Born of Jewish parents in Cape Town on St Andrew's Day 1924 - it was his light-hearted claim to a Scottish connection at rallies in Glasgow and Edinburgh - Pentz was educated at St Aidan's College, Grahamstown, before going on to the University of Cape Town. Winning Honours in Physics and Electrical Engineering, he graduated BSc in 1944, and MSc in Physics with distinction in 1945. Pentz's activity between 1943 and 1946 in the African Adult Night-Schools Association contributed to his detestation of the policies of Daniel Malan, father of institutional apartheid, and his somewhat rapid exit to Britain.
It was Pentz's good fortune that his interest in microwave spectrometry made him welcome at Imperial College, in London. Here new horizons were opened by Professor L.C. Martin, an expert on microscope theory, and Professor William Wright, with a transatlantic reputation in Photometry and Light.
Most fortunate of all was the fact that the head of the Physics Department in 1948-50 was Sir George Thomson, son of ''J.J.'' and himself a Nobel prizewinner (1937). In collaboration with Dr R. Latham and Dr M. Blackman, Pentz constructed a plasma betatron device directed at studies of controlled fusion. It was one of the earliest such studies, described by Pentz himself as "somewhat naive". Work on controlled fusion in university laboratories was stopped in 1950, for "security reasons" associated with the first hydrogen bomb explosions. Pentz declined the option of working elsewhere, on the principle that he would not help to create a hydrogen bomb. So he spent the early 1950s constructing a high-resolution microwave spectrometer, and used it to study Zeeman and Paschen-Back effects in molecular rotation spectra. Thermonuclear fusion control was one of Thomson's interests; and he directed Pentz to this field, giving him, later in 1957, a glowing reference for Cern, at Geneva.
As a 26-year-old, Pentz was one of the catalyst founders of Science for Peace, a progenitor of a number of other such organisations; and in the early 1950s he was also editor of the Science for Peace Bulletin. In this activity, he had the sympathy of Sir George Thomson's successor, Patrick Blackett, who had commanded a gun battery on HMS Barham at Jutland, but was sceptical about policies based on the atomic bomb.
I first met Pentz at Cern in January 1963, when my wife and I were the (honeymooning) guests for a couple of days of Victor Weisskopf, the Director of Cern, and John Adams, on secondment from Umist as Deputy-Director. Pentz, newly promoted from Research Fellow to Senior Physicist, was deputed to act as our guide to the mysteries of High Energy Particle Acceleration, and the linear accelerator. He invited us to dinner and let rip with his passionate concerns that young MPs should understand the supreme danger involved in ever more sophisticated nuclear weapons. ''Do you,'' he barked at me, ''really understand the total lethality of missile-bomb strategic nuclear weapons?''
At Cern, Pentz was appointed leader of 30 scientists to develop a storage machine known as Cesar, an accelerator facility whose construction was enormously difficult. Pentz used Cesar to research the basic problems of radio-frequency beam- stacking and beam instabilities.
Though he respected Weisskopf and Adams, for whom the advancement of particle physics, and the understanding of matter, was central to their lives, and to science, Pentz believed that it was even more important to alert human beings to the perils of nuclear conflagration. Weisskopf and Adams went out of their way to express their high regard for his expertise as a physicist, and their affection for him as a person. No scientist on the planet was in a better position to judge Pentz's work than Weisskopf and Adams at that time.
Therefore it was no surprise that he accepted the invitation of that shrewd chooser of people, Walter Perry, first Vice-Chancellor of the Open University, to become the first and pioneering head of the Physics Department in 1968. On the occasion of Pentz's retirement in 1985, Lord Perry reminisced:
As Dean and Director of Studies of the Science Faculty, [Pentz's] contribution to the establishment of the university as a whole and to that of the Science Faculty in particular has been unequalled.
In 1970, when there were only some 300 members of the staff at Walton Hall, most of them knew that, unless the university was "airborne" within a year, a change of government might mean that it would never take off. For Mike, this meant working from early morning till late at night six or seven days a week. He was one of the first to realise the essentially hybrid nature of the OU (part academic, part industrial) and all the implications of that fact. This was probably because his previous training and experience . . . was as a physicist and engineer. He understood that planning, scheduling, establishing production norms (however alien they might seem to normal academic life) were essential if the primary aim of the OU - to produce effective, academically viable, distance-learning courses - was to be achieved.
At the Open University he soon became close to a kindred spirit, the Professor of Biology, Stephen Rose. Together, they made a formidable contribution, by speech, and by article, to the peace movement. Together, in 1980, they were instrumental in founding Scientists against Nuclear Arms - Sana.
Curious as it may seem, Pentz earned the goodwill and respect of Earl Mountbatten of Burma. Both were united in the belief that the nuclear arms race was leading us to the brink of irreversible escalation, to the point of no return. No presentation by Pentz was complete without a quotation from Mountbatten, speaking in May 1979: ''The world stands on the brink of the final abyss. Let us all resolve to take all possible practical steps to ensure that we do not, through our own folly, go over the edge.'' It was no accident that Pentz's powerful polemic, published in 1980, was called Towards the Final Abyss.
Pentz was uninhibited about taking on the most distinguished personages of science. On 1 December 1982, Sir Andrew Huxley, then President of the Royal Society, was reported to have warned Fellows of the Royal Society against the dangers of making public pronouncements on political issues such as nuclear weapons. ''By pronouncing on such issues,'' Huxley contended, ''scientists are pretending an authority we are not entitled to claim.''
A little further on in the same report, retorted Pentz:
We find Sir Andrew himself "pronouncing" that pledges by nations not to be the first to use nuclear weapons, would destroy such value as nuclear weapons possess against starting a war with conventional weapons, and so the risk of nuclear warfare would probably be increased by a pledge of no first use.
Caustically - and it has to be said Pentz was caustic to the heavyweights of his time, and to politicians, but never, I am told, to his students, Pentz replied:
Presumably Sir Andrew does not consider this to be a pronouncement on "political issues" such as nuclear weapons, since a) it was made by himself and b) it accords comfortably with the establishment views as expressed by Mr Reagan and Mrs Thatcher.
Pentz made it clear that he had no objection to Huxley's saying what he thought about nuclear weapons, deterrence, no first use or whatever. But Huxley was profoundly wrong, he said, to suggest that scientists should not have anything to say about nuclear weapons and how to get rid of them. Like it or not, scientists were deeply implicated in the (so far) endless escalation of nuclear armaments, and would be implicated in the final catastrophe of nuclear war if the escalation were not stopped soon. Pentz believed that scientists could and should place their knowledge at the service of those in the peace movements, the churches, and the political parties who were trying to stop what he perceived as the insane race to oblivion, but who lacked the tools to do this vital job.
When I said to Pentz that I regarded Huxley both as an extremely kind and thoughtful man, and one of the considerable scientists of the age, he responded, ''Well, so do I. But that is all the more reason for challenging his opinion.'' Then he added, with a chuckle, ''I feel it is rather like Huxley versus Bishop Wilberforce in the last century: only, this time, I am Huxley, and Andrew is Bishop Wilberforce.''
Pentz was probably the originator of the phrase ''nuclear winter'', and certainly the individual who did more than any other to make sure that it impacted on politicians, not least Denis Healey. In November 1984, he was instrumental in organising a visit by Professor Paul Ehrlich, Dr Anne Ehrlich, from California, and Dr Georgy Golitsyn, then head of the Laboratory of Atmospheric Physics in Moscow, to 11 British cities. They held meetings to discuss their findings on ''nuclear winter'' with the councillors, scientists, students, and MPs.
Pentz was indefatigable in urging local authorities to declare themselves nuclear-free zones. The ridicule he encountered in a number of quarters, some of which resided in the Labour Party, bothered him not at all. What mattered to Pentz was that he had succeeded in driving home the message that even a limited nuclear war would inject enough dust and smoke into the atmosphere to blot out the sun, and reduce temperatures to below zero throughout the northern hemisphere.
Pentz's continuing theme was that a Third World War would come about, if what he described as the ''Doomsday machine'' was left to its own devices. Deterrence, which included the threat to use nuclear weapons, Pentz saw as immoral, irrational, and, above all, unstable. For Nato's doctrine of flexible response to carry conviction, and an effective deterrent, ''the adversary had to be convinced that we were mad, as well as bad".
Early in 1985, I heard Pentz at one of the innumerable briefings he held for MPs, pointedly quoting Robert McNamara, one of the authors of the doctrine of flexible response, saying that it would be inconceivable for a limited nuclear war to remain limited. The way to break the machine was by a ''massive democratic intervention'' by the peace movement in the nuclear states. This was why, in almost every peace march of significance in the 1970s and 1980s, a formidable and sturdy Professor of Physics was to be seen at the head of the column. There was no better candidate for the as yet not created post of Her Majesty's Peacenik-in-Waiting.
Pentz retired to France for health reasons, to Bonnieux, near Avignon, where leukaemia took over in February 1995. Devotedly nursed by his wife Anne, with splendid back-up from French district nurses and pharmacists, Pentz managed to complete the draft of his memoirs. I hope they are published, for Pentz was an unusual and interesting man.
Michael John Pentz, physicist, peace campaigner: born Cape Town 30 November 1924; Research Assistant, Department of Physics, Imperial College 1948- 49, Assistant Lecturer 1949, Lecturer 1949-57; Research Fellow, Cern, Geneva 1957-58, Senior Physicist 1958-68; Dean, Faculty of Science, Open University 1969-85; died Bonnieux, Provence 29 May 1995.