Geoffrey Ivan Opat 1935-2002

Written by A. G. Klein.

Introduction

Geoffrey Ivan Opat, Professor of Experi­mental Physics at the University of Mel­bourne, died suddenly at home on 7 March 2002, at the age of 66. He was one of Australia’s most versatile and highly respected physicists, scholars and teachers and his death came as a profound shock to the staff of the University of Melbourne and to the physics community in Australia.

His enthusiasm for teaching physics at all levels, from kindergarten to post­graduate, and his enormously creative ideas in many different areas have been the hallmarks of a remarkable career in research and in service to the physics profession and to education in Victoria, in Australia and internationally.

Family Background and Childhood

Geoffrey Opat was born in Melbourne on 16 November 1935, the eldest of four sons born to Samuel and Leah Opat (née Mecoles). His mother was born in Aus­tralia, one of five children of a Russian immigrant and his Swiss wife whom he met in Australia, both having migrated to Australia in their twenties. Geoff’s father, Sam, came to Australia from Poland in 1929, as a penniless young man seeking his fortune. Having studied shoe design in Europe, he set up a very modest factory, making ladies’ felt slippers. He later shifted to fashion leather shoes because, as quoted by Geoff, he realised ‘that women nowadays don’t want anything felt’ – thus illustrating the Opat predilection for wit and risqué humour. Indeed, Sam Opat is remembered as a very witty as well as kind-hearted man – character traits inher­ited and perhaps amplified by Geoff. Before the Second World War, sensing the impending disaster in Europe, Sam Opat was instrumental in bringing to Australia his parents and many members of the extended family – particularly his brothers whom he took into partnership in the factory that eventually became Opat Brothers. Many of the family members who stayed behind perished in concen­tration camps. The few who survived the holocaust emigrated after the war and were helped by Geoff’s father to establish them­selves in Australia. Their tales of horror and survival left a profound impression on Geoff and no doubt shaped some of his attitudes towards immigrants, refugees and people (including students) from different cultural backgrounds.

Sam Opat also owned, and helped run, a mixed farm in Gladysdale, not far from Melbourne. Many of Geoff’s childhood memories and interests came from this farm, with its machinery, animals and, in particular, technological contraptions such as the Diesel engine and generator, the 110-volt battery bank and DC lighting system, the centrifugal pumps and the early model radio sets. All these things fascinated young Geoff and moulded his interests and his deep-seated desire to learn how things work. He also liked to tinker by inventing and building toys that worked, as opposed to inanimate models in the shape of real objects such as the dinky cars or dolls that other boys and girls played with. (One of Geoff’s earliest inventions was an electric fence for snails in the form of two strips of foil connected to a battery –– enough to deter snails by electrocution.)

All in all, Geoff had a very happy childhood at home and on the farm, sur­rounded by loving parents and family who were quite permissive and who exposed him to a rich physical and cultural environ­ment. Their Jewish background implied a respect for books and learning and a joyous calendar of holidays and festivities that left a lasting impression on Geoff. Though not a strictly observant Jew, he closely identified with his faith and its traditions and was a loyal member (and some-time Vice-President) of the Temple Beth Israel in Melbourne.

Although they appear to have led a comfortable middle-class existence, the family was by no means opulent, Sam Opat having spent most of his fortune on helping his extended family. They did, however, buy Geoff all the books he wanted as a boy (such as ‘The Lively Youngster’ series of six volumes by T. G. S. Rowlands that were still in his library almost sixty years later). They also sent Geoff to a private school –– Brighton Grammar School – then a small boys’ school where Geoff had some very fortu­nate experiences in being taught by a generation of highly talented people who saw in the teaching profession a secure way of surviving the great depression. He was particularly influenced by a science teacher, John Asche, an Australian Bach­elor of Engineering and Master of Science who had spent most of his career teaching in a mission school in China, before the revolution. He taught Mathematics, Physics and Chemistry and had knowledge far beyond the average, thus being able to satisfy Geoff’s growing thirst for knowl­edge.

In fact, Geoff decided to become a scientist at a very early stage – he couldn’t remember how early – partly because of the interests acquired on the farm and partly from reading his favourite books. This preference was strongly reinforced by Mr Asche: Geoff couldn’t have fallen into better hands. Though not very good at sports and not very keen on some other school activities such as cadets, he did very well in all subjects, not just Science and Mathematics, and ended up, in 1953, as Dux of Brighton Grammar – a considerable achievement and a great boost to his self-confidence.

University Education

It was a foregone conclusion that Geoff would go to University, his desire to do Science – particularly Physics – being tempered by his father’s wish that he do ‘something professional’ such as Engi­neering. A compromise was reached allow­ing Geoff to enrol in Science and Engineering at the University of Mel­bourne in 1954. It was in the First Year Engineering class – in the Drawing Office, to be precise – that he and I met and struck up an instant rapport. However, Geoff disappeared from this class not long afterwards because of the rigorous though somewhat mindless Engineering Drawing practice. Having spilt Indian ink on his first assignment, he balked at having to re-do it and promptly abandoned Engineering. Aware that there was not much joy in science unless one is very good at it, he convinced his parents that he could always fall back on the shoe trade if he couldn’t achieve his aims as a scientist.

It was an interesting time to be studying at the University of Melbourne. Student numbers had settled down to about 7500 after the post-war glut of returned service­men and Physics was still basking in the aura of its Second World War successes. The staff of the Physics Department was engaged in several interesting research projects: David Caro and John Rouse were building a variable-energy cyclotron; Victor Hopper was building up his cosmic ray research with high-altitude balloons carrying photographic emulsions; low- energy nuclear physics was being pursued with several accelerators built in the Department – such as a several hundred keV Cockcroft-Walton chain, a 17 MeV electron synchrotron and a giant free-air Van de Graaf generator that was something like 10 metres tall and could throw impres­sive lightning bolts. Along with this were some smaller projects in thermal physics and the beginnings of theoretical physics research. All this was ruled (a carefully chosen word!) by Professor Leslie Martin (later Sir Leslie, Kt, FRS) who, following the example set by his predecessors, Pro­fessors Thomas Lyle FRS and Thomas Laby FRS, strongly encouraged research in a university and a department that were slowly emerging from the colonial era.

Geoff enjoyed his studies and the kind of teaching that encouraged students (the keener ones, anyway!) to look up things for themselves in the library. In this way, several lecturers noted for their fairly mediocre presentation were later remem­bered with gratitude. In his First Year he was taught by Dr Walter Kannuluik, an unexciting lecturer whose lectures were nevertheless quite popular because he wrote excellent summaries on the black­board. By contrast, Dr Russell Love who, according to Geoff, was an outstanding lecturer stimulated his interest in mathe­matics. Second-year Physics was shared between Professor Martin, who lectured on electromagnetism and modern physics, and Associate Professor Eric Hercus, who covered all other aspects of the subject. Martin used an ancient set of notes that he didn’t revise because he was far too busy and often absent on account of his duties as the Australian Government’s chief defence science adviser. These notes contained a few arcane gems to be found only in some of the older textbooks, hunted down by Geoff and a few of his eager classmates. (Among these was, for example, the quad­rant electrometer – a very clever form of classical parametric amplifier upon which Geoff would expound with glee many decades later. At the time, students enjoyed explaining these things to each other, which no doubt contributed greatly to their education.) Likewise with Hercus’s lec­tures: students found them very stimu­lating, often hard to understand, and very conducive to private study in the classical textbooks. There were even a few lectures on Astronomy, which Geoff greatly enjoyed, having read the popular books by Jeans and Eddington. The lectures on optics were somewhat dry and hard to comprehend but it didn’t seem to matter because optics seemed a pretty dead subject then. (The laser revolution was in the distant future!) The lecturer in Pure Mathematics was Dr Angas Hirst (later Professor of Mathematical Physics at the University of Adelaide and a Fellow of the Australian Academy of Science) who demanded a very high standard from serious students and who was probably responsible for steering Geoff in a theoret­ical direction.

Third-year Physics lecturing was shared by quite a few people, a notable feature being the theoretical physics courses given by Courtney Mohr who had been a close collaborator of Sir Harrie Massey in England and was one of the few people in the Department who really understood quantum mechanics. Mohr, who later became the Foundation Professor of Theoretical Physics at the University of Melbourne, became Geoff’s mentor and postgraduate supervisor. David Caro’s famous course on electronics attracted students from far and wide, including some from Electrical Engineering. It con­tained all the new material discovered and used during the Second World War, such as pulse techniques, then being freshly applied to nuclear instrumentation. (All done with vacuum tubes, of course – the impact of transistors was just around the corner). Along with the lecture courses, a rigorous programme of practical work was an essential part of the Physics course. Beyond the useful but often mundane laboratory exercises in first year lay the arduous hurdles of second- and third-year ‘prac’, the latter administered with mili­tary discipline by Richard O. Cherry who held the rank of colonel in the Army and who, in earlier years, had participated in the introduction of radio broadcasting to Melbourne. One of Geoff’s favourite anec­dotes concerned one of the standard labo­ratory exercises in Third Year, namely the measurement of the field strength pro­duced by one of the local radio stations, 3LO (now 774 ABC). In his youth Dick Cherry had ridden his motorbike all over Melbourne, carrying a dipole antenna and portable measuring gear. The results were recorded in ‘the’ book that was used to check and assign marks to the measure­ments made by several generations of stu­dents. When it came to Geoff’s turn – horror of horrors, his result was in dis­agreement with ‘the book’ and he was sent back to do it again. He obtained the same result over and over again and, to his credit (or perhaps as an early sign of the scientist that he was to become), he stood his ground. In the eventual showdown, it turned out that the transmitter was under­going extended maintenance and the field strength of the temporary standby was indeed different! (It is not known for how long that state of affairs had prevailed and, indeed, how many compliant students had produced ‘the’ expected result.)

Geoff enjoyed his studies and excelled in them, being almost always at the top of the class or not too far from it, in spite of stiff competition from some excellent classmates. He enjoyed and greatly bene­fited from the scholarship involved in finding things out for himself from text­books: he thus acquired extremely well- developed study skills that stood him in good stead and that he, in turn, tried to inculcate in his students. Somewhat more surprisingly for someone who was to become a theoretical physicist, he also greatly enjoyed the practical work and excelled at it. His childhood experiences with machinery, with woodwork and with electrical things such as radio sets, had resurfaced. For example, he was rather proud of the fact that in 1956, in his third year, he built himself a very high fre­quency radio receiver, using military surplus vacuum tubes and other compo­nents bought from a disposals store. To his great surprise, when he turned it on he heard voices right away. It was the groundsmen at the Melbourne Cricket Ground using walkie-talkies during the Melbourne Olympic Games! However, that was more by the way of a hobby. By Third Year, Geoff was strongly mathematical in orientation and determined to pursue theo­retical physics.

Another formative experience in Geoff’s undergraduate years was National Service – made compulsory by the Menzies Government – which consisted of one three-month stint of Basic Training one summer and two six-week summer camps in subsequent years. Geoff did his ‘Nasho’ with the Melbourne University Regiment at Watsonia Army Camp and subsequently at Puckapunyal, near Seymour, Victoria. Not exactly a model soldier, Geoff sometimes fell foul of the Drill Sergeant for being untidy or for not having sufficiently well-polished brass. The punishment for such offences was to be put on guard duty. This suited Geoff down to the ground: he took a copy of Weatherburn’s Vector Calculus with him to the guardhouse and by the end of summer had studied it from cover to cover. This stood him in good stead in later years: decades later, he could still derive all the standard formulae. Being an amiable and good-humoured character, Geoff made many life-long friends at Nasho, including George Isaak (later Professor of Physics at the University of Birmingham) and me. We have fond memories of discussing scien­tific problems with Geoff to alleviate the boredom of army life, and we often reminisced about our times in the ‘Pucka­punyal campaigns of Her Majesty’s Armed Forces’. There were lots of anecdotes, many of which kept being embellished as the years went on. One vivid memory concerns Geoff’s stint in the Puckapunyal Army Hospital (which was said to exist mainly to deal with social diseases acquired by soldiers). Geoff was hospital­ized for a different infection altogether – in fact by a case of measles – and had many weekend visitors among his army friends. One of his nurses turned out to be the daughter of the Physics Department’s tea lady, who regaled Geoff with inside stories about various senior staff that he promptly passed on to the rest of us.

Geoff obtained his BSc with high honours in 1956 and decided to continue at Melbourne with postgraduate studies in theoretical physics under Courtney Mohr, who pointed him in the direction of theo­retical studies of gamma-ray emission by nuclei. Whilst always available, friendly and ready with wise counsel, Courtney left Geoff fairly much to his own devices – a situation that suited both of them. Geoff was a serious, scholarly and mathemati­cally very able student who taught himself all that he needed to know to tackle the problems posed by the research. His MSc thesis entitled ‘Photonuclear Reactions’ was completed in 1958 and already showed a thorough grasp of the field. Geoff then went on to do a PhD at the University of Melbourne. Though the University had been awarding PhD’s since 1948, this was a somewhat unusual choice on his part since most students who could do so con­tinued to go overseas to do their PhD – usually to Cambridge, Oxford or one of the other British universities. Geoff chose to stay in the comfort of the parental home, secure in the knowledge that he could continue his researches on his own with the financial help of a General Motors Holden’s Postgraduate Scholarship. Indeed he succeeded and submitted a very fine PhD thesis in 1961 entitled ‘Theoretical Investigations concerning Photonuclear Reactions’. This contained important results, the so-called sum rules in gamma- ray transitions in nuclei. The publications resulting from it continue to be cited in textbooks and review articles, being funda­mental to the field.

Some of Geoff’s numerical calculations involved the CSIRO-built computer, CSIRAC, one of the very first general- purpose digital computers in the world, which was then housed in the Physics Department in Melbourne. It was a very slow and cumbersome machine by present standards but was a great advance on mechanical calculators and gave its users a thorough appreciation of how computers work. As one of its early users, Geoff received a grounding in computational methods, machine language and digital systems in general that far exceeded the understanding of theorists before or since. However, the greatest outcome of Geoff’s PhD studies was the remarkable self- reliance and self-confidence in approach­ing any problem in Physics that he devel­oped. Somehow he never lost faith in his ability to get somewhere with the most recondite problems, even if he could not arrive at an actual solution. This dogged perseverance, coupled with formidable analytical skills, was the hallmark of Geoff Opat as a physicist.

However, the fact that his work was never tied to a realistic time-scale was, later in his career, sometimes very frustrat­ing for his students and collaborators. Geoff could supply solutions but could never be relied upon to do so on time or to a deadline. When faced by seemingly insurmountable difficulties, his usual ploy was to side-track to some other fascinating problem and give learned discourses on some topic of little or no relevance to the problem at hand, never admitting that he was stumped. People frequently gave up in desperation and abandoned the problem or worked out a rough and ready answer for themselves. Geoff would come up with the correct and elegant solution at some indef­inite time later, sometimes too late to be of any material help.

Upon completing his PhD, Geoff won a prestigious Fullbright travelling fellowship that took him to the USA for post-doctoral studies from 1961 to 1964. However, before taking up his fellowship, he married Diana (née Rogers) who accompanied him to the USA.

Postdoctoral Fellow at Pennsylvania

Just as it was for Australian postgraduate students, the usual track for Australian post-docs at this time was Oxford, Cam­bridge or perhaps one of the better red- brick British universities such as Birming­ham where Mark Oliphant had attracted several young Australian physicists. How­ever, Geoff received wise advice from Ed Muirhead, then a relatively new senior lecturer in the Physics Department who was doing experimental work on photonu­clear reactions, and Keith Mather, another Physics staff member who had worked at Washington University in St Louis (and who later became Director of the Alaska Geophysical Institute). All three realised that, in the post-war world, the centre of gravity of Physics had shifted away from Europe to the United States. Keith Mather recommended Geoff to an old friend, the theorist Henry Primakoff, who was then at the University of Pennsylvania. Ed Muirhead had recently won a fellowship to the same university. In due course Primakoff appointed Geoff as a post- doctoral fellow on what seemed a princely salary of $US 6000. So the Muirheads and the Opats proceeded to Pennsylvania at about the same time and the two families ended up as close friends, living just one street away from each other.

Henry Primakoff was a very distin­guished theorist who, by that time, had made two important contributions – one to the theory of weak interactions and another to the study of magnetic materials. He was a very versatile physicist from whom Geoff learned a great deal in depth, in breadth and in style. Together they studied an interesting problem, namely the capture by atomic nuclei of muons – particles found in cosmic rays or in high- energy interactions.

The University of Pennsylvania had an excellent Physics Department and Geoff, who had very wide interests, learned a great deal in all sorts of different areas of Physics – largely by sitting in on all the department’s graduate courses. There was, for instance, Robert Schriefer, who later shared a Nobel prize for explaining super­conductivity, who gave a course on mag­netism. A visitor from Japan, Ryogo Kubo, gave a course on statistical physics, partic­ularly stochastic theory. Another short course, given by E. T. Jaynes, explored the connection between information theory and thermodynamics. These and others like them were avant-garde courses that left a lasting impression on Geoff’s under­standing of physics.

Geoff also attended graduate ‘summer courses’ at Brandeis University in Boston where he heard J. D. Jackson (who wrote the definitive text on electromagnetism) on the latest advances in particle physics, and the Swedish physicist Gunnar Kallen, one of the leading quantum field theorists of the day. Coming from a smaller place with no formal graduate courses, Geoff was now exposed to the richest possible post­graduate education. Furthermore, his amiable and friendly character once again meant that he was befriended by all and sundry who gave him the best possible ‘private lessons’ in their chosen fields. By the time Geoff returned to Australia, he was not only a highly accomplished theo­retical physicist but he had a smattering of ultra-fast electronics, cryogenics, solid- state physics and a plethora of experi­mental techniques in nuclear and particle physics –– all acquired by looking, listen­ing and learning from experts. He pos­sessed an altogether formidable, encyclopaedic knowledge base that never ceased to amaze his colleagues.

Meanwhile, Geoff’s research activities with Henry Primakoff bore fruit: their results were published only at the end of the investigation, as was customary in the days before the pressure for serial and piece-meal publication of smaller, inter­mediate results became mandated by the granting bodies. Their published paper on muon capture was definitive work that stood the test of time. Some of their results received experimental verification only several decades later – for example from experiments at the Tri-University Meson Factory (TRIUMF) in Vancouver in the 1990s.

Geoff also taught several graduate-level courses. It is reported by Ed Muirhead that Geoff was always available to students and very popular with them. He would fre­quently be seen – just as in Melbourne many years later – giving tutorials or mini-lectures to groups of them who invaded his office.

The years from 1961 to 1964 were happy times for the Opats in Philadelphia, where Diana gave birth to their two daugh­ters, Andrea and Vicki, and they enjoyed life with a circle of good friends – fore­most among whom were the Muirheads. However, their stay came to an abrupt end with a telephone call from Melbourne: Sam Opat, Geoff’s father, had died sud­denly at the age of 57. Geoff was clearly concerned about any genetic implications of his father’s untimely death – more so in later years when he was approaching his fifties. He had thorough check-ups and was under regular medical supervision. He was proud of the fact that he was found to be in excellent health with no indications of any cardiac or vascular symptoms. He took regular exercise on most days by walking around the tan at the Melbourne Botanic Gardens. His sudden death from heart failure at the age of 66 was, indeed, a bolt out of the blue.

In 1964 Geoff and Diana and the two little girls returned to Melbourne and Geoff took up a Senior Lectureship in Physics in his Alma Mater in what was by then the multi-professorial School of Physics, headed by Professor David Caro. In the years following their return, Diana gave birth to another two children, both boys, Stephen and David who, along with the two girls, grew up and settled in Melbourne.

Senior Lecturer in Physics

Geoff took up his appointment as Senior Lecturer in Physics in August 1964. Several other new staff members were to join the School around that time, including me, recruited from the Australian Atomic Energy Commission. At that time the School of Physics was running the 12 MeV variable-energy cyclotron staffed by Professor Caro and Dr John Rouse. Then there was a 35 MeV Siemens Betatron acquired and run by Brian Spicer who was to be promoted to a Personal Chair in the following year and who was designated as Director of Nuclear Studies. He was later joined by Dr Ed Muirhead and Dr Max Thompson, returning from post-doctoral appointments in the USA. A 600 keV electrostatic accelerator, dubbed the Stati­tron, was run by Drs Graeme Sargood and Colin McKenzie. A completely separate ‘empire’, the Diffraction Group, was pre­sided over by Professor John Cowley, a noted electron diffraction and electron microscopy expert, formerly at the CSIRO, who had been appointed to a Chair around 1962, and was supported by Dr Hein Wagenfeldt and in due course several younger staff members, including Dr Alan Spargo, Dr Zwi Barnea and Dr Bill Swindell. Each of the above research groups had several lively PhD students, as had the small Theoretical Physics group consisting of Professor Courtney Mohr (nuclear physics) and Dr Ken Hines (plasma physics). Geoff was a welcome addition to the theory group and soon acquired several highly talented Honours students. These included, in the first two years, Graham Lister, Ed Smith, Rod Crewther and Chris Hamer, all of whom later became successful academics.

Geoff’s presence in the School of Physics was like a breath of fresh air. With strong support from David Caro, he articu­lated a fresh vision for the School. With help from several young colleagues he set about revolutionizing the curriculum by introducing designated core subjects (such as Classical Mechanics, Quantum Mech­anics, Thermal Physics and Electro­magnetism) and optional subjects (Optics and Diffraction, Nuclear Physics, etc). A lively Curriculum Committee debated the contents of each of these courses and how the subject matter was to be distributed among the undergraduate years.

In parallel with this radical shake-up of the undergraduate courses that was cata­lyzed and led by Geoff, the undergraduate laboratory exercises, some of which had remained unchanged for decades, received an equally thorough revamp at the hands of some of the ‘young turks’. The increasing number of staff members who had been exposed to North American practices all gave their strong support to these reforms, that resulted in a high-quality and up-to- date curriculum in the Melbourne School of Physics.

Another important reform, also spear­headed by Geoff, was the institution of formal course work in Fourth Year (Honours). The rational analysis of the undergraduate curriculum carried out by the Curriculum Committee made it clear that quite a few topics indispensable to a well-trained physicist could not be covered in three years and the rising number of research students meant that it was more economical to give formal courses of lectures on such topics. This was, at the time, quite a radical departure; it was not adopted by other Science Faculty depart­ments for many years.

Geoff and his research students, mean­while, were pursuing various aspects of theoretical particle physics. Geoff became increasingly aware, however, of the need for the kind of closer contact with the experimental aspects of the subject that he had enjoyed in Pennsylvania. The same thoughts were beginning to be articulated by Professor Dave Peaslee, an American physicist then in the Research School of Physical Sciences at the ANU.

Peaslee had great trouble trying to ‘sell’ experimental particle physics (otherwise known as high-energy physics) to the ANU School of (mostly) low-energy nuclear physicists. In his frustration, he came to Melbourne, joined forces with Geoff and convinced David Caro that the future lay in experimental high-energy physics. The upshot was the formation of the Melbourne High Energy Physics (HEP) Group – led by Geoff and David Caro. With help from Dave Peaslee, they mapped out a research programme, obtained a substantial grant from the then recently established predecessor of today’s Austra­lian Research Council (then called the Robertson Committee – later to become the Australian Research Grants Commit­tee) and wrote up a proposal for experi­ments to be carried out at the Brookhaven National Laboratory in the USA. The research programme was designed to hunt for a set of excited sub-nuclear species that had been predicted to arise in the inter­action of antiprotons with neutrons. The experiments needed a beam of antiprotons, a species of anti-matter then available in copious beams at the Brookhaven proton synchrotron, and a target of deuterium (heavy hydrogen). The interactions, which exemplified the annihilation of matter by anti-matter, were to be observed in a bubble chamber filled with liquid deuterium at around 20° above absolute zero, as trails of bubbles left when incident antiprotons reacted with the deuterons and spat out a bunch of other particles – the products of the reactions.

Brookhaven National Laboratory had such a bubble chamber as well as the beam of antiprotons and, furthermore, had a gen­erous policy of allowing external ‘user groups’ of researchers from universities (American or foreign!) to bid for free access to the apparatus. The budding Mel­bourne HEP Group sent their experimental proposal to the director of the Brookhaven facility and followed it up with a personal visit by Geoff in 1968. Geoff didn’t let on that he was actually a theorist, and was cordially received by Dr Ralph Shutt and told that his proposal was accepted. How­ever, the experiment had to be done the following week, when a group from the University of Syracuse, New York, were finishing their run. With amazing audacity, Geoff accepted the challenge and spent the following days understudying the Syracuse group, making firm friends with its leader, Professor Ted Kalogeropoulos, and his staff, and receiving a veritable ‘brain trans­fusion’ from them (to use a typical Opat turn of phrase).

The following week, Geoff single- handedly retuned the antiproton beam-line to his specifications and then spent several days and nights, non-stop, accumulating a quarter of a million photographs in quad­ruple-view stereo, recording the inter­actions of the antiprotons with the deuterons in the bubble chamber. In the process, he learned almost everything that there was to be known about the ‘trade’ from other physicists, and from the local crew of technicians who were running the bubble chamber. This fantastic technical feat by a so-called theorist and the auda­cious self-confidence and self-reliance that it demonstrates could only be compared with something like landing a jumbo-jet after only one week of flying lessons.

The 250,000 frames of 70-mm film, technically ‘on loan’ from the Brookhaven National Laboratory, were shipped to Mel­bourne and arrived some time after Geoff returned. (They were duly examined by Australian Customs who telephoned Pro­fessor Caro for his assurance that the film contained no ‘R-rated’ material, because they couldn’t find anything on it that made sense to them!)

However, that was only the beginning of the experiment: the tracks on the film still needed to be measured, reconstructed in three dimensions and analyzed frame by frame (at least those frames that showed the type of interaction that was being sought). This required optical projectors and precision measuring machinery as well as computer programs for doing the recon­struction and the analysis. At this stage, Geoff and David Caro were joined by me (then an instrumentation expert) and by Bill Wignall who had studied particle physics at Cambridge.

The mammoth task was divided eight ways. Two people did the optical design for the projectors; two people designed the measuring machines; two people adapted and rewrote the computer programs, and two people analyzed the high-energy physics. But there were only four of us, so everyone did at least two things – and Geoff did a bit of everything!

After about a year the results started to come through and the other members of the group went to Brookhaven for more experimental runs and more film to bring home. Several new research students joined the group and some of the prelim­inary results were written up for publi­cation. These preliminary data, which roughly classified the different types of sub-nuclear reactions and estimated their relative prevalence, was a valuable contri­bution to the literature. Twenty or so years later, long after bubble chambers became obsolete, higher-precision experiments carried out with more advanced instrumentation at CERN in Geneva veri­fied and validated our results.

The so-called ‘resonances’ – the excited states of particles that were being sought – never actually materialized in spite of valiant efforts by Dave Peaslee to extract statistically significant ‘bumps’ from the data. (He even tried to convince the rest of the group of the existence of ‘negative bumps’ caused by a low-lying data-point, provoking Geoff to comment that all camels have one hump – only some have a positive hump and some have a negative hump.) Nevertheless, the time spent pondering the meaning of the experi­ments bore fruit. Geoff reinterpreted the data and discovered a very interesting result that verified an important property of the strong nuclear interaction. The experiments verified that a new quantum number called ‘g-parity’ was conserved, as expected by the rapidly emerging quark theory of sub-nuclear phenomena. Further­more, a much more surprising phenome­non was also shown to exist, namely that there would be as many particles thrown forward as backward under the condition of the experiment. This so-called beam- target reversal symmetry in the anti- proton–neutron system was one of the most interesting outcomes of the research programme. All in all, about twenty papers in international journals and several PhD theses resulted from this experimental pro­gramme over the approximately six years of its existence.

The Chair of Experimental Physics

In 1971 David Caro, who had been increasingly preoccupied with the Univer­sity’s central administration, resigned from the Chair of Experimental Physics to take up a full-time Deputy Vice-Chancellor­ship. (He later left the University of Mel­bourne to become Vice-Chancellor of the University of Tasmania, returning a few years later to become Melbourne’s Vice- Chancellor.) A protracted worldwide search ensued for a new professorial appointee in the area of experimental high- energy physics. In 1973, a year or so after the Opats’ return from sabbatical leave at the Rutherford Laboratory near Oxford where Geoff spent a lot of time in forging fresh international links, it was revealed that the Selection Committee had unani­mously agreed that an internal candidate, namely Geoffrey Opat, was to be appointed to the Chair of Experimental Physics. He was 37 years old at the time and a little diffident, but he nevertheless accepted with alacrity. The news of an internal appointment was very well received in the School since everyone rec­ognized Geoff’s outstanding contributions to both teaching and research. With hind­sight it was indeed an excellent appoint­ment. The fact that Geoff had originally trained as a theorist, and had joined the staff as a theorist, was by that time largely irrelevant in view of his successful activi­ties in the experimental area. Meanwhile, Courtney Mohr having retired, the Chair of Theoretical Physics was filled in 1972 with the appointment of a brilliant young Sydney physicist, Bruce McKellar, who came via the Princeton Institute of Advanced Studies and who took over the leadership of theoretical nuclear and parti­cle physics.

Two new staff members joined the Experimental HEP group: Stuart Tovey was recruited from CERN and Ches Mason from England, both of them experi­enced particle experimentalists who broad­ened the skill base of the group. However, by the mid-1970s it became clear that bubble chambers were becoming obsolete as experimental tools and that other, hugely more expensive particle detectors were coming into service. Some attempts were made to enter into collaborations with other groups in order to participate in more advanced experiments (e.g. using heavy liquid bubble chambers with inter­nal hydrogen or deuterium targets) but it was becoming increasingly clear that the Melbourne Group – along with many similar-sized outfits overseas – was no longer able to compete with more richly endowed organizations. Several group members started looking for alternative research projects. Stuart Tovey, who was a highly respected member of a CERN group before coming to Melbourne, suc­cessfully continued in that capacity and became ‘our man at CERN’. Other research groups in a similar position, from other universities all over Europe, com­bined their efforts and joined very large, multi-institution, multi-national collabora­tions, thus continuing experimental particle physics with a completely differ­ent modus operandi. That was the direction in which the Melbourne HEP Group con­tinued too, and in later years flourished. For a few years it remained the only group to represent Australia at CERN. Later it was joined by a small group from the University of Sydney and various theoret­ical particle physics groups from else­where in Australia to form the Australian Institute of High Energy Physics that, to this day, continues its activities at CERN and elsewhere.

Geoff and I, meanwhile, went off in a completely new and unexpected direction following a 1973 visit to the university by the noted Israeli physicist Professor Yuval Ne’eman of Tel Aviv University. In a private conversation about mutual acquaintances, Ne’eman mentioned some recent theoretical work by Yakir Aharonov and his student Leonard Susskind purport­ing to show that rotations of fermions by 360° would lead to observable effects. Ordinary macroscopic objects, as well as particles with integral spin – called bosons –– when rotated by 360° about any axis, return to where they started from and thus show no signs that they have under­gone a rotation. On the other hand, fermi­ons, which are the class of particles with half-integral spin and include electrons, protons and neutrons, behave differently: their wave-functions develop a minus sign when rotated by 360°. Since observable quantities depend on the square of the wave-function, however, it was thought that the minus sign was simply a mathe­matical artefact, not an observable effect. Aharonov and Susskind proposed a ‘thought experiment’ in which half of a box containing a single electron was to be rotated by 360° and allowed to recombine with the remaining half. An interference effect (in the quantum-mechanical sense) would reveal the minus sign.

After meeting Ne’eman, Geoff and I, who used to drive home together, contin­ued discussing this intriguing effect and realised that the rotation effect could be accomplished simply by placing particles that had a non-zero magnetic moment in a magnetic field. However, particles such as electrons would be swept away because of their charge. Hence a realistic experiment ought to be done with neutral particles such as neutrons. I had had some previous experience with neutron beams and pro­posed running a slow neutron beam past a current-carrying wire (which has oppo­sitely directed magnetic fields on either side) and observing the interference pattern a long way downstream. It was agreed that this would work in principle but in the following few days calculations showed that the currents required could not be carried by wires of the required very small diameter. Thus the proposed experi­ment was nearly stillborn. However, shortly thereafter, Geoff’s ingenuity saved the day. He proposed that, instead of using a fine wire, the neutrons be diffracted by a magnetic domain boundary – the border between regions of opposite magnetization in a crystal of magnetic material (in prac­tice a common iron alloy). The details were soon worked out in a remarkable coopera­tive effort and with mounting excitement a feasible experiment was arrived at. After preliminary research with an optical analogue and computer simulations of the expected effect, a paper was written up for publication and for use as an experimental proposal that was duly accepted at the Institut Laue-Langevin in Grenoble, which had the world’s most intense neutron beams and whose director, Nobel laureate Rudolph Mossbauer, saw the beauty of the experiment (though he admitted later that he had doubts about its feasibility).

I went on a six-month sabbatical to Grenoble in September 1974 and Geoff came later on an extended visit, staying with us over the Christmas–New Year period. During that time Geoff and I worked feverishly to align the beam and to assemble and test the apparatus shipped from Melbourne. The experiment was finally ready to run in January 1975. An excited exchange of Telexes between Grenoble and Melbourne in February announced that the experiment was indeed working and that the results looked hope­ful. Detailed measurement and analysis after I returned to Melbourne showed that the predicted effect was verified. It was a remarkable tour-de-force that would not have been possible except through the collaboration of two people who came from opposite ends of the academic spec­trum: I an electrical engineer who had gone in the direction of abstract physics and Geoff a theoretical physicist who had gone a long way towards pure experimen­tation. We met somewhere in the middle and struck sparks off each other.

The great appeal of this experiment was that it was not simply a measurement but a fundamental experiment that verified a theoretical prediction. For Geoff it had the additional attraction that it could be regarded as an experiment in geometry. In fact, he interpreted it as showing that geometry was not a property of empty space but that it depended on the kind of objects – bosons or fermions – that existed in that space. With a long-standing interest in geometry as applied to general relativity, he was thrilled to have contrib­uted to that notoriously difficult field of experimentation.

Geoff continued to lead the High Energy Physics Group for a few more years but changed its name to ‘Particles and Fields Group’ on the semi-facetious grounds that since everything could be thought to be made up of particles and fields, the group could do any experiments that could be conceived! Further neutron experiments did indeed follow, generally exploiting the techniques that the rotation experiment pioneered and demonstrating other quantum-mechanical effects that depend on the wave-like properties of neu­trons. In the following decade, Geoff and I and our students published a large number of papers on such experiments, carried out initially at the Institut Laue-Langevin in Grenoble, and later at the Missouri Univer­sity Research Reactor (MURR) in collabo­ration with Professor Samuel A. Werner. With quite a few experiments carried out jointly, Sam Werner became a firm and loyal friend to us, with reciprocal visits to Australia and to Columbia, Missouri cementing the friendship.

In 1983, with characteristic generosity, Geoff proposed me for a Personal Chair, to which I was duly appointed in 1983. Our collaboration and close friendship contin­ued unabated and resulted in several other noteworthy experiments. Some of these were concerned with topological effects, again based on theoretical work by Yakir Aharonov of Tel Aviv University. The demonstration of the so-called Aharonov– Casher effect with neutrons led to our being jointly awarded the Walter Boas Prize of the Australian Institute of Physics in 1990. We were also proposed for fellow­ship of the Australian Academy of Science and were both elected in 1994, following another successful fundamental experi­ment that demonstrated the so-called Scalar Aharonov–Bohm Effect. Some of this work, known under the heading of Neutron Interferometry, was noted and commented upon in the general scientific literature – Nature, Science, New Scien­tist, Scientific American, and so on – and some of it found its way into the textbooks. Much of the research was, of course, carried out by research students and partic­ularly noteworthy contributions were made by Alberto Cimmino, who started out as a technical officer with the group but later rose through the ranks, becoming a Profes­sional Officer in the School of Physics and obtaining a Masters’ degree and eventually a PhD.

In 1976–1977 the Opats spent another sabbatical year abroad, this time at the University of British Columbia and the TRIUMF Accelerator Facility in Van­couver. There Geoff was pleased to see the experimental confirmation of his early work on muon capture that he had done as a postdoctoral fellow in Pennsylvania. While there he met and was greatly influ­enced by Professor Bill Unruh, a noted theorist in the field of general relativity and gravitation – a field that was always close to Geoff’s heart. Of particular interest was the detection of gravitational waves emitted by cosmic objects, something that was attempted in those days with large, superconducting metal cylinders. Geoff realised that the coupling of gravitational waves (which travel with the speed of light) with sound waves in the solid detec­tors was extremely inefficient because of the enormous mismatch of the wave veloc­ities. He set about trying to invent an electromagnetic detector, initially based on the idea of a large chamber ‘filled’ with a very intense magnetic field. (Such objects had indeed been used as bubble chambers.) The coupling of gravitational waves with the finite energy content of the magnetic field could, in principle, lead to detectable signals. However, the effect of even static gravitational fields, such as the Earth’s gravity, on metallic objects such as the walls of an empty bubble chamber were not well understood, and so the behaviour of the proposed gravity-wave detector could not be deduced with certainty. There were some confusing and contradictory experimental results in the literature (sev­eral of which later turned out to be simply erroneous) and the whole field was in need of some definitive experiments. Upon Geoff’s return to Melbourne in 1977, several excellent new research students joined the group (still ‘Particles and Fields’ but soon to change to ‘Funda­mental Experiments’ in order to avoid con­fusion) and set about constructing exquisitely sensitive experiments to inves­tigate the effects of gravity and inertia upon the electromagnetic properties of materials. Progress was very slow, partly because signals of the order of magnitude of picovolts (millionths of a millionth of a volt) required great ingenuity and a lot of very hard work, and partly because the false results in the literature acted as ‘red herrings’.

Nevertheless, by the early 1980s a suite of beautiful experiments had been per­formed and several seminal papers were published by Geoff with his students Tim Davis, Tim Darling, Frank Rossi and Gareth Moorhead. They concerned the electromagnetic properties of metals under gravity, inertia and stress, with results that remain unchallenged in the literature. This work found application in an ambitious experimental programme undertaken by a research group at the Los Alamos National Laboratory (and later continued at CERN) concerning the fall of antiprotons in the Earth’s gravitational field. The interest in electromagnetic detectors of gravitational waves was, however, overtaken by large optical interferometers ‘filled’ with laser light, several of which were developed around the world.

The above work went on in parallel with some of the neutron interferometry activi­ties and in parallel with yet another new departure named ‘GAMBLE’ – the Gravity Assisted Molecular Beam Line Experiment. The idea behind the latter was Geoff’s constant desire to do gravity experiments and the fact that neutrons were of too small a mass, and too feeble in beam intensity, to make such experiments feasible. The successes of the neutron experiments as well as some ingenious ideas for experiments with beams of mole­cules led to a protracted undertaking to build an ultrahigh-vacuum beam line for polar molecules. It took several years before eventually a couple of very nice papers came out of this work but, alas, no significant gravity experiment. The episode illustrates Geoff’s willingness to undertake extremely difficult and (with hindsight) unrewarding work in preference to more routine experiments. However, it also underscores his extraordinary confi­dence in attacking new problems and learning new techniques that did not always bear fruit – certainly not in the finite time allowed by contemporary grant­ing agencies. Nevertheless, the few highly significant publications that resulted are still a valid justification for such work, not to mention the outstanding educational opportunities that their challenges pro­vided for the training of graduate students.

The molecular beam work, which suf­fered from some intrinsic limitations, was discontinued around 1990, upon Geoff’s return from another sabbatical year that he spent at the University of Washington, in Seattle, learning new techniques and pon­dering other gravitational experiments relating to the so-called ‘fifth force’ that was very much in the air at the time (but that has since been discredited).

In 1991, at my suggestion, Geoff joined forces with Dr Peter Hannaford from the CSIRO Division of Chemical Physics (which in 1987 had merged with another Division to become the Division of Materials Science and Technology) to propose and carry out very ingenious experiments in the field of atom optics – the logical successor to neutron optics. Significantly, this field, which makes use of the wave-like properties of neutral atoms, would allow one to contemplate gravity experiments. Opat and Hannaford pro­posed to build an atom interferometer, analogous to a neutron interferometer but much more sensitive to gravitational effects because of the greater mass of the atoms and the much more intense beams that were available. In particular, an atom interferometer, if it could be built, would be highly sensitive to gravitational gradi­ents such as the ones produced by under­ground ore bodies and hence could be of enormous value in mineral exploration.

Hannaford, in the spirit of the ‘New CSIRO’ that was by then required to obtain a large fraction of its operating expenses from industry, was very keen to obtain support from the Australian mining indus­try through the Australian Mineral Indus­tries Research Association (AMIRA). He later succeeded in obtaining a sizeable Generic Technology Grant from the Government. At that stage – around 1990 – atom interferometers existed only on paper. Atom-optical components such as mirrors and diffraction gratings had to be invented and developed. That is where Geoff’s ingenuity and experience with neutrons was invaluable, complementing Peter Hannaford’s expertise in handling atoms and laser beams. With help from other CSIRO physicists (Russell McLean, David Gough), several post-doctoral fellows (Andrei Sidorov, Wayne Rowlands, Sile Nic Chormaic), and several graduate students, remarkable progress ensued. Not fast enough, however, for the short-term interests of industry or the CSIRO. The work was too ‘pure’ and too fundamental – in other words, too much real research had to be carried out before the develop­ment phase could be reached. While this was consistent with Geoff’s temperament, it did not suit the short-term, business-like outlook of CSIRO. By 2001, just as really beautiful results started to emerge and attract great interest and acclaim inter­nationally – in particular, the demonstra­tion of magnetic mirrors on which atoms would bounce as if on a trampoline – CSIRO support ceased and the group moved to Swinburne University of Tech­nology in Melbourne. Peter Hannaford was appointed a Professorial Fellow there and a more far-sighted institutional policy allowed the work to flourish, leading to several very significant publications. Around that time the phenomenon of Bose–Einstein condensation of atoms became an experimental reality (leading to the 2001 Nobel prize in physics) and showed promise of supplying a coherent atomic beam for atom interferometry. The work of the Hannaford–Opat group was highly regarded internationally and looked like having a great future. This was the state of affairs at the time of Geoff’s sudden death. The group was devastated. Geoff, who had retired from the Chair of Experimental Physics at Melbourne in the previous year and had been appointed Adjunct Professor at Swinburne while continuing as a Professorial Fellow in the Melbourne School, was a vital contributor, without whom the group at Melbourne simply fell apart. Hannaford’s group at Swinburne, however, has recovered and is soldiering on.

Educational Activities and Scholarship

Geoff’s contributions to undergraduate and postgraduate education in the School of Physics have already been described. He continued as a key member of the Curricu­lum Committee and as its Chairman for most of his 37 active years and continued to keep an eye on the syllabus of each subject. He also instituted and annually updated a ‘Lecturer’s Manual’ – a docu­ment that contained all the useful informa­tion that lecturers, new and old, needed for teaching and examining each of the courses offered.

Beyond this vital involvement with teaching in the School of Physics, Geoff took a serious interest in high school edu­cation in Victoria. He was a member and later Chairman of the Physics Standing Committee of the Victorian Universities and Schools Examinations Board (VUSEB) and served as Chief Examiner in 1966 and 1967. He also became a member of VUSEB itself, representing the Univer­sity of Melbourne, and stayed on in that capacity for several decades through suc­cessive changes of that organization, which later became the Victorian Institute of Secondary Education (VISE) and later still the Victorian Curriculum and Assess­ment Board (VCAB). During that time, participation in secondary education soared and concomitantly, standards unavoidably fell. Geoff’s was a lone voice crying out for rigorous intellectual stand­ards in a period when successive govern­ments were implementing mass education. He became used to being outvoted time after time and had no illusions about his political effectiveness. Nevertheless he soldiered on, realising the importance of keeping rigorous intellectual values alive in the face of expediency and cynicism.

In parallel with this essentially thank­less political activity, Geoff instigated and participated in numerous activities aimed at making contact with secondary school science teachers, particularly physics teachers, and providing in-service training, enrichment material and general support. The so-called ‘July Lectures in Physics’ – a series of four annual lectures aimed at high school physics teachers and the inter­ested lay public were inaugurated in 1967 and have taken place each year since then, with Geoff giving one of the lectures each year except when he was overseas. He usually lectured on some topic of advanced physics from an elementary standpoint (and occasionally one of elementary physics from an advanced standpoint). This highly popular lecture series, which packed large lecture theatres year after year, was supplemented by an annual in- service training day for physics teachers, organized by Geoff, that addressed particu­lar topics in the high school curriculum. He later participated in international efforts along similar lines, in the Asia Pacific Science Education Network (ASPEN) supported by UNESCO. In 1989 he organized a highly successful ASPEN conference on the teaching of optics, held in Melbourne.

In 1988, realising that there was a strong demand for curriculum enrichment for bright, high-achieving secondary stu­dents, Geoff organized another activity that he dubbed the ‘Physics Gymnasium’ that held several after-hours sessions each year. For this he enlisted some of the School’s best undergraduate lecturers and sometimes graduate students. He often gave highly illustrated talks himself, one of his favourites – repeated several times to fresh audiences – was ‘The Physics of Boomerangs’, which was greatly enjoyed by the students as well as by Geoff. He was a true enthusiast who never tired of pre­senting the excitement of physics to what­ever audience he could find. This included colleagues from other parts of the Univer­sity who, over lunch, were exposed to learned discourses on whatever physics topic was in the news or was uppermost in Geoff’s mind at the time.

Of course colleagues and students in the School of Physics were the prime targets for this kind of informal teaching, which was clearly one of Geoff’s favourite pastimes. He spent an inordinate amount of time explaining physics to other physicists, to postgraduate students and to the occa­sional undergraduate student – indeed to anyone who found their way into his office. Invariably people left his office enlightened – not necessarily on the question that they had come about but always by something interesting and illuminating on any one of an enormously wide range of subjects. Geoff’s encyclopaedic grasp of physics was extraordinary. He was interested, and very well read, in a remarkable range of topics, covering all areas of the subject, picked up in a lifetime of scholarship and by very wide reading: In fact, Geoff had a ‘private’ arrangement with the Physics Librarian who regularly brought him every new book that was bought for the library, to be pre-read and internalized by him before it appeared on the shelves. He was, indeed, a true scholar who followed the talmudic precept of never ceasing to learn. And having learned, he had a burning desire to pass on his knowledge.

Geoff’s breadth as a scholar was widely recognized and led to his advice being sought nationally and internationally. He served on numerous Chair selection com­mittees and several departmental review committees at other universities in Aus­tralia and in other countries, as well as on the Australian Research Council’s physics grant-selection committee for several years.

However, the time taken up by scholar­ship was often at the expense of Geoff’s own creative work. Many colleagues felt that he could have achieved more if he had focused his interests to a greater extent. Arguably, however, he made a greater impact on physics by being such a superb scholar and teacher as well as a successful researcher. This also explains why his research was almost always in collabora­tion with others who helped to channel his creative efforts into more goal-oriented directions. However, his collaboration was very highly valued – and not only for his scholarship. He often exhibited his creative streak with flashes of insight into problems providing unusual or unexpected solutions. Geoff was, indeed, a physicist’s physicist!

One way in which this was manifested was in Geoff’s phenomenal talent to do calculations, usually in front of an audi­ence of research students and group mem­bers. Without ever consulting data sheets or handbooks, he could estimate practi­cally any physical quantity, starting with his collection of ‘desert-island’ formulae and basic data. These were the things that one would carry on to a desert island where no libraries, computers or calcula­tors were to be found. Other formulae would be derived, on the spot, from an irreducible set that he simply carried around in his head. The data were a seem­ingly odd but very shrewdly selected set of numbers in an easily remembered form. Instead of numbers for things like the mass of the electron or the gravitational constant in SI (or cgs) units, he had things like Plank’s constant as ‘200 MeV-fermi’, the mass of the sun as ‘6 kilometres’ (which is actually the Schwarzschild radius) the length of a year as p.107  seconds – and so on. He would typically say seemingly incongruous things such as ‘multiply top and bottom by the square of the velocity of light’ that led to very effective numerical short cuts.

Other Activities

Along with inventing new experiments, one of Geoff’s favourite activities was inventing new gadgets –– some of which were more useful than others. One of the more useful ones, invented jointly by Geoff, Alberto Cimmino and me, was a wide-range extensometer or length trans­ducer, dubbed the ‘Rubbery Ruler’ by the University’s patent attorney. It eventually led to worldwide patents and an ‘R&D 100 Award’ as one of the 100 most technologi­cally significant new products in the year 1995. Geoff was inordinately proud of this achievement and never tired of telling people about it. It was intended, initially, to replace a physiological transducer based on the electrical resistance of a column of mercury contained in a thin latex tube. With the ‘Rubbery Ruler’ one measures the capacitance between two strands of a double helix of fine wire contained inside a rubber tube. It found various medical, physiological and agricultural applica­tions, and was even used in the instrumen­tation of the space suits of European astronauts. Alas, it did not turn into a commercial success because it lacked the ‘killer application’ that would have gener­ated a mass market.

Throughout his life, Geoff undertook many voluntary activities and accepted several honorary positions. He was an active board member of the Temple Beth Israel Hebrew Congregation, rising to the position of vice-president of the Alma Road Temple Beth Israel. With a special interest in Jewish music, he organized several very successful concerts.

Service to professional societies included active membership of the Vic­torian Committee of the Australian Insti­tute of Physics for many years. He also served in 1989 as President of the Austra­lian Optical Society, which elected him to honorary life membership after his retire­ment. In 1994 he took up a three-year position on the Physical Sciences and Mathematics Panel of the Australian Research Council. A few years after his election to Fellowship of the Australian Academy of Science in 1994, he became Chairman of the Victorian Group of Fellows and with the help of his faithful secretary, Mrs Mikki Narielvala, organized very successful social functions several times a year for several years.

Finally, in recognition of his bound­lessly creative ideas, he was invited to become a Board Member of the Museum of Victoria, and to chair its Research Com­mittee. He also chaired the Research Com­mittee of the Victorian College of the Arts where he was highly respected for his original ideas on research in the arts.

Geoff’s enthusiasm spilled over into many other areas. He was a notable opera lover and, for many years, a keen ‘bath­room tenor’. Some time in the 1980s he decided to take singing lessons, from which he derived enormous enjoyment. Characteristically, he read everything he could find about the physics of the human voice and would give impromptu dis­courses on the subject to anyone who would listen. On the occasion of one of his daughters’ weddings, he gave a memorable Pavarotti impersonation – complete with white handkerchief – at the conclusion of which it was unanimously agreed that his singing was very much better than Pavarotti’s physics. From opera, it was but a short step to learning Italian, taken up with gusto and practised on several trips to Italy – as a tourist on some occasions and as an invited lecturer at a European Physics Summer School, held in Sicily, around 1994.

Geoff’s other principal hobby was farming, though not very seriously, on a holiday property at Red Hill on the Morn­ington Peninsula. Typically, Geoff revelled in pumping water between different tanks, devising irrigation systems for fruit trees, taking his grandchildren on donkey rides and so on. He bought two Irish donkeys one of which, unbeknownst to him, was pregnant at the time – so he ended up with three donkeys! He called the mother donkey Hazel (from the German for donkey: Esel) and its progeny was named Annie (from the French for donkey: Ane). Geoff delighted in such word games, in fact he had a whole fictitious cast of char­acters, for example among Olympic ath­letes, the Russian high-jumper ‘Upanova’ and the Chinese high-jumper ‘Lee Ping’.

Wit and humour played a very impor­tant part in Geoff’s life. Not the least aspect was the swapping of jokes with whoever would listen. He was indeed a delightful character, full of good humour and harmless wit, and was universally loved by friends, colleagues, administra­tive and technical staff, and students.

First and foremost, however, Geoff was a devoted husband and father who took great pride in his two daughters and two sons, all of whom grew up to be successful adults who inherited their father’s sense of humour. Family life was a great source of satisfaction to Geoff and this is to the great credit of Diana who not only ran two highly efficient households – one at Moorakyne Avenue, Malvern, and the other at the holiday place at Red Hill – but who also, according to humorous con­fessions made at Geoff’s 60th birthday party, kept the children ‘off his back’ so that he could get on with his beloved physics. Between them, Diana and Geoff provided boundless hospitality to students, colleagues and visiting academics. They had a very wide circle of close friends, to whom were added all the new friends that they made while on sabbatical leave over­seas. Apart from the extended sojourns in Philadelphia, Oxford, Vancouver and Seattle, the Opats travelled widely – to conferences in Europe, the USA, Israel and Japan, as well as on tourist trips in later years to Turkey, Italy, Sweden and else­where. Geoff attracted new friends wher­ever he went and particularly enjoyed the linguistic adventures involved in learning new words and phrases. For instance, he taught himself a few dozen characters of Japanese, treating the whole thing like a new mathematical formalism. He even tried to translate jokes into Japanese! In 1999, a year before his retirement and a year after mine, a special session in our honour was held by the Australian Optical Society at its Sydney conference. This was well attended by quite a few overseas friends and collaborators from the USA, Austria and Italy, in addition to numerous former students and younger colleagues. Several interesting papers were presented and several anecdotes retold, to Geoff’s great pleasure and amusement.

In later years, one of Geoff’s principal sources of delight and satisfaction was the time he spent with his grandchildren, of whom there were ten at the time of his death. He was telling them jokes or teach­ing them things – usually science ––At every opportunity. On one occasion, bright spark Oscar – clearly destined to become a scientist! –– told his kindergar­ten teacher that ‘my Grandpa knows every­thing’. Geoff was promptly invited to demonstrate this and, in due course, turned up at the kindergarten equipped with simple science demonstrations with which he proceeded to delight the children. A photo of Geoff sitting with all his grand­children on a big couch took pride of place in his office. He simply revelled in their uncritical admiration and in the warmth of their unconditional love.

On Australia Day 2002, in recognition of Geoff’s outstanding contributions to education and of his unstinting voluntary activities in various organizations, he was appointed an Officer in the Order of Aus­tralia (AO). He was enormously pleased by this honour, as were his family and his friends. It was recognized by everyone that this was a richly deserved accolade. Geoff had this to say in reply to the many con­gratulatory messages that poured in:

As you know, I have spent much of my life in a labour of love, trying to understand a little more about the world, trying to let oth­ers know about it, and hopefully interesting them in it. Most people do not have the good fortune to spend a life working at what they love. To be recognized for it as well is an added pleasure. I have every intention of continuing my pursuits into the future.

Alas, he did not have the chance. He died suddenly, at home one morning, only two months later. The funeral service and commemoration at the Temple Beth Israel, as well as the one in the School of Physics a short while later, were very moving occasions – packed by hundreds of people whose lives had been touched, irre­versibly, by this larger-than-life character.

About this memoir

This memoir was originally published in Historical Records of Australian Science, vol.16, no.1, 2005. It was written by A. G. Klein, School of Physics, University of Melbourne, Parkville, Victoria.

Numbers in brackets refer to the bibliography.

Acknowledgments

This memoir is based largely on the author’s personal knowledge, supplemented by Geoff Opat’s highly detailed curriculum vitae that has been deposited in the Basser Library of the Australian Academy of Science. A further important source of information was the record of an extensive interview of Geoff by Dr Ragbir Bhatal for the Oral History Section of the National Library of Australia, in May 1998. A trans­cript of this interview may be accessed as Document TRC 3726. I am very grateful to Professors Caro, Hannaford, Muirhead and Wignall and to Mrs Diana Opat who have read and commented on the draft and par­ticularly to Professor Rod Home whose help and advice were invaluable.

Bibliography

  1. Opat, G.I. (1959). The electric dipole sum rule. Nucl Phys 14, 506.
  2. Opat, G.I. (1962). Electromagnetic sum rules. Nucl Phys 29, 486.
  3. Opat, G.I. (1964). Radiative muon capture in hydrogen. Phys Rev B 134, 428.
  4. Opat, G.I. (1966). The displacement current. Lab Talk 9, 12; and Opat, G.I. (1967). The displacement current. Aust Sci Teachers J.13, 63.
  5. Frankel, N.E., Opat, G.I., and Spitzer, J.J. (1967). Exact statistical mechanics of a rela­tivistic anomaly. Phys Lett A 25, 716.
  6. Opat, G.I. (1968). Electromagnetic waves. Lab Talk 12, 14.
  7. Opat, G.I. (1970). Bulk matter and atomic physics. Lab Talk 14, 6.
  8. Burrows, R.D., Caro, D.E., Gold, E., Klein, A.G., MacDowell, C.E., Olney, J.L., Opat, G.I., Starr, J., Wignall, J.W.G., and Peaslee, D.C. (1970). p - d Topological cross- sections in the momentum range 50–920 MeV/c. Aust J Phys 23, 819–821.
  9. Aitchison, J.L., Caro, D.E., Gold, E., Klein, A.G., Lamb, P.R., Langdon, J.F., MacDowell, C.E., Opat, G.I., Starr, J., Wignall, J.W.G., and Peaslee, D.C. (1971). The odd/even ratio of annihilations of anti­protons on neutrons in flight. Lett Nuovo Cimento 2, 1009–1010.
  10. MacDowell, C.E., and Opat, G.I. (1972). Analysis of breakup scattering in a deuterium target. Application to antiproton deuteron breakup scattering. Nucl Phys B 49, 333–344.
  11. Caro, D.E., Gold, E., Klein, A.G., MacDowell, C.E., Opat, G.I., and Wignall, J.W.G. (1973). Elastic antiproton- deuteron scattering below 1.0 GeV. Nucl Phys B 52, 239–247.
  12. Caro, D.E., Gold, E., Klein, A.G., MacDowell, C.E., Opat, G.I., and Wignall, J.W.G. (1973). Antiproton-nucleon scattering in deuterium below 1.0 GeV. Nucl Phys B 52, 301–315.
  13. Opat, G.I. (1974). Reaction rates and the T-matrix. Aust J Phys 42, 597–599.
  14. Caro, D.E., Gold, E., Klein, A.G., Opat, G.I., and Wignall, J.W.G. (1975). A test of the Orfanides Rittenberg Model using p-n data in flight. Nucl Phys B 90, 221–226.
  15. Klein, A.G., and Opat, G.I. (1975). Observa­bility of 2 p rotations. Phys Rev D 11, 523–528.
  16. Opat, G.I. (1976). Limits placed on the exist­ence of magnetic charge in the proton by the ground-state hyperfine splitting of hydrogen. Phys Lett B 60, 205.
  17. Klein, A.G., and Opat, G.I. (1976). Observa­tion of 2 p rotations by Fresnel diffraction of neutrons. Phys Rev Lett 37, 238–240.
  18. Klein, A.G., Martin, L.J., and Opat, G.I. (1977). Fresnel diffraction of slow neutrons. Am J Phys 45, 295–297.
  19. De Pommier, P., Martin, L.J., Poutissou, J.-M., Poutissou, R., Berghofer, D., Hasinoff, M., Measday, D., Salomon, M., Bryman, D., Dixit, M., MacDonald, J.A., and Opat, G.I. (1977). New limit on the decay mu+ to e+ and gamma. Phys Rev Lett 39, 113.
  20. Gold, E., Mason, G.C., Opat, G.I., Parker K.R., Wignall, J.W.G., Chapman, G.J., DeRoach, J.N., King, P.A., Klein, A.G., Martin, L.J., and Tovey, S.N. (1977). Beam-target reversal symmetry in antiproton-neutron interactions in flight. Phys Rev D 16, 2679–2686.
  21. Gold, E., Mason, G.C., Parker, K., Opat, G.I., Wignall, J.W.G., Chapman, G., DeRoach, J., King, P., Klein, A.G., Martin, L.J., and Tovey, S.N. (1977). G-parity conservation in antiproton-neutron interactions in flight. Phys Rev D 16(9), 2679–2685.
  22. Tovey, S.N., Parker, K.R., Chapman, G., DeRoach, J., Gold, E., King, P.A., Klein, A.G., Martin, L.J., Mason, G.C., Opat, G.I., and Wignall, J.W.G. (1978). The reaction p-n to pi–pi–pi+ at incident momenta below l GeV/c. Phys Rev D 17, 2206–2215.
  23. Rangaswamy, T.N., Gurtu, A., Malhotra, P.K., Raghavan, R., Subramanian, A., Sudhakar, K., Chapman, G.J., Klein, A.G., Mason, G.C., Opat, G.I., Tovey, S.N., and Wignall, J.W.G. (1979). A search for direct electron production in p-p interactions at 2.0 GeV/c. Nucl Phys B 151, 71–80.
  24. Unruh, W.G., and Opat, G.I. (1979). The Bohr-Einstein ‘weighing of energy’ debate. Am J Phys 47(8), 743–744.
  25. Kasper, P., Chapman, G., DeRoach, J., Gold E., Klein, A.G., Martin, L.J., Mason G.C., Opat, G.I., Parker, K., Tovey, S.N., and Wignall, J.W.G. (1979). Resonance production in the reaction pbar-d  pispi+pi–pi–pi0 at 0.4–0.9 GeV/c antiproton momenta. Nucl Phys B 156, 207–224.
  26. Klein, A.G., and Opat, G.I. (1979). Applica­tions of the Fresnel diffraction of neutrons. In Neutron Interferometry, ed. U. Bonse and H. Rauch (Oxford University Press, Oxford), pp. 97–107.
  27. Martin, L.J., Mason, G.C., Opat, G.I., Chapman, G., DeRoach, J., Kasper, P., Klein, A.G., Parker, K.R., Tovey, S.N., and Wignall, J.W.G. (1980). Interpretation of enhancements in the pn spectrum from pD annihilation. Phys Lett B 92, 358–362.
  28. Kearney, P.D., Klein, A.G., Opat, G.I., and Gahler, R. (1980). Imaging and focussing of neutrons by a zone plate. Nature 287, 313–314.
  29. DeRoach, J., Chapman, G., Kasper, P., King, P., Klein, A.G., Martin, L.J., Mason, G.C., Opat, G.I., Parker, K.R., Tovey, S.N., and Wignall, J.W.G. (1980). The reaction p-bar d to 2pi+3pi-p for antiproton momenta in the range 0.35–0.92 GeV/c. Nucl Phys B l76, 321–332.
  30. Klein, A.G., Kearney, PD., Opat, G.I., Cimmino, A., and Gahler, R. (1981). Neutron interference by division of wavefront. Phys Rev Lett 46, 959–962.
  31. Klein, A.G., Kearney, P.D., Opat, G.I., and Gahler, R. (1981). Focussing of slow neutrons with cylindrical zone plates. Phys Lett A 83, 71–73.
  32. Klein, A.G., Opat, G.I., Cimmino, A., Treimer, W., Zeilinger, A., and Gahler, R. (1981). Neutron propagation in moving matter: the Fizeau experiment with massive particles. Phys Rev Lett 46, 1551–1554.
  33. Opat, G.I. (1981). In the realm of the quanta – Waves and particles. The Age 4 August, 16.
  34. Opat, G.I. (1982). This is your problem! Physics in the lower secondary school. Aust Physicist 19, 131.
  35. Opat, G.I. (1982). Understanding and entropy: Reflections of a university lecturer. Uni Melb Gazette 33(1), 9.
  36. Davis, T.J., and Opat, G.I. (1983). Elastic vibrations of rods and Poisson’s ratio. Am J Phys 51, 161–163.
  37. Horne, M.A., Zeilinger, A., Klein, A.G., and Opat, G.I. (1983). Neutron phase shift in moving matter. Phys Rev A 28, 1–6.
  38. Klein, A.G., Opat, G.I., and Hamilton, W.A. (1983). Longitudinal coherence in neutron interferometry. Phys Rev Lett 50, 569–572.
  39. Hamilton, W.A., Klein, A.G., and Opat, G.I. (1983). Longitudingal coherence and inter­ferometry in dispersive media. Phys Rev A 28, 3149–3152.
  40. Darling, T.W., Opat, G.I., Tovey, S.N., and Wignall, J.W.G. (1983). Observation of struc­ture in the annihilation reactions p-n to pions. An Fis 79A, 43–47.
  41. Opat, G.I. (1983). Molecular interferometry: A possible gravitational field measuring tech­nique. In Proceedings of the Third Marcel Grossmann Meeting on General Relativity, ed. H. Ning (Science Press and North Holland Publishing Co., Amsterdam), pp. 1491–1495.
  42. Darling, T.W., Opat, G.I., Tovey, S.N., and Wignall, J.W.G. (1984). A study of the reaction p-bar n to pi-pi-pi+ at centre-of-mass energies between 1.9 and 2.3 GeV. Nuovo Ciment A 79, 181–192.
  43. Darling, T.W., Opat, G.I., Tovey, S.N., and Wignall, J.W.G. (1984). A study of the reaction p-n pi–pi–pi+ at centre-of-mass energies between 1.9 and 2.3 GeV. Nuovo Ciment A 79, 181–192.
  44. Klein, A.G., and Opat, G.I. (1984). Neutron wave packets and longitudinal coherence. J Phys–Paris 45(C3), 235–238.
  45. Opat, G.I. (1984). Matter – its ultimate struc­ture. Recent developments in our understand­ing of the basic constituents of matter and their interactions. Lab Talk 1, 14–23.
  46. Darling, T.W., Klein, A.G., Opat, G.I., and Tovey, S.N. (1984). Direct measurement of rotation by a laser speckle method. Opt Acta 31, 813–821.
  47. Arif, M., Kaiser, H., Werner, S., Cimmino, A., Hamilton, W.A., Klein, A.G., and Opat, G.I. (1985). Null Fizeau effect for thermal neutrons in moving matter. Phys Rev A 31, 1203–1205.
  48. Grigg, M.W., Davis, T.J., Cimmino, A., Klein, A.G., and Opat, G.I. (1986). Elastic moduli of solids – a method suitable for high temperature measurements. J Phys E Sci Instrum 19, 1059–1063.
  49. Hamilton, W.A., Opat, G.I., and Wark, S.J. (1987). A self aligning white light mono­chromatic interferometer consisting solely of a mirror and a reflection grating. J Mod Opt 34, 1375–1384.
  50. Hamilton, W.A., Klein, A.G., Opat, G.I., and Timmins, P.A. (1987). Neutron diffraction by surface acoustic waves. Phys Rev Lett 58, 2770–2773.
  51. Wark, S., Hamilton, W.A., and Opat, G.I. (1987). A self-aligning white light or mono­chromatic interferometer consisting solely of a mirror and a reflection grating. J Mod Opt 34(10), 1375–1384.
  52. Davis, T.J., and Opat, G.I. (1988). Electric fields in accelerated conductors. Classical Quant Grav 5, 1011–1028.
  53. Kaiser, H., Arif, M., Berliner, R., Clothier, R., Werner, S., Cimmino, A., Klein, A.G., and Opat, G.I. (1988). Neutron interferometry investigation of the Aharanov–Casher effect. Physica B 151, 68–73.
  54. Opat, G.I. (1988). ASPEN: Asian Physics Education Network. Aust Opt Soc News 2, 2.
  55. Hajnal, J.V., and Opat, G.I. (1989). Diffrac­tion of atoms by a standing evanescent light wave – a reflection grating for atoms. Opt Commun 71, 119–124.
  56. Goodman, P., Grigg, M., Opat, G., Peele, A., Drennan, J., and Rohan, P. (1989). Depend­ence of YBaCuO superconductor properties on constituent oxide preparation I. CuO and BaCO3 pre-treatment. J Am Ceram Soc 72, 856–859.
  57. Cimmino, A., Klein, A.G., Opat, G.I., Kaiser, H., Arif, M., Berliner, R., Clothier, R., and Werner, S. (1989). Experi­mental verification of the Aharonov–Casher effect by neutron interometry in a perfect crystal interferometer. Phys Rev Lett 63, 380–383.
  58. Opat, G.I. (1989). Polarisation of light by scattering and its rotation in optically active media. In Proceedings of the Asia Physics Education Network (ASPEN) Confer­ence/Workshop on the Teaching of Optics, (Melbourne, 23–27 September 1989), pp. 24–27.
  59. Cimmino, A., Hamilton, W.A., Klein, A.G., Opat, G.I., Arif, M., Clothier, R., Kaiser, H., and Werner, S.A. (1989). Fizeau-type experi­ments with neutrons. Nucl Instr Meth A 284, 179.
  60. Cimmino, A., Opat, G.I., and Klein, G.I. (1989). Observation of the topological Aharonov–Casher phase shift by neutron interferometry. Phys Rev Lett 63, 380–383.
  61. Kaiser, H., Arif, M., Berliner, R., Clothier, R., Werner, S., Cimmino, A., Klein, A.G., and Opat, G.I. (1989). Neutron interferometry observation of the topological Aharonov– Casher effect. Nucl Instr Meth A 284, 190–191.
  62. Cimmino, A., Opat, G.I., Klein, A.G., Kaiser, H., Arif, M., Clothier, R., and Werner, S.A. (1989). Neutron interferometry observation of the Aharonov–Casher effect. In Proceedings of the 3rd International Sym­posium on the Foundations of Quantum Mechanics, (Tokyo, 1989), pp. 51–56.
  63. Hajnal, J.V., Baldwin, K.G.H., Fisk, P.T., Bachor, H.-A., and Opat, G.I. (1989). Reflec­tion and diffraction of sodium atoms by evanescent optical wave. Opt Commun 73, 331–335.
  64. Hajnal, J.V., Baldwin, K.G.H., Fisk, P.T.H., Bachor, H.-A., and Opat, G.I. (1990). Diffracting atoms from evanescent light fields. In Coherence and Quantum Optics VI, ed. J.H. Eberly, L. Mandel and E. Wolf (Plenum Press, New York), pp. 461–466.
  65. Opat, G.I. (1990). Coriolis and magnetic forces: The gyrocompass and magnetic com­pass as analogs. Am J Phys 58, 1173–1176.
  66. Baldwin, K.G.H., Hajnal, J.V., Fisk, P.T., Bachor, H.-A., and Opat, G.I. (1990). Optics for neutral atomic beams: reflection and dif­fraction of sodium atoms by evanescent laser light fields. J Mod Opt 37, 1839–1848.
  67. Opat, G.I., Cimmino, A., Klein, A.G., Kaiser, H., Arif, M., Werner, S.A., and Clothier, R. (1990). Experimental verifi­cation of the Aharonov–Casher effect for neutrons with a crystal interferometer. In Quantum Coherence, ed. J.S. Anandan (World Scientific Publishers, Singapore), pp. 150–159.
  68. Opat, G.I. (1991). Statistical analysis of neutron interferometer detection systems. Rev Sci Instrum 62, 1947–1950.
  69. Opat, G.I. (1991). The precession of a Foucault pendulum viewed as a beat phenom­enon of a conical pendulum subject to a Coriolis force. Am J Phys 59, 822–823.
  70. Opat, G.I., and Unruh, W. (1991). Theory of an earth-bound clock comparison experiment as test of the principle of equivalence. Phys Rev D 44, 3342–3344.
  71. Hajnal, J.V., and Opat, G.I. (1991). Stark effect for a rigid symmetric top molecule: exact solution. J Phys B–At Mol Opt 24, 2799–2805.
  72. Opat, G.I., Wark, S., and Cimmino, A. (1992). Electric and magnetic mirrors and gratings for slowly moving neutral atoms and molecules. Optics and Interferometry with Atoms. Appl Phys B 54, 396–402.
  73. Allman, B., Cimmino, A., Klein, A.G., Opat, G.I., Kaiser, H., and Werner, S.A. (1992). The scalar Aharonov–Bohm experi­ment with neutrons. Phys Rev Lett 68, 2409–2412.
  74. Darling, T., Rossi, F., Opat, G.I., and Moorhead, G. (1992). The fall of a charged particle under gravity – a study of experi­mental problems. Rev Mod Phys 66, 237.
  75. Wark, S., and Opat, G.I. (1992). A self- aligning interferometer suitable for white or monochromatic light consisting solely of a mirror and a reflection grating. II. Experi­mental results. J Mod Opt 39, 637–644.
  76. Wark, S., and Opat, G.I. (1992). An electro­static mirror for neutral polar molecules. J Phys B 25, 4229–4240.
  77. Rossi, F., and Opat, G.I. (1992). Gravity and strain-induced electric fields outside metal surfaces. Phys Rev B 45, 11249–11261.
  78. Rossi, F., Opat, G.I., and Cimmino, A. (1992). Modified Kelvin technique for meas­uring strain-induced contact potentials. Rev Sci Instrum 63, 3736–3743.
  79. Rossi, F., and Opat, G.I. (1992). Observation of the effects of adsorbates on contact poten­tials. J Phys D Appl Phys 25, 1349–1353.
  80. Allman, B., Klein, A.G., Nugent, K.A., and Opat, G.I. (1993). Lloyd’s mirage – a variant of Lloyd’s mirror. Eur J Phys 14, 272–276.
  81. Opat, G.I. (1993). On the effects of gravita­tional fields on the electrical properties of matter. Aust J Phys 46, 647–650.
  82. Gudkov, V., Opat, G.I., and Klein, A.G. (1993). Neutron reflection interferometry. Physical principles of surface analysis with phase information. J Phys–Condens Mat 5, 9013–9024.
  83. Gudkov, V., Opat, G.I., and Klein, A.G. (1994). Neutron reflection interferometry. Physical principles of surface analysis with phase information. Erratum. J Phys–Condens Mat 6, 1081.
  84. Allman, B., Klein, A.G., Nugent, K.A., and Opat, G.I. (1994). Refractive index profile determinations using Lloyd’s mirage J Appl Opt 33, 1806–1811.
  85. Hannaford, P., McLean, R.J., Opat, G.I., Rowlands, W.J., and Sidorov, A. (1994). Towards a cold-atom matter wave interfero­meter. Quantum Opt VI, Springer Proc Phys 77, 18–26.
  86. Opat, G.I. (1995). Interferometry with parti­cles of non-zero rest mass: Topological experiments. In Advances in Quantum Mechanics, Ettore Majorana School in Erice (Sicily) Italy, 16–28 February 1994 (Plenum Press, New York), pp. 89–112.
  87. Kearney, P.D., Klein, A.G., Opat, G.I., and Gahler, R. (1996). Imaging and focussing of neutrons by a zone plate. In Selected Papers on Zone Plates, ed. J. Ojeda-Castaneda and C. Gomes-Reino (SPIE Optical Engineering Press, Bellingham, Washington DC), pp. 398–399.
  88. Feng, X.-P., Witte, N.S., Hollenberg, L.C.L., and Opat, G.I. (1996). Reflection and diffrac­tion of atomic de broglie waves by evanescent laser waves – Bare state method. Aust J Phys 49, 765–775.
  89. Rowlands, W.J., Lau, D.C., Opat, G.I., Sidorov, A.I., McLean, R.J., and Hannaford, P. (1996). Manipulating beams of ultra-cold atoms with a static magnetic field. Aust J Phys 49, 577–587.
  90. Rowlands, W.J., Lau, D.C., Opat, G.I., Sidorov, A.I., McLean, R.J., and Hannaford, P. (1996). Stern–Gerlach deflec­tion of a beam of ultra-cold caesium atoms. In Laser Spectroscopy XII, ed. M. Inguscio, M. Allegrini and A. Sasso (World Scientific, Singapore), pp. 134–137.
  91. Rowlands, W.J., Lau, D.C., Opat, G.I., Sidorov, A.I., McLean, R.J., and Hannaford, P. (1996). Magnetostatic state- selective deflection of a beam of laser-cooled atoms. Opt Commun 126, 55–60.
  92. Rowlands, W.J., Lau, D.C., Opat, G.I., Sidorov, A.I., McLean, R.J., and Hannaford, P. (1996). Magnetostatic manipu­lation of beams of laser-cooled atoms. Laser Physics 6, 274–277.
  93. Rowlands, W.J., Lau, D.C., Opat, G.I., Sidorov, A.I., McLean, R.J., and Hannaford, P. (1996). Magnetostatic manipulation of beams of laser-cooled atoms. In Proceedings of the International Symposium on Modern Problems of Laser Physics, ed. S.N. Bagayev and V.I. Denisov (Siberian Division of the Russian Academy of Sciences, Novosibirsk), pp. 199–206.
  94. Sidorov, A.I., McLean, R.J., Opat, G.I., Rowlands, W.J., Lau, D.C., Murphy, J.E., Walkiewicz, M., and Hannaford, P. (1996). Magnetostatic manipulation of beams of laser- cooled atoms. Quantum Semicl Opt 8, 713–725.
  95. Sidorov, A.I., Lau, D.C., Opat, G.I., McLean, R.J., Rowlands, W.J., and Hannaford, P. (1997). Magnetostatic optical elements for laser-cooled atoms. Modern Problems of Laser Physics, ed. S.N. Bagayev and V.S. Denisov (Siberian Division of the Russian Academy of Sciences, Novosibirsk), pp. 299–316.
  96. Sidorov, A.I., Lau, D.C., Opat, G.I., McLean, R.J., Rowlands, W.J., and Hannaford, P. (1998). Microfabricated magnetostatic mirrors for cold atoms. In Laser Spectroscopy, eds Z.J. Wang, Z.M. Zhang and Y.Z. Wang (World Scientific, Singapore), pp. 252–255.
  97. Richmond, J.A., Nic Chormaic, S., Cantwell, B.P., and Opat, G.I. (1998). A mag­netic guide for cold atoms. Acta Phys Slovaca 48, 481–488.
  98. Minogin, V.G., Richmond, J.A., and Opat, G.I. (1998). Theory of the time orbiting (TOP) quadrupole trap for cold atoms. Phys Rev A 58, 3138–3145.
  99. Sidorov, A.I., Lau, D.C., Opat, G.I., McLean, R.J., Rowlands, W.J., and Hannaford, P. (1998). Magnetostatic optical elements for laser-cooled atoms. Laser Phys­ics 8, 642–648.
  100. Lau, D.C., McLean, R.J., Sidorov, A.I., Gough, D.S., Koperski, J., Rowlands, W.J., Sexton, B.A., Opat, G.I., and Hannaford, P. (1998). Magnetostatic optical elements for laser- cooled atoms. Proc 6th Symp Laser Spectrosc 6(3), 24–32.
  101. Opat, G.I., Nic Chormaic, S., Cantwell, B.P., and Richmond, J.A. (1999). Magnetostatic optical elements for laser-cooled atoms. J Opt B–Quantum S O 1, 415–419.
  102. Lau, D.C., Sidorov, A.I., Opat, G.I., McLean, R.J., Rowlands, W.J., and Hannaford, P. (1999). Reflection of cold atoms from an array of current-carrying con­ductors. Eur Phys J D 5, 193–199.
  103. Lau, D.C., McLean, R.J., Sidorov, A.I., Gough, D.S., Koperski, J., Rowlands, W.J., Sexton, B.A., Opat, G.I., and Hannaford, P. (1999). Magnetic atom optical elements for laser-cooled atoms. J Korean Phys Soc 35, 127–132.
  104. Lau, D.C., McLean, R.J., Sidorov, A.I., Gough, D.S., Koperski, J., Rowlands, W.J., Sexton, B.A., Opat, G.I., and Hannaford, P. (1999). Magnetic mirrors with micron-scale periodicities for slowly moving neutral atoms. J Opt B–Quantum S O 1, 371–377.
  105. Gough, D.S., McLean, R.J., Sidorov, A.I., Lau, D.C., Koperski, J., Rowlands, W.J., Sexton, B.A., Hannaford, P., and Opat, G.I. (1999). A magneto-optically recorded mirror for cold atoms. In Laser Spectroscopy, ed. R. Blatt, J. Eschner, D. Leibfried and F. Schmidt-Kaler (World Scientific, Singa­pore), pp. 340–341.
  106. Sidorov, A.I., McLean, R.J., Sexton, B.A., Gough, D.S., Davis, T.J., Akulshin, A., Opat, G.I., and Hannaford, P. (2001). Micron- scale magnetic structures for atom optics. CR Acad Sci IV 2(4), 565–572.
  107. Akulshin, M., and Opat, G.I. (2001). The ‘storage of light’ and very large variations of the group velocity of light in coherently pre­pared atomic media. AOS News 15(2/3), 30–35.
  108. Sidorov, A.I., McLean, R.J., Scharnberg, F., Gough, D.S., Davis, T.J., Sexton, B.A., Opat, G.I., and Hannaford, P. (2002). Perma­nent magnet microstructures for atom optics. Acta Phys Polonica B 33, 2137–2155.
  109. Richmond, J.A., Cantwell, B.P., Nic Chormaic, S., Lau, D.C., Akulshin, A.M., and Opat, G.I. (2002). A magnetic guide for neutral atoms. Phys Rev A 65, 033422.
  110. Akulshin, A.M., Cimmino, A., and Opat, G.I. (2002). Negative group velocity of a light pulse in caesium vapour. Quantum Electron 32, 567.
  111. Akulshin, A.M., Cimmino, A., Sidorov, A.I., Hannaford, P., and Opat, G.I. (2003). Light propagation in an atomic medium with steep and sign reversible dispersion. Phys Rev A 67, 011801.

Books

  1. Opat, G.I. (Editor and part author.) Physics in General Science: Worksheets for Years 7-l0 (S.T.A.V., February 1983).
  2. Opat, G.I. (Editor and contributor.) Proceed­ings of the ASPEN Conference/Workshop on the Teaching of Optics (Melbourne, Septem­ber 1989).

Films

  1. Opat, G.I. et al. The Ammonia Maser (with Audio-Visual Aids and the Post Office, 1961).
  2. Opat, G.I. Connections Between Electricity and Magnetism. (Made by Media Unit, Uni­versity of Adelaide, September 1984, and Media Unit, University of Western Australia, October 1985).

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