Pergamon

Radiul. Phys. Chem. Vol. 45, No. I, pp. v-viii, 1995 Elsevier Science Ltd. Printed in Great Britain

A TRIBUTE TO ARTHUR CHARLESBY

For 45 years Professor Charlesby has been a dominant figure in the field of radiation science and technology. Few of us can recall a meeting of our freemasonry in which he was not a principal speaker, and a major contributor to provocative and stimulating discussions. Year after year, articles have flowed from his pen illuminating almost every aspect of our field.

Despite impressions to the contrary, Professor Charlesby did not, like Minerva, spring full-grown from the head of Jupiter. He was, like most of us, born of parents. A native of London, he received some of his early education in Antwerp. At the Royal Atheneum, a French school in a Flemish city, he was the only English student. He returned to London for his university studies: engineering at what is now the City University, and physics at the Imperial College of Science and Technology. It was at the latter he collected the first group of many prizes for scholarship while on his way to the award of the B.Sc. and Ph.D. degrees. In normal times, he would have devoted his talents to electron diffraction and the wave-particle problem, the field in which he performed his doctoral research. However, his graduation in 1939 coincided with the start of World War II. The events of the War and the five years that followed directed his career elsewhere. Because of his scientific credentials, his efforts to enlist in active service were rejected so that he could do research associated with “Special War Duties”. He was engaged in the study of scientific military problems for three years; surprisingly, much of it was related to infrared and radar research involving the recently discovered “polythene”. He was then assigned to perform a series of operations research missions for the Royal Air Force, starting as a Squadron Leader in Italy (which are the basis of some of Charlesby’s best stories) and ending with the 1949 Berlin Air Lift during which he served the Air Ministry as Chief Scientific Officer for Planning.

At this time, he could have continued his career in the new field of operations research. Instead he returned to materials science. During 1949-55, he was the Head of the Radiation Effects Group at the Atomic Energy Research Establishment at Harwell. There he organized a team with the objective of developing a firm understanding of and solutions to the materials problems associated with the design, construction and operation of nuclear reactor systems. In this setting, polymers are largely sources of trouble when compared to metals. It was soon clear to him, however, that radiation induced effects on polymers could give rise to a wide variety of useful products with unusual properties. His special recognition of the profound changes in their mechanical behavior resulting from relatively small doses was the basis of several technical articles and patents. These contributions contain ingenious physical insights and mathematical modeling methods which pervade the literature until this very day. They earned for him the D.Sc. degree.

VI A tnbute to Arthur Charlesby

The prospects of industrial development of his ideas led to his departure from Harwell in 1955 to become Head of the Tube Investments Nuclear Labs at Hinxton. There he assembled a constellation of some of the finest radiation and polymer chemists. Once again, patents and papers flowed out to the edification of the scientific and technical world, but somehow T.I. proved to be less capable or fortunate than Raychem in its

efforts to convert the intellectual gold of the Charlesby group to metallic form. After two years Charlesby left to accept an academic appointment.

From 1957 until his retirement in 1977, he was Professor of Physics and Head of the Physics Department at the Royal Military College of Science at Shrivenham. Those 20 years are marked by many achievements but the one that has thus far been the most enduring and influential is his book Atomic Rudicrtion and PO~~WKVS. published by Pergamon in 1960 and translated into French, Japanese, Russian, Chinese and Polish. It is now an old work with archaic units and which contains concepts that have been extensively revised or abandoned. But it remains a very useful resource. The newcomer to the field will find almost every concept of radiation and polymer science that it covers described with exceptional clarity. To the experienced practitioner in our

field, it offers insights which are still not fully appreciated or exploited. Of course, even I/W book cannot obscure other developments during this period. Once again, Professor Charlesby was able to assemble collaborators and students of such a calibre as to make Shrivenham a major laboratory. The two decades are marked by an admirable profusion of papers, patents, symposium chapters, lectures. prizes. visitmg professorships and so on. Only Antarctica has not had the benefit of a Charlesby visit and penguins arc all the poorer for it. Every other continent and almost every country in each continent is marked by his footprints. And his are almost invariably productive visits. Not only in instruction and inspiration of the audience. hut in terms of papers co-authored by host and guest. Another important contribution during this period is Professor Charlesby’s successful efforts to increase the understanding of industry of the potential advantages (and limitations) of radiation processing. His efforts to counter the anti-rational outpourings of the anti-radiation activists in the U.K. have been less successful; even his witty and sound arguments a~-c. sad to say, inadequate in such circumstances.

Even for a distinguished professor, it is not easy to maintain an active research career upon retirement. After his R.M.C.S. period, Charlesby did so without any detectable decrease in productivity. His visits to and collaborations with many laboratories have provided the basis for many of his papers in his “post-retirement” period. But there arc three aspects of this period which are particularly noteworthy. First. there is his service as the Editor-in-Chief of this journal. Previously emphasizing more fundamental papers. Rudiution P/l.l,\ic~.c md Chemistry, under his editorship broadened its coverage. In consequence, it is now the principal organ for publication of applied research articles in these fields, as well as articles on radiation processing. Although many publishing alternatives were advanced, all eight sets of the International Meetings on Radiation Processing were published in Rudiution Physics und C/zrw~istr~~. Special issues on individual topics and meetings. and birthday and memorial issues for honored scientists have become enduring archival literature because of his editorial leadership. Second, is his return to research in fundamental problems of physics deriving from his Ph.D. studies at the Imperial College. The regular reader of Rudiutim Phj,.cic,s trrrd C‘lrcwi.ct~~~~~ is well aware of several articles he has included in this journal on his complete reformulation of quantum mechanics. Another research interest in recent years also dates back to the early days of his cat-ccr: pulsed NMR measurements as a means of determining chain entanglement and crosslink dcnsitles in elastomers.

The above constitutes a brief biographical summary of the professional life of Arthur Charlcshy. A listlnp of his appointments, honors, etc. is appended. Following is an assessment of the scientific impact of his lift’s work to date; happily, there is more to come.

Professor Charlesby is undoubtedly the dominant figure on the subject of radiation-induced crosslinking and scission in thermoplastics and elastomers. There is scarcely a work on this topic in which chc authors

fail to make reference to his exceptional contributions. His papers are not the first to consider the question of random crosslinking of elastomers, but he has expanded our knowledge and insights far beyond that 01 earlier work. They not only provide fundamental enlightenment but they have also provided clca~- paths to the development of new and useful materials and industrial processes. However. Charlesby’s stalistical theory of crosslinking is in too many instances employed inaccurately. The fundamental assumptions of the theory are that for each polymer composed of repeating structural units, (I) there is a fixed radiation yield of crosslinks and another fixed yield of scissions; (2) both processes occur randomly; (3) and the Iwo G values are independent of the degree of polymerization, the molecular weight distribution, the dose and the dose rate (provided and volatile radiation products are removed during irradiation). However. these arc ideal conditions not always encountered in practice. Morphology is one complication. Samples of the same polyethylene, heat-treated so as to endow them with different crystallinity, yield different G values when the Charlesby equations are applied; this is so because almost all the crosslinking in this system occurs in the amorphous region. Unsaturation, particularly in the end groups is another complication, one which Charlesby recognized quite early and regarding which he has provided much enlightenment. Another problem is that the theory

A tribute to Arthur Charlesby vii

is often applied using data at high doses where the chemical composition of the polymer is altered enough to invalidate the assumption of constant yield. Thus, the theory is, in essence, limited to linear long chain polymers in the amorphous state treated with low doses in dynamic vacuum. However, it has proved to have Far greater usefulness. Even for the irradiation of semicrystalline polymers with branching and end-group complications, the theory provides a handy method of summarizing the data and providing a semi-quantitative insight for making modifications in irradiation conditions to bring about desired changes in polymer properties. Hundreds of papers have been published attesting to the practical value of Charlesby’s approach in systems where its application is not firm. does not yield “true” G values.

Charlesby is also an early and prolific contributor in such chemical matters as radiation-induced ionic polymerization, graft polymerization and sensitization of crosslinking. Chemistry is an area that should be off-limits to physicists. They almost always make a botch of it. Enrico Fermi won a Nobel Prize in Physics for reporting that the slow neutron cffcct on uranium was to produce transuranic nuclides, all of which turned out to be fission products. Professor Charlesby’s encounters with matters chemical have been more felicitous.

The characterization of networks and the measurement of their properties has been a substantial interest from his earliest days in polymer research. Direct measurement of crosslink in gelled systems is yet to be accomplished. But indirect measurements obtained from static elastic properties. gel fraction and solvent studies, as well a thermomechanical. rhcological and NMR methods have been applied, all based on assumptions relating to elastomers with ideal behavior. Charlesby has written and lectured extensively on this matter. He continues to produce stimulating articles on the pulsed NMR technique. He has demonstrated it to be a simple and powerful method and it is surprising that it has failed to take hold.

Although radiation and polymer science is the area of his recognized accomplishments. it is the wave-particle picture of matter, spaceetimc relationships and quantum mechanics which combine to form his principal current interest. The equations of relativistic quantum mechanics yield real solutions of motion for an electron with the peculiar property of a negative kinetic energy. This is equivalent to a positive electron with a positive kinetic energy. The subsequent discovery of the positron had the physicists breathing a sigh of relief. Young Charlesby was inspired by all of this to develop a novel concept of the photon as consisting of two particles: the usual electron with its negative charge and a new anti-particle, a positive electron with a negative mass. His article in N~rure describes how this model fits the properties of light including the photoelectric effect, spin properties, etc. This intriguing proposal seems to have been ignored.

In recent years, he has taken dead aim at the prevailing model of quantum mechanics. There is no doubt of the triumph of the model in its ability to fit measurements and to predict new phenomena with unexcelled accuracy. However, its current form appears to deny causality to anything other than the wave function. It requires the acceptance of apparently bizarre concepts as. in one hypothetical experiment. an unobserved cat being simultaneously half-dead and half-alive until the moment of actual observation. There is the Be-Quiet-and-Calculate group which considers quantum mechanics as a handy set of rules. for finding out things-nothing more. Then there is the Who-Can-Possibly-Accept-Such-Rubbish-as-Fund~~~llent~~l-TrL~tll group to which Einstein belonged and in which Charlesby is an active mcmbcr. Einstein. Podolsky and Rosen proposed experiments which they expected would falsify the “new ” mechanics. The results are in and are contrary to their expectations. Charlesby’s approach is based on some “comtnonscnsical” concepts which would preserve causality for all observablcs. In articles published in this journal. he has described an original and remarkably simple model of quantized spaceetime. The model lcads directly to the Heisenberg uncertainty principle, the Schroedinger equation and other related matters without requiring the existence of an observer to detcrminc the fate of an unobserved object. It is fascinating work and. if it ever gets the attention it appears to merit. may establish the name Charlesby as one of the major scicntihc figures of our time.

NO tribute to Professor Charlesby would be complete without rcfcrcncc to his personal qualities. In appearance, he is a character out of Dickens. Some twenty years ago, I sent two graduate students to meet him at Union Station in Washington. D.C. They asked for his description. I provided none. assuring them that none was needed. They spotted him at once. There he was. a stocky, chubby-checked. twinkly-eyed man arrayed in rumpled tweeds and a cap, and carrying somehow four pieces of luggage. a camera slung over his shoulder and a small Dutch cigar in his smiling face. The same vision has appeared many times in my lab. minus luggage, camera and cap. (The cap is rarely seen and the hair beneath it has long been contined to a curly tonsure: neither pipe nor cigar have been spotted of late.) He spent more than a year with mc at Maryland and I had the privilege of a five-month visit with him at Shrivenham. Those were heady times we shared, both personally and professionally. He is wonderful company, witty and widely read with an inexhaustible fund of stories and penetrating comments on political and cultural matters throughout the world.

Now approaching the end of his eighth decade, Professor Charlesby has relinquished his editorial responsibility for Radiation P/~~v,sics und Chemistr~~. He is now Emeritus Editor-in-Chief. We are profoundly

wn A tribute to Arthur Charlesby

grateful to him for all he has done for Radiarion Physics and Chemistry and for science, and can expect more. John Hubbell and Arne Miller have succeeded him and now share the awesome task of continuing and extending the fine record compiled by their distinguished predecessor. They have our best wishes and our pledge to assist them in their efforts.

JOSEPHSILVERMAN

CURRICULUM VITAE (SUMMARY)

ARTHUR CHARLESBY D.Sc., F. Inst. P., Ph.D., D.I.C., A.R.C.S. Emeritus Professor

Born 12 October 1915 London, Educated London; French section, Royal Atheneum, Antwerp, Belgium. Engineering: City University, London. Physics: Royal Scholar, Imperial College of Science and Technology. 1st Class Honours Governors Prizeman 1937.

B.Sc. (1st Class Hnrs; A.R.C.S.) Research Student, Electron Diffraction, Imperial College Ph.D 1939, D.I.C. Post-graduate Polymer Research. Special War Duties to 1942. Ministry of Supply Research to 1943. Squadron Leader, Volunteer Overseas Duties, Royal Air Force, Mediterranean H.Q.; Special Duties, Mentioned in

Despatches, to 1945. Principal Scientific Officer, Air Traffic Planning to 1948. Chief-Scientific Officer, planning Berlin AirLif< Germany to 1949. Atomic Energy Research Establishment, Harwell. Head Radiation Effects Section. Effects in metals. surface reactions.

polymer m:dification including crosslinking (original patents on crosslinking of polyethylene, rubber, memory effect etc), biological effects.

Head Nuclear Research Department, Hinxton Hall, Cambridge. Professor of Physics, Head of Physics Department, Royal Military College of Science (part-time University of London)

to retirement 1977. Distinguished Visiting Professor at several Universities, including Brussels, Maryland. Chairman or Main Speaker at many international conferences; also specially invited speaker or consultant. Lecturer and Adviser at Advanced Courses Overseas. Adviser on behalf of International Atomic Energy Agency, etc. Committee member or Chairman of Scientific Societies. Editor in Chief: Radiation Physics and Chemistry. Marie Curie Medal 1989; Doctor Honoris Causa 1990. Author: Atomic Radiafion and Polymers translated into four languages; some 250 scientific papers published.