Ian McCarthy was one of Australia’s outstanding theoretical physicists. He was born in country South Australia and, after a PhD at the University of Adelaide, and periods of work in the UK and USA, he returned to South Australia where for several decades he led an outstanding research program at Flinders University. Ian’s career had two major stages. In the first, he made major contributions to nuclear reaction theory, including very important insights into the physical consequences of the optical model and state-of-the-art calculations of proton knock-out from nuclei. In the second phase, he imported the concept of the knock-out reaction to atomic, molecular and solid state physics. Using the (e,2e) reaction, for which he and his colleagues developed the theoretical framework, his group made major contributions in these areas.
Ian Ellery McCarthy was born on 19 June 1930 in Adelaide, South Australia, the eldest son of James Cremeen Ellery and Gwendolen Helen McCarthy (née Ure), both South Australians. The law was a major influence in the McCarthy household, with both parents involved in the firm of J. C. E. and G. H. McCarthy at Kadina, South Australia. Ian’s father was an outstanding barrister with a reputation for never having lost a case in the State Supreme Court. His mother was an early woman Law graduate of the University of Adelaide, and her outstanding undergraduate career included being awarded the Stow medal in 1923. Both of Ian’s brothers followed their parents in the law. Ian’s only close scientific relative was a great-uncle on his mother’s father’s side, Robert Ramsay Wright, who was a professor of biology at the University of Toronto.
Ian’s childhood was spent in Kadina, South Australia, where the family had a house with a large garden and a small paddock on the edge of the town. His father served as Mayor of Kadina for several terms after the Second World War. The town was poor since its major industry, copper mining, closed in the Depression. It was, however, the centre of a prosperous farming district. Ian attended Kadina Primary School from 1936 to 1942. The school was too poor to have sporting facilities. Recreation consisted of swimming at Wallaroo six miles away.
At Kadina Primary School, Ian’s favourite and best subject was history. Surprisingly, his worst subject at this stage of his career was mathematics, of which he was frightened, perhaps because of the influence of his mother, who said she could never do it. Nevertheless, Ian was dux of the school in 1942 and won a half-fees scholarship to St. Peter’s College in open competition. Thus, at the age of 12, Ian went to school in Adelaide, where he lived with an unmarried Scottish great-aunt, Christian R. Ure. During this time, Ian developed a life-long interest in sport. He rowed in the School VIII and played football and cricket for the 3rd teams. He also had some aptitude for tennis. His participation in cricket continued after school days, and he developed into a village-green standard all-rounder. His favourite sport was football, but he felt he had little ability as a player. He was a fanatical supporter of the North Adelaide Football Club, which was not one of the league steamrollers, but won its share of premierships. It was great for those who knew him well to see him at a game in later years, taking enormous joy in the game and looking little like the image at that time of a university professor.
In his last year at school, Ian learnt to play the clarinet and developed a life-long interest in New Orleans jazz and European classical music. His jazz interest led to a desire to travel and he played with a South Australian band at interstate jazz conventions. At the height of his musical career, after the fifth and sixth Australian jazz conventions, Ian was described by critics who subscribed to the New Orleans philosophy as the best clarinet player in Australia.
At St. Peter’s College, Ian did not consider himself particularly good at schoolwork. Nevertheless, in 1947 he gained first place in the general honours list at the Leaving Honours examination of the State Public Examinations Board, with first places in German, physics and chemistry, and second place in mathematics. Since he was below the age at which most of his schoolmates went to university, he returned to school in 1948 and studied history (which completely bored him) and economics (the mathematical formulation of which he regarded, with typical frankness and honesty, as charlatanism). His favourite subject was physics, taught by Eric G. Stephens—yet another example of just how important good teachers are to stimulating bright students into physics. He won the Young Exhibition for dux of the school in 1948 and received a St. Peter’s Collegians’ scholarship that largely supported him at St. Mark’s College during his undergraduate life. Another important influence on his life was F. H. Schubert, who was in charge of the School Cadets, where Ian was Company Sergeant-Major and a member of the Earl Roberts Trophy rifle-shooting team that won the South Australian section in 1948.
Ian entered St. Mark’s College at the University of Adelaide in 1949 as a medical student, still having no overt interest in science. This decision was influenced by the fact that it was what most intelligent students did at the time and represented the next step towards a secure career. At the end of the first term, he was thoroughly depressed by the atmosphere of the medical school and the prospect of life-long conformity. He missed his favourite subjects, physics and mathematics. Ian felt that he owed a lot to the Master of St. Mark’s, Archibald Grenfell Price, to Professor L. G. H. Huxley of the Physics Department, and to J. V. Statton of the Mathematics Department, who convinced him that it was possible to pursue a career in physics and mathematics, an idea that had never occurred to him previously.
In the first year of the BSc course, Ian was exempted from first-year mathematics and chemistry because of his public examination results, and began second-year mathematics and applied mathematics in June. He continued with physics, which was at that time part of the medical course, as well as with zoology (largely to prove to himself and others that he didn’t leave medicine because he couldn’t do it). He was very pleased to achieve a Credit (at that time the highest grade) in zoology at the end of the year.
The undergraduate courses that interested him most were third-year mathematics and applied mathematics. Pure Mathematics was taught by George Szekeres, who became a friend in later life. He convinced the whole class that they wanted to be professional mathematicians, even though most realised that they did not have the talent. Ian believed that he passed the examination on the basis of having managed to solve ‘one or two homework problems during the year’. He was very good at the Cambridge-tripos style of mechanics that constituted applied mathematics, and from the course taught by H. W. Sanders gained a confidence and ability in tackling and formulating problems that served him well throughout his career.
Ian received the ordinary degree of BSc in 1951 and began the fourth-year Honours course in physics. The supervisor of his experimental project was Robert W. Crompton, who was at the beginning of a distinguished career in the accurate measurement of low-energy electron-atom cross sections. His project was to dismantle and rebuild an old electron camera that had been used for undergraduate demonstrations. He spent a long time detecting leaks and painting the thing battleship grey and remembered at the end of the period pumping it down and producing strange lights. However, to his knowledge it never worked again. From later observations, Ian believed that he received a typical Australian physics education. He recognised L. G. H. Huxley, who taught a very precise and interesting course on electromagnetic theory and waveguides, as a professional practitioner of the subject, but he was never interested in this field. Roy S. Burdon, who taught statistical mechanics with a biting sense of humour, was also a professional physicist who had done excellent research on surface tension. Ian developed enormous respect for all three people after more experience with physics in later life.
At this time, Ian felt that quantum mechanics was regarded as an obscure branch of philosophy or a slightly illegitimate branch of frontier algebra, according to whether you talked to a physicist or a mathematician. He had a one-term course in wave mechanics, taught directly from the textbook of Pauling and Wilson. It got about as far as the non-relativistic hydrogen atom and struck him as an exercise in the application of special functions. He was nevertheless interested to know more about quantum mechanics, and he devoted his honours seminar to its formulation as exposed in the first few chapters of Dirac’s treatise.
Ian told some fascinating stories concerning the atmosphere of the Physics Department at Adelaide University at that time. For example, he was amused later in life by the respect given to Huxley’s predecessor as professor, Kerr Grant, who used to have discussions round a table with the honours students and impressed them (Ian included) very much with the story that he ‘had once seen Einstein’s name on a door’.
A new influence had entered the University of Adelaide in 1952 with the formation of the Department of Mathematical Physics, staffed by a professor, Herbert
S. Green, and a lecturer, Harry Messel. Messel was a flamboyant character who taught an honours course on cosmic ray shower theory and convinced Ian that he was a link with the world of real physics overseas. Green taught an excellent and intelligible course on special relativity that clearly came from first-hand experience, rather than a textbook.
When Ian received first-class honours in 1952 and the promise of whatever financial assistance the University gave to graduate students at the time, he asked to enrol for a PhD with Messel as his supervisor, but was very disappointed to learn that Messel was leaving for the University of Sydney. Ian’s supervisor would have to be Green. However, Green was very deaf and quiet and completely overawed everyone, including physics and mathematics staff members, being thought to be so intelligent that he would not be interested in communicating with ordinary people. Ian very soon discovered Green to be warmly human and patiently helpful. Nevertheless, there was some consternation when Green told Ian that he was leaving to spend a year at the Dublin Institute for Advanced Studies, headed at the time by Erwin Schrödinger. Green gave Ian the 1949 paper by Freeman Dyson on quantum electrodynamics, Feynman’s 1949 paper on the theory of positrons, and his own paper on generalized statistics (later called para-statistics), and suggested that Ian spend the year trying to calculate the effect of generalized statistics on Feynman scattering amplitudes.
Ian had never heard of a ‘scattering amplitude’ and he never did find out, before he left Adelaide, the precise experimental meaning of a differential cross section! (Nor did he hear of a Clebsch-Gordan coefficient or a partial-wave expansion.) During Green’s absence in 1953, Ian developed the ability to abstract the mathematical essence of a problem without necessarily understanding the physical context. By the time Green returned, Ian had produced what he felt was a clumsy but valid derivation, which was published in the Proceedings of the Cambridge Philosophical Society.
His next problem was to consider Green’s suggestion that the newly discovered hyperon was a manifestation of the 3–3 resonance in pion-nucleon scattering (now called the Delta). His first reaction was that the masses are not the same, but neither he nor Green were deterred, and he proceeded to calculate the second-order Fredholm solution of the integral equation for the pion-nucleon scattering problem, using pion-nucleon field theory. Since they had no computer, integrations had to be done analytically, and Ian was amazed at Green’s ingenuity in finding transformations that ultimately enabled the calculation to be done. (1–3) These two problems constituted Ian’s PhD thesis, which was completed in 1955 and for which he was awarded the William Culross Prize for Scientific Research by a student at the University of Adelaide. In 1955, he was awarded a Shell Scholarship for two years’ study at the University of Cambridge.
During his time in the Department of Mathematical Physics at Adelaide University, Ian recalled meeting Otto Bergmann, a general relativity expert, and John C. Ward. The latter gave him the advice he gave most young people seeking guidance, namely that physics was too difficult for the average student. He advised Ian to get a job mending roads!
In 1953, Ian met an undergraduate student, Janet Furze, with whom he shared an interest in sport since she was a top-level tennis and basketball player. They were married soon after Ian went to Cambridge. They were a very well-matched couple who were blessed with five extremely talented children in whom they took great pride. All studied science or engineering and have pursued successful careers. The eldest, Catherine Mary, obtained a BSc from Flinders University and an MSc in theoretical chemistry from the University of Sydney. Helen Margaret earned a BE in civil engineering from the University of Adelaide, followed by a Masters in civil engineering from the University of Illinois and a PhD in civil engineering from the University of Melbourne. James Greig (Jim) obtained his BSc at Flinders University and his PhD in theoretical physics from Rockefeller University. Yet another physicist, Jane Frances obtained her BSc in mathematical physics at the University of Adelaide before moving to Cambridge for her PhD. The youngest, Patrick Ian, obtained his BE in chemical engineering at the University of Adelaide, followed by a Masters in petroleum engineering from the University of Kansas.
Under the terms of the Shell Scholarship, Ian was in statu pupillari at Cambridge, where he started in October 1955. This had the advantage that he was associated with a college. He chose Jesus because of its rowing fame, and he rowed for the second Fairbairn and third May boats in his first year. Since he already had a PhD, he considered the position equivalent to a postdoctoral fellowship. His formal supervisor was James H. Hamilton, who headed a loosely-knit group of theoretical physics students and recent post-doctoral fellows in the mathematics department, including Abdus Salam, John C. Taylor and John G. Taylor. There were interesting seminars on various aspects of quantum field theory in Hamilton’s rooms at Christ’s College, including some discussion by Salam on parity non-conservation in connection with K-mesons. This did not lead, however, as it might have, to the conclusions that Lee and Yang reached on this subject later that year.
Ian felt that he did not really have the background to benefit from contact with these people and was made to feel even smaller by the atmosphere of oneupmanship that pervaded the place. He shared a large room with about six others, all of whom were too frightened of the others to speak, as he found out many years later from one of them, David Thouless, who became famous in many-body theory.
The head of the mathematics department was P. A. M. Dirac. He came to the weekly seminars, in which he always seemed to sleep. At the end, he would usually ask one of two questions. If the talk was on field theory, he asked ‘what about the electromagnetic field?’, but if it was on particles, he asked ‘what about the electron?’. Since these things were always exceptions, he never got satisfactory answers. The most famous victim of this was Werner Heisenberg, who talked about his unified theory of particles, which did not include the electron. In a seminar Ian gave on the Fredholm solution of the pion-nucleon integral equation, Dirac complained that he was squeaking the chalk on the blackboard and keeping him awake. He suggested Ian should break the chalk and use the broken end. Ian noted that this was his first and last lesson on classroom teaching techniques.
A visitor to Cambridge in 1955–1956 was Hans Bethe, who gave some lectures to graduates on pions and nucleons. When Ian asked him what he thought of the idea that the 3–3 resonance was a hyperon, Ian was considerably deflated by the remark that this was not very sensible because the masses were not the same. Bethe did think, however, that the second-order Fredholm solution was interesting because of the method used. Bethe was at that time very interested in the new many-body theory of nuclear matter. He asked for a student to help him on this subject. The student was Jeffrey Goldstone, who did his well-known work on many-body perturbation theory while Bethe was spending a few weeks in Europe.
A seminar visitor to Cambridge that year was Wolfgang Pauli. With two other very junior people, Ian was asked to take him to lunch at a restaurant. Since the others wanted to talk about physics, Pauli talked primarily with Ian. He told him that Cambridge had always insulted him and that being sent to lunch with three junior people was another example of this. He then discussed English women and beer, neither of which met with his approval. After lunch, Pauli gave a seminar on his version of Heisenberg’s unified particle theory. He had an interesting argument with Dirac, who accused him of being too ambitious in trying to solve all of physics at once. Pauli accused Dirac of being trivial because he was still trying to understand the vacuum. Dirac’s reply was ‘A good general attacks the enemy at its weakest point.’
In his second year, Hamilton suggested that Ian might look at some problems in nuclear physics, in particular the scattering and absorption of anti-protons (newly discovered in 1956) by protons. (4) This brought him into contact with the experimental group of Denys H. Wilkinson, who made frequent visits to the USA and was up to date with experimental information, especially from Brookhaven National Laboratory where he was a regular visitor. Ian’s anti-proton work was his first contact with the optical potential, which was a recurring theme in his work from then on. Wilkinson used to ask very difficult and stimulating questions. One of these, which Ian puzzled over for some years and was eventually able to answer, arose from the idea that a direct reaction can be considered as a measurement of a momentum-transfer distribution and yet it is localized to the nuclear surface. (5–9) The question was, if this is so, how is it compatible with the uncertainty principle? The answer led to considerable insight into the mechanism of direct reactions, which was one of Ian’s major contributions to nuclear physics. Ian found his friendship with Wilkinson a source of stimulation throughout his career in nuclear physics.
A visitor to Cambridge for the year 1956–1957 was Robert Eisberg, an American nuclear physicist of about the same age as Ian. Eisberg had just come from Brookhaven, where he had done experiments showing that proton inelastic scattering could be a direct reaction in which the compound system lasts so long that it loses all memory of how it was formed before it decays, rather than a statistical reaction. His friendship with Eisberg became a large influence on his subsequent life.
Another important influence was a seminar given by William J. Tobocman, who discussed a direct-reaction theory of deuteron stripping similar to the theory discovered independently by Huby and Newns at Liverpool and Stuart Butler at Birmingham. Ian realized for the first time that non-relativistic quantum mechanics was interpretable quite simply in physical language.
Another contemporary at Cambridge was Lawrence Spruch, whose work in rigorous few-body atomic theory led this field for many years. Spruch, Eisberg and Wilkinson suggested to Ian that he could get a postdoctoral position in the USA quite easily. He wrote to several people and was accepted by all of them.
From these offers, Ian chose to work on the Atomic Energy Commission contract at the University of Minnesota to which Eisberg was moving in 1957. They planned to attack the problem of proton-induced direct reactions in terms of a semi-classical theory. Eisberg also had plans to prove conclusively that direct collisions were important in nuclear physics by detecting a vestige of the proton-proton billiard-ball collision kinematics in a (p,2p) experiment—that is, a coincidence measurement of two protons after a proton-nucleus collision. Minnesota at that time had a new proton linear accelerator of energies 10, 40 and 68 MeV, one of the few machines in existence for doing nuclear reaction experiments at high enough energy for the direct mechanism to dominate.
Moving to Minnesota in August 1957, Ian was officially assigned to work under the direction of a theorist, Warren Cheston. The leader of the nuclear group and the person responsible for the linear accelerator was John Williams, a respected older physicist who was at that time an Atomic Energy Commissioner. Ian’s first impression was amazement at the fact that, in contrast to his Cambridge experience, he was treated by these people as a fellow physicist. After a few months, he attended a meeting on nuclear shapes and sizes at Stanford, where Williams introduced him to a bewildering collection of people whose names he had seen in the Physical Review.
It was made clear to Ian that he was entirely free to work as he liked and he decided to try to understand the initial stage of a proton-induced collision by calculating the flux of protons in a nucleus under the influence of the optical potential, a suggestion made by Eisberg. This was to be the first stage of their semi-classical theory. He calculated the flux and its divergence (showing where the reactions take place) by modifying a computer program that had been written by Alfred Glassgold in machine language for a Univac ERA 1103 computer with 2,000 words of electrostatic memory. This was one of the largest and most powerful computers in existence. Input-output was by paper tape or by directly pushing binary buttons on the console. It became obvious that reactions were localized not only on the nuclear surface, but to small areas on the surface, particularly the front surface and the focal region at the back, the existence of which Ian discovered. This intensified the puzzle set by Wilkinson’s question about the uncertainty principle.
Ian presented three-dimensional drawings of his flux patterns at a conference on the optical potential at Tallahassee in 1958 and was disconcerted by the loud laughter that greeted them! However, he discovered that this arose from the surprise of the audience to see that a direct nuclear reaction really looked like what one would expect from a light wave in a cloudy crystal ball. He was very excited to be complimented on the work by Victor Weisskopf, Keith Brueckner and David Saxon, who were among the leaders in nuclear theory. He felt accepted as a nuclear physicist and determined to follow up this work by contributing further to the understanding of direct reactions.
Not long after Ian’s return to Minnesota, the group was joined by Charles Porter who, as a student of Weisskopf, had been the first to recognize the connection between the compound-nucleus model of Niels Bohr and the direct-reaction theory of elastic scattering. The paper of Feshbach, Porter and Weisskopf is one of the classics in the history of nuclear physics. Porter had also, with R. G. Thomas, been one of the first to use a statistical theory of matrix elements to predict distributions associated with nuclear reactions. Ian shared a room with Porter, whom he felt to be one of the most inspiring people he had met, particularly in his approach to physics and physicists. His absolute insistence on openness and fair play in scientific communication helped Ian to form the ethical standards to which he conformed during his scientific life. They developed a very strong friendship.
Porter and Ian had long discussions on Wilkinson’s uncertainty puzzle. They decided to calculate the Wigner phase-space distribution for bound nucleons moving according to the shell model, obtaining negative probabilities unless the distribution was folded over a phase-space region that obeyed the uncertainty principle. They did this for a Gaussian region and discovered that, for a given Gaussian position localization smaller than the nucleus, the momentum distribution is governed more by the localization function than by the details of the shell-model wave function. The paper describing this work was written in collaboration with George Baker of Los Alamos Scientific Laboratory, who was an expert on the Wigner distribution. The significance of this for understanding direct reactions was great, since Ian had already shown that the momentum transfer occurs in highly localized regions of the nucleus. In particular, the momentum spread due to localization completely invalidates any semi-classical explanation. The computations for this work were begun on the IBM 704 at Los Alamos, using the newly invented, high-level language FORTRAN. They were among the first physics computations in a language that has since become universal.
A highlight of Ian’s period at Minnesota was the visit of Niels Bohr. Minneapolis was the centre of the US Danish community, and all staff members were introduced to Bohr, who had a discussion with them round a table. He was almost totally unintelligible and communication was not helped by his habit of continually lighting his pipe. Once when he put it down on the table, someone discreetly removed it, but he was used to this and produced another from his pocket.
In Ian’s second year at Minnesota, Eisberg produced some data on the (p,2p) reaction. Unfortunately, the desired 90◦ angular correlation was not obvious. The analysis of the data, with the help of two students, Albion Kromminga and Edward Jezak, showed that the reactions were direct in the sense that the recoil momentum of the residual nucleus was small in every case. (8) The incident energy, 40 MeV, was too small for the observation of the 90◦ (billiard ball) angular correlation. Not long after this work, the results of (p,2p) experiments at 180 MeV were published by the group at Uppsala. They did show the angular correlation expected from first-order (plane-wave) direct reaction theory. The plane-wave interpretation of the (p,2p) reaction is that the distribution of measured recoil momenta is the distribution of momentum of the struck proton before knockout. It thus gives direct information on shell-model wave functions.
Not long before leaving Minnesota, Ian read a preprint on a semi-classical direct reaction theory by Stuart Butler, Norman Austern and Colin Pearson. He wrote them a letter pointing out what he had discovered with Porter about the effect of the uncertainty principle. This started a controversy with Austern, who regarded himself, justifiably, as a leader in the direct reaction field. It was also his first contact with Butler, who became one of his closest friends in physics.
In June 1959, Ian moved to University of California, Los Angeles (UCLA) where he took a postdoctoral position with David Saxon (who later became President of the University of California). One attraction was the Western Data Processing Center, which had a new IBM 709, the most powerful computer in the world at the time. Saxon’s group had written a very-well documented program for the phenomenological nuclear optical model and used it to demonstrate the usefulness of the model (which is the direct reaction model for elastic scattering). (11–19) Much of Ian’s subsequent work in nuclear and atomic physics was based on this program.
At UCLA, Ian met a Scottish particle physicist, Derek Pursey, who was attracted by the uncertainty-principle questions in direct reaction theory. Together they constructed a theory of alpha-particle inelastic scattering that described the localization of the reaction on the nuclear surface in detail with some geometrical parameters. The uncertainty principle then gave an amazingly accurate description of the momentum spread in the reaction. Alpha particles (strongly absorbed) were used, rather than protons (weakly absorbed), because the focus is less important in that case. In fact, the angular distribution is quite a simple diffraction pattern. This would not be true for protons, where the focus would complicate the localization. The semi-classical model predicted the opposite. The qualitative effect of the focus in proton inelastic scattering remained to be understood.
A significant step in direct reaction theory at that time was the construction by Carl Levinson and Manoj Banerjee at the University of Maryland of a direct reaction theory of proton inelastic scattering in the distorted-wave Born approximation. This is the extension of the optical model to direct reactions. The theoretical work Ian and his collaborators had done could be regarded as insightful approximations to this theory. However, their calculations gave surprisingly poor fits to proton inelastic data.
At UCLA, Ian also worked with Derek Prowse on an explanation of K-meson capture. (10) The problem was that K-mesons had to be captured in the far nuclear surface because of the strength of their absorption, but their decay could only be explained by simultaneous interaction with two nucleons, which were unlikely to be found sufficiently close together in the surface. Their explanation was that the K− was scattered into the centre by the first interaction. This explanation was independently adopted by Judah Eisenberg, who assumed that the scattering was resonant. He was able to deduce the parameters of the resonance, which were later confirmed by experiments designed to investigate its properties.
The experimental nuclear physics group at UCLA included cyclotron builders Reginald Richardson (who later built TRIUMF, the Canadian national accelerator in Vancouver), Kenneth McKenzie and Byron Wright. They were building the first isochronous (spiral ridge) cyclotron with a small magnet gap, which considerably reduced the size and cost. They expressed their interest in building one in Australia, an idea Ian thought was excellent because it would have brought Australia into the field of direct reactions and hence into the investigation of nuclear dynamics (details of wave functions and mechanisms) rather than spectroscopy. They estimated the total cost at $500 000, which was within the reach of Australian funding at the time. Indeed, one was built with their help at the University of Manitoba for this price and provided very useful data for many years.
In March 1960, Ian took up the offer of Bert Green of the position of lecturer in the Department of Mathematical Physics at the University of Adelaide. In 1961, he was visited by Albion Kromminga, who had received a Fulbright fellowship after his PhD at Minnesota. Together they calculated the qualitative effects of the focus in proton inelastic scattering and deuteron stripping, showing that it is responsible for backward peaks at some energies. These had previously been ascribed to vestiges of the low-energy statistical mechanism first proposed by Niels Bohr. They also discovered the general reason for the parity rule for inelastic scattering that had first been noted by Norman Glendenning at Berkeley. This may be summarized as a cross-section minimum for forward scattering involving a change of parity, and a maximum (due largely to the focus effect) if there is no parity change.
At Adelaide, Ian was fortunate to have three excellent graduate students: Lim Khaik Leang (later head of the Malaysian atomic energy research effort), Lindsay Dodd (later a staff member in mathematical physics at Adelaide), and Kenneth Amos (later a staff member in physics at Melbourne). They began to build the computational technology required for a serious, quantitative study of direct reactions in nuclear physics. (20–38) This was helped by the insight gained from the simple qualitative understanding achieved by the localization arguments. The computer they used was the IBM 7090 that had recently been installed at the Weapons Research Establishment at Salisbury, South Australia. This was the largest computer in Australia and essentially state-of-the-art at that time.
The quantitative theory was the distorted-wave Born approximation. Lim made the program for (p,2p) and produced an excellent analysis of the Uppsala data that confirmed the promise of high energy (>200 MeV) (p,2p) as the most direct means of understanding single-particle properties of nuclei. This was the first step in a quantitative understanding of nuclei, which must involve using realistic nucleon-nucleon forces to calculate single-particle properties and the effects of correlations not taken into account in the independent-particle model. It was also believed that an understanding of the distorted waves at lower energy (∼50 MeV) would enable the single-particle description to be continued to the lower energy.
Amos made a program for proton inelastic scattering from which quantitative fits to data were not obtained, but which showed the strength of some effects, such as the localization to the surface radial region. At that time, no one could get a quantitative explanation of direct reactions using the independent-particle model for the target states. John Blair at the University of Washington was brilliantly successful for some induced excitations, which he identified as rotational or vibrational following a suggestion made by two Russians, Sergei Drozdov and Evgenii Inopin. The distorted-wave theory of such reactions was developed principally by Ray Satchler’s group at Oak Ridge. In later years, Amos persisted with inelastic scattering and, in collaboration with Heinz von Geramb at the University of Hamburg, was able to obtain quantitative results with essentially the same reaction theory, but a much more detailed bound-state description that incorporated the detailed microscopic description of rotational and vibrational excitations.
In the early 1960s, Ian believed that theoretical techniques based on the distorted-wave Born approximation would provide the basis for a quantitative understanding of nuclei in collaboration with the direct-reaction experiments that could be performed using the new spiral-ridge cyclotrons. He was able to communicate this to a number of Australian nuclear physicists and they set out to make Australia one of the centres of this effort, starting with the cyclotron that Richardson and others had offered to build. Such a large effort (approximately $1 million overall) required the backing of an institution such as a university or university consortium. It was a great disappointment to Ian that his group was never successful in obtaining this. They kept the idea of a front-line nuclear physics institute alive until the early 1970s, although the required equipment changed and its cost escalated as previous proposals became outdated. His principal helpers in this effort were Brian Spicer at the University of Melbourne and David Peaslee at the Australian National University.
While at Adelaide, Ian met a new lecturer in the Physics Department, Erich Weigold, who had just completed his PhD in nuclear physics at the Australian National University. He believed that one could set up the same types of experiments in atomic physics as Ian had proposed for nuclear physics, in order to obtain a similarly complete understanding of atomic structure. Together they decided that the (e,2e) experiment, which had first been proposed in Ian’s 1960 paper with Baker and Porter on the Wigner phase-space distribution in the independent-particle model, should provide the same basis for the understanding of atomic structure as the (p,2p) experiment promised to do in nuclear physics. Detector technology for the required electron-scattering experiments was just being introduced at that time.
In 1962, Ian decided that the only way to continue a competitive level of involvement in nuclear physics was to return to the USA. He therefore contacted the Department of Physics at the University of California at Davis, which had been recommended to him by Saxon. The University’s plan was to make Davis its major nuclear physics campus by implementing a proposal to build a large, modern cyclotron there, starting with the original magnet of the Crocker cyclotron whose useful life at Berkeley had ended. The principal architect of the proposal was a cyclotron builder, John Jungerman. Ian visited Davis for one or two months as a cyclotron-building consultant, his first and last involvement in the building of scientific machines. He made a mathematical model of the proposed magnetic field and used it to calculate the best method of electrostatic beam extraction of positive ions, using computing technology at Berkeley.
Ian accepted the tenured position of associate professor at Davis and moved there in July 1963. His position there as a nuclear reaction theorist complemented that of William True, who was a well-known nuclear structure theorist. They shared an Atomic Energy Commission research grant. However, there were no experienced or promising nuclear experimentalists. The idea seemed to be that good equipment would produce good physics in the hands of whoever was using it, an idea not confined to Davis.
Ken Amos accepted a postdoctoral fellowship at Davis and together he and Ian continued their proton inelastic scattering work. Lim also spent a summer there, and they implemented an off-shell impulse approximation in the distorted-wave (p,2p) program, thereby enabling an estimate of the effect of different assumptions for the nucleon-nucleon force in (p,2p). Ian’s conviction that (p,2p) could be continued to lower energies was tested by a 60 MeV experiment on 12C performed on the Berkeley 88-inch cyclotron by Howel Pugh and David Hendrie. In fact, the data could not be adequately explained by the distorted-wave impulse approximation. (39,40) The probable reason for this was discovered some years later by Amos and von Geramb, who showed the effect of giant multipole resonances in direct reactions below 100 MeV.
The situation with the (p,2p) reaction at that time was unsatisfactory. It required an accelerator with a 100% macroscopic duty cycle, such as the spiral-ridge cyclotron. Existing machines, however, were limited in energy to below 100 MeV, and it was obvious that the impulse approximation only worked above that energy. For synchrocyclotron experiments such as those at Uppsala, the counting statistics were inadequate for detailed data. The modern cyclotrons planned at Maryland (150 MeV) and Indiana (200 MeV) promised to yield the clean and decisive structure information of which (p,2p) should be capable. During Ian’s time at Davis, the planned cyclotron, which should also have been capable of good (p,2p) results, was never brought to fruition, and it became obvious that the experimental manpower was inadequate. In later years, the cyclotron did work, but the group lost most of its Federal funding support.
While at Davis, Ian had two discussions with Edward Teller, who was a part-time professor in the Davis Engineering School in addition to his other duties at the Livermore radiation laboratory. This was risky in the context of campus politics, because Teller’s stand against Oppenheimer was unpopular with physicists. However, Ian felt it would be stupid not to take advantage of Teller’s presence. He found him an extremely charming man who seemed entirely immersed in his high-level dealings and had not kept up with nuclear theory.
In 1965, Ian yielded to campus political pressure not to renew his share of the AEC contract with True. Promotion committees were very insistent that a professor should find his own independent research funding. Ian obtained a research contract with the Air Force Office of Scientific Research, whose nuclear physics division was led by his ex-Adelaide friend Erich Weigold. At that time, such contracts were given for work suggested by the Principal Investigator, with no requirement for applications.
It had become obvious that the promise that Davis would become the University of California’s nuclear physics centre would not be fulfilled. In fact, UCLA had taken over the role by having more enterprising experimentalists with much less funding. Ian decided to find another position, which was very easy to do at the time since there were many universities wanting to reinforce their theoretical physics groups. The University of Oregon was ideal, partly because it had just received the first National Science Foundation centre-of excellence grant, through which it planned to develop a major effort in theoretical physics and chemistry. Another motivation was the beautiful location and climate at Eugene, which contrasted with the oppressive heat of the Sacramento Valley. In 1965, Ian accepted the position of Professor of Physics at Oregon, with duties half-time in the Department of Physics and half-time in the Institute of Theoretical Science, which was a pure research institute. The leading research group at Oregon was in solid state physics, where Gregory Wannier had been an inspiration for some years. Wannier was a very simple man who insisted on understanding every piece of physics work at a very basic level. One had to think very clearly to satisfy him with an explanation.
In 1966–1967, the Institute of Theoretical Science was fortunate in having as a visitor Manoj Pal (later a Professor at the Saha Institute of Nuclear Physics, Calcutta) who was one of the world’s leading nuclear-structure theorists. Ian learnt a great deal about nuclear structure theory from him and did some work on deuteron stripping with his wife Dipti Pal, who was a nuclear reaction theorist.
In about 1966, it was suggested by Eisberg and others that Ian should write a graduate-level textbook on nuclear theory. Since several publishers were interested, he began this task, using lecture notes from previous years as a basis. He had a great deal of help from Manoj Pal in writing the chapters on nuclear structure. The book took most of his time in 1967 and was published in 1968 by John Wiley. (299) It was an extremely useful and original introduction to nuclear theory and was widely appreciated. In 1967, Ian met Dirk ter Haar of Oxford University, who was the editor of a Pergamon Press series in which the author wrote about half the book as an introduction to a collection of reprints of what he considered the major papers in a field. He suggested that Ian should prepare a volume on nuclear reactions for the series. The knowledge he had recently gained from writing the textbook proved very useful, and the Pergamon book was published in 1970. (300)
One of Ian’s main jobs at Oregon was to hire one or two other nuclear theorists to build up a group. In trying to do this, he encountered a problem common in developing US universities that continues to this day. Institutions are often more interested in the appearance of prestige in their staff than in actual merit. Although he could have hired several people whom he knew to be doing very promising work (that later came to full fruition), they were all vetoed by the Dean, since they did not have the conventional marks of prestige, such as a PhD from an Ivy League university.
From 1963 to 1967, Ian attended most of the international conferences that were relevant to nuclear reactions and gave invited talks at many of them. He got to know most of his contemporaries in nuclear physics, including NormanAustern, Robert Lawson, Malcolm McFarlane, John Blair, Lawrence Wilets, Ray Satchler, Dieter Kurath and Daniel Koltun among the theorists. He also met many of the original theorists in the field including Rudolf Peierls, Gregory Breit and Eugene Wigner.
In 1967, Kenneth Le Couteur suggested to Ian that he should seriously consider the second professorship of physics at the Flinders University of South Australia. In discussions with the founding professor, Maxwell Brennan, during a visit by Brennan to Oregon, it was decided that Ian would be responsible for hiring about four new staff members. Ian believed he could hire excellent people who would form the basis of a first-rate group. He consulted Erich Weigold, who agreed to join with his ex-student Peter Teubner, who had done excellent experimental work in atomic scattering as a postdoctoral fellow at the University of Pittsburgh. He also invited Iraj Afnan, who had obtained his PhD at MIT and had been doing very original work on the question of resolving the ambiguities in nuclear forces, determined by fitting two-body (on shell) data, by calculating their effects in nuclear matter (off shell).
Ian’s own research interests had developed in the direction of studying the nuclear force ambiguities by direct reactions, which are essentially three-body reactions. (41–43)
He was therefore also interested in the new applications of the ideas of Faddeev in nuclear physics. Among the leaders in this field were an old friend, Ian Sloan of the University of New South Wales, and his student Reginald Cahill. Ian sought to hire Cahill. Ian believed that with this group, his ambition to have an Australian group that would lead the world in the dynamic study of the nuclear many-body problem (46–56) could be transferred to atomic and molecular physics. At that time, there were about six staff members at Flinders. All research projects were related in some degree to plasma physics, in which Ian could find no interest in spite of attending seminars and research meetings. In his first few years at Flinders, Ian kept up his interest in looking for effects in nuclear reactions that would help to resolve nuclear force ambiguities. He was a member of the advisory committee for several few-body international conferences and an invited speaker at the opening of the University of Maryland cyclotron.
One of Ian’s early graduate students was Peter Tandy, who came from the University of Queensland. They calculated the (p,2p) reaction on the deuteron. After a seminar by Cahill, they decided to calculate an idea of his on the effect of off-shell potential details in three-nucleon reactions, finding that the reactions are sensitive to such details in some circumstances. (49,51,53,54,56) This formed the basis of Tandy’s thesis. After a successful postdoctoral career at Surrey and Maryland, which with its new cyclotron had become the type of experimental-theoretical centre in nuclear reactions that Ian had wanted for Australia, Tandy became a professor at Kent State University.
Max Brennan and Ian agreed to keep one academic post unfilled so they could use the salary to top up the funds required by visitors. Early visitors were Manoj and Dipti Pal (45,48) as well as Robert Eisberg. Cahill joined the group in 1972.
The first highlight of Ian’s new group occurred not long after Afnan arrived in 1970.After a seminar he gave on the nuclear force ambiguity, a question was asked by a third-year student, Anthony Thomas, who had been introduced to nuclear theory by Ian through working on a vacation project calculating (p,2p) reactions to compare with Manitoba data. (44,47) He had been studying pion-nucleon physics because Ian and Afnan wanted to learn about the new field of intermediate-energy physics that would start with the development of proton accelerators at Los Alamos (LAMPF),Vancouver (TRIUMF) and Zurich (SIN, later PSI). The question was whether it would be possible to calculate the pion, two-nucleon three-body problem and get information on far-off-shell nuclear forces from pion production. Afnan and Thomas began independent calculations of this model in which both obtained the same results, showing the expected sensitivity and providing a quantitative explanation of known phenomena for all the pion two-nucleon reaction channels. After a successful career in a permanent position at TRIUMF, Thomas moved to a staff position at CERN before becoming Elder Professor at the University of Adelaide, and later Chief Scientist at the Thomas Jefferson National Accelerator Facility in the USA.
Afnan pursued the ideas further, finding a satisfactory formal theory of the coupled πNN–NN systems. He was helped in this by Boris Blankleider, his graduate student, who then moved to TRIUMF and later to a staff position at Flinders University, and Andris Stelbovics. Ian did not participate directly in this work, but actively encouraged and supported it with his typically infectious enthusiasm. Apart from two-month periods of collaboration with Heinz von Geramb at Jülich and Hamburg, his interest was moving to atomic physics. Afnan showed, in collaboration with another student, Jeffrey Read, that the exact Faddeev solution of the bound three-nucleon problem could not reproduce the triton binding energy or form factor with any phenomenological force. His later work has shown explicitly that one needs pion (and heavier meson) degrees of freedom to explain these phenomena quantitatively.
When Ian first came to Flinders, a new physics syllabus had just been introduced for the Matriculation examination of the State Public Examinations Board. Max Brennan organized several annual summer schools in which university and school-teaching staff familiarized teachers with the new ideas. Ian’s involvement in these led to an invitation to be co-author of a book Physics, a Laboratory-Oriented Approach, (301) that was written with the new syllabus in mind, but also with an eye on a wider market. It was published by Rigby Ltd and sold well throughout Australia. Ian later served a term as Chairman of the Physics Committee of the Public Examinations Board.
When Teubner arrived in 1969, he started building equipment for electron elastic and inelastic scattering on atomic beams. Together with Weigold, who arrived in 1970, and a student, Robert Lloyd, he produced the best relative electron-hydrogen elastic differential cross-sections up to that time. He also determined relative elastic angular distributions on all the inert gases up to xenon. Together with a student, Janet Furness, Ian developed an optical model that described these data quite well. (57–66) The model was semi-phenomenological, since it started with calculated atomic wave functions, but required knowledge of the total reaction cross-section in order to fix the strength of the electron absorption. It also included an equivalent-local exchange potential that became standard in the field.
Upon arrival, Weigold started the (e,2e) project that he and Ian had planned for some years. They were encouraged by the success of Ugo Amaldi, who had observed coincidences in atomic (e,2e) reactions using the electron beam at the Italian nuclear laboratory INFN at Frascati. Ian visited Amaldi and they agreed to keep closely in touch on the progress of the (e,2e) reaction. The first successful (e,2e) angular correlation experiment was reported in 1972 by the Italian group at CNEN (now ENEA), which is across the road from INFN at Frascati. The scientists in this group, inspired originally by Amaldi, were Anna Giardini-Guidoni, Rossana Camilloni and Giovanni Stefani. The experiment observed the 1s state of solid carbon. It used 7 keV electrons, with several hundred eV resolution, and agreed in detail with the distribution expected from the clean knock-out of an electron the momentum distribution of which is given by the Hartree-Fock orbital.
Weigold had been concentrating on the valence electrons of gaseous targets, because they are the important ones from the point of view of atomic reactions and chemical structure. The first data were obtained in 1973 by Weigold, Stephen Hood (graduate student) and Teubner. They were for 400 eV electrons on the 3s and 3p electrons of argon. The resolution of about 2 eV was enough to separate electronic states. The group was quite surprised that there were more than two ion states excited. The first had an angular correlation that agreed in detail with the plane-wave theory for the Hartree-Fock 3p state, while the four others agreed in equal detail with the Hartree-Fock 3s state.
The detail with which atomic momentum distributions could be determined was remarkable. Quite respectable orbitals from the chemistry point of view (such as hydrogenous orbitals with variationally determined effective charge or even Hartree-Fock-Slater orbitals) gave markedly inferior agreement. The experiment had succeeded beyond their wildest expectations and clearly would provide the detailed account of atomic and molecular structure that had been hoped for in nuclear physics with (p,2p).
The very first experiment provided the basis for the illumination of structure. Ian interpreted the four ion states with 3s momentum profiles as components of the 3s orbital split by electron-electron correlation. This interpretation has been confirmed by analysis of spectroscopic factors for higher-energy experiments on inert gases and a wide range of molecules, where the cross-section ratios are independent of incident energy. The (e,2e) experiment gives the details of momentum profiles, which is all the information allowed by quantum mechanics on single electron orbitals in the target, and details of correlations between electrons in the orbitals through the ratios of cross-sections for states that are components of split orbitals. (67–82)
The theory of the reaction was refined by various distorted-wave approximations, the simplest being the averaged eikonal approximation, which has successfully fitted a wide range of data, particularly later Frascati data on inert gases, with an energy-independent constant average complex potential. Clifford Noble, a postdoctoral fellow, calculated the full distorted-wave theory using the semi-phenomenological optical model for inert gases. This extended the range of accurate prediction of momentum profiles from about 1.5 to 3 atomic units of momentum.
In 1975, Ian travelled to the USA where he talked to several quantum chemists prominent in the field of atomic and molecular wave function calculations. The idea was to publicize (e,2e) and to promote collaboration with the quantum chemists, since (e,2e) spectroscopy is the most direct and accurate test of their wave functions. These people were Paul Cade (University of Massachusetts), Lawrence Snyder (Bell Telephone Laboratories) and Paul Bagus (IBM Laboratory, San Jose). Ian gave an invited paper on (e,2e) at the annual Sanibel Island meeting of quantum chemists sponsored by the Universities of Florida and Uppsala. He also spent time at Indiana University working with nuclear physicists involved with the new 200 MeV spiral-ridge cyclotron and with Russell Bonham in the Department of Chemistry planning a workshop/seminar on momentum wave functions in atomic, molecular, nuclear and solid state physics.
The momentum wave functions workshop, sponsored by the National Science Foundation and the Australian Department of Science, was held at Indiana in 1976. Ian gave the opening paper, summarizing the history and status of (p,2p) and (e,2e). (80) It was said to be the only meeting in anyone’s memory where physicists and chemists from such diverse fields had come together and talked at the level of practical details. This was because of the common ground provided by the (e,2e) and (p,2p) reactions. Much progress in understanding the (p,2p) mechanism had been made by the Maryland group, but it had still not been as fully utilized in understanding structure as had (e,2e), even at that early stage. Other methods that yield some momentum information were also discussed, notably Compton scattering in atoms and molecules and positron annihilation in solids.
The early (e,2e) experiments yielded accurate information about molecular orbitals and correlations for a wide range of molecules. Ian was involved in their interpretation in terms of several quantum-chemical methods: molecular orbital calculations, configuration interaction, and generalized overlap amplitudes from the one-particle Green’s function. (84–12)1 The quantum chemists involved were Paul Bagus, the German group of Cederbaum, Domcke and von Niessen and an Australian, Geoffrey Williams. In 1982, the (e,2e) experiments expanded in two directions, molecular structure with second-generation energy resolution (less than 1 eV) and solids. The prospect of elucidating the band structure of solids was most exciting, because (e,2e) spectroscopy of molecules had far outstripped its rival, photoelectron spectroscopy, because of its ability to identify the group representation of a state by its momentum profile, as well as the ease of extracting the structure information from the experimental data.
Ian’s major research effort over the last years of his career was to calculate every possible aspect of the reactions initiated by electron collisions with atoms and ions. (122–298) It started with the semi-phenomenological optical model made to analyse Teubner’s early data on elastic scattering from inert gases. It received much impetus from the 1975 visit to Flinders of Brian Bransden from the University of Durham, who had been one of the leading theorists introduced to the field by Harrie Massey. Bransden introduced Ian to many ideas and techniques peculiar to atomic phenomena. The detailed experiments of Teubner on electron-photon angular correlations and spin effects provided a strong challenge for the theory.
In 1977, Ian spent a year in Europe with his family. The first five months were shared between the University of Surrey and Royal Holloway College of the University of London. At Surrey, he worked with Ronald Johnson, who had been one of the leaders in the field of direct nuclear reactions, and Daphne Jackson, whom he had known for some time because of their mutual interest in (p,2p) calculations. At Holloway, he worked with Coulter McDowell, who had done much work with Bransden on atomic reactions, and with Lesley Morgan. He began to formulate ideas on the calculation of atomic optical potentials from first principles in much more explicit detail than in the closure approximation current at the time. He spent two months with Bransden at Durham developing more insight into the optical potential and into coupled-channels calculations in co-ordinate space, for which the equivalent local approximation that he had developed with Furness was shown to give sufficient accuracy with much-reduced computational labour.
A month in the group of Frits de Heer at the FOM Institute for Atomic and Molecular Physics in Amsterdam led to a collaboration with the group of Poppe at the Zeeman Laboratory, with whom he calculated the spectroscopic factors for the argon ion, which had been observed in the first (e,2e) experiment on valence electrons. They used a phenomenological shell model with Hamiltonian matrix elements parameterized by fitting many relevant energy levels. The calculation was not quite detailed enough for a full explanation of the data and, indeed, the (e,2e) spectroscopic factors remain a challenge to quantum chemistry that is just beginning to be met for small molecules by the Green’s function methods of Cederbaum.
In September 1977, Ian visited Frascati, where he worked on the mechanism of the (e,2e) reaction. By using experimental kinematics designed to bring out the effect of the two-electron interaction, it was shown that the full interaction (t-matrix) is a necessary ingredient and that the potential (Born approximation) is insufficient to explain data with large momentum transfer. In 1978, Ian was honoured to be the only physicist who had not been directly associated with Sir Harrie Massey to be asked to be a session chairman at the Royal Society conference to mark Massey’s 70th birthday.
On his return to Adelaide in 1978 from the sabbatical year in Europe, Ian succeeded in hiring Andris Stelbovics as a postdoctoral fellow. Andris had completed a PhD at the University of Adelaide in the nuclear three-body problem and had returned to Australia and decided to take a tenure-track position in mathematics at the South Australian Institute of Technology (now the University of South Australia). Ian rang Andris one day and invited him to apply for an AINSE fellowship. Andris pointed out to him that this was not a particularly attractive proposition since he had a secure career path; furthermore, the conditions of the AINSE fellowship would preclude a theorist from applying because they stipulated that the fellow would have to use the facilities at the Australian Atomic Energy Commission’s establishment at Lucas Heights, on the outskirts of Sydney. Ian countered by saying that Stuart Butler, head of ANSTO at that time, would approve. Ian’s persuasiveness worked and Andris came to Flinders University, initially to work on atomic ionization processes.
Ian and Andris had quite an empty canvas since for many decades progress in modelling electron impact ionization had stalled and Born approximation models were still very much the norm. Motivated by the state-of-the-art experiments that Eric Weigold, Peter Teubner, and Jim Williams were performing, Ian and Andris developed a model for electron-atom collisions based on the Feshbach formalism that explicitly included discrete elastic and inelastic channels of interest and modelled closed channels including ionization by optical potentials. (115) A special feature of their work was that having entered atomic physics from the non-traditional route of nuclear few-body theory, they were able to bring new techniques to the field. The work they initiated and developed to a high degree is now commonly referred to as momentum-space close-coupling. Andris collaborated with Ian for a period of six years during which the basic model and formalisms were developed, mainly for hydrogenic target atoms. Through their work, the importance of accurately modelling the effect of transitions to the continuum was firmly established.
In February 1982, Ian organized the second Australian conference on Atomic and Molecular Reactions and Structure at Flinders. This conference and its 1980 predecessor in Sydney showed the strength of the field in Australia. There were active experimental groups in four or five universities and much theoretical interest. The meeting attracted seven overseas speakers in the fields of physics and chemistry, the most senior of whom was the pioneer of electron coincidence reactions, Helmut Ehrhardt of the University of Kaiserslautern, who had used them in the late 1960s to study the mechanism of ionization, but not to investigate electronic structure.
Immediately following this meeting, Flinders hosted the reciprocal meeting to the 1976 Indiana workshop on momentum wave functions in atomic, molecular and nuclear physics. By this time, a satisfactory understanding of the higher-energy (p,2p) reaction mechanism had been achieved by the group at Maryland, which was represented by Nicholas Chant. In the case of atoms and molecules, the chemical interest was in low momenta (large distances), where (e,2e) has been confirmed as the only serious method of investigation. Ian presented the summary talk for the meeting, which noted the common approach and the essential differences of the two fields.
At this time Ian also hired another postdoctoral fellow, Bidhan Saha, to work on these projects. When Andris left to take up a lecturing position at Murdoch University in 1984, Ian brought in Jim Mitroy to continue this work. Jim had recently completed a PhD with Ken Amos at the University of Melbourne in nuclear structure theory. Jim improved the quality of the calculations through his background in configuration interaction modelling of the target wave functions. (143–151) The early 1980s proved to be an exciting period for Ian’s theory group because the experimentalists were performing ground-breaking experiments, using electron-photon coincidence spectroscopy not only to measure discrete elastic and inelastic cross-sections but also to measure angular correlations that provided information about the phase of the complex amplitudes. The angular correlation measurements were a more stringent test of the theory models and further confirmed that more accurate modelling of the continuum channels was required.
In the mid 1980s, another young postdoctoral fellow, Igor Bray, was appointed by Ian. Perhaps unsurprisingly, the appointment was once more non-traditional, in that Igor came from the Department of Mathematical Physics at the University of Adelaide and his PhD was in general relativity. Not long afterwards, Jim Mitroy was successful in obtaining a lectureship at the newly formed Northern Territory University (now Charles Darwin University). For the next five years, Ian and Igor collaborated on increasingly sophisticated coupled optical potential formalisms. The progress was made possible by the rapid increase in computer speed and memory at that time.
From the early 1990s, Ian was increasingly taking a back-seat role in the new developments. He had played a key role in developing young talent that was now increasingly driving the progress in the calculations. Ian continued to play a pivotal part in publicizing the talented researchers he had nurtured, (302,303) ensuring that they had increasing exposure in international conferences and workshops. His keen interest in physics and in the people he had inspired continued through the extended battle with lymphoma that preceded his death on 23 April 2005. He is survived by his wife Janet to whom he was happily married for more than forty years.
Ian’s legacy of contributions to physics stretches far beyond his scientific publications. He adopted a very entrepreneurial approach to attracting new researchers to atomic collisions, focusing on their innate ability rather than specialization in the research area. As far as his atomic collision research is concerned, his mentoring and encouragement has led to a significant, continuing tradition of excellence in atomic collision theory both in Australia and internationally.
In speaking of his experience at Flinders, Ian reported that he had found it extremely exciting. He had achieved his life-long dream of being a member of an experimental-theoretical collaboration that worked in the best possible way. The people mainly concerned were Afnan, Noble, Stelbovics, Teubner and Weigold. The work was made possible by ARGC and ARCS research grants—including the award to him and Erich Weigold in 1988 of the Commonwealth Special Research Centre for the Study of the Electronic Structure of Matter—the farsighted policies of the university in providing computing and other research facilities, and in no small measure the encouragement given by Max Brennan. He was also very appreciative of the support of the Vice-Chancellor for most of the period, Roger Russell, who gave decisive help at one or two critical points.
Ian was a remarkable person and one of Australia’s most outstanding scientists. No one who worked with him could fail to appreciate his infectious enthusiasm and encouragement.
This memoir was originally published in Historical Records of Australian Science, vol.19, no.2, 2008. It was written by:
Numbers in brackets refer to the bibliography.
© 2024 Australian Academy of Science
