of the need for fissionable materials, both for reactors and for atomic weapons. Sufficient production facilities in Oak Ridge and elsewhere were constructed for this purpose forming the basis for our present pre-eminence in atomic energy.

In 1947 Oppenheimer left Berkeley (and Pasadena) to become director of the Institute for Advanced Study at Princeton, a position which he held until 1966.

Wide Range of Research

As a physicist, Oppenheimer's original work covered a tremendous range corresponding to his extraordinarily wide interests. With Born, he wrote a fundamental paper on the quantum mechanics of molecules (1927); the Born-Oppenheimer method has been applied also in other situations in which particles of widely different masses interact with each other. Oppie was the first (1928) to call attention to the importance of particle exchange in scattering processes. He was also the first (1928) to recognize the possibility of the "leaking" of the electron from a hydrogen atom in an intense electric field. He was also first to understand (1930) that the unfilled, negative-energy states cannot correspond to protons, as originally suggested by Dirac, but must be associated with (anti) particles of the mass of electrons. Jointly with Ehrenfest, he showed how the statistics obeyed by nuclei could be determined from the statistics of their constituents. This work gave strong evidence against the existence of electrons within nuclei a year before the discovery of the neutron. With his students, H. S. Snyder and G. M. Volkoff, and his associate, R. Serber, Oppie was the pioneer (1938) in the general relativistic treatment of the gravitational collapse of highly massive stars. This pioneering work is one of the basic ideas in current attempts to understand the recently discovered quasars.

Oppie also first (1947) suggested the role of the neutral pi meson in the origin of cosmic ray showers. With H. W. Lewis and S. A. Wouthuysen, he developed one of the first (1948) theories of multiple meson production in very high energy proton collisions. Finally, with W. A. Arnold, he published (1950) an influential paper on transfer of energy in biological molecules. Of almost as great importance as his own papers, only a few of which are mentioned here, was his participation in the work of many students and colleagues and his ever inspiring leadership in scientific conferences and informal discussions. A great many papers and conference reports of the last 35 years contain comments by and acknowledgments to Oppenheimer. Although his own work was distinguished by originality and diversity, of at least equal significance was his fabulous grasp of what was going on in science in general, physics in particular. Few scientists had his wide, and still deep, knowledge of physics. His incredibly quick mind absorbed new ideas like blotting paper. Moreover, he always believed that physics is an experimental science and maintained close contacts with the research groups headed by Lawrence at Berkeley, and Millikan, C. C. Lauritsen and C. D. Anderson at Pasadena.

As a teacher of theoretical physics, Oppenheimer created two great schools at Berkeley and Pasadena in the 1930's and at Princeton in the last twenty years. Following his years in Europe, it is not much exaggeration to say that he almost singlehandedly carried quantum theory to the U.S. His brilliance as a teacher with an extraordinarily vivid personality and extremely wide range of interests helped form many of the great theoretical physicists in the U.S. In Pasadena and Berkeley, all aspects of quantum theory, electrodynamics, nuclear structure and reactions, the then newly discovered positrons and mesons, cosmic rays, general relativity, and statistical mechanics were intensely discussed in Oppenheimer's group.

At Princeton, Oppenheimer was the guiding spirit for dozens of the best and most active young postdoctoral theoretical physicists. He created the world's center for theoretical high-energy physics and field theory. In the 1950's Princeton became the "Mecca of Theoretical Physics." Among young post-doctorals spending some time in Princeton and receiving, so to say, final training and taste were Gell-Mann, Goldberger, Thirring, Chew, Low, N ambu and many others from this country and from abroad. In addition to these young people, many established leaders like Pauli, Dirac, and Yukawa were more or less frequent guests at the Institute. The superb, permanent staff, assembled by Oppie, included Placzek, Dyson, Pais, and Lee and Yang, who did their revolutionary work on parity non-conservation at the Institute.

Concern for Science and Culture

In his Princeton period, Oppenheimer became deeply concerned with the relations between the various sciences and, even more, with the interrelations of the sciences with our culture in general. The inevitability of increasing specialization in the sciences made communication between neighboring fields of knowledge more and more difficult. Still harder, he felt, was the communication of the impact of science to intelligent man (" . . . thus progress in learning about the world of nature has changed rather profoundly not only what we know of nature, but some of the things that we know ourselves as knowers. ") He had "a strong conviction that this experience is one which we would gladly extend beyond the range of limited technical communities."

Oppenheimer was also eager to acquaint the non-physicist with the generality of the idea of complementarity, introduced originally by Niels Bohr: " . . . an atomic system ... may have billions and billions of atoms in it, but always it is a finite part of the world; and in order that you can make an observation of it, you must use the rest of the world for the machinery with which you do it." Especially Bohr has pointed out the analogies between this situation of complementarity and familiar traits in life: "He has had, I think, a double purpose: one to illuminate the situation in physics and one to reinforce our interest in complementary aspects of human life."

Oppenheimer also emphasized the limitations of science. " ... The sense of having to live and act in response to tradition, good judgement, and wisdom, which we have now, will not ever be alleviated by any development of the sciences." Still, he hoped that science and the scientist can and will contribute "to the making of a world which is varied and cherishes variety, which is free and cherishes freedom, and which is freely changing to adapt to the inevitable needs of change in the twentieth century and all centuries to come, but a world' which, with all its variety, freedom, and change, is without nation states armed for war and above all, a world without war. "

As an apostle of international cooperation in general, science in particular, Oppie played an important part in the years 1947 to 1949 in the discussion which, finally, led to the establishment of CERN, the European organization for nuclear research, in Geneva.

His post-war ordeal which resulted in the withdrawal of his security clearance has been discussed time and again. Finally, however, our government made proper amends. In April 1962, President Kennedy invited him to a White House dinner for Nobel prize winners. And in 1963, just after taking office, President Johnson presented Oppenheimer with the highest honor given by the U.S. Atomic Energy Commission, the $50,000 Enrico Fermi award. In his acceptance remarks Oppenheimer said, "I think it is just possible, Mr. President, that it has taken some charity and some courage for you to make this award today."

Oppenheimer's work continues to live in the accomplishments of his many students and friends. His truly brilliant mind is best described by his long-time friend, C. C. Lauritsen, "This man was unbelievable. He always gave you the answer before you had time to formulate the question."