Dr. Alan Burgess, eminent atomic astrophysicist, who has died aged 78, was the person who explained the discrepant measurements of the solar coronal temperature problem, a feat that had eluded many.
The papers which resulted from Burgess’s PhD thesis immediately established him as an outstanding theoretical atomic astrophysicist. He had become an expert in how atoms in the gaseous nebulae seen in the night sky, like Orion, lose their electrons by interaction with photons from stars (photo-ionisation) and in how these electrons manage to re-attach themselves to their nuclei (electron-ion recombination). From his work, the astrophysics community now had precise models for hydrogen, which fitted observations, but also parametric formulae which allowed them to work out details and predictions for many other atoms, such as carbon and nitrogen.
Matters were less clear for very high temperature ionised gas or plasma such as that of the solar corona. The corona is the tenuous atmosphere of the sun seen at eclipses. Different estimates of its temperature did not make sense. Some suggested lower temperatures, while others suggested much higher temperatures.
In a very different vein, there had just been a declassification of research into obtaining limitless energy from controlled fusion of hydrogen in magnetically confined plasma. That is, taming the reactions of the hydrogen bomb, which are the same as take place in the core of the sun, for peaceful purposes.
Magnetic confinement fusion also had atomic problems. These plasmas do not rely on photons but rather collisions with free electrons to ionise atoms. In the solar corona, it seemed that atoms ought to ionise perhaps one hundred times more slowly than theory suggested or else they recombined again a lot faster. Mike Seaton, Burgess's PhD supervisor, and the then Head of Physics at University College, Sir Harrie Massey, encouraged Burgess to engage with Culham Laboratory, the UK laboratory for fusion research, as well as with astrophysics to help with these problems.
Burgess actually turned his mind first to collisional ionisation. This was a time when there was a sudden and unexpected return of interest to classical rather than quantal treatments of the process. Burgess introduced hybrid methods between the two which were very promising, and so in 1961 he found himself invited to spend time at Berkeley, California; New York; and then at the Institute for Advanced Study, Princeton–quite an honour–which he did in the Autumn of 1963, occupying Einstein’s old office. Robert Oppenheimer, a father of the atomic bomb, who subsequently tried to stop developments which he had set in train, had by then been reinstated in American science from his isolation and was the Director of the Institute. When Burgess gave a colloquium about his binary encounter ionisation work, Oppenheimer was in the front row, along with two other Nobel Prize winners. As was his wont, Oppenheimer asked a very simple question first and all the young Turks murmured behind, feeling that the Director was losing his grip. But Oppenheimer asked another question and another, going further and further until Burgess said he felt convinced that Oppenheimer already knew almost everything about his work and wondered what else was hidden under the classified stamp. Burgess always rather admired the quiet, penetrating way in which Oppenheimer got down into a problem.
But Burgess's mind was also turning back to his speciality, recombination, and then he struck gold, or rather dielectronic recombination. This is rather a subtle process by which two electrons can work together to get re-attached to a nucleus. Burgess's famous guide and mentor, Mike Seaton, had examined this process and decided it was not important. Burgess's paper on dielectronic recombination was a masterpiece and somehow typifies him. It was short, only two or three pages. It very gently and delicately showed that Seaton had got it wrong by a factor somewhere between a hundred and a thousand. But it also included a very effective and economical method for working the process out and then concluded with a formula, a neat, clever fit to the results of all his calculations, which the scientific world now knows as the Burgess General Formula for dielectronic recombination. This formula is still used today and the coronal temperature problem was solved. Seaton did not hold this against Burgess. Seaton himself worked on in further aspects of dielectronic recombination, but using Burgess's correct formulation. Seaton was very proud of Burgess. Many years later, he said that academically Burgess was like a son to him and Burgess's students like his grandchildren.
Thousands of papers have been written on dielectronic recombination since then. Just a few months ago, discussion took place on embedding Burgess's dielectronic recombination studies for denser plasmas into the current leading codes in the world for modelling the ionisation state of active galactic nuclei – cutting edge research. Also, to cope with dielectronic recombination for very complex heavy elements such as tungsten in the latest international fusion experiment, ITER, as well as for astrophysics, it is agreed that the best route is to go right back to the neat methods of Burgess's original paper of nearly fifty years ago. The latest theoretical studies of ionisation from highly excited states of ions on very large computers suggest that Burgess's hybrid binary-encounter method is only out by a very modest factor and so continues to be a preferred method. Burgess's legacy to atomic physics is assured.
Burgess was born in Oldham, Lancashire. His father, James Burgess, was awarded the Imperial Service Medal for his work during the Second World War (installing telecommunications equipment for Churchill at an RAF aerodrome and naval submarine bases and directing the reinstallation underground of the telephone system of Manchester to safeguard it from any further enemy air attacks). Burgess attended Count Hill Grammar School Oldham, obtained a degree (1955) and a PhD (1958) in Physics at University College, London University. His first post-doctoral research was working on the Atomic Energy Research Zeta Programme at Harwell.
Burgess was invited to Cambridge in 1965, where he was a research fellow and lecturer at DAMTP (the Department of Applied Mathematics and Theoretical Physics) until his retirement in 2000, aged 67. He was a Fellow of the Royal Astronomical Society. In 1970 he completed a sabbatical at the Joint Institute for Laboratory Astrophysics at the University of Colorado, Boulder, USA. In 1986 he visited Moscow and Leningrad as part of the 1st Soviet-British Symposium on Spectroscopy of Multicharged Ions.
To work with he was a quiet man of science. He did not flood the journals with mass produced papers or talk loudly at meetings. The many tributes which have flowed in for Burgess all confirm that he was a gentle, modest, supportive person, with such a clear, clear mind. He gave time, relaxed and unpressured, to his colleagues, students and friends. You were fortunate when he sat down with you in the tea-room at DAMTP, to think about a problem. When he focussed on a problem, he started simply and then went deeper and deeper until finally, perhaps hours later, still in the tea-room, there was a picture in your mind of what the atoms were really about. Then the black propelling pencil would come out and the mathematical equations would take shape. Finally there would be the computer code, compact, terse, without a comment in sight, which worked perfectly. There can be few large atomic physics codes in the world which do not have one of Burgess's perfect little sub-routines or mathematical algorithms, probably unrecognized, embedded within them. // A great researcher and lecturer like Burgess initiates a cascade of knowledge as students become teachers in turn and pass the knowledge on–a sort of academic family who share common ideas and methods, and speak the same mathematical jargon. Burgess may not have known it, but in this sense of an academic family, he is already a great-grandfather.
In 2001, following his retirement, he was appointed an Emeritus Fellow of Wolfson College. His final paper On proton excitation of forbidden lines in positive ions was published 13th July 2005.
A devoted family man, whose wide interests included classical music, photography and steam locomotives, Burgess was married in 1961 to Lore (nee Freudenthal) and widowed in 1988; he is survived by his daughter, Gina, his son, Neil, and three grandchildren.
