Extract from Bill Fox's Departmental History

[Text in RED indicates revisions made under the HEP History project]

Department of Physics: 1950-72

Massey was the unanimous choice to succeed Andrade in the Quain chair. Before accepting the offer, he satisfied himself on two counts, namely the possibility of co-operation with A.E.R.E., Harwell, whose Director was Sir John Cockcroft, involving its accelerator facilities, and the recruitment of H. S. Tomlinson to develop the technical services and to look after the equipment and use of the research space to be provided in the New Block, the first stage of the College's plan for development of the department. Tomlinson had worked with him and Burhop at Berkeley and was then at A.E.R.E., Harwell. To avoid any problems with the existing senior technical staff, a position of the right seniority for Tomlinson was found by the creation of a new post on the academic staff with the title of Assistant. Burhop, Buckingham and Bates came over with Massey as Readers, Burhop filling the established readership vacated by King, and two more established readerships being created for the other two. Gunn had resigned from the Mathematics department in February 1948 on his appointment as Professor of Theoretical Physics at Glasgow University. L. Castillejo, T. C. Griffith, and M. J. Seaton became Assistant Lecturers, Castillejo and Seaton having been research students, and Griffith an experimental assistant in the Mathematics department; incidentally Seaton having served as a navigator in the Pathfinder Force of Bomber Command, joined the Physics Department in 1946, graduated with first-class honours in 1948, only to transfer to the Mathematics Department as a postgraduate student working on certain reaction rates applicable to astrophysical and geophysical problems under Bates. Another appointment as Assistant Lecturer was F. F. Heymann, a South African electrical engineer, who had been working on the development of an experimental 22 MeV Betatron at Metropolitan-Vickers Electrical Co. Ltd., Manchester. Boyd and Hasted having been awarded I.C.I. Fellowships, transferred to the department in these roles, and M. J. Bernal and P. Swan were appointed as D.S.I.R. research assistants to Massey. Two of the research students changing departments were A. Dalgarno and B. L. Moiseiwitsch, who were completing their Ph.D courses. Mr. J. Baserga, who had run the workshop in the Mathematics Department, also came over to set up another workshop in the Department. Massey's friendly reception of the old departmental staff can be illustrated by the author's experience; having received an invitation to go to the R. I. with Andrade, financed by the British Rayon Research Association, Massey made it quite clear that he would welcome his staying on in the department.
Massey and his accompanying staff soon settled down in the makeshift accommodation of the department. A vigorous programme was initiated of theoretical and experimental research on many aspects of the physics of collisions both at low and high energies. This involved collision processes in gas discharges, slow collisions of atoms and ions, basic optical excitation processes, and the measurement of concentrations of atomic hydrogen by micro-calorimetry with the view to its application in the determination of cross-sections operative in certain electron-atom collisions. A 20 MeV electron synchrotron was generously loaned by Sir John Crockcroft and erected in the department. Construction began on a 4.5 MeV microton, two high-pressure cloud chambers to operate at 100 atm., and a magnetic lens to focus electrons of energy up to 4 MeV. In the first session there was a marked increase in the number of postgraduate students, there being 29 reading for higher degrees. Special lecture courses for these students were given in radiation theory, theory of spectra, nuclear physics, and atomic collision phenomena. In addition seminars in nuclear physics, and electronic and ionic physics were held regularly throughout the session. A very successful conference on the Dynamics of Ionized Media was held in the department during March, it being attended by 100 people from England and the Continent. Massey gave three lectures per week throughout the session on modern physics to the third-year students and several members of the old departmental staff, including the author, attended them. An alternative Part II course on Mathematical Physics was introduced and students opting for this course sat a Part II special, six-hour, theoretical problem paper. In addition to Massey's lectures, third-year students attended three lectures per week on selected topics in either experimental or mathematical physics according to their specialized Part II option. David Bates resigned at the end of the session on his appointment to the Chair of Applied Mathematics in Queen's University, Belfast. 1951-52 saw progress on all fronts; the laboratory was chosen as one of the four to receive support from the Warren Research Fund of the Royal Society in connection with research in the physics of electrical discharges; and a special meeting of the Physical Society on nuclear physics was held in the large theatre, all the papers being contributed by members of the department.
The 1952-57 quinquennium saw the start of work, in collaboration with Dr. G. R. Evans of the University of Edinburgh, on the nature of particles produced by cosmic rays interacting in the earth's atmosphere, observations being taken in a high-pressure cloud chamber on Mt. Marmolada in the Dolomites: grants to assist this work were made by the D.S.I.R. and the Central London Research Fund. Progress in ionic physics was reported at a three-day conference, held in the department in April 1953, for the university physics teams, whose research in this field was financed by the Warren Research Fund. May 1953 brought the offer of rockets from the Ministry of Supply for scientific research, and in June 1953 the deuterium filled, high-pressure cloud chamber was operated continuously in connection with the 150 Mev proton source available from the A.E.R.E., Harwell synchrotron. The new Physics Wing, the first stage in the provision of permanent facilities for the department, was occupied before the end of the 1953-54 session, and despite the disorganization associated with the transfer of complicated apparatus from one site to another, research continued to develop on existing lines. A grant was made by the U. G. C. for Dr. A. D. Booth of Birkbeck College to make a copy of his electronic computer for installation in the department.
On 4 May 1955 the formal opening of the new Wing by Sir James Chadwick took place in the presence of some 450 guests from industrial firms, scientific institutions, colleges and schools. The guests were received by the Provost, and, after tea in the Housman and Haldane Rooms, Sir James delivered an address in the North Cloisters. They were conducted in parties round the new wing during the course of the afternoon and evening. To mark the occasion, there appeared, in Nature, Vol.175, p.1069, 1955, a description of the new Wing, including its facilities for teaching and research, and some account of the research being carried out in the department. The Wing, which had six floors, was designed by Prof. A.E. Richardson and built by Messrs. Dove Bros. Ltd. Three of the six floors were devoted to teaching laboratories, each of which occupied a floor space of 4,600 sq. ft., containing some sixty or seventy student benches and including dark rooms for optical experiments, apparatus stores and technicians' rooms; in addition there were photographic dark rooms, a balance room, and workshop facilities for undergraduate use. The research facilities were housed on the lower ground, the ground and fourth floors. The lower ground floor had a ceiling 16.5 ft. high, the greater part of the floor being occupied by the electron accelerator laboratory, which extended along the whole length of the floor and over about two-thirds of the width. An overhead travelling crane ran the full length of the laboratory. This floor also housed a store, glass-blowing shop, dark rooms, a spectroscopy laboratory, and a room for storing and handling small quantities of radioactive isotopes. The ground floor contained a number of staff rooms and offices, but research laboratories comprised its greater part. The top floor contained rooms for staff and for research students working in theoretical physics, the departmental library, the computing laboratory, and a small lecture theatre.
During the 1955-56 session the development of instruments for use in rockets for upper atmospheric research proceeded intensively and preliminary launching trials were carried out at the artillery range at Shoeburyness. The bubble chamber group took off after Cyril Dodd returned from his five-month visit to leading U.S.A. laboratories working in the field. A new project involving co-operation with the University of Bristol was the study of nuclear emulsions exposed to the meson beam from the Bevatron at Berkeley, California. The Booth computer was installed in the department and operated to good effect. W.E. Duncanson left in 1956 to become Principal of the Kumasi College of Technology in the Gold Coast.
The 1957-62 quinquennium saw the department participating in a special Royal Society soiree to celebrate the opening of the International Geophysical Year, 1957-58, by exhibiting instruments for use in the programme of upper atmospheric research and demonstrating the techniques. Arrangements were made for a collaboration between A.E.R.E., Harwell and the department to send a joint team to C.E.R.N., Geneva to work on two experiments involving the first C.E.R.N. accelerator, the 600 MeV synchrocyclotron. This enabled departmental staff to participate in experimental work overseas in addition to carrying out their share of undergraduate teaching. A large D.S.I.R. grant of £22,000 for three years from August 1957 allowed the recruitment of technical staff and a research assistant, who were able to be based at C.E.R.N. "This, together with the developments in Space Research, was the beginning of the era of 'big physics' at U.C.L. The pattern of research became atomic and theoretical physics 'in house' and space research and high-energy physics split between planning, instrument development and data analysis at home, and experiments carried out with major facilities outside the college, largely abroad." (B.B.D.). The first experiments in the programme of upper atmospheric research, using equipment in the Ministry of Supply's rocket, 'Skylark', were carried out at Woomera, Australia, in November 1957. The College allowed staff to be absent on projects in term time provided satisfactory arrangements were made for their teaching duties. In fact Massey had an arrangement with the Provost, Sir Ifor Evans, that certain areas of the world were designated as parts of the College so that staff going there for their research were not regarded as requiring leave. A new microton started to operate, providing electrons of energy 28 MeV, and a 500 keV van der Graaf accelerator was largely constructed and awaiting installation in the new laboratories to be provided in the former Seamen's Hospital at 25 Gordon Street. Plans were made to work on the 50 Mev proton linear accelerator, which was destined to be the first piece of equipment operated by the new National Institute for Research in Nuclear Science. 1958 saw the award of Royal Medal of the Royal Society to Massey to accompany the Hughes Medal awarded to him in 1955. In 1959 the conversion of the Seamen's Hospital was completed, providing sufficient accommodation for the department to relinquish most of its territory in the central block of the College; this year also saw the start of a major design study of a large propane bubble chamber with N.I.R.N.S. support, the engineering team being led by Tomlinson and the physicists by Henderson. In 1957 R.A. Buckingham was made Director of the University of London Computational Unit; and L. Castillejo joined Prof. R.E. Peierls in the Theoretical Physics Department at Birmingham University, being replaced by S. Zienau, formerly an honorary research assistant. 1960 saw Massey created a Knight Bachelor in the Queen's Birthday Honours. A second chair of physics was established in that year and filled by a former Queen's University student of Massey's, namely J. Hamilton, an expert in theoretical high-energy physics, and at the same time the title of professor was conferred on Eric Burhop.
In 1962 planning began on an extension of the Physics Wing, the second stage of the building programme envisaged for the department in the College rebuilding plans. D.G. Davis, an old student, who had been appointed in 1960 as a lecturer with special responsibilities for administration instead of teaching, was concerned with the detailed plans. On asking Massey how he wanted the planning carried out, he recalls Massey remarking "that all the postwar developments of the department could not have been forseen more than a couple of years before they occurred and that the prime requirement of the new building was flexibility". No big research laboratory was required, since large equipment would be used in shared national or international centres. A 'loose-fit' philosophy was to be adopted, with laboratories planned roughly right for a variety of possible users, a well equipped workshop forming a central part of the development. "Massey's approach to the building was like his organization of the Department essentially pragmatic. There was no grand plan, rather a series of steps building on existing strengths, with a bias towards the more fundamental, and a strong technical base for development of new experimental techniques". (B.B.D.).
On 26 April 1962 the first British satellite, named Ariel 1 on its establishment in orbit, was launched by a Thor-Delta rocket from Cape Canaveral; five of the seven experiments aboard were the responsibility of the U.C.L. group, four being successful and continuing to provide results up to November 1964. A discussion meeting on the results then obtained was held at the Royal Society on 2 and 3 May 1963 under Massey's chairmanship. There being no opportunity to expand its space research on the College rectangle, the department sought external benefactions for the provision of an additional laboratory outside London. The Mullard Company made provision for a gift of £65,000 in 1964 and this accounted for some three-quarters of the cost of buying and adapting Holmbury House, a country mansion at Holmbury St. Mary, near Dorking. About one-fifth of the academic staff of the department, together with their technical support staff, equipment, etc., was moved to the so-called Mullard Space Science Laboratory (M.S.S.L.), which came into full use in October 1966 and was formally opened on 3 May 1967 under Boyd's directorship. The group, the largest space science research group in Britain, had embarked on a major programme involving experiments on eight satellites and over thirty sounding rockets, the main fields of investigation being in ultra-violet and X-ray astronomy of the sun and other celestial objects, and the study of the ionosphere, the magnetoshere and the interplanetary medium.
Burhop spent the 1962-63 session at C.E.R.N., serving as secretary of the Amaldi Committee appointed to study and report on the future policy for accelerators in Europe. Its report was adopted by the European Committee for Future Accelerators as providing the policy for accelerator developments during the next 15 years; both the recommended machines, the Intersecting Storage Rings and the Super Proton Synchrotron, were subsequently built and formed the backbone of high energy physics in Europe until the eighties. In 1963 he was elected to the Fellowship of the Royal Society for his work in atomic and particle physics. It was in that year that he proposed that by combining spark chamber and emulsion techniques it would be possible to locate rare neutrino interactions in an emulsion enabling very short-lived particles to be detected. The U.C.L. Spark Chamber and Emulsion Groups were involved in establishing the viability of the method in 1964. However it aroused little interest for almost ten years until the discovery of weak neutral currents and the possibility of unified theories gave a renewed impetus to the search for new quark flavours, in particular, charm. As a consequence Burhop and others suggested the experiment, E247, which was supported by the Director of Fermilab and ran during 1975-76 in the wide band neutrino beam there, successfully locating 37 neutrino interactions in emulsion, from one of which a very good candidate for a charged charmed particle was seen to emerge.
The academic staff numbered 28 at the start of the 1962-63 session; there were 3 Professors, Massey, Burhop and Hamilton; 7 Readers, Gibbs, Boyd, G.B. Brown, Dodd, Hasted, Heymann and Seaton; 2 Senior Lecturers, R.C. Brown and Jennings; 15 lecturers, Aitken, Davis, M.J.B. Duff, Fox, Gilbody, Griffith, Groves, Heddle, Henderson, Heyland, Rand, Stannard, Willmore, Zienau and P.W. Roberts, an old student, who was also the College Adviser on Protection against Radiation Hazards; and 1 Assistant, Tomlinson. The Calendar for the 1962-63 Session also listed on the research side 12 Temporary Research Assistants, 5 Honorary Research Associates and 19 Honorary Research Assistants. Senior promotions soon followed, namely, Boyd and Seaton, Professors by conferment of title in 1963; Groves and Willmore, established Readerships, Heddle, Henderson and Jennings, Readerships by conferment of title in 1964; and Griffith and Zienau, Readerships by conferment of title in 1965. In October 1965 R.F. Stebbings returned from America to fill an established readership specially created for someone of experience and distinction in the field of experimental physics. Hamilton left in 1964 for a Professorship at the Nordic Institute for Theoretical Physics, Copenhagen, and Heddle went to a Readership at the new University of York. Castillejo returned from Oxford (where he had gone with Peierls in 1963) in January 1967 to fill the established Chair, which had remained vacant since Hamilton's departure. Meanwhile Heymann had been appointed Professor by conferment of title. The first appointments of Visiting Professors to the College was made in the 1967-68 session to establish a close academic association with persons of distinction working in research institutions and elsewhere outside the College. Dr. J.A. Saxton, Director of the Radio and Space Research Station, S.R.C., Slough, became the first such Professor in the Department. 1967 saw the election of Seaton to the Fellowship of the Royal Society for his contributions to atomic physics and astrophysics, and the departure of Henderson for a Senior Lectureship in the Department of Natural Philosophy, University of Aberdeen; in 1968 Hasted took up the Chair of Experimental Physics and the Headship of the Department at Birkbeck College, but retained his leadership of that part of his Ionic and Electronic Physics Research Group remaining behind; and Willmore and Groves were appointed Professors by conferment of title in 1968 and 1969 respectively. Boyd was made a Fellow of the Royal Society in 1969 for his contributions to ionospheric physics, and X-ray and ultra-violet astronomy, and to the exploitation of space science techniques in these fields. Then in 1972 both D.H. Davis and A.C.H. Smith were appointed Readers by conferment of title.
After the acceptance of the Robbins Report by the Government in late 1963, some expansion of the Department was planned to increase the maximum intake of undergraduates from 48 to 60 and the academic staff was increased by four lecturers. The first Departmental Tutor was appointed in 1963, Dodd assuming that office. In January 1965 the Secretary of State for Education and Science set up a Council for Science Policy, with Massey as Chairman, to advise him on the exercise of his responsibilities for civil science policy.
Gibbs retired at the end of September 1965, fifty years after his entry to the College as a potential engineer; he transferred to physics one year later. His studies were interrupted in May 1917 when he went to the Admiralty Experimental Station at Harwich to work on anti-submarine measures with Rankine and Bragg. Returning to the College in the second term of the 1918-19 session, he graduated with first-class honours in 1920, and was awarded the M.Sc. degree in 1923 for his research work. When Sir William Bragg went to the Royal Institution in 1923, Gibbs and other members of his research team accompanied him. Gibbs worked on X-ray crystallography, carrying out an investigation of the lower members of the fatty acid series, and becoming an authority on the structure and properties of quartz. He returned to College as a Research Assistant in 1927, became a Lecturer in 1931, and a Reader in 1936. From 1939-45 he worked at the Royal Aircraft Establishment, Farnborough, one project involving collaboration with Uffa Fox on the airborne lifeboat. He was responsible for Harold Billet joining the College after the war, Billet later becoming Professor of Mechanical Engineering, Vice-Provost, and then Acting Provost in the 1978-79 session between the departure of Lord Annan and the arrival of Sir James Lighthill. Gibbs was Acting Head of the Department during the second and third terms of 1950; then from 1950-65 he was in charge of the undergraduate laboratories, formerly as Superintendent and latterly as Deputy Director. During this period he lectured on modern physics to the second-year special physics students. In 1952 he succeeded Orson Wood as Sub-Dean of the Faculty of Science and Tutor to Science Students, carrying out those arduous duties for thirteen years with his characteristic quiet efficiency, giving his time and attention unsparingly to a countless number of students, many of whom remember his help most gratefully. He served on the Professorial Board from 1935-39 and 1957-65, and on the College Committee from 1949-54. At the University his services included membership of the Senate, Academic Council, Finance and General Purposes Committee, Vice-Deanship of the Faculty of Science, and Chairmanship of the Board of Studies in Physics. He was made a Fellow of the College in 1962. Gibbs was succeeded by Dodd as Sub-Dean and Faculty Tutor, the author taking over the Departmental Tutorship.
G.B. Brown retired at the end of September, 1966, having been a member of the Department for forty years. He joined the Department as an Assistant, having graduated at Manchester University in 1924, and worked as a Research Assistant to Professor W.L. Bragg on the structure of certain silicates, gaining the M.Sc. degree in 1925. He became a Lecturer in 1931 and Reader in 1946. His fine experimental work in acoustics on sensitive flames and edge tones received general recognition, being extensively cited in modern text books, e.g., Acoustics by Alexander Wood. His book on "Science; its Method and its Philosophy", published by Allen and Unwin in 1950, and his later writings on the historical and philosophical aspects of science attracted considerable interest. 'G.B.' gave regular courses of lectures to general and special students, in particular the special lectures on classical electricity and magnetism, and finally those on properties of matter; he regularly demonstrated in the undergraduate laboratories. In 1982 he had published his "Retarded Action-at-a-Distance: The Change of Force with Motion" by Cortney Publications Luton.
The following year saw the retirements of E.C. Rowe and R.J. Fisher. Rowe joined the department in April 1922 to take over Byron's duties in the laboratories, having previously spent five years in the instrument shop of Johnson and Phillips and three years with the Dictograph Telephone Co. In 1935 he was awarded the Diploma in Laboratory Arts, then introduced by the Institute of Physics, and in 1947 he became a Founder Member of the Institute of Science Technology. Rowe's work during the Bangor evacuation, including the establishment of the laboratory in the High Street, has been described earlier; however reference is again made to the photograph of him standing at the door of his partitioned room in the corner of that laboratory, (H.&N. 349:188). He became a Chief Technician in 1950 and a Principal Technician in 1960. When the College decided in 1962 that one senior member of the laboratory staff in each department should be appointed as Head, Rowe became the first Laboratory Superintendent in the Department. Countless students remember gratefully the help given to them in the laboratory by Ted Rowe.
Fisher joined the workshop of the department in October 1923, filling a vacancy left when Jenkinson went to the R.I. with Sir William Bragg. He served under W. Fox, who succeeded Jenkinson as Chief Mechanic in May 1924, until Fox's retirement in July, 1937; and under E.J. Faulkener, Fox's successor, from September 1937 until 1957, with the exception of the war years, when both of them were seconded to the Ministry of Supply Inspectorate. In 1957 Fisher succeeded Faulkener as Technical Officer in charge of the large workshop, then housed in the old basement laboratory, employing some dozen skilled technicians engaged on the construction of apparatus and instruments required by the research groups working in atomic, nuclear and space physics. Fisher was a skilled craftsman and he took a great interest in the work of the Physical Society to encourage apprentice instrument makers, becoming the Senior Judge in the Class 1 (Instrument) competition held for them at the time of the Annual Exhibition. His long distinguished service was greatly valued by the department. Fisher was succeeded by J.E. Pitcher from A.W.R.E., Aldermaston, who was responsible for equipment of the new workshop housed in the old electron accelerator laboratory.
In 1966 the University introduced a new B.Sc. degree structure enabling certain Colleges of the University to offer College-based courses extending over three years. This was particularly welcomed by the Biological Science Departments since it enabled their students to select suitable combinations of courses and to defer their choice of specialist subject or combination of subjects until the end of their first year of study. The Department rather reluctantly had to adopt the course-unit system, but insisted upon its main-stream physics students following a common course structure directed towards their becoming professional physicists. The introduction of the new structure made heavy demands on the Faculty with the result of Dodd becoming employed full-time therein. Burhop assumed his three-year Deanship of the Faculty in 1967, so the Department played a prominent part in the administration of the new-degree structure. A new joint degree course in Chemistry and Physics was introduced in 1969 for a small entry of well qualified candidates and this was followed by the introduction of an Applied Physics degree course in 1970.
In the mid-sixties Massey realised that developments in the manufacture of plastic film for balloons were making it possible to carry instruments to altitudes where the absorbing effect of water vapour was negligible. Thus in 1966 he started an Infra-Red Astronomy Group to make observations in the far infra-red, the only part of the spectrum in which modern astronomical observations were not being made. Jennings and Aitken were turning their interests from high-energy physics towards infra-red astronomy, and Tomlinson and some of his bubble chamber design team were becoming available for a new project - a stabilized balloon-borne gondola carrying a 40cm. telescope, which was first flown at Mildura, Australia in 1970; hence it was a propitious time for the formation of the new group. Towards the end of the decade there was another development in astronomy, this time in the optical region, when Boksenberg conceived a new approach to astronomical detection, namely, the Image Photon Counting System for the observation of very faint extragalactic objects; this was developed with S.R.C. funding and used on the Palomar 200-inch telescope with great success towards the end of 1973.
In 1967 Burhop had taken over the leadership of the Bubble Chamber Group and soon realized the advantage of large heavy liquid chambers in studying neutrino interactions. He directed the activities of the Group towards participation in a research programme set up in conjunction with a number of European Bubble Chamber Laboratories using the Gargamelle Chamber at C.E.R.N. This proved very successful establishing in particular the existence of weak neutral currents which was of great significance for the development of unified electromagnetic and weak interactions.
Massey had an abiding interest in positrons and positronium and for some years had been anxious to develop an experimental programme on positrons in gases. Following his attendance at the first conference on positron annihilation, organized by Stewart and Roellig at Detroit in July 1965, he began to look around for colleagues to realise his objective. The experimental research programme involving the 50 MeV Proton Linear Accelerator at Harwell with measurements of the polarization parameters in double and triple scattering of nucleons by protons was being completed. This, together with the availability of radioactive positron sources, led Massey to suggest to Griffith that he should turn his attention to experiments with slow positrons. Moreover he persuaded Heyland, an electronics expert, who had devoted his time in running the third-year undergraduate laboratory, to join Griffith in forming the Positron Physics Group in 1968. The Group got off to a good start with Roellig spending a sabbatical year with it and Canter, who had worked with Roellig on positron annihilation in helium at low temperatures, joining it the following year.
To mark Massey's 60th birthday in 1968 some 120 of his friends, colleagues and former students contributed to the commissioning of his portrait by Claude Rogers, and some 20 of them also contributed to a Festschrift volume of 'Advances in Atomic and Molecular Physics', and donated the royalties to the portrait fund. The presentation of the portrait to Sir Harrie by Prof. P.M.S. Blackett, P.R.S. was witnessed by some 160 diners assembled on 3 December 1968 for the Physics Department Dinner, presided over by the Provost, Lord Annan. In 1969 Massey's term of office as Chairman of the Council for Science Policy ceased, but he took on new responsibilities, namely Physical Secretary and Vice-President of the Royal Society, and Vice-Provost of the College, and in 1970 he became the Royal Society assessor on both the Astronomy and Space Policy and Grants Committees of the S.R.C. Astronomy, Space and Radio Board.
At the beginning of the quinquennium in 1962 ten former D.S.I.R. supported research projects, mainly in atomic and nuclear physics, were taken over by the University Grants Committee, an earmarked sum of £30,555 p.a. being added by the U.G.C. to the University Court grant to the College in the financial year 1962/63 for that purpose. In August 1967 the earmarking ceased and was assimilated into the normal College budget at the rate of £47,500 p.a providing posts for 22 of the research staff involved, 10 being tenured lectureships; there was also approximately half the cost of another lectureship, and £5000 was added to the departmental grant. In 1967 a second transfer of support for research work from the Research Councils to the U.G.C. was agreed; this time the arrangements were very closely scrutinised by all parties as the Treasury insisted on reducing the budgets of the Research Councils by exactly the amount by which the U.G.C. budget was increased. Four of the department's big science programmes were taken over, two in high energy physics and two in space research; the transfer funds were again earmarked for the five years of the quinquennium, 1967-72, after which they were to be assimilated in the normal College block grant of U.G.C. support from the University Court. In August 1972 the assimilation provided for 38 posts, including 8 lectureships, with £20,562 added to the departmental grant, at a cost of £106,000 p.a.
The Department suffered a great loss in the death of Harry Tomlinson on 5 February 1971; the College Report for 1970-71 described him as "one of the most effective and original designers of scientific instruments in the country" and acknowledged "the outstanding value of his work in the Department". It recalled that "For a number of years he was fully engaged in the development by the Department of a Heavy Liquid Bubble Chamber for the National Institute for Research in Nuclear Science. Recently he had been responsible for the design and construction of a controllable telescope to be carried on balloons for infra-red astronomy". The Department issued its own Harry Tomlinson obituary booklet, with contributions from Massey, Towlson and Venis, covering the man and his work for the Department on Cloud Chambers, The Bubble Chamber and Balloon Platforms.
August 1972 saw the resignation of Willmore to take up the Chair and the Headship of Space Research in the University of Birmingham. After rejoining the Department from A.E.R.E., Harwell in 1957, he played a prominent part in the space science programme, becoming deputy leader of the largest research group in the Department. The Copernicus satellite, launched on 27 August 1972, four days before Willmore's departure, carried the group's grazing incidence parabolic reflectors, with proportional counters at the foci, as an auxiliary experiment to the main ultra-violet observing system. The design of the system had been undertaken before the existence of observable cosmic X-ray sources had been established and the proposal to include it in the payload of this, the third U.S. orbiting, satellite had been accepted in 1963. By good fortune the long delay of the launch of the satellite took place at a most opportune time, as will be made clear later.
In the 1967-72 quinquennium the U.G.C. for the first time had asked the College specifically to spend extra in certain indicated areas, of which physics was one. However the quinquennial grant, finally announced in January 1968, was too small even to cover existing commitments. It heralded a gloomy policy of general economy, the College being forced carefully to scrutinise all its expenditure. In October 1969 the Provost, Lord Annan, actually wrote to Massey about the possibility of achieving a 6% reduction in staff numbers and in July 1971 he met the Professors of Physics and Chemistry to explain why enquiry should be made into the expenditures of two of the largest and most expensive departments in College. Then in 1973 five Committees were set up to look into the level of resources of these two Departments, the School of Environmental Studies, the Slade School, and the Library.

Department of Physics and Astronomy: 1972-75

A Department of Astronomy was formed in College in 1951 when C. W. Allen was appointed to the newly-created Perren Chair of Astronomy, provided by an endowment under the will of Mr. F. Perren. The Court of the University having decided that responsibility for the direction of the University Observatory at Mill Hill should be transferred to the College from 1st. August 1951, the new Professor also became Director of the Observatory, and responsibility for the Observatory was formally transferred to the College at the beginning of the 1952-57 quinquennium. Previously Allen had been the Principal Assistant at the Commonwealth Observatory, Canberra (now the Mount Stromlo Observatory). At College he began the task of building up a first degree course in Astronomy - at that time the only one in England and Wales. Allen played a leading part in British astronomy and continued his researches in solar and laboratory astrophysics. His best known work was his volume of critical astrophysical data, 'Astrophysical Quantities', first published in 1955 and about to appear in a third edition on his retirement in 1972.
In the summer of 1972 the Committee appointed by the Professorial Board to consider the steps to be taken on the retirement of Professor Allen reported and recommended that the two Departments of Physics and Astronomy be amalgamated from 1 October 1972; the Perren Chair be filled; and Professor Sir Harrie Massey be Head of the combined Department. Dr. R. Wilson, formerly Head of the Astrophysical Research Unit of the Science Research Council, Culham, was appointed Perren Professor of Astronomy and Director of the Observatory; he joined the new Department in January 1973, the old Astronomy academic staff - Drs. D. McNally (Assistant Director of the Observatory), W. B. Somerville (Tutor to Astronomy Students), J. E. Guest and D. R. Fawell, and Mr. E. W. Foster - having transferred in the previous October. Wilson was well known in the old department from the early sixties onwards firstly through his involvement in a programme of ultra-violet spectroscopy of the solar corona and the stars by rocket-bourne equipment, and then in the development of satellite ultra-violet astronomy, leading up to the realisation of the International Ultra-Violet Explorer satellite (I.U.E.). He had been the second Visiting Professor appointed in 1968.
The amalgamation of the two departments was very timely and even necessary in that Wilson was only prepared to accept the Perren chair on that basis; moreover it was fortunate to have occurred under the wise leadership of Massey. On the research side it brought together active groups in X-ray, ultra-violet, optical and infra-red astronomy, as well as in astrophysics and geophysics. On the teaching side it brought welcome relief to the management of the astronomy undergraduate entry which had leapt from 9 in 1969 to 23 in 1970 and was to reach 30 in 1975 owing to the popularity of the subject generated by the space programme.
R. C. Brown retired in 1973 having served the College for forty-seven years. He joined the Department of Physics as a Demonstrator in 1926, became an Assistant in 1928, a Lecturer in 1930 and a Senior Lecturer in 1945; in 1961 he succeeded Orson Wood as Careers Adviser, retaining his Senior Lectureship on a part-time basis. 'R. C'. was a valuable member of the department, being a very good teacher both in the lecture theatre and the laboratory. For many years he taught physics to 1st M. B. students and properties of matter at all levels; latterly he taught optics. His research was in the field of surface tension and he was an acknowledged authority on the subject. He wrote an excellent text-book of physics for Intermediate and 1st. M. B. (later A-level) students, and served as a Chief Examiner and Moderator for Advanced and Scholarship Level Physics for the London Board. He also served as Secretary of the Board of Studies in Physics. In College his membership of Committees included the Vice-Chairmanship of the Student Health Association Committee. His work as Careers Adviser extended over a period of rapid growth in student numbers and of incredible complications in the employment situation. Successive generations of students have had cause to be grateful to him for his humanity and understanding and for the range of knowledge and experience he brought to their careers problems. Departmental Tutors were also grateful to him for the confidential notes on their third-year students which he issued to them.
E. W. Foster also retired in 1973, having joined the Department of Astronomy in 1953 after various research appointments elsewhere. His experience and high standards in spectroscopy and experimental physics enabled him to make considerable contributions to the measurement of fundamental spectroscopic quantities of astrophysical importance. His teaching in astrophysics and molecular spectroscopy was greatly valued.
The titles of Reader were conferred on Wilkin and Bullock in 1973 and 1974 respectively. On 30 September 1974 the first students were admitted for the new joint Astronomy and Physics degree. In 1975 Wilson was elected to the Fellowship of the Royal Society for his contributions to solar and general astronomy in the ultra-violet through the use of space vehicles.
C. A. R. Tayler retired at the end of July 1975, having joined the Department of Physics direct from school on 9 March 1925. On Friday, 7 March 1975, Massey had a luncheon party in the Whistler Room to mark the fiftieth anniversary of Tayler's appointment; Gibbs, R. C. Brown, and Brinsden from Botany (and Microbiology) also attended the luncheon. After some experience in the teaching and research laboratories, Tayler became Lecture Assistant in 1929; 1953 saw him assume the new grade of Senior Technician, with two assistants, and in 1958 he was promoted to become Chief Technician. When Rowe retired he was made Laboratory Superintendent, still being based in the theatres, but with many additional duties and responsibilities. In 1935 he was awarded the Institute of Physics Diploma in Laboratory Arts and in 1960 he was elected to the Fellowship of the Institute of Science Technology, becoming a Council Member for the next three years. Tayler was a skilled glass blower and an expert photographer, and was always ready to help members of staff or research student; his preparation of, and help with, lecture demonstrations were invaluable.
October 1974 was a significant month for the department. A new half course-unit structure for the degree courses offering greater flexibility was introduced. Massey started his last series of lectures, giving the ¹/₂ c.u. on Modern Physics and Astronomy to the Astronomy and joint Astronomy and Physics students, and Wilson started his first series, giving the ¹/₂ c.u. on Foundations of Modern Astronomy to the same students. The fifth U.K. satellite, the first to carry a cosmic X-ray scientific payload, was launched on 15 October 1974 as Ariel 5. It carried two M.S.S.L. instruments, a rotation collimator for the accurate positing of new sources and a multi-anode gas proportional counter for X-ray spectral measurements.
The 1974-75 Calendar listed the academic staff of the new department as follows:- Sir Harrie Massey, Quain Professor of Physics and Director of Laboratories; R. Wilson, Perren Professor of Astronomy; R. L. F. Boyd, E. H. S. Burhop, L. Castillejo, G. V. Groves, F. F. Heymann and M. J. Seaton, Professors of Physics; L. R. B. Elton, M. O. Robins and J. A. Saxton, Visiting Professors; F. W. Bullock, D. H. Davis, C. Dodd, T. C. Griffith, R. E. Jennings, A. C. H. Smith, C. Wilkin and S. Zienau, Readers in Physics; J. W. Fox, Senior Lecturer and Tutor; D. McNally, Senior Lecturer and Assistant Director of Observatory; D. G. Davis, E. B. Dorling and M. J. Esten, Senior Lecturers; W. B. Somerville, Lecturer and Tutor to Astronomy Students; J. McKenzie, Lecturer and Tutor to Physics students; D. K. Aitken, J. H. Bartley, A. Boksenberg, P. J. Bowen, J. A. Bowles, S. J. B. Corrigan, J. L. Culhane, B. G. Duff, M. J. B. Duff, M. M. Dworetsky, D. R. Fawell, W. M. Glencross, J. E. Guest, G. R. Heyland, J. W. Humberston, D. C. Imrie, T. W. Jones, G. J. Lush, B. R. C. Martin, A. J. Metheringham, D. J. Miller, D. L. Moores, W. R. Newell, K. Norman, J. H. Parkinson, T. J. Patrick, Gillian Peach, W. J. Raitt, D. Rees, P. W. Sandford, S. J. Sharrock, W. A. Towlson, T. E. Venis, D. A. Wray and G. L. Wrenn, Lecturers; P. W. Roberts, Lecturer and Adviser on Protection against Radiation Hazards; A. F. D. Scott, J. J. Todd and D. N. Tovee, Research Assistants; S. M. Fisher, Demonstrator; R. F. Berthelsdorf, P. J. N. Davison, A. D. Johnstone, A. C. Newton, F. D. Rosenberg and P. H. Sheather, Associate Research Fellows; K. G. R. Allen, W. Allison, K. Birkinshaw, J. C. Blades, D. J. Carnochan, D. H. Clark, C. I. Coleman, P. G. Coleman, A. M. Cruise, J. S. Dolby, I. Furniss, F. J. Hawkins, J. C. Ives, Barbara Jones, B. Kirkham, A. R. Malvern, Helen Mason, S. D. Pepper, M. K. Pidcock, C. G. Rapley, M.Salem, I. R. Tuohy, D. M. Watson and J. Zarnecki, Associate Research Assistants; A. H. Gabriel, Carole Jordan, R. P. W. McWhirter, H. Rishbeth and L. Thomas, Hon. Lecturers; Prof. P. H. Bodenheimer, Prof. R. A. Buckingham, J.-F. Germond, Prof. J. B. Hasted, D. G. Obsorne and Prof. F. R. Stannard, Hon. Research Fellows; J. D. Argyros, D. C. Black, J. A. R. Dubau, A. G. Michette, Hon. Research Assistants - a total of 111, the largest departmental academic staff in the College.

Departmental Resources

The College Report for 1973-74 was headed "Living in Deficit" and recorded that, anticipating trouble to come, five committees were set up in 1973 to look into the level of resources which should be allocated to the Departments of Physics and Astronomy, and Chemistry, the School of Environmental Studies, the Slade School, and the Library. The effect on College finances of successive cuts made by the Government in December 1973 and January 1974 was such that by October 1974 it was clear that if the College received no supplementation for inflation it could be running an annual deficit of over £400,000 at the end of the current financial year. This led the College Committee to take immediate measures to restrict expenditure in 1974-75 and outline policies to alleviate the worst effect of the shortfall in funds. These involved economies in administration, reduction of expenditure on academic staff by about 5% during 1975-77, and short-term provision for maintenance of buildings. Each Faculty set about identifying which posts and what expenditure could in the immediate future be curtailed in each Department. After intensive work the Deans were able to report that they could contemplate a target of £365,000 p.a. at October 1974 rates for reductions in staff establishments to be achieved by 1 August 1977. Departments were then asked to define their contributions to the overall target which would involve the least damage to academic commitments; they responded by indicating the suppression or down-grading of posts that were expected to fall vacant through retirement or resignation up to 1977. The Deans were required to monitor the agreed economies, flexibility being preserved by allowing equivalent substitutions; requests to fill vacant posts were to be referred to the Provost, who would consult the Vacancies Committee, the final arbiter, if necessary. In March 1975, while arrangements for the economy programme were being completed, it was announced that a Supplementary Grant of £548,000 had been allocated to the College, this sum being additional to earlier relief grants. The U.G.C. claimed that the total additional grants for 1974-75 approached 50% of the full cost of inflation, assuming that rate were to be about 20%; it warned that the revised grants for 1975-77 would be unlikely to enable making good any accumulated deficit at the end of 1974-75. Although the previously anticipated deficit was made good and £148,000 was allocated to academic departments, it was inevitable that the economies had to stand, no provision being made for additional posts.

Resources Survey of the Department

The ad hoc Committee, under the Chairmanship of Professor G. C. Drew, Dean of the Faculty of Science, was set up by the Professorial Board Executive Committee in November 1973 to review the resources in staff, space, equipment and finance available to the Department of Physics and Astronomy in relation to its academic activities; to report upon the extent of the current research activity supported by external grants, its relationship to the teaching programme, and the interdependence of the research groups concerned, together with an assessment of future continued external support for such activities; and to consider the situation arising from the retirement in 1975 of Sir Harrie Massey, and to make proposals. Members of the Committee were Professors H. Billet (Mechanical Engineering), A. L. Cullen (Electronic & Electrical Engineering), S. P. Datta (Biochemistry), A. G. Davies (Chemistry), C. A. Rogers (Mathematics), and D. M. Wilson ( Scandinavian Studies & Dean of the Faculty of Arts); Professors Boyd and Seaton, Dr. Davis and the author from the department.

Professor Massey presented the Committee with a comprehensive survey of the Department covering its history, geography, research, teaching, resources and problems. In his introductory section the Department was described as "a loosely integrated group of staff and students carrying out a variety of research and teaching activities in many areas of physics and astronomy... The objective ever since 1950 has been to encourage both research and teaching to the maximum extent possible within the limits of national policy on the provision of resources." The research was classified under four main groups, namely, Atomic and Molecular Physics, High Energy Physics, Astronomy and Space Research, and Image Processing, with a varying number of experimental and theoretical sub-groups in the first three, as follows:-

Atomic and Molecular Physics
Experimental:	Leader:
Ionic & Electronic Physics	Prof. J. B. Hasted
Atomic Physics	Dr. A. C. H. Smith
Positron Physics	Prof. H. S. W. Massey
Molecular Physics	Dr. S. J. B. Corrigan
Theoretical:
Atomic Physics & Astrophysics	Prof. M. J. Seaton
General Physics	Prof. H. S. W. Massey
High Energy Physics
Bubble Chamber & Emulsion	Prof. E. H. S. Burhop
Spark Chamber	Prof. F. F. Heymann
Theoretical	Prof. L. Castillejo
Astronomy and Space Research
Engineering & Balloon Platform Projects	Mr. T. E. Venis & Dr. W. A Towlson
University Observatory	Prof. R. Wilson
Infra-red Astronomy	Dr. R. E. Jennings
Ultra-violet Astronomy	Dr. A. Boksenberg
Mullard Space Science Laboratory	Prof. R. L. F. Boyd
Space Science & Atmospheric Structure	Prof. G. V. Groves
Image Processing	Dr. M. J. B. Duff

All groups provided statements summarizing their work in hand. The staff involved in the groups were 57 academic; 36 associate and honorary; 94 technical, 46 being grant paid; and 12 clerical, making a total of 199; in addition there were 65 research students. The Service Groups listed were:- Stores, Workshop, Graphics, Mechanical Design, Photographic and Glass Laboratory; these employed 28 technical staff, 5 being grant paid.
High Energy Physics and Astronomy and Space Research are in the big science area, requiring facilities beyond the capacity of any university or indeed, in many cases, of any country, to provide. It is national policy, described in detail by the Council for Scientific Policy in its "Report of a Study on the Support of Scientific Research in the Universities" (1971) that big science should be supported jointly by the U.G.C. and the Research Councils, the so-called dual support system. The Department's budget in 1973-74 was c.£1.29m of which some £822k came from U.G.C. funds and some £468k from outside grants, mainly from the Science Research Council. As indicated earlier, the high level of support from the College Block Grant is explicable in part by takeovers and transfers during the two quinquennia, 1962-67 and 1967-72. Thus in 1972-73 the Department estimated that £183,330 of the College block grant for that year was derived from the two quinquennial take-overs, resulting in an increase of staff paid from College funds of 18 full-time and half part-time lecturers, 2 research fellows, 7 research assistants of various grades, 29 technicians ranging from higher technical officers to machine operators, and 1 M3 secretary - 57 posts in all. The total departmental expenditure for academic purposes in that year was £1,158,568, the Research Councils and other non-UGC sources providing £477,160 and the College block grant from the University Court and from the earmarked provision for scientific equipment accounting for the remaining £681,408.
On investigation the departmental costs were found to be not badly out of line, in absolute terms, with those of five big science Physics Departments. However the swing from the physical sciences among candidates seeking admission to universities during the past decade had hit the department badly on the physics side; the entry to read physics dropped from 54 in 1968 to 24 in 1973, with a further 4 to read applied physics and 7 to read joint chemistry and physics; fortunately 22 were entered for the astronomy degree. The short-fall of the undergraduate entries for physics courses meant that the department in 1973-74 was significantly more expensive in terms of weighted per capita undergraduate student cost than the majority of other science-based subjects in College, and other comparable Physics Departments. It was however recognised by the Committee that per capita student cost was a quite inadequate criterion on which to base a judgement of the Department. The economies programme adopted by the Faculty of Science was based on a system of allocating to each Department a savings target based on the ratio of that Department's annual expenditure to that of the Faculty as a whole, modified by the ratio of the Departmental student unit cost to the Faculty mean unit cost; it therefore took account both of the absolute cost of a Department and its relative success in attracting students. Since the Department was expensive and relatively unsuccessful in attracting undergraduates, having a staff/student load ratio of 1/4.83, it was given a very high savings target; it accepted having to reduce its annual expenditure from College sources by £92,511 by the end of the 1977-78 session, an enormous saving, amounting to some 25% of the total savings required from all the Faculties in College. The Department's response to this challenge was magnificent, its projected annual savings exceeding the target by almost £6000; none of the savings were detrimental to teaching; on the contrary, re-deployment of staff and some re-allocation of duties provided some increase of resources for teaching.
Members of the Committee visited many of the groups in Gower Street, at the Mill Hill Observatory, at M.S.S.L., at C.E.R.N., Geneva, and at Flaxman Terrace. The Committee was impressed by the very high standard of the research, both theoretical and experimental, throughout the Department. As was to be expected, attention was concentrated on those areas of high expenditure, namely the High Energy Physics, and the Space and Astronomy Groups.

High Energy Physics

The Bubble Chamber Group's two main collaborative projects, neutrino interactions in the Gargamelle Heavy Liquid Chamber at C.E.R.N. and low energy K^- meson interactions in a track-sensitive target in the British National Bubble Chamber at the Rutherford Laboratory, were examined. The Group's contribution to the C.E.R.N. experiment, singled out by the Director-General as being the most important one in the almost twenty years' existence of the Centre, was acknowledged by all as being of crucial importance to the exciting discovery of neutral currents, confirming a unified field theory which linked the weak and electromagnetic interactions as different aspects of the same force law. It was recommended that the Group should be encouraged to restrict itself to one project requiring technical effort in the Department at one time as soon as the Rutherford Laboratory experiment was completed.

MIKE ESTEN adds: "Prior to the grant to the Bubble Chamber Group for work on Gargamelle, it was my understanding that the plan was actually to close down the UCL BC Group leaving counter work only" [e-mail to J Grozier, 4 November 2012]
The Spark Chamber Group's involvement in four collaborative experiments, three at the Intersecting Storage Rings and one at the Proton-Synchrotron, at C.E.R.N., was also examined. It was appreciated that these experiments demanding continuous interaction by those involved, meant that members of the Group had to be away from College more frequently and for longer periods than those in the Bubble Chamber Group. However the S.R.C. covered almost all of the cost of work apart from academic and technical staff salaries. The Committee concluded that, as long as it was national policy for the United Kingdom to join in collaborative work in high energy physics, it was manifestly to the advantage of the College for staff and postgraduate students of the Department to be involved in the work of C.E.R.N., since it brought great credit to the College at relatively little expense.

Astronomy and Space Research

The Committee noted that the amalgamation of the Departments of Physics and Astronomy had brought together theoretical and experimental groups working in infra-red, optical, ultra-violet and X-ray astronomy, as well as in geophysics and astrophysics. The groups involved in astronomical and space research made use of global facilities such as telescopes at Herstmonceux, South Africa, Teneriffe, Australia and California; balloon launch and recovery facilities in Australia, Texas and Argentina; rocket and satellite launch facilities in the Hebrides, Norway, Sweden, Pakistan, India, Australia, and U.S.A. The fact that the groups were so successful in obtaining use of these eagerly sought-after facilities was a tribute to the excellence of their work. As an illustration, in 1977 the I.U.E. satellite was due to be placed in orbit as an international space observatory for ultra-violet astronomy. Its development was being undertaken jointly by the U.S.A., E.S.A. and the U.K. One of the Department's groups was responsible for the overall scientific definition of the project, the evaluation and calibration of the sophisticated television detector system and the optical design of the telescope sun-baffle system needed to observe faint stars and galaxies in the orbital condition of full sunlight. Similarly the U.C.L. Photon Counting System was proving highly successful on the Mount Palomar 200-inch telescope.
The Mullard Space Science Laboratory was the largest single group in the Department, having a complement of staff and research students of 76 at 1 November 1973. It was the senior and substantially the major U.K. university space research centre. Its main areas of research were X-ray astronomy, solar physics and geophysics involving orbital satellites and sounding rockets. Satellite experiments averaged four to five years preparation before launching and provided data perhaps for another four to five years. About two opportunities to participate in such experiments were being taken up each year. Sounding-rocket experiments averaged about half the corresponding time for preparation and provided data requiring a year or so for analysis. M.S.S.L. was heavily supported by S.R.C.; out of its total budget of c.£384k in 1973-74, rather more than £205k came from S.R.C. It was the only space science group in the country to be financed by S.R.C. in the same way as Jodrell Bank and Sir Martin Ryle's team at Cambridge, i.e., by means of a rolling block grant with annually updated four-year look ahead. Although M.S.S.L. was expensive, it was playing its full part in the Departmental economies programme; over the two-year period 1975-77 it planned to have reduced the annual College expenditure on its staff and other costs by an amount in excess of £43,000. The Committee concluded that the work at M.S.S.L. was of the highest standard; it expressed its conviction that the College would lose greatly in academic distinction if M.S.S.L. ceased to be part of it; and therefore it recommended that the Laboratory should continue to be part of the Department.
In considering the situation at the Mill Hill Observatory, it was appreciated that, although the Observatory was of little use for research, it was of great value for undergraduate teaching, as evidenced by the large amount of observing time logged by undergraduates. A proposal to move the Observatory to a better site, e.g., Holmbury St. Mary, was rejected on the grounds of expense and relative inaccessibility for undergraduate teaching. However the desirability of moving the staff then occupying the Observatory Annexe at 33-35 Daws Lane to Gower Street as soon as possible was stressed. The need soon to replace much of the telescope equipment in the Observatory was underlined, and at the Committee's request the funds for the then-current replacement of the Wilson telescope by one specially designed for teaching were obtained from the Perren Fund, the balance being provided by the Department.

Image Processing

Members of the Committee who visited the Image Processing Group were very impressed by the high standard of the work in progress, namely the development of very sophisticated special purpose computers for the automatic processing of images and recognition of patterns, which had multi-disciplinary implications and very practical significance. The Committee was convinced that the Group should remain in the Department, but that it should be re-housed in Gower Street, preferably near to both the Department and the Department of Statistics and Computer Science when the Flaxman Terrace lease expired.

General Comments on the Research Work

The Committee had recorded its appreciation of the very high academic standard of the research throughout the Department. However it wished to direct attention to some aspects of research in big science areas relevant to its recommendations. Experiments in these areas often had a considerable time-span; for example, ten years or more could elapse between agreement to include a particular experiment in a space vehicle and the completion of the analysis of data. Some experiments under development at M.S.S.L. would be launched in the 1980s; any cancellation or curtailment of such an agreed project would have both national and international repercussions. Once a project, which involved either national or international facilities, had been agreed its timing was out of the control of the U.C.L. group. N.A.S.A. determined the date and timing of the launch of an American space vehicle; if a U.C.L. project was to be included in that vehicle, the equipment had to be tested under simulated and sterile space conditions before being incorporated in the vehicle, and the timing of such tests was again decided by N.A.S.A. Optical and ultra-violet astronomers had to be in South Africa, Teneriffe or California when and for as long as they were allocated access to the respective telescopes; similarly infra-red astronomers, operating from ground sites or balloon platforms in the Argentine, Australia or Texas, had to conform to the conditions imposed upon them. The C.E.R.N. programme determined the work of the high energy physics groups; staff could be required to be absent from College during term time, as well as in vacations, the duration of such absences varying considerably from several days to many months in the case of the spark chamber group. The Committee considered that, as long as it was national policy for such research to be undertaken by universities, it was of the paramount importance that the Department should be encouraged to continue in big science and that it should not be unduly penalised for so doing.

Teaching

On the postgraduate side the Committee noted that there was an increase of postgraduate students from 65 in 1973 to 70 in 1976 when its final report was issued. Although the capacity was 100 there was little chance of this figure being realized owing to the numbers of studentships and suitably qualified candidates then available. Postgraduate training was an integral part of the activities of all research groups, and in many of them students were afforded unique opportunities to participate in research programmes of national importance, using equipment and facilities not available elsewhere. The students in their submissions to the Committee expressed their awareness of this and, with very few exceptions, were highly appreciative of the opportunities available to them. The Committee made no specific recommendations for changes in postgraduate teaching.
The Committee noted the swing away from the physical sciences among candidates seeking admission to Universities during the past decade, affecting physics much more than astronomy. Furthermore in the 1973-74 Session some 28% of the first-year physics students in the Department had failed to qualify for entry to the second-year courses at the end of the Session, compared with 5% of the astronomy students. On the other hand, the more able students derived great benefit from the courses, as evidenced by the number of University prizes and other distinctions gained by them. A questionnaire distributed to the teachers attending the 1973-74 Schools Conference revealed that many of the teachers thought that the Department was only interested in "high-flyers", actively discouraging the less able from applying for entry. At that time the Department had an extremely favourable staff/student load ratio of 1/4.8 based on total staff number or 1/5.4 if effective staff number was used. As with the economies programme, the Committee was impressed by the Department's response to this situation. Active recruitment was showing gratifying results; undergraduate entry had risen from 53 in 1973 to 69 in 1974, with the introduction of a joint astronomy and physics degree course, and 79 in 1975. Extensive changes had been made to the course-unit degree structure, the introduction of half-unit courses allowing a degree of flexibility, reducing the work-load of some students by some 15%, and enabling the less-able student to select less demanding courses, but not retarding the "high-flyers". More staff were involved in the teaching, each half-course unit in the first and second years including separately scheduled discussion periods, to allow teachers to revise difficult topics, to solve specific problems that had arisen, and generally to assess progress. These changes produced an immediate reduction in the drop-out rate of first-year students, namely from the foregoing 28% in 1973-74 to 17% in 1974-75, and of these only, 7% were due to academic failure. The combination of increased entry, reduced drop-out, and the reduction of staff in the economies programme meant that by 1980-81 the staff/student load ratio should be approximately 1/8. The Committee believed this to be a major achievement by the Department.

Effective Staff-Numbers

It being recognised that some members of the Department occupied posts in which they were wholly, or for a significant part of their time, engaged on College rather than Departmental duties; nevertheless they continued to be counted as full-time members of the Department in determining staff/student ratios. Such ratios had become, and were likely to continue to be, important variables in the allocation of resources. The Committee considered it unreasonable to expect departments to be placed in double jeopardy by losing all or a significant part of the services of a member of staff, who accepted an invitation to perform essential College duties, and thereby endangered its claim on any additional resources. The problem affected other departments in College and the Committee believed that such staff should have their College-based time discounted in calculating staff/student ratios. This was already recognized in the cases of the full-time College Safety Officer and the Audio-Visual Aids Co-ordinator. Examples in the Department of Physics and Astronomy were the Tutor to Science Students (whole-time) and the Schools Liaison Officer (part-time). Consideration of unavoidable absences in term-time for internationally based research and the time spent on College duties in the posts cited above, led the Committee to recommend that in the calculation of staff/student ratios an effective staff number of eight less than the absolute number should be assigned to the Department on the understanding that this number should be reviewed periodically.

Quain Professor

The Committee considered that an appointment to the Quain Chair of Physics and Headship of the Department was closely linked with the future development and resources of the Department; consequently it proposed that eight members of the Committee should serve on the Chair Sub-Committee together with two co-opted members. This proposal was endorsed by the Executive Committee. The Sub-Committee was dissolved when its recommendation was accepted that Professor F. F. Heymann should be appointed to succeed Professor Massey in the Quain Chair.

Survey of Research A: Experimental

Gas Discharge Studies

On entering the Physics Department Boyd continued the study of gas discharges by means of his screened Langmuir and radio-frequency mass-spectrometric probes, which he had begun in the Mathematics Department. With D. Morris a 12-stage instrument using a series of distributed r. f. fields was developed and applied to study the ions present in helium discharges. The operation of Langmuir probes in electro-negative plasmas was studied with J. B. Thompson, who went on to determine the concentration of negative ions in the positive column of an oxygen discharge. The theory of the collection of positive ions in a low pressure plasma was extended with J. E. Allen and P. Reynolds. With N. D. Twiddy there was developed an electronic method for the Druyvesteyn analysis of the electron energy distribution in plasmas, which was then applied to study the mechanism of striation structure in hydrogen discharges under certain pressure and current ranges; it was to form the basis of many subsequent ionospheric studies.

Optical Techniques

D. W. O. Heddle joined the Department in 1952 as an Experimental Research Assistant to initiate work on the measurement of optical excitation functions and polarization; he had worked with Professor R. W. Ditchburn at Reading on absorption cross-sections in the vacuum ultra-violet. With A. H. Gabriel there was studied the radiation emitted by helium under controlled electron impact to obtain the excitation functions of S, P and D states; the dependence of apparent excitation cross-sections on pressure was also investigated. Heddle and C. B. Lucas carried out a systematic study of the excitation and polarization of electron impact radiation as a function of helium pressure in order to determine the conditions for which secondary processes do not cause significant depolarization of the observed radiation; optical excitation functions and polarization as a function of electron energy were determined for a number of transitions. Then the threshold behaviour of electron excitation and polarization functions in helium was investigated by Heddle with R. G. W. Keesing. Heddle played a leading part in the first observations of ultra-violet radiation from stars in the Southern hemisphere made by two 'telescopes' flown in an unstabilised Skylark rocket launched from Woomera on 1 May 1961 (see p.90). He was primarily involved in the determination of the refractive indices of gases in the vacuum ultra-violet by the Cerenkov method, with Jennings and A. S. L. Parsons (see p.77), and the Rayleigh scattering method, with P. Gill. Heddle's departure to York in 1964 brought the work to an end.

Atomic Physics

The determination of the concentration of atomic hydrogen in mixtures of atomic and molecular hydrogen by continuous flow calorimetry and microcalorimetry formed one of the first projects undertaken in the early fifties, with the view to developing a microcalorimetric probe for measuring the concentration of atomic hydrogen in collision chambers during the determination of various electron impact cross-sections. Dr. A. W. Tickner, a Canadian National Research Council, Overseas Fellow, joined Boyd and Fox for a year on the work, and just before he returned to Canada in 1952, Dr. E. J. Smith, a physical chemist from Newcastle University, joined them as a Warren Research Research Fellow. The microcalorimetry proved extremely troublesome owing to the variability of the recombination of hydrogen atoms on the inside of a small platinum box, situated behind an orifice system through which atoms and molecules of hydrogen effused. This led E. J. Smith, A. C. H. Smith and Fox to make a study of the variability of recombination of hydrogen atoms on metallic surfaces, but eventually the microcalorimetry had to be abandoned.
A. C. H. Smith and Fox determined the viscosity of partially dissociated moist hydrogen, containing up to c. 45% atomic hydrogen, by measuring the rate of decay of the oscillations of a small, bifilarly suspended, hollow glass sphere at pressures in the intermediate region between viscous and free-molecular flow. It was discovered that the viscosity of molecular hydrogen containing 2.5% by volume of water vapour at 20 C was about 7% greater than that of the dry gas, and this was confirmed by computation of the viscosity of mixtures of hydrogen and water vapour over the complete range of water vapour content. This result and the fact that Amour's 1936 values of the viscosity of atomic hydrogen, derived from the 1928 flow experiments of Harteck, based on the dissociation of moist hydrogen, were about 20% greater than the theoretical values calculated by Buckingham, Fox and Gal, led R. Browning and Fox to repeat the flow experiments, but using effectively dry molecular hydrogen. From the viscosities of mixtures of atomic and molecular hydrogen containing up to 70% atomic hydrogen, the mean values obtained for the viscosity of atomic hydrogen at 190, 274 and 373 K were in good agreement with the aforementioned theoretical values. An alternative analysis of the experimental results gave values of the mutual diffusion coefficient for atomic and molecular hydrogen at the foregoing temperatures.
Boyd and G. W. Green developed a modulated crossed beam method for the measurement of the ionization and other cross-sections of unstable atomic gases such as atomic hydrogen. The principle underlying the method was similar to that used by Branscomb and Fite in their measurements of photodetachment of electrons from negative ions. Dr. Wade Fite collaborated in the early part of the work during his sabbatical visit to the department. Ionization cross-sections for molecular hydrogen and for helium up to electron energies of 200 volts justified application of the method to the more difficult case of atomic hydrogen for which preliminary results were obtained. The work was resumed by Boyd and A. Boksenberg, who used an r.f. discharge source and a trochoidal mass spectrometer, having a 100% collection efficiency, for the analysis of the ions. Ionization cross-sections of atomic hydrogen, atomic and molecular oxygen, and molecular nitrogen for electron energies up to 300 volts were obtained and compared with the results of Fite and Brackmann for the first three species.
A notable piece of work on gaseous and surface reactions involving He metastable atoms and resonance photons was carried out by R. F. Stebbings for his Ph.D. degree under the supervision of Hasted; this included the measurement of the absolute yield for He (2³S) metastable atoms incident on a gold surface, and the total cross-sections for collisions between metastable He atoms and He, Ne, Ar and Kr.

Atomic Physics Group

By the early sixties the low energy, experimental work on atomic physics had ceased owing to the dispersal of the personnel. This led Massey to secure an additional established Readership with the special aim of appointing someone of experience and distinction in the field of experimental atomic physics. Stebbings, who had been at the Atomic Physics Laboratory of General Atomic Division, General Dynamics Corporation, San Diego, California since 1958, first as a Staff Physicist and then from 1963 as Scientist-in-Charge, was just the man, and he was appointed to this Readership in October, 1965. He was joined by A. C. H. Smith, who returned to the Department as a Lecturer in 1966, having been working on atomic physics at the General Dynamics Corporation from 1959 to 1962, and thereafter at the A. E. A. Culham Laboratory. Hence the formation of this integral group in atomic physics.
In the initial programme of the Group, mapped out by Stebbings, there were three major experimental projects. The first involved studies of the differential elastic and inelastic scattering of monoenergetic electrons from atoms of the alkali metals, helium and atomic hydrogen using modulated crossed beam techniques. The second was devoted to metastable atom studies, involving the measurement of electron emission coefficients for thermal energy rare gas metastable atoms incident on reproducible controlled surfaces, with the view to making absolute metastable detectors permitting absolute cross-section determinations for a variety of atomic collision cross-section processes. The third was for atomic hydrogen studies, initially to measure the total and differential cross-sections for excitation from the 1s to the 2s state by electron impact with increasing degrees of refinement, surface detection of the metastables being used throughout. It was planned to install a PDP8 computer in the laboratory to collect, process and display data and to provide some degree of experimental control.
By 1968 the Group included nine additional members, namely three postdoctorals and six research students. Unfortunately Stebbings then returned to America to take up a Professorship at Rice University, Houston, Texas, leaving Smith in charge of the Group. W. R. Newell, a post-doctoral Research Fellow with experience in the determination of excitation and ionization cross-sections at the University of Southampton, joined the Group on his appointment as a probationary Lecturer in January, 1974.
D. E. Burgess, M. A. Hender and T. Shuttleworth obtained their Ph.D. degrees for their contributions in the studies of zero-angle, energy-loss spectra of electrons scattered from sodium and lithium. The first measurements were made of the differential (0-20 deg) cross-sections for the sodium resonance transition (3²S - 3²P) at 54.4, 100, 150 and 250 eV, the results being expressed as absolute differential cross-sections and generalised oscillator strengths by Shuttleworth, Newell and Smith. Further measurements of the differential inelastic scattering of electrons by sodium at zero angle were reported by these authors, absolute generalised oscillator strengths being given for excitation to the 4S, 3D, 4P, 5S and 5P doublet states, and values of reduced matrix elements, optical oscillator strengths and quadrupole transition probabilities deduced for S - S, S - P, and S - D transitions respectively. Shuttleworth, Burgess, Hender and Smith reported the measurement of zero-angle, energy-loss spectra for lithium with incident electron energies from 15 - 190 eV and their analysis to give generalised oscillator strengths for transitions between the 2S doublet ground state and the 2P, 3S, 3P, 3D, 4S, and 4P+4D+4F (unresolved) excited doublet states. The quadrupole transition probability for the 2S - 3D doublet transition, the Racah reduced matrix elements for the 2S - 3S and 2S - 4S doublet transitions were also given.
B. F. Dunning and Smith applied two different methods to determine the secondary electron emission coefficients for rare gas metastable atoms incident with thermal energies on metal surfaces. The crossed beam method with helium, neon and argon metastable atoms incident on atomically clean cadmium surfaces gave values of the coefficient less than 0.5 in all cases, and values in excess of 0.5 for contaminated stainless steel surfaces. The gas cell method was applied for measurements on electrodeposited gold, chemically cleaned stainless steel and copper surfaces, and atomically cleaned cadmium and tungsten surfaces; the results indicated that rather larger coefficients than those previously used should be applied for gold surfaces. The investigations led to the development of an absolute detector for rare gas metastable atoms. Measurements of the ratio of cross-sections for Penning ionization by helium singlet and triplet metastable atoms were made by a beam - gas cell method; the results with Ar, Kr, Xe, O₂, N₂, CO, NO and H₂ showed good agreement with previous gas cell measurements, but disagreement with results obtained in afterglow studies.
Some measurements were made of the total cross-section for excitation of atomic hydrogen to the metastable 2S state and of the distribution of recoil angles of the 2S atoms by means of a modulated crossed beam technique; they indicated that the differences between earlier experimental and calculated values of the cross-sections may have been due to the absence of thermal equilibrium in the beam sources. Research students, M. W. Evans and M. I. Gillespie were involved in this work.
The international reputation of the group was underlined by its attraction of overseas visitors for long and short periods from U.S.A., Canada, France, Germany and Australia.

Ionic and Electronic Physics Group

On entering the Department, Hasted continued with a systematic experimental study of charge exchange for ions with energies between 25 and 900 eV., his first paper reporting agreement with near-adiabatic theory for processes involving only atomic ions and atoms with quite definite energy discrepancies. Then he proceeded to measure charge exchange cross-sections for a large number of singly charged positive, ions in argon, krypton and xenon at energies up to 4000 eV, finding agreement with the 'adiabatic maximum rule'. Electron detachment cross-sections for a number of singly charged negative, ions in collisions with rare gas atoms, measured with the same apparatus, showed unexpectedly high values at low energies with O^-, Cl^- and F^-, possibly due to the presence of excited states of these ions, of low electron affinities, in the beams. However a further investigation of these collisions discounted this explanation.
Hasted then started a collaboration with research students to form a large experimental research team studying the collision of atoms and ions in gases, which was to bring international recognition for him and the work of his group. Measurements were made to establish the region of validity of the adiabatic criterion; to investigate the role of pseudo-crossing of potential energy curves in inelastic heavy particle collisions; to study ion-atom interchange using both drift-tube and afterglow techniques; to investigate 'resonances' or short lifetime, compound negative ion, states in molecules by electron spectroscopy; and to study the further ionization of multiply-charged ions by means of the hollow-beam ion trap. In parallel with these collisional studies, he carried out a programme involving the microwave absorption properties of liquids. His book on the 'Physics of Atomic Collisions' was first published in 1964, a second edition appearing in 1972. On taking up the Headship of the Department of Physics at Birkbeck College on 1st. October 1968, part of his Group went with him, the remainder staying behind under his leadership in the basement of 25 Gordon Street. The latter involved the injected ion drift tube, the curve-crossing spectroscopy, and the hollow electron beam projects.
The first measurements for charge transfer and ionization of gases by heavy ions in the kilovolt region were made by Ph. D. research student, H. B. Gilbody, in collaboration with Hasted. 17 charge transfer cross-sections measured in the 3-40 keV range could in most cases be explained on the 'near-adiabatic' theory, but Ar⁺ in Kr, Ne⁺ in Ar and C⁺ in Kr showed anomalies varying slowly with energies in the 'near-adiabatic' range, possibly due to pseudo-crossing of the potential energy curves; and 23 cases of ionization cross-sections of atoms by positive ions did not appear to conform to the simple adiabatic theory, the value of the cross-section in the adiabatic region appearing to depend upon the reduced mass of the system. Measurements of charge exchange cross-sections for protons, molecular hydrogen and helium ions in hydrogen and the rare gases, and electron detachment cross-sections for negative atomic hydrogen ions in the rare gases were carried out by Hasted in the 100-4000 eV range and by J. B. H. Stedeford in the 3-40 keV range. R. A. Smith collaborated with Hasted in measurements of collisional detachment cross-sections for O^- in O₂, N₂, H₂O; H^- in H₂; O₂^- in O₂; and Cl^- in Cl₂ between 10 and 2500 eV: in all cases, except O₂^- in O₂, charge transfer was found to be negligible. Measurements were also made of partial charge transfer cross-sections for C⁺⁺, N⁺⁺, Ar⁺⁺ in He, Ne, Ar and the results were discussed in terms of divergence from near-adiabatic conditions caused by the crossing of potential energy curves; the single endothermic C⁺⁺ in H₂ behaved adiabatically, but the others, exothermic, showed large cross-sections at low energies; contributions from double charge transfer could not be distinguished in Ar⁺⁺ in Ar.
Hasted and A. Y. J. Chong determined electron capture cross-sections for doubly, triply, and quadruply, positively charged, krypton ions in neon and helium in the energy range, 100-3000 eV. These and the previously measured cross-sections of Hasted and Smith were interpreted in terms of the pseudo-crossing of potential energy curves. On the assumption that for each capture process, the transition only occurred at a certain nuclear separation, an attempt was made to relate the potential energy curve separation at that point with the reciprocal of the separation. Total cross-section measurements of these processes were superseded by differential measurements, e.g., Hasted, S. M. Iqbal and M. M. Yousaf measuring the probabilities of single-electron capture by doubly positive charged, carbon, nitrogen, and oxygen ions, colliding with helium, neon, and argon atoms, as a function of laboratory angle of scattering at energies between 1 and 3 keV. The oscillatory variation of the probabilities with scattering angle was interpreted in terms of the pseudo-crossing of potential energy curves for the initial and final states.
Static-afterglow studies were carried out by G. F. O. Langstroth and Hasted; they used an r.f. mass spectrometer of the Boyd-Morris type, which was inserted as a probe into the afterglow, generated in a glass tube, 90 cm long and 10 cm diameter; they used exciting pulses of 2 ms duration, with a repetition rate of 10 per second, and carried out all observations, including mass-spectrometric adjustments, in less than 2 min. to minimize the 'clean up' of oxygen that occurs through successive pulses of discharge operation. They measured the rate constants for the reactions:

O⁺ + O₂ -> O₂⁺ + O
O⁺ + N₂ -> NO⁺ + N
the latter being important in the interpretation of the behaviour of the ionosphere at altitudes up to a few 100 km. M. M. Nakshbandi and Hasted repeated the experiment in a vessel designed to permit variation of the gas temperature, obtaining values of the rate constants at 77, 200, 300 and 375 K. These showed discrepancies with the group's drift tube measurements, which agreed with flowing afterglow measurements at N.B.S. Boulder, Colorado. Since it was becoming increasingly clear that the excited species inevitably present in time-dependent afterglows put this technique at serious disadvantage in comparison with the flowing afterglow technique, it was abandoned in favour of the latter. A 12-inch diameter afterglow tube was developed, excited by pulsed, hollow-graphite cathode, discharge, with approximately laminar gas flow in the range, 10-100 m/s, measured by probe detection of an electric pulse applied across filter-grid wires upstream; electron density and temperature were monitored by floating double probe, and ion density by quadrupole mass spectrometer, both instruments being traversable 30 cm along the axis of the tube. M. R. Mahdavi, M. M. Nakshbandi and Hasted made the first measurements with the tube, namely, to study the dissociative recombination processes following excitation of CO₂ and also CO₂ - He discharges. The temperature of the gas and electrons was of the order of 1000 K, comparison of the rate with that at room temperature suggesting an inverse three-halves power dependence. Further high temperature studies of recombination, including spectroscopic investigations were planned, the programme being supported by the Chemistry Division of U.K.A.E.A., Harwell.
In an investigation of two-photon transition in helium, the time-dependent afterglow proved incapable of supporting the requisite He 2¹S populations. Therefore a small flowing afterglow, with microwave cavity excitation was installed; the transition 2¹S -> 6¹S was achieved by the absorption of two photons of red ruby laser light; and pulses of radiation were detected from the upper level.
Advances were made in the application of the drift-tube method, the foremost method for bridging the energy gap between thermal energies and those involved in ion beam-experiments. Measurements were undertaken of rate constants for charge transfer, ion-atom interchange and other collision processes at mean impact energies of c. 0.05-10 eV. C. H. Bloomfield and Hasted were the first to carry out experiments involving the mass analysis of ions entering a drift tube; they relied upon mobility measurements to discriminate between ions arriving at the end of the tube, but it proved difficult to interpret the mobility spectrum unless it had a simple double-peaked form. To overcome this difficulty Y. Kakapo, L. R. Megill and Hasted added a second mass spectrometer, of the Boyd-Morris type, at the exit end. The apparatus was then improved by the addition of an ion source of controllable electron energy to yield only ground-state ions, and the replacement of the Boyd-Morris r.f. mass spectrometer by a quadrupole mass filter of resolution better than 1/120. A 'merged-drift' apparatus was then designed, providing facilities for the simultaneous injection into the drift tube of two separate beams, positively or negatively charged, or neutralized; for the variation of the length of the tube in vacuo; and the control of the temperature of the tube. As illustrative of the measurements made in this field, D. K. Bohme, P. P. Ong and Hasted determined the rate constants for O⁺ in O₂ and N₂ using ground state O⁺ ions; P. P. Ong and Hasted measured the rate constants for charge-transfer processes, Ar⁺ in N₂, O₂, CO and NO; for dissociative charge transfer for He⁺ in N₂; and for the three-body process,

He⁺ + 2He -> He₂⁺ + He.
K. Birkenshaw and Hasted improved both the experimental technique and the calculations of the cross-sections (by Bohme, Ong, Moore and Hasted) based on the nearest resonance method, achieving better agreement between the measured and calculated values for the foregoing reactions involving Ar⁺.
M. J. W. Boness and Hasted, designed one of the first four, very low energy (0.1 - 20 eV.), electron spectrometers ever built, and with it observed resonances or short life-time, compound negative ion states in N₂, NO, CO, O₂, and CO₂. The spectrometer used a relatively large 127 deg. electrostatic analyser to produce an incident electron beam, with an energy spread of the order 50 meV, directed into a gas collision chamber so designed that only those electrons scattered through less than 1 deg. emerged from the chamber to be collected, the gas pressure in the chamber being adjusted to produce 20% absorption. They made corrections for the electro-optical focussing effect in their experiments to obtain the true variation of the transmission with electron energy. With I. W. Larkin, compound negative ion states of molecules, N₂, NO, N₂O, NO₂, O₂, CO, and CO₂, detected as structure in the electron total cross-section functions, were interpreted in terms of the Beutler-Fano equation and partially identified by comparison with certain isoelectronic species. L. Moore joined the trio in observing resonances in C₆H₆, C₂H₄, and CH₄; he was involved in the data analysis, devising a convenient numerical method of deconvolution of physical data, based on a Fourier series expansion A second transmission spectrometer, with both monochromator and analyzer, having an energy resolution in the range 15-30 meV, was used in studies of the decay of diatomic molecular resonances into vibrational channels, enabling potential energy curves for the appropriate negative ion states to be calculated; A. M. Awan and I. W. Larkin collaborated with Hasted in these studies. The old transmission spectrometer was phased out in favour of a scattering spectrometer being developed with a view to inferring the azimuthal quantum numbers of the molecular resonances previously studied. The monochromated electron beam was to be crossed with a molecular beam, the post-collision electron momentum analyzer being traversable through polar scattering angles 0 - 120 deg. The development continued with a view to possible commercial exploitation, as envisaged in a S.R.C. Co-operative Award.
In the mid-sixties, Hasted on leave of absence at the Institut Battelle, Geneva, collaborated with F. A. Baker in the use of a Nier source operated as an ion trap to study ionization potentials for step ionization processes of positive ions and the behaviour of the cross-sections for such processes near threshold. This so-called 'sequential spectrometry' was then taken up by several groups. Back at College a more sophisticated experiment was developed in which a toroidal cathode produced an electron beam of annular cross-section, through which a molecular beam was passed, the ions formed being trapped for periods of c. 1s, oscillating radially, and passing through a second, axial, electron beam of variable energy; ions of different charged states were extracted axially through an orifice into a quadrupole mass spectrometer and channeltron detector. In this way, with G. L. Awad, cross-section functions for ionization of multiply charged ions were obtained between threshold and 500 eV., namely for singly, doubly and triply charged argon ions, and doubly and triply charged neon ions.
In the microwave field, Hasted in collaboration with G. W. Roderick made measurements of dielectic constant and loss on a range of aqueous and alcoholic electrolytic solutions at wavelengths from 1.25 - 51.5 cm at temperatures in the range from 3 - 25 C, providing information on the behaviour of the water molecules in the neighbourhood of the ions. Then, with M. A. Shah and P. R. Mason, observations were made of a Stark shift in the microwave relaxation of nitrobenzene. In a microwave absorption study of dielectic mixtures with relaxing components, extensive studies were undertaken of the microwave properties of water absorbed physically in brick and aerated concrete, and chemically in cement, computer calculations of the dielectric theory of mixtures, applied to complex dielectric constants, successfully interpreting the physical absorption data (with L. Moore and M. A. Shah); and a phase change technique was applied to the problem of classifying absorption as physical or chemical (with P. Firth and S. P. Lovell). These studies were followed by 10 cm. wavelength cavity resonator measurements of water complex permittivity at 0.5 C intervals in the range, 15 - 75 C, and then at 0.1 C intervals; the repeatability of the structure in the temperature function, particularly of the dielectric loss, demonstrated that these intervals were sufficiently small to reveal most of the 'thermal anomalies'. Further work was planned with capillaries of different diameters to establish whether the anomalies were surface or volume effects. Filled cavity resonator measurements at 10 cm. wavelength of the dielectric properties of liquid ammonia and sodium-ammonia solutions were carried out with S. H. Tirmazi, the results being consistent with the existence of ionic plasma resonance. The microwave studies of aqueous and ammoniacal solutions were complemented by measurements in the submillimetre band. Hasted and M. S. Zafar collaborated in measurements on water at laboratory temperatures using the new double modulation Fourier spectroscopy technique developed at the National Physical Laboratory under the supervision of Dr. J. Chamberlain; temperature variation, D₂O studies and ionic solution measurements were planned to follow.

High Energy Atomic Collisions Group

After obtaining his Ph.D. degree in 1956, H. B. Gilbody worked as a Research Assistant in Hasted's group until November 1959, playing a leading part in the design of the van de Graaff accelerator. He then joined the General Atomic Division of the General Dynamics Corporation, San Diego, Calfornia as a Research Physicist. This group was formed under his leadership on his return to the Department as a Lecturer in 1961. It studied inelastic ion-atom collision processes at energies ranging up to 500 keV, the van de Graaff accelerator providing mass-analysed beams of the required ionic species. Collisions involving charge rearrangement and excitation were studied, the methods applied including total collection, charge or mass analysis, of the collision products; spectroscopic study of radiation induced in collisions under carefully controlled conditions; and the modulated crossed beam technique.
Collisions involving rare gas ions included the measurement of total cross-sections for slow ion production and electron production and the total apparent charge transfer cross-sections in collisions of rare gas ions with rare gas atoms in the energy range 60 to 450 keV by Gilbody with Hasted, J. B. Ireland, E. W. Thomas and A. S. Whiteman; a study of excitation in rare gas ion-atom collisions in the energy range 100 to 400 keV, including the determination of cross-sections for the emission of some of the more intense lines in the spectral range from 3900 to 6000 Å by Gilbody and Thomas; a study of small angle scattering in charge transfer collisions when beams of protons, singly charged He, Ne, Ar and Kr ions at energies within the 60-250 keV. range were passed through thin targets of H₂, He, Ne, Ar and Kr gases by Gilbody and A. B. Wittkower; and the study of charge neutralization of 60 to 450 keV., singly charged Ne, Ar and Kr ions during passage through both thin and thick targets of the previously mentioned gases by Gilbody and Wittkower. The total cross-sections for slow ion production and for ionization were determined for protons, of energies between 100 and 450 keV, in H, He, Ne, Ar and Kr by Gilbody and A. R. Lee. Proton collisions with atomic hydrogen were studied by Gilbody and G. Ryding, cross-sections for the charge transfer process

H⁺ + H(1s) -> H(n,l) + H⁺
involving capture into all states (n,l) of atomic hydrogen being determined by means of a modulated crossed beam technique in the energy range from 40 to 250 keV. The apparatus was then modified to permit study of the 2s capture process in targets of atomic and molecular hydrogen and helium, the yield of fast metastable atoms being determined by recording the Lyman alpha radiation produced by electric field quenching; Wittkower joined Gilbody and Ryding in this later work.
On 1 January 1967 the personnel and associated equipment, including the van de Graaff accelerator, of the Group was transferred to the Department of Physics, Queen's University, Belfast, on Gilbody taking up his appointment to the second Chair of Physics at Belfast.

The Microtron Group

One of the first projects undertaken in the Department was the design and construction of a 4.5 MeV electron accelerator (microtron) for electron scattering studies by Henderson and Jennings under the leadership of Heymann, who had been involved with electron accelerators at Metropolitan Vickers. This, the second such machine constructed, operated at a wavelength of 10 cm, the diameter of the final orbit being c. 30 cm in a magnetic field of 1000 gauss; and a circulating current of c. 2 mA mean was observed at a duty cycle of 0.0004, with a 500 kW peak microwave source. The stability of the machine was studied, the limits of phase and energy within which electrons could be stably accelerated being calculated for a number of voltages by two different methods; generally speaking, the energy and phase of a stable electron could not vary from that of the ideal electron by more than ± 0.1 rest masses and ± 10 deg, the stable regions being independent of the energy of the electrons with the result that the beam from a microtron becomes relatively more monoenergetic as the final energy is increased. The beam had an energy spread of about ±50 keV, and by using a double focusing magnetic spectrometer a 'monoenergetic' beam with a spread of only ±4 keV could be obtained; its sea-angular spread was 1.5 deg horizontally and 0.3 deg vertically. A method of measuring absolutely the energy of the beam itself was developed using a variable pressure gas Cerenkov counter detector; then a Jamin interferometer was incorporated into the pressure system to enable the refractive index of the gas to be determined directly, M. R. Bhiday and P. I. P. Kalmus being involved with Jennings in this work. As mentioned on p. 71, Heddle collaborated with Jennings and A. S. Parsons in applying the Cerenkov radiation method to determine the refractive indices of gases in the vacuum ultra-violet. Heddle working next door to the microtron group, realised that this could be done by comparing the threshold pressures for Cerenkov radiation in the ultra-violet and visible regions for electrons of the same velocity.
Heymann and Jennings carried out experiments on the multiple scattering of 4.5 MeV electrons by Al, Cu, Mo, Ag and Pt foils applying the photographic method to measure the variation of scattered electron intensity with angle; the results were in good agreement with the theory of Moliere into the region of plural scattering, this being the upper limit of angles covered by the observations. Later Bhiday collaborated with Jennings in measurements of the radiative correction for scattering of 4.5 MeV. electrons at different angles from high and low Z foils, with results in reasonable agreement with theory. The facilities of the group enabled K. K. Damodaran and R. M. Curr to establish that the single scattering of 4.33 MeV electrons by heavy nuclei such as Ag, Pt and Ur agreed with Mott's theory, within their experimental accuracy of a few percent, for angles from 45 to 90 deg.
Following the successful operation of this microtron, Heymann and Jennings were joined by D. K. Aitken and P. I. P. Kalmus in the development of a larger machine, based on a 20 ton magnet of pole diameter 7.5 ft. It was brought into operation in the Summer of 1958, the extracted beam being of c. 10^-8 A mean at an energy of 29 MeV; pulsed at a repetition rate of 100 pulses per sec., it had an electron pulse duration c. 2 ms; and by means of a quadrupole lens system, the extracted beam was focused to a spot of c. 2 mm in diameter, corresponding to an angular spread less than 1 deg.
During the development a null method for the measurement of small energy losses in gases at 29 MeV by Aitken, Jennings and R. N. F. Walker, it was noticed that the threshold was not as sharp as had been anticipated from the 4.5 MeV data. This could not be explained until it was realised as being due to transition radiation, which occurs when the environment of a constantly moving electron changes. It was found possible to photograph this radiation, emitted below threshold, using very long exposures. Parsons joined the aforementioned trio in measuring the angular distribution, the variation with pressure, and also the intensity and polarization of this transition radiation.
An experiment to measure Bremsstrahlung spectra emitted at large angles to the incident beam was performed at an energy of 27.6 MeV by Jennings, J. F. Hague and R. E. Rand; the target used was aluminium and the results indicated a cross-section about two standard deviations greater than given by the Bethe-Heitler formula for a point nucleus, the discrepancy being larger when allowance was made for finite size effects. A total absorption spectrometer, which had previously been calibrated by measurement of the 'Bremsstrahlung electron' by Hague and Rand, was used in the experiment. The intensity of the incident beam was measured with a small Faraday cup, the efficiency of which had been determined by a null method applying a toroidal transformer.
Energy loss distributions for 28 MeV electrons after passage through tungsten foils were measured by Jennings and G. R. Davies. Good agreement with theory was obtained for the variation of the most probable energy loss with thickness (maximum c. 2 gm/cm²), but the widths of the distributions were slightly narrower than predicted. The group completed its experimental programme on the machines in 1963.

Double Magnetic Lens Spectrometer

Another of the first projects undertaken in the Department was the design and construction of a beta-ray spectrometer for investigating the nuclear scattering of electrons and positrons, of energies up to 4 MeV, by thin metallic foils. In such an experiment an intense beam of nearly monoenergetic particles is required to be incident on the scatterer in accurately determined directions. G. P. Rundle was awarded the Aithison Travelling Scholarship by the University of Melbourne to join the Department in 1950 as a Ph.D. student and he was assigned to the project; also involved was another Ph.D. student, J. Ellis, together with Griffith and Tomlinson. Both coils of the spectrometer were capable of very fine adjustment in five degrees of freedom; these fine adjustments enabled a detailed study to be made of the effect of coil alignment and separation on the resolution and transmission of the instrument, the incorporation of ring focus notably improving the resolution. The extensive testing of the instrument also included a study of the variation of spherical aberration with coil separation, and the use of a quick and accurate experimental method of plotting trajectories.
The first scattering experiments with the spectrometer were carried out by Henderson and Ellis. Electrons and positrons from a radioactive source were scattered under identical conditions at 0.7 and 1.4 MeV by Al, Ag and Au foils, the incident and scattered particles being counted by means of scintillation counting equipment developed by Heyland and Roberts. The incident beam was a divergent hollow cone of semi-vertical angle of c. 10 deg, the effective angles of scattering being 22.8, 34.5 and 47.5 deg. The results within experimental accuracy of ±5% were in accordance with the predictions of the Dirac theory. Further experiments were performed by Henderson and A. Scott on the multiple scattering of electrons and positrons of energy 0.4 MeV on foils of the same elements using a more strongly collimated, converging hollow beam. The difference between the distribution width for electrons and that for positrons after scattering was found to be smaller than previous measurements had indicated; it was given approximately by the calculations of Mohr. Further work with electrons only using silver and Ilford G5 emulsion as scattering foil materials showed good agreement with the theory of Moliere.

The Emulsion Group

In the Mathematics Department, Burhop had begun to use the nuclear emulsion technique as a means of resuming research in nuclear physics, and was soon on very good terms with C. F. Powell of Bristol who had initially developed the technique. However on moving over to the Physics Department, he became heavily involved in the high pressure cloud chamber, cosmic ray programme, one of the first projects in particle physics to be undertaken by the Department. With the closure of this programme, he turned his attention back to the emulsion technique and in 1956 formed the Emulsion Group, the other members being Drs. W. B. Lasich and F. R. Stannard, research assistants, and D. H. Davis, R. C. Kumar and M. A. Shaukat, research students. The work of the Group was to involve participation in the design, preparation and operation of particle beams for emulsion exposures, followed by the location, measurement, and computer analysis of events occurring inside the emulsion, a team of scanners helping with the more routine of these tasks. As a consequence of the Collaboration (referred to later), frequent meetings were necessary to formulate standard experimental procedures, assemble data and discuss results.
Work began with the examination of a stack of emulsions, which had been exposed to a negative unseparated beam from the Bevatron at Berkeley, in order to study the interaction of K^- mesons with nuclei. However, with this work hardly begun, separated beams of low energy K^- mesons became available and, in February 1957, it was learned at a conference in Bristol that the University of Bristol had just obtained an emulsion stack exposed to such a beam. At a meeting between Powell, G. P. S. Occhialini and Burhop, it was decided to share this new stack of emulsions with other laboratories; thus began the European K^- Collaboration by groups from Bristol, Brussels, Dublin, Milan, Padua and U. C. L., the first large international collaboration of its kind.
The first investigation of the collaboration was a systematic study of the interactions at rest of K^- mesons with nuclei, which established the peripheral nature of the nuclear absorption process and revealed the then surprising result that about 20% of K^- meson capture occurred on more than one nucleon, confirming the importance of nuclear correlations in the nuclear surface, first suggested by D. Wilkinson. The group's involvement with the collaboration was published in three Nuovo Cim. papers (1959-60) dealing with the general characteristics of K^- interactions and analyses of events in which a charged pion is emitted; the emission of hyperons from K^- interactions at rest; and on the observations of fast sigma hyperons emitted from the interaction of K^- mesons with emulsion nuclei. In 1961 the Italian groups left the collaboration, but later it was extended to include groups from Warsaw, Westfield College, Prague, East Berlin and Belgrade, thus becoming the first to include physicists from both sides of the Iron curtain, a step towards an East-West rapprochement so welcomed by Burhop.
After gaining his Ph.D. in 1959, Davis continued to work in the group as a research assistant. He spent 1961-62 as a Fulbright Travel Scholar and Research Associate, working with Prof. Levi Setti at the Fermi Institute in the University of Chicago, and developing his interest in the study of hypernuclei, a field in which he was to become a leading world authority. On returning to UCL he became a lecturer in 1963 and assumed increasing responsibility for the organisation of the work of the group, Burhop maintaining an avuncular interest in the activities of the group and of the collaboration as a whole.
During the period 1962-74 many papers were published on hypernuclei binding energies, spins, decay modes, lifetimes and production mechanisms, and on low energy K^-p scattering and production processes. As highlights, there are selected the study of hyperfragment production by K^- mesons in emulsion stacks irradiated in the separated K^- beam at CERN, Geneva, leading to the discovery in 1963 of the production and subsequent cascade decay of a double hyperfragment, i.e. a nuclear structure containing two bound lambda hyperons, by J. E. Allen, M.J. Beniston, D. A. Garbutt with Davis et al; this led to a determination of the binding energy of the two hyperons in a double hypernucleus. In 1965 a determination was made of the lambda-nuclear potential well-depth from the observed energy releases in the p^--mesonic decays of the heavy spallation products of silver and bromine by P. Allen, Elizabeth Fletcher, D. A. Garbutt, M. A. Shaukat, Davis et al. Burhop's insistence that the anomalies in p⁺ and p^- meson absorption rates following K^- meson capture in nuclei, which had been apparent in the earlier work, could be explained by a 'neutron skin' in heavy nuclei led to a more selective study in 1967 of K^- meson captures in emulsion nuclei by Susan Lovell, Davis et al, which was aimed to ascribe captures involving specific proton and neutron absorption processes to either light (C, N, O) or heavy (Ag, Br) muclei. The result of the study, namely that K^- meson captures on neutrons are about five times more likely in heavy, than in light, nuclei, confirmed Burhop's insistence. Similar, later studies by several workers, including Bethe and Teller, endorsed the result that the extreme periphery of a heavy nucleus was rich in neutrons.
Evidence for the existence of particle-unstable states of the L¹²C and L¹⁴N hypernuclei produced by the absorption at rest of K^- mesons in light emulsion nuclei in 1969 and the subsequent confirmation of the existence of a particle-unstable state of the L¹²C hypernucleus by Davis et al - the so-called discovery of analogue resonance states, which initiated the growth of a thriving hypernuclear spectroscopy 'industry' at CERN, Brookhaven National Laboratory and KEK, Japan. In 1971 an experiment was performed in a six litre stack of Ilford K5 emulsion exposed to stopping K^- mesons at the Brookhaven A.G.S. machine by D. N. Tovee, Davis et al. During the course of an extensive study of the properties of hypernuclei produced by c. three million stopping K^- mesons, a sample of some 7500 meson interactions at rest on hydrogen giving rise to charged S hyperons were recorded, and the interactions were used as a source of monoenergetic hyperons to determine their properties in conditions different from those existing in a hydrogen bubble chamber. The decay branching ratio of the S⁺ hyperon, the ratio of S^- to S⁺ hyperon production, the lifetime of the S^- hyperon, the mean orbital capture time of S^- hyperons in emulsion, and the masses of the charged hyperons were determined.
In 1963 Burhop made what was to become a very important proposal, namely, that the combination of spark chamber and emulsion techniques would permit the location of rare neutrino interactions in a large emulsion stack. Once located the high spatial resolution of the emulsion technique, shorter than 10^-3mm, would allow the direct resolution of the production and decay vertices of any particles, with lifetimes as short as 10^-14s, to be detected. The experiment was carried out at CERN in 1965 by a combined UCL spark chamber and emulsion team, together with the University of Brussels group and the European K^- collaboration representative, demonstrating the viability of the method even though only a few low-energy neutrino interactions were found. The experiment aroused little interest since at that time there was little expectation that such short lifetime particles existed.
The 1966-67 departmental research report records the concentration of the work of the Bubble Chamber and Emulsion Groups into a single group having three sections, (i) Gargamelle, (ii) RHEL-UCL chamber, (iii) Emulsion, under the leadership of Burhop. It states that "The nuclear emulsion section is gradually being run down although it still has an interesting physics programme for the immediate future." Fortunately Davis refused to believe that the technique had become obsolete with the advent of bubble chambers. His persistence received its reward with the resurgence of the hybrid techniques in the seventies.
The discovery of weak neutral currents in 1973, supporting the unification of the electromagnetic and weak interactions and theoretical predictions of new quark flavours, particularly charm, reawakened interest in such hybrid techniques. Consequently Burhop and others suggested an experiment in which neutrino interaction vertices were to be located by estimating the points of convergence in the emulsion stacks of tracks seen in external wide-gap spark chambers. The experiment, E247, was accepted for running in the wide-band neutrino beam at Fermilab in 1975, Burhop, Davis and Tovee taking part. It was successful in locating 37 neutrino interactions in the emulsion, each within a search volume of c. 1 cm³. From one of these a very good candidate for a charged charmed particle was seen to emerge and decay after a path length of 182 x 10^-3mm and a flight time of a few multiples of 10^-13s.
Then in 1979 a second experiment, WA17, similar in concept was performed in the wide-band neutrino beam of the Super Proton Synchrotron at CERN, some 30 litres of emulsion being placed in front of the entrance window of the large hydrogen bubble chamber, BEBC. A total of 169 charged current neutrino interactions were located in this work and from these 5 positively charged, and 3 neutral, charmed particles were seen to emerge and subsequently decay. Their life times were shown to be in the region of 10^-13s as expected from theoretical models. One of the events was uniquely identified as the decay of a L_c⁺ baryon via the mode pK^-p⁺ after a time of flight of (7.3 ± 0.1) x 10^-13s. This was the first observation of this mode of decay of the L_c⁺ baryon and the first unambiguous determination of the true time of flight of any observed particle. Mention is also made of the Group's participation in the WA75 experiment, using a combination of electronic and emulsion techniques at CERN in 1985, which revealed the first example of the hadronic production of a pair of beauty particles, together with their decays into charmed particles, both of which also decayed in the emulsion.

Cloud Chambers

During the 1951-52 Session Tomlinson, at Massey's suggestion, began work on the construction of two high pressure cloud chambers, based on a design of the late Professor E. J. Williams and subsequently operated by Dr. G. R. Evans at Aberystwyth, where Massey had been an external examiner in physics. It was planned to use one alongside the synchrocyclotron at AERE Harwell to study the scattering of protons and deuterons in light gases, and the other for cosmic ray research at high altitudes when Helmholtz coils, producing a magnetic field of about 7,000 G, had been constructed. In November 1952 he and Massey visited cosmic ray research stations in Switzerland and Italy to select a site for such research. This led to acceptance of the hospitality offered by the Physics Department of the University of Padua at its laboratory on La Marmolada in the Dolomites at an altitude of 2,020 m. A joint programme of research on elementary particles in cosmic radiation was initiated in 1953 with Dr. Evans, then at the University of Edinburgh, and his chamber was installed on La Marmolada in the summer of 1953. Operations continued for nearly three years until it became apparent that accelerators were becoming capable of achieving energies adequate for the production of at least some strange particles. Some 8000 photographs were taken of local penetrating showers produced by the cosmic radiation. This was the most systematic work then carried out using such a chamber and it enabled a thorough evaluation to be made of its usefulness as a research tool; provided valuable experience in the study of analysis techniques; and information about the production of V particles, interactions in the chamber gas, and electron pairs accompanying local penetrating showers. It led to some dozen papers, six of which appeared in the Report of the Conference on Recent Developments in Cloud Chamber and Associated Techniques held under the joint auspices of the Physical Society and UCL in March 1955. Departmental members involved in the project included J. P. Astbury, P. Baxter, F. W. Bullock, E. H. S. Burhop, H. S. W. Massey, A. J. Metheringham, N. Morris, F. R. Stannard and H. S. Tomlinson.
The long recycling time of the high pressure cloud chamber imposed serious limitations to its applications with cosmic rays or particle accelerators. In its original form this time was 15-20 minutes between expansions, M. J. B. Duff and N. Morris showing that the magnitude of the temperature gradient established in the gas during the cycle was the determining factor. As a result of the difficulties found by A. P. Banford, W. E. Duncanson, T. C. Griffith and W. S. C. Williams in finding suitable operating conditions for the investigation of the scattering of 144 MeV protons by deuterons at Harwell, Tomlinson introduced a more elaborate cycle requiring the use of sophisticated high pressure techniques involving either fast recompression or overcompression, thereby reducing the recycling time to 1 minute. However this improvement alone was not sufficient to permit efficient use of the Harwell proton beam. D. J. Cairns, T. C. Griffith, G. J. Lush, A. J. Metheringham and R. H. Thomas established that satisfactory efficiency could be attained by using a selection system of scintillation counters to trigger the expansion only when specific interactions occurred in the gas, thereby allowing up to 30 useful events per hour to be photographed.

Nuclear Physics Group

This group (of Esten, Lush and Metheringham)* under the leadership of Griffith exploited the counter-controlled, high pressure, cloud chamber for investigations of nuclear reactions involving the measurement of low energy particles. The photographs, usually gathered at c. 40 per hour, were analysed for the runs at 145 MeV on the Harwell cyclotron* using a semi-automatic measuring table devised by Esten to cope with these higher event rates. This also required improved speeds in analysis and so geometric reconstruction and kinematic analysis of the events was programmed on the new University Ferranti Mercury computer by Esten.*
[*Mike Esten to JG 4.11.12. Original referred to the later University of London Atlas computer.]
In an investigation of p-He⁴ scattering, the afore-mentioned quintet determined the differential cross-section for elastic scattering and for the pick-up process, He⁴(p,d)He³ at 53 ± 4 MeV, the 147 MeV, 46% polarised, proton beam from the Harwell synchrocyclotron being degraded by an aluminium absorber to give that mean energy at the centre of the cloud chamber. The total cross-section for inelastic p-He⁴ reactions, with no fast particles at laboratory angles less than 10 deg, was found to be 107.7 ± 4.4 mb at that energy. The ratio of inelastic to total cross-sections was found to be 0.40. J. E. Nicholls and A. Craig joined Messrs. Griffith, Imrie, Lush and Metheringham in an extension of p-He⁴ scattering to 141 ± 2 MeV at Harwell. Some 3000 interactions were analysed, the results including the differential cross-section for elastic scattering and the total cross-sections for all the interactions energetically possible at 141 MeV. The former were in good agreement with other results at that energy, the latter being the then only available data. The total cross-section of each reaction channel was observed, that for the afore-mentioned pick-up process being very small; the ratio of inelastic to total cross-section at 141 MeV was found to be 0.49. The differential cross-section for the neutral spectrum for the He⁴(p,pn)He³ reaction was also determined. Messrs. Esten, Griffith, Lush and Metheringham investigated the inelastic scattering of 135 MeV protons by deuterium. The differential cross-section and energy spectra for both the fast neutron and for the low energy spectator protons emitted in the d(p,n)2p reaction were measured. The results were compared with impulse approximation calculations and, in the case of the energy spectrum of the spectator protons, the ratio of the theoretical to experimental cross-section was extrapolated to the pole at -1.113 MeV.

MIKE ESTEN adds: This latter work constituted the PhD thesis of Esten who was subsequently awarded a Fellowship at CERN (1960-61) where he worked on the large atmospheric Cloud Chamber. The only experiment carried out with that chamber on the newly opened PS during the period involved filling the chamber with steel plates in what was possibly the first experimental study of interactions from an accelerator produced neutrino beam. An unfortunate error in the beam calculation meant that the neutrino flux was orders of magnitude less than expected and no useful results were obtained. Nevertheless this experiment was a precursor of the highly successful neutrino experiments conducted later by the Bubble Chamber Group to which Esten returned to after leaving CERN.

[*Mike Esten to JG 4.11.12.]
The group also undertook a series of scintillation counter experiments using 50 MeV protons from the Proton Linear Accelerator at the Rutherford Laboratory. For the investigation of polarisation parameters in p-p scattering at low energies, G. J. Lush, D. C. Imrie and T. C. Griffith developed a proton polarisation analyser for a measurement of the triple scattering parameter 'D' in p-p scattering at 50 MeV. A. J. Metheringham then joined them in the use of the analyser to measure the depolarisation parameter for 50 MeV p-p scattering at 70 deg (c. m.). This enabled the magnitude of the 3P_o phase shift to be determined with higher accuracy than theretofore and hence improved the phase-shift analysis of the 50 MeV data. This work was followed by a measurement of the spin rotation parameter, beta, for p-He⁴ elastic scattering at 48 MeV. The parameter was measured at 9 laboratory scattering angles between 11 and 90 deg, the results helping to minimise the number of acceptable phase-shift solutions in such elastic scattering; L. A. Robbins replaced Metheringham in the quartet of experimenters involved in this work. With C. J. Batty of the Rutherford Laboratory, the differential cross-section for p-p elastic scattering at 49.41 MeV was measured at 30 angles between 13 and 90 deg (c. m.) with an absolute precision of 0.5 to 0.7 % over most of the angular range, the results being included in a phase-shift analysis of all the then available 50 MeV p-p scattering data.

The Bubble Chamber Group

The bubble chamber was invented by D. A. Glaser at the University of Michigan, U.S.A. in 1952, for which he was awarded a Nobel Prize in 1960. Shortly afterwards, Dodd, who had been in charge of the work on the electron synchrotron, entered the field, building one of the first small chambers in Europe. In June 1955 he was awarded an Astor Foundation Fellowship as a Visiting Professor to spend five months in the U.S.A. at the Brookhaven National Laboratory and Glaser's Laboratory. On his return the Group was formed, first exploring 'clean' chambers, but soon concentrating on heavy liquids. In 1959 the Department was commissioned with the design and construction of a large, heavy liquid, bubble chamber in conjunction with the Rutherford High Energy Laboratory, Tomlinson being the project leader. The chamber costing nearly £400k was built at the Rutherford laboratory. Its internal dimensions were 145 x 55 x 46 cm and it was capable of operation at pressures in the range, 15 - 35 atmos. and temperatures between 30 - 80 C in a magnetic field of c. 21.5 T. The chamber could be used with a wide variety of liquids ranging from the hydrogen rich propane, C₃H₈, to such liquids as trifluorobromomethane, CF₃Br, whose chief virtue is the high conversion rate of gamma rays to electron-positron pairs. It was operated for the first time on 29 October 1965. The UCL group involved in the project numbered at times fourteen, the bulk of the design work being carried out by a team of six, namely Tomlinson, W.A. Towlson, T. E. Venis and three draughtsmen. During the six years of the project this team produced over 650 drawings and the manufacturing specifications besides vetting numerous tenders and contract drawings, close liaison being maintained with the National Institute for Research in Nuclear Science, which handled the services and placed the contracts. Among the physicists involved in the project were Henderson, Stannard, Bullock and Esten.
Before the first experiments were carried out with the chamber, the group were involved in the analysis of film obtained from Berkeley and CERN. In the Berkeley experiment (23), 230,000 pictures were taken involving stopped K^- mesons from the Bevatron in a 30" chamber containing a mixture of equal parts of C₃H₈ and CF₃Br, the Group receiving a third of the film. In the CERN experiment (T8), 250,000 pictures were taken involving 1.5 GeV/c K^- mesons from the proton synchrotron entering the 1m Ecole Polytechnic chamber containing C₂F₅Cl; the Group took one quarter of the film, the remainder being shared equally between the Ecole, CERN, Bergen, and the Rutherford Laboratory. The CERN experiment (T11) yielded 150,000 pictures, 3.4 GeV/c K^- mesons from the proton synchrotron entering the 1m CERN chamber containing CF₃Br; the collaboration was similar to that in T8.
Beta-decay of L^o-hyperon: the short radiation lengths characteristic of heavy liquids, typically between 11 and 25 cm in the foregoing experiments, are particularly suited to the detection of electrons; hence much of the Group's work concentrated on the leptonic decays of hyperons. The first investigation was into the decay:

L^o -> p + e^- + n
The decays were recognised by the characteristic spiralling of the secondary electron. One of the more difficult aspects of the work was the correct evaluation of the probability of the electron stopping in the chamber. Bremsstrahlung and ionization energy loss, scattering, and magnetic curvature had to be taken into account. The problem was solved by D. J. Miller's Monte Carlo programme, which formed the basis of the analysis used in the E23* and T8 experimental results. The two experiments yielded values of (0.82 ± 0.13) x 10^-3 and (0.78 ± 0.12) x 10^-3 for the branching ratio into the modes:

L^o -> (p + e^- + n) / L -> (n + p),
the most accurate determination then available. The investigations of the form of the interaction in the beta-decay of the lambda hyperon were the first of their kind. Henderson and Stannard were the other members of the Group involved in these investigations.
Muonic-decay of the L^o-hyperon: the other leptonic decay mode of the lambda hyperon, namely:

L^o -> (p + m^- + n)
was looked for in experiments E23* and T8, the event being recognised by observation of the muon coming to rest and decaying into an electron. The background arising from the chain of events:

L^o -> p + p^- : p^- -> m^- + n
presented difficulties. With the negative pion decaying in flight, it was often impossible to distinguish the negative pion-negative muon decay from a scattering of a negative muon. The background events were about fifty times more numerous than the genuine muonic decays. However the UCL group involving Knight and Stannard were able to show that some genuine lambda-mu decays would have configurations that could not be simulated by the background chain of events, and based on four events of this type, the combined result of the two collaborations was:

L^o -> (p + m^- + n) / L^o -> (h + p) = (0.13 ± 0.07) x 10^-3.
This value was consistent with that from phase space considerations, namely that it should be a factor of 6.2 less abundant than the lambda-beta mode.
Beta-decay of the charged S-hyperons: the T8 collaboration was one of the first groups to publish a value for the decay rate:

S^- -> n + e^- + n
The analysis made extensive use of the UCL Monte Carlo method developed in connection with the Lb experiment. A value of (1.15 ± 0.4) x 10^-3 was found for the branching ratio:

S^- -> (n + e^- + n) / S^- -> (n + p^-)
by Miller, Stannard et al. No examples of the leptonic decay of the S⁺ hyperon were found in a sample of 11,000 normal-mode decays of S⁺ particles.
A search was made in the T8 film for the decay:

w^o -> e⁺ + e^-
Only one probable event was found by B. S. Luetchford, Stannard et al; this allowed an upper limit of 2.8 x 10^-3 to be placed on the ratio of the decays:

w^o -> (e⁺ + e^-) / w^o -> (p⁺ + p^- + p^o).
Investigations into X-hyperon properties: although the heavy liquid bubble chamber has no particular advantages over the hydrogen chamber in the study of the decays of X^--particles:

X^- -> L^o + p^-
the detection of g-rays from p^o by conversion into electron pairs is an ideal technique for studying X^o-decays:

X^o -> L^o + p^o
Film from the T8 and T11 experiments was used for investigations into the properties of X hyperons. These included determinations of the masses of X^- and X^o, giving a mass difference of (6.8 ± 1.6) MeV/c² in excellent agreement with the value of (6.7 ± 0.4) MeV/c² deduced from the SU₃ model; the lifetimes of these hyperons, including the first determination of that of X^o ; and the asymmetry parameters in the X^- decay.
Low energy p - p interaction: study from Ke₄ decays:
In the autumn of 1965 the Group initiated and organized an experiment at CERN involving collaborating groups from Berkeley and Wisconsin to study the rare K⁺ decay mode:

K⁺ -> p⁺ + p^- + n + e⁺
530,000 pictures were taken at the CERN proton synchrotron in the CERN heavy liquid bubble chamber, the exposure yielding 13 x 10⁶ stopping K⁺. The chamber was filled with C₂F₅Cl which has a radiation length of 25 cm. The film was equally divided between the three collaborating teams and yielded 269 events of interest, a significant increase on the previous world total of 69. The branching ratio for the rare decay mode was found to be (3.25 ± 0.35) x 10^-5 and the values of four form factors were determined, the importance of two of them being established for the first time. Perhaps the most important result to emerge from this work was an estimate of the low energy p - p S-wave phase shift.
No evidence was found for the existence of a s-meson. The study provided further weight to the principle of time reversal invariance and the locality of lepton production.
No example was found of the mode:

K⁺ -> p⁺ + p⁺ + n + e^-
giving an upper limit of 7 x 10^-7 at the 95% confidence limit. The absence of such a decay provided evidence in favour of the DQ = DS rule for axial-vector currents in weak interactions. Messrs. Billing, Bullock, Esten, Govan, Henderson, Knight, Miller, Tovee and Treutler took part in the work.
[*Prefix E added at suggestion of D Miller, email to JG, 10.12.12]

Search for evidence of C-violation:
On returning to England the Group became involved with what started as an engineering run of the newly commissioned UCL-RHEL heavy liquid chamber at the Rutherford laboratory. A 930 MeV/c p⁺ beam from Nimrod was directed in the chamber containing CF₃Br, its short radiation length of 11 cm making possible the search for the suggested C-violating decay mode:

h -> p^o + e⁺ + e^-
where the decay gammas from the p^o are detected by their conversion to e⁺e^- pairs in the liquid. In the experiment, which was carried out in collaboration with Oxford, 600,000 pictures being taken. It resulted in no example of the decay mode being found, leading to an upper limit to the branching ratio of 3.7 x 10^-4 at the 90% confidence level, a value smaller than any previous result by a factor better than two. The aforementioned team members, except Treutler, were joined by Owen, Stannard and Miss E. Tompa in the search. The decay modes of the eta meson were also studied in the experiment, a measurement of the ratio:

h -> 3p^o / h -> p⁺ + p^- + p^o
being made. 170,000 pictures from the run yielded 260 events with five gammas and 70 events in which all six from the 3p^o mode converted, the events being selected by means of a template which excluded subjective assessment of background arising from bremsstrahlung gamma-rays. The final evaluation of the ratio was R = 1.47 (+0.20, -0.17), an estimate in satisfactory agreement with theory. The Group members involved in this measurement were Bullock, Esten, Miss Tompa, Govan, Henderson, Owen and Stannard. The experiment also led to the observation for the first time of electron pairs of high invariant mass in 830 MeV/c p⁺-nucleus interactions by Esten, Govan, Knight, Miller and Tovee. This was one of the first manifestations of vector meson dominance of the coupling of the photon to strongly interacting particles.
The second major experimental investigation with the UCL-RHEL chamber was a study of the lifetime and decay parameters of the X hyperons, which started in the autumn of 1968. The chamber, filled with a propane-freon mixture of radiation length 30 cm, was exposed to a 2.1 GeV/c separated K^- meson beam from Nimrod. 640,000 pictures were taken with a mean of 2.8 interacting K^- per picture. Workers from CERN, Brussels University and Tufts University, USA joined the Group in the investigation. The X^o and X^- lifetimes and parameters were measured to be (3.04: +0.26,-0.23) x 10^-10 and (1.73: +0.08,-0.07) x 10^-10 sec respectively; and (- 0.84 ± 0.27) and (-0.42 ± 0.11) respectively. These values agreed with measurements using different techniques and were consistent with predictions of the I = ¹/₂ rule. The experiment also permitted a direct determination of the X^o and X^- masses, namely (1315.2 ± 0.9) MeV/c² and (1312.12 ± 0.41) MeV/c² respectively. Messrs. Azemoon, Bartley, Miller and Stannard joined in the investigation.
During the 1966-67 Session the Group became actively concerned with the CERN project, initiated by the French under Prof. A. Lagarrigue, for building a very large, heavy liquid chamber, called Gargamelle. The following Session saw the combination of the Bubble Chamber and Emulsion Groups under the general leadership of Burhop, the work of the former being split into two sections, Gargamelle, headed by Esten, and UCL-RHEL, headed by Stannard, Davis remaining in charge of the Emulsion Section. The sections were not exclusive, members of the combined group assisting in machine exposures for a particular section and some work involving different sections. In the 1968-69 Session a grant of £201,000 was received from the SRC for setting up a Gargamelle film analysis unit. This enabled the recruitment of technical staff and the purchase of a Honeywell DDP516 computer for the on-line analysis of Gargamelle film when the chamber became operational. Thus the team became the only British one involved in the European Gargamelle collaboration, consisting of laboratories from Aachen, Brussels, CERN, Ecole Polytechnique, Milan, Orsay and UCL.
The UCL team consisting of Bullock, Esten, Jones, McKenzie, A. G. Michette, R. H. Schafer and R. G. Worthington, were involved in obtaining a 'double first' from Gargamelle in 1972, namely the first observation of hyperon production by antineutrinos in the first experimental results from the chamber. The production of L^o and X^o- hyperons by the CERN antineutrino beam traversing the chamber was used to estimate the production cross-section on protons, the result being compared with predictions of the Cabibbo theory for the process. However this was completely overshadowed by the discovery of the existence of neutral currents in the summer of 1973, an event acclaimed by the Director-General of CERN as the most important and significant discovery made in fifteen years of experimentation at CERN. A search was carried out for neutrino-like interactions without muons or electrons among their secondaries, the motivation being the lack of experimental data on semi-leptonic interactions induced by neutral currents. Interest in the subject had been revived by the development of renormalizable theories which unified the weak and electromagnetic interactions and required the existence of neutral currents. In the experiment, the Gargamelle chamber, of length 4.8 m, diameter 1.8 m, was filled with heavy freon, CF₃Br of density 1.5 x 10³ kg m^-3, providing a total detector mass of about 10 tons, situated in a magnetic field of 2 T; and it was exposed to the CERN neutrino and antineutrino beams. In the analysis based on 83,000 neutrino and 207,000 antineutrino pictures, the former pictures yielded 102 events not containing a muon or electron, and 428 containing only one muon, among the interaction products, whereas in the latter pictures the corresponding numbers were 64 and 148. The UCL team involved consisted of the aforementioned members, with the exceptions of Messrs. Schafer and Worthington being replaced by Messrs. G. Myatt and W. G. Scott. The personal contribution of Bullock, the leader of the UCL team, was so outstanding that he was selected by the European collaboration to make the first presentation of the discovery at the International Symposium on Electron and Photon Interactions at High Energies held in Bonn, August 1973.
Other experiments of the collaboration in the Massey period included (1) a search for elastic muon neutrino electron scattering which revealed for the first time one event in which a muon antineutrino scattered off an electron; (2) a measurement of high energy, total cross-sections for electron neutrino and antineutrino scattering by nucleons, including a test of the muon number conservation law, and the placing of a limit of 2.4 GeV/c² for the mass of the 'Georgi-Glashow' type heavy lepton; (3) a measurement of total cross-sections for muon neutrino and antineutrino scattering by nucleons as a function of energy, the results being compared with predictions of scaling and charge symmetric hypotheses; and (4) a determination of the differential cross sections in freon of inclusive charge-changing neutrino and antineutrino interactions on nucleons in the energy range 1-11 GeV with respect to Bjorken scaling variables, the observed quark and antiquark momentum distributions being compatible with the predictions of quark-parton models fitted to electron scattering data. The common members of the UCL team, namely Bullock, Esten, Jones, McKenzie and Michette, were joined by Myatt, J. Pinfold and Scott in (1); by Myatt and Pinfold in (2); by M. Derrick, Myatt and Scott in (3); and by Myatt and Scott in (4).
In the spring of 1969 the UCL-RHEL section of the Group was associated with physicists from CERN and RHEAS in testing a new technique, involving a track-sensitive target (TST) of liquid hydrogen in a hydrogen-neon chamber, in the 1.5 m cryogenic bubble chamber at RHEL. It was demonstrated that adequate measurement accuracy on tracks within the hydrogen target could be obtained whilst recognising the characteristic spiral of electron tracks in the heavy hydrogen-neon mixture outside. In 1973 the UCL group collaborated with groups from the universities of Durham and Warsaw in a TST experiment which was to become the most complete study to date of the low energy K^-p interaction. The liquid outside the target was a molar mixture of 0.78 neon and 0.22 hydrogen, chosen to give enhanced conversion of gamma rays to electron pairs with a radiation length of c. 45 cm compared with c. 10 m in hydrogen. A negative kaon beam, produced at 0 C from a copper target in a proton beam extracted from the RHEL, NIMROD accelerator, was transported at 620 MeV/c to the chamber, where it was degraded to c. 250 MeV/c by a block of aluminium inside the chamber in order to stop most of the kaons inside the hydrogen. 225,000 pictures were taken and analysed, the results being presented in a series of five papers. These were entitled 'Charged sigma hyperon production by negative kaon meson interactions at rest' (R. J. Nowak, J. Armstrong, D. H. Davis, D. J. Miller and D. N. Tovee et al); 'The Kbar-N channels at low energies' (D. J. Miller); 'Kaon scattering and charged sigma hyperon production in K^-p interactions below 300 MeV/c' (J. H. Bartley, D. H. Davis, D. J. Miller, D. N. Tovee and T. Tymieniecka et al); 'Charge-exchange scattering in K^-p interactions below 300 MeV/c' (J. E. Conboy, D. J. Miller and T. Tymieniecka et al); and 'Neutral hyperon production in K^-p interactions at low momentum' (J. E. Conboy, D. J. Miller and T. Tymieniecka et al). The results of this TST comprehensive study of the low energy K^-p interactions corrected previous measurements of the ratios of the charged sigma hyperons produced at rest, and measured the difference between the I-spin 1 and I-spin 0 scattering lengths with great precision. They also demonstrated the persistence of p-waves in the lambda-final state down to the lowest accessible energy.

Spark Chamber/High Energy Physics Counter Group

Before establishing this group Heymann and his collaborators, namely D. G. Davis, R. C. Hanna and C. Whitehead, took part in an international successful experiment with the CERN synchrocyclotron to test the conservation of parity in strong interaction processes. Later, in a co-operative project with AERE, Harwell, he led the UCL team, including Messrs. Davis and Ghani, who were joined by R. C. Hanna, A. L Read and G. Heymann, in a study of the polarization of protons recoiling from collisions with neutral pions at 265 MeV. This was a difficult experiment because of the poor quality of the available meson beams, but Heymann devised a new polarimeter, the 'Venetian blind counter', to overcome these difficulties.
It was early in 1961 that Heymann began work on the development of spark chambers when they were still in the initial development stage. Rapid progress was made and in 1963, in collaboration with the Westfield College Spark Chamber Group, spark chambers and scintillation counters were used to study the production of neutral pions in collisions between ingoing 600 MeV protons and stationary protons in a liquid hydrogen target at CERN, enabling a comparison to be made between experiment and Selleri & Ferrari theory. The collaboration then undertook a study of the elastic scattering of positive and negative pions by protons at a range of energies near 2 GeV to investigate the spins and parities of two pion-nucleon excited states, N*_1/2(2190) and N*_3/2(2420), then recently discovered in that energy range. The experiments were carried out at RHEL using pion beams produced by bombarding an internal target with protons in NIMROD, the 7 GeV proton synchrotron. Ten differential cross-sections were measured in the range 1.72-2.80 GeV/c pion laboratory momentum for both positive and negative pion-proton collisions. The results were analysed on the bases of optical models and Legendre polynomial expansions, and the interpretation of the structure of differential cross-sections in terms of interference between resonant and background amplitudes was critically examined. The data provided by this group of experiments continued to be used in new and improved phase-shift analyses of the pion-nucleon system. Members of the group involved in this work were W. Busza, B. G. Duff, D.A. Garbutt, F. F. Heymann, C. C. Nimmon, K. M. Potter and T. W. Swetman.
Then in 1965 a combined UCL spark chamber and nuclear emulsion group, together with the University of Brussels group and the European K^- collaboration representative, demonstrated at CERN the viability of the combined techniques to locate rare neutrino interactions in a large emulsion stack.
Following the development of a PDP-8 computer-controlled, system of scintillation counters and core-readout wire spark chambers, the group collaborated with RHEL in a series of experiments on kaon-proton elastic scattering to advance the understanding of the kaon-nucleon interactions. Firstly the differential cross-section for K⁺p elastic scattering was measured at 26 incident laboratory momenta between 1.4 and 2.3 GeV/c in an experiment using an unseparated beam from NIMROD at RHEL. Diffractive behaviour was found at the lowest measured momentum, becoming more prominent with increasing momentum. An expansion of the angular distributions in terms of Legendre polynomials showed no marked structure of the expansion coefficients as functions of the incident momentum. The measurements could be adequately described by a number of existing phase-shift solutions within 5% of their published values; also Regge-pole extrapolations represented the data satisfactorily. This was followed by measurements of the differential cross-sections of K^-p elastic scattering at 13 incident laboratory momenta between 1.094 and 1.377 MeV/c, a region where there had been few previous measurements, and thereafter at 19 momenta between 1.732 and 2.466 GeV/c. The former data showed the characteristic forward diffraction-like peak and backward dip, and were adequately described in shape by certain published partial-wave analyses of the KN system. Strong diffractive peaks, followed by dips, were exhibited by the latter data. The differential cross-sections were fitted to a linear superposition of Legendre polynomials, there being some structure in the coefficients at c. m. energies near 2180, 2270, 3214 and 2370 MeV, but it was not possible to extract possible resonance parameters without a full partial-wave analysis.
The UCL-RHEL collaboration also used the computer-controlled system of scintillation counters and spark chambers to measure the differential cross-sections for elastic scattering of negative pions by protons at 16 momenta between 996 and 1342 MeV/c corresponding to a centre of mass energy range of 1670 to 1850 MeV, where there was some confusion about the existence and properties of nucleon resonances with masses near 1700 MeV. Some of the data and previously published cross-sections were in excellent agreement. The cross-sections were compared with the predictions from two recent phase-shift analyses of the energy-independent type, from which it was possible to obtain good fits over the entire momentum range. Messrs. P.A. Barber, T. A. Broome, B. G. Duff, F.F. Heymann, D. C. Imrie, G. J. Lush, E. N. Mgbenu. K. M. Potter, L. A. Robbins, R. A. Rosner, S. J. Sharrock and A. D. Smith comprised the UCL team involved in these collaborative investigations. When the International Storage Rings (ISR) became operational at CERN in 1971, the Group became involved in an international collaboration between British and Scandinavian universities, RHEL and CERN to carry out ISR experiments. B. G. Duff, who was attached to CERN as a Visiting Scientist from 1971-72, played a leading role in these experiments. In the first experiment a large solid angle, muon detector was used to measure the high energy, transverse momentum, muon spectra to provide evidence for the existence of the intermediate vector boson, a carrier of the weak electroforce. A study of selected events from c. 500,000 pictures showed agreement with muon spectra predicted by Monte Carlo calculations, but no evidence for the production of the boson. However the upper confidence limit for the production cross-section of single muons with momentum greater than 6 GeV/c implied a new, very much higher, minimum mass limit for the existence of the boson. Another experiment involved measurements on massive particle production at 62.5 deg to the bisector plane of the ISR for 53 GeV c. m. energy, including a search for quarks. Although no quarks were seen among the 7 x 10⁷ charged particles entering the detector, a remarkably large number of antideuterons were observed, the relative rate of production of antideuterons to negative pions being (5 ± 1) x 10^-5 at transverse momentum 0.7 GeV/c, the deuteron to antideuteron rate being 3.7 ± 1.2. In a series of experiments, single-particle inclusive spectra were obtained for charged pions, kaons and protons in proton-proton collisions at c. m. energies from 23 to 63 GeV at angles from 30 to 90 deg and for the transverse momentum range 0.1 to 4.8 GeV/c. Over ten million events were recorded on magnetic tape and analysed using the RHEL 370/195 computer. The observed charged-particle, production spectra indicated the existence of two domains, a low and a high transverse momentum domain, with a transition region at 1.0 to 1.5 GeV/c. The domains were different with respect to the form of the transverse momentum distributions, the dependence of the production cross-sections on the collision energy, and the composition of the charged-particle flux. The low transverse momentum data in the central region did not show a constant energy-independent particle production as suggested by the Feynman scaling laws. The profusion of particles produced with high transverse momentum provided strong indications of an inner structure of the proton. Finally, the particle ratios provided an important test for the various models of the strong interaction at high energies. Messrs. B. G. Duff, F. F. Heymann, M. N. Prentice, K. M. Potter, D. R. Quarrie and S. J. Sharrock were involved in these ISR experiments.
In the last collaboration undertaken in the Massey period, elastic scattering and coherent single, and double, pion production in proton-helium interactions at 18.6 GeV/c were investigated with groups from Uppsala and CERN. The elastic t-distribution was found to have a somewhat steeper slope than predicted by the Glauber approximation, and the inelastic angular distributions involving single-pion production were consistent with several spin-parity states contributing at all nucleon-pion masses. The main aim of the double-pion production experiment was to look for features in the distributions of mass and angles of the p^+- system, which could originate from the fact that the system was produced only by isospin-zero exchange. Two enhancements in the p^+- mass spectrum were found at 1.49 and 1.71 GeV/c², both well fitted by Breit-Wigner resonances. The decay angular analysis indicated the presence of several interfering states in the 1.5 GeV/c² mass region and one state of spin, possibly ⁵/₂, in the 1.7 GeV/c² mass region. Some preference was shown for t-channel helicity conservation. The similarity of the data to proton-target results provided independent support for the hypothesis that vacuum exchange was dominant in the production of low-mass double pion states in pp interactions around 20 GeV/c. Members of the group involved in the collaboration were P. C. Bruton, J. K. Davies, S. M. Fisher, F. F. Heymann, D. C. Imrie, G. J. Lush and J. Nassalski.
As already mentioned the Group participated in the WA75 experiment, using a combination of electronic and emulsion techniques at CERN in 1985, which revealed the first example of the hadronic production of a pair of beauty particles, together with their decays into charmed particles, both of which also decayed in the emulsion.

Space Science

The Gassiot Committee of the Royal Society had taken the lead in developing a research programme in atmospheric, including upper atmospheric, physics through its three sub-committes since 1941. The possibility of the exploration of atmospheric structure and the direct observation of solar ultra-violet and X-radiation by means of rocket-propelled vehicles greatly interested British research workers. Following a proposal by Prof. S. Chapman in 1951, the Committee invited the American Upper Atmosphere Rocket Panel to participate in a conference on rocket exploration of the upper atmosphere. Massey, who had become Chairman of the Gassiot Committee in 1951, chaired the small sub-committe appointed to organise the conference. Rather surprisingly, it was left to F. Singer, the American liaison officer in London who was involved in both the scientific and technological aspects of space exploration, to suggest that certain key personnel in the Ministry of Supply, concerned with rocket development, should be invited to attend the conference. This was done immediately and the conference was held in Queen's College, Oxford from 26 to 29 August 1953.
Meanwhile, on the morning of 13 May 1953 when Massey was just preparing to leave his room at UCL for the annual departmental cricket match between staff and students at Shenley, he received a telephone call from a Ministry of Supply official asking whether he would be interested in using rockets from the Ministry for scientific research. Immediately he replied "Yes" and went in search of Boyd and repeated the question! Naturally Boyd welcomed the prospect of the direct application of his probes in the exploration of the ionosphere. He spent two months of the 1953 summer vacation at the Royal Aircraft Establishment, Farnborough gaining experience on the technical side of rocketry. During this period he first met M. O. Robins, who was later seconded to assist Massey in all matters relating to rocket and satellite research. Initially Robins was based in the department, but in the early part of 1963, the small team which had grown up under him, moved to office premises in Chester Gate, Regent's Park, becoming the Space Research Management Unit. In March 1954 Massey was awarded a grant for the employment of G. V. Groves, for one year in the first instance, to undertake preliminary work on rocket instrumentation in the department; Groves had been a Scientific Officer at the Royal Aircraft Establishment and the Headquarters of the Ministry Aviation since graduating at Cambridge in 1948. His experience of rocketry, combined with his ability in theory and practice, proved invaluable, and he was appointed to a lectureship in 1956.
The first experiment, selected by Boyd and Groves, was designed to measure the temperature, density and wind distribution in the atmosphere up to c. 80 km by application of a sound-ranging method, based on a series of 18 explosions from grenades ejected at regular intervals during the upward trajectory of a Skylark rocket. After much experimentation at various locations in the UK, including Shoeburyness, the first successful experiment was carried out at the Woomera range in Australia on the night of 13 November 1957, using ballistic cameras, photoelectric flash detectors and an array of microphones on the ground. The cameras photographed the flashes against the star background enabling them to be located accurately in position; the flash detectors recorded the arrival of light from each grenade flash thereby enabling the times of each explosion to be determined; and the array of microphones recorded the time of arrival of the sound pulse from each explosion at a number of known locations - an array rather than a single microphone being necessary owing to the tilting of the wave front of the sound by horizontal winds and refraction. These data enabled the mean value of the speed of sound between each explosion, and hence the mean atmospheric temperature, and the mean horizontal wind speed to be determined; of course a great deal of analysis was involved, the method being worked out by Groves. In the second experiment on 17 April 1958 grenades exploding above c. 100 km were found to produce a conspicuous bright glow arising from photochemical reactions between the explosion products and atomic oxygen. The glow lasted for about 20 min. and observations of its motion through the air and its rate of expansion enabled the wind speed and the diffusion coefficient of the glow gases through the local atmosphere, which gave an estimate of the local air density, to be obtained. In this way the range of the experiment was extended beyond the 80 km limit set by the background noise in the microphones. On 3 December 1958 there occurred the first successful grenade firing producing a strong twilight glow of sodium vapour ejected from the rocket at an altitude of 100 km. Observations of the Doppler width of the sodium D lines by D. R. Bates (who had suggested the experiment in 1950 - the first suggestion of an active experiment from a rocket) and E. B. Armstrong yielded data on the ambient atmospheric temperature, and those by Groves on the motion of the vapour cloud gave the wind speed. This was the last of seven grenade experiments, which, by good fortune, took place during the International Geophysical Year.
An account of the first grenade experiments at Woomera during 1957-59 was given by Messrs. P. J. Bowen, R. L. F. Boyd, M. J. Davies, E. B. Dorling, G. V. Groves and R. F. Stebbings in Proc. Roy. Soc. Vol. 280, 170, 1964. Almost the entire staff of the department concerned with space research co-operated in the development of the grenade programme until Groves took over responsibility for the whole programme. Further consideration of this aspect of the work is therefore deferred until the section dealing with Groves's Space Science and Atmospheric Structure Group (pp.100-103).
Early on Boyd and Willmore prepared to determine the electron concentration and temperature in the ionosphere by means of a Langmuir probe mounted ahead of the rocket on a four-foot spur to diminish the effect of disturbance by the rocket. They also prepared to measure the intensity of the solar Lyman-alpha radiation by means of the Friedman technique involving a tubular counter containing nitric oxide and provided with a LiF window so that the counter responded to radiation in a narrow band around 121.6 nm. Experiments were also initiated for the measurement of the solar X-ray radiation firstly by means of a photographic method, then with photon counters having different foil thicknesses as windows, and thereafter obtaining higher resolution by pulse height analysis. These experiments were first flown in Skylark rockets in 1959, thus initiating solar X-ray studies by British physicists. In 1960 K. A. Pounds, who had worked on these detectors as a research student, joined the Department of Physics at Leicester University, the head of department, Prof. E. A. Stewardson, an X-ray physicist, having taken a close interest in the work from the start. Thus began a second major X-ray astronomy group in the UK. From the outset there was close collaboration between the two groups. By the end of 1958 several of these experiments were ready for flight, the remainder being in an advanced stage of development.
In March 1959 it was announced that the USA through the National Aeronautical and Space Administration (NASA) would be prepared to launch research satellites for other countries. The offer was taken up by Britain and in December 1959 the payload of the first satellite was planned, taking advantage of experience gained in the Skylark rocket programme. It was largely concerned with observations of the high altitude ionosphere and of solar radiations effective in producing the ionosphere. The UCL group was responsible for five of the seven experiments involved; these including the principal people involved were as follows:-
(i) measurement of electron density and temperature by Langmuir probes (Boyd & Willmore);
(ii) determination of ion composition and temperature by positive ion spectrometer (Boyd & Willmore);
(iii) measurement of solar radiation in a particular waveband by X-ray spectrometer (Boyd & Willmore in association with Stewardson & Pounds);
(iv) detection of solar Lyman-alpha radiation (Bowles & Willmore);
(v) detection of solar aspect angle (Alexander & Bowen).
The probes were operated in the a.c. mode, which has many advantages over the d.c. mode for use in satellites; the properties of the ionosphere were deduced from the first and second derivatives with respect to probe voltage of the current-voltage characteristic, the derivatives being transmitted in real time by the satellite telemetry system. The positive ion spectrometer was of an unusual type depending on measurement of the energy density of the ions relative to the satellite; it took into account the kinetic energy of an ion relative to the satellite due to the satellite's velocity.
The satellite was named Ariel 1 on its establishment in orbit by a Thor-Delta launch vehicle from Cape Canaveral, later renamed Cape Kennedy, on 26 April 1962. All of the experiments were successful except (iv), in which none of the three sensors produced any data, presumably owing to an electronics package breakdown. Fortunately this loss was not important since by the time the satellite was launched it was known that the secular variations of solar Lyman-alpha were of negligible ionospheric significance. Despite the setback due to the hydrogen bomb explosion, code-named "Starfish" on 9 July 1962, results were obtained up to 9 November 1964. A total of 11,910 data tapes were received from the tracking and data acquisition stations; from these tapes no less than 3,307 hours of data were successfully processed, representing 595 million data points. The orbit finally decayed and the satellite was destroyed on entering the atmosphere on 24 May 1976.
On 2-3 May 1963, a discussion meeting on the results then obtained was held at the Royal Society under Massey's leadership (Proc. Roy. Soc. A. Vol. 281, 438, 1964). At this meeting Bowen, Boyd, W. J. Raitt and Willmore described their observations of ion composition, the first systematic observations of both the light ions H⁺ and He⁺ and the heavier ions such as O⁺, although earlier observations of He⁺ and O⁺ had been made on separate occasions. Positive ion transition altitudes as a function of solar zenith angle were presented. For O⁺ - He⁺ this is the altitude at which the O⁺ and He⁺ concentrations are equal, He⁺ being dominant at higher altitudes until the H⁺ - He⁺ transition altitude is reached. A large number of systematic observations of this kind were made and proved very useful for the interpretation of the behaviour of the high atmosphere. Bowen, Boyd, C. L. Henderson and Willmore gave an account of measurements with two probes, one located flush with the satellite skin on the spin axis, the other on a boom, c.1.2 m in length, with the normal to the probe surface parallel to the spin axis, but oppositely directed to the normal to the other probe, showing the ionospheric electrons to have a Maxwellian energy distribution, any non-Maxwellian, high energy 'tail' including less than 1% of the total. Measurements of the charge distribution round the satellite were in good agreement with theory, the satellite exhibiting no 'ram' effect, but a very marked depletion of charge was noted in the wake; no associated effect on the electron temperature was detected; and some evidence was found for the occurrence of plasma oscillations in the wake. The electron temperature distribution between 400 and 1200 km was found to be subject to strong control by the geomagnetic field, and to exhibit an increase with geomagnetic latitude and altitude. The daily average temperature was correlated with solar 2800 Mc/s radiation and increased at about the same rate as the neutral gas temperature. Measurements of the solar spectrum in the X-ray wavelength band from 0.4 to 1.4 nm were described by Bowen, K. Norman, Pounds, P. W. Sanford and Willmore. Such observations were of special interest during solar flare disturbances leading to communication blackout through enhancement of ionization and hence absorption at D region heights. Many such observations were made from Ariel 1. The variation of X-ray intensity with wavelength emitted by the sun at different stages of a solar flare showed that at the height of the flare not only was the overall intensity increased, but it extended to much shorter wavelengths. This was the first satellite study of soft X-rays using proportional counters.
Boyd and Susan Laflin analysed in detail the ion mass spectrometric data obtained from Ariel I in its survey of the topside ionosphere over the latitude range of ± 55%. The ion energy spectrometer measurements showed the ions O⁺ and He⁺ to be the major massive components of the ionosphere and enabled a global study of the composition over the northern summer of 1962 to be made. Earlier analyses of parts of the data had shown a diurnal and seasonal variation in the composition, a strong geomagnetic control and a suggestion of a departure from hydrostatic equilibrium in the diffusive separation of the ions. Their definitive presentation of the computer analysis of almost all of the ion composition data obtained by the energy spectrometer, and its regression analysis in terms of geomagnetic latitude, altitude and local solar time, confirmed and strengthened the earlier conclusions. Total ionization density measurements and a study of the effect of vehicle aspect on them were also given.
The notable achievement of Ariel I in making the first world-wide survey of the topside ionospheric composition and temperature, showing the strong effect of the earth's magnetic field and the control of the electron temperature by ionic concentration, was responsible for the invitation to instal similar instrumentation on the NASA ionospheric satellites, Explorer XX and XXXI. Studies by the topside sounder satellite Alouette I had revealed the importance of including equipment to give direct measurements of ion mass spectra and temperatures. Hence a UCL positive ion mass spectrometer was included in the US topside sounder satellite, Explorer XX, launched on 25 August 1964. This provided a large amount of data on the ion composition and temperature of the upper F-region at an altitude of c. 1000 km, and over a latitude range of 80 deg N to 80 deg S. Initial analysis showed that the resolution of the spectrometer was far superior to that flown on Ariel I; the shapes of the peaks agreed much closer with theoretical predictions. Data from high magnetic latitudes showed a marked deficiency in the ion density, further investigation confirming that the onset of ionization when emerging from the region could be very rapid.
Explorer XXXI and Alouette II topside sounder were launched on 29 November 1965 into an 80 deg prograde polar orbit, with a perigee of 500 km and an apogee of 3000km, as part of the ISIS (International Satellites for Ionospheric Studies) programme. An important objective of the mission was to compare the sounder measurements with simultaneous direct ones made at the same position by the satellite in order to improve the understanding both of the techniques involved and the physics of the ionosphere. There were six direct measurement probes on Explorer XXXI: planar ion trap for ion density, temperature, and composition; planar electron trap for electron density and temperature; cylindrical electrostatic probes for electron density and temperature; magnetic ion mass spectrometer for ion density and composition; planar Langmuir plate for electron temperature; and spherical ion probe for ion density, temperature, and composition. The first four were US probes, the last two being UCL ones. Electron temperatures measured by the three different probes generally agreed to within 10%; ion compositions measured by the planar ion trap and the spherical probe showed good agreement with those by the high resolution magnetic mass spectrometer; ion temperatures measured by the ion trap were consistently higher than those by the spherical probe; and plasma densities measured by the various probes generally agreed with simultaneous Alouette II sounder values to within 20%. Measurements of electron temperature, ion composition and temperature by the UCL instruments were compared with corresponding values determined by RSRS from Alouette II ionograms for selected passes 11when the two satellites were close together only seconds apart. Electron concentration measurements by the sounder were used for in-flight calibration of the probe total positive ion concentration measurements, and an effective grid transparency for the probe was obtained. This transparency, apparently different for different ion species, was 38% for hydrogen ions and 42% for oxygen ions. Data were combined with Alouette II scale height determinations to test the adequacy of thermal diffusion theory in the topside ionosphere.
The composition of the ionosphere during the early months of the satellite's life changed from O⁺ near perigee to H⁺ at apogee; He⁺ was not observed as a dominant ion at intermediate altitude as with Ariel I in 1962. However in 1966 He⁺ rapidly reappeared as a major constituent, thereby showing its strong solar cycle variation. The height of transition of ion composition from O⁺ to H⁺ was found to depend markedly on local time, being some 150 km higher during the evening than at early morning, and varying significantly with longitude, but showing little dependence upon latitude up to 50 deg. Observations during a series of six magnetic storms in the first half of 1967 showed that in mid-latitudes, for altitudes up to 1500 km, strong enhancements of electron temperature, of order 800 K, were common, generally being accompanied by depressions of total ion density. This contrasted with earlier observations of Ariel I in which storm temperature enhancements were practically absent. Mid-latitude variations in ion composition showed no consistent pattern; for a storm in February 1967 O⁺ showed an increase of only about 30%, while the light ions increased by up to a factor of 4; in the great storm of May 25, the light ions showed no variation, while O⁺ increased by a factor of 3; and in a storm on 6 June, there was negligible variation in O⁺, but the light ions decreased by a factor of 2. Variations in ion temperature had not then been reliably observed. Simultaneous observations of electron temperature, ion temperature and electron (or total ion) density were made with the Thomson backscatter group in France when the perigee of the satellite was near the latitude of the scatter station at St. Santin. Although the scatter measurements referred to the altitude range, 275-425 km, while the nearest satellite ones were at 550-600 km, the agreement between the extrapolated scatter and Langmuir probe data was excellent. The comparison made clear the necessity for caution in interpreting satellite probe data in terms of altitude profiles in view of the presence of strong latitude variations, since in the comparison the satellite data for 520-540 km were at a higher latitude and showed the the then well-known increase in electron temperature with latitude.
Starting in 1959 with a Skylark rocket launched from Woomera on 8 July, some sixty rockets were involved in experiments on atmospheric, ionospheric and solar physics, and stellar ultra-violet astronomy before the Space Research Group, under Boyd, became fully operational as the Mullard Space Science Laboratory at Holmbury St. Mary at the start of the 1966-67 session. That first rocket, which attained a height of 93 km, carried Langmuir probes to determine electron and ion concentrations, and solar X-ray detectors. The majority were unstabilised Skylark rockets, launched from Woomera in the British national programme, although a low accuracy sun pointing Skylark was included, being flown on 5 May 1966. In the European Space Research Organisation (ESRO) programme two Skylark rockets, carrying electron temperature probes to study the electron temperature in the middle ionosphere, were launched from Sardinia in 1965. In this programme six Centaure rockets were launched from Andoya, Norway in 1966, four carrying positive ion probes to study the fine structure of auroral ionisation, and two carrying ion energy spectrometer probes to study the identification and concentration of ions in aurorae. In the ESRO expedition to Greece for the annular solar eclipse on 20 May 1966 two Centaure and five Arcas rockets were launched from Euboea at various stages of the eclipse, the former carrying electron temperature probes and hydrogen Lyman-alpha detectors to study the electron temperature in the lower ionosphere and the solar Lyman-alpha flux, and the latter carrying fixed potential positive ion probes to study the D-region ionization. Earlier on 15 May two rockets had been fired, a Centaure rocket to study the total solar X-ray flux in the 1-3 Å band, and a prototype Arcas rocket. It was shown that the X-rays rather than the Lyman-alpha radiation were responsible for the ionization. Eight Centaure rockets were also fired from Hammaguir in the Sahara in French co-operative programmes in the study of sporadic E ionization. Positive ion probes were flown in the first pair in 1963, electron temperature probes being added to the second pair in 1964, and to the quartet, which in the 1965/6 winter made altitude profile measurements of electron temperature and density, positive ion density and wind speed.
The first observations of stars in the Southern sky at ultra-violet wavelengths between 1700 and 2000 Å were made by Heddle, Alexander and Bowen during the flight of an unstabilised Skylark rocket launched from Woomera on 1 May 1961. Five 'telescopes', each consisting of 10 cm lengths of aluminium honeycomb, were fixed at different angles in the rocket head. Photocells with sharply peaking sensitivity at c. 1900 Å detected radiation collimated by the telescopes as the rocket rolled and changed attitude during flight. The attitude of the rocket was to be measured by means of a moon detector, a magnetometer, and a camera photographing the star background, but only the records of the moon detector proved satisfactory. Two of the telescopes detected ultra-violet radiation from 22 stars; these were identified and the ratios, in each case, of the flux at 1900 Å to that at 5390 Å was determined.
The proportional counter spectrometer on Ariel I had recorded the intensity of X-radiation from the solar disc in the wavelength range 5-12 Å, and although the occurrence of the solar flare stood out against this background, it could not be localised. The UCL and Leicester teams planned an extensive programme after Ariel I, proposing X-ray cameras as standard auxiliary equipment on each Skylark rocket. In anticipation of sun-stabilised Skylark rocket, they planned to study the distribution of X-ray sources over the sun using a grazing incidence paraboloidal reflector with a suitable detector at the focus.

By 1966 the newly formed Mullard Space Science Laboratory was carrying out or planning experiments on both the neutral and ionized atmosphere, on the magnetosphere, on the quiet and disturbed sun, on aurorae, and on stars in both ultra-violet and X-ray wavelengths. Its programme of instrumental preparation for satellite launchings and rocket firings was most impressive, as is shown by the following table, listing satellite, instrument, and experiment.

OSO-D	Broad-band X-ray spectrometer; total solar soft X-ray flux * Ultra-violet monochromator; total solar flux of He II 304 Å radiation
OSO-F	X-ray scanning spectroheliograph; solar X-rays from quiet and disturbed regions *
OSO-G	Extreme ultra-violet polychromator; solar 170-1000 Å flux
OAO-C	X-ray telescope; X-rays from galactic sources
OGO-E	Electron temperature probe; electron temperature in magnetosphere
ESRO I	Electron temperature probes & positive ion energy spectrometer; polar ionosphere
ESRO II	Broad-band X-ray spectrometer; total solar soft X-ray flux *
TD2	Extreme ultra-violet polychromator scanning spectroheliograph; solar extreme ultra violet Ionosphere probes; polar ionosphere

OSO, OAO and OGO are NASA's Orbiting Solar, Astronomical and Geophysical Observatories; TD 2 is an ESRO satellite; and * denotes collaboration with Leicester University's Physics Department.
Scheduled rocket flights listed in the ESRO programme were six Arcas rounds to study polar cap absorption and D-region ionization; four Centaure rounds, two to study the fine structure of auroral ionization, and two to identify and determine the concentration of ions, and the electron temperature in the lower ionosphere, all fired from Kiruna, Sweden; four Skylark rounds to determine the electron temperature in the lower ionosphere; two Centaure and two Skylark rounds to study the total flux of solar Lyman-alpha radiation, all fired from Sardina. In the British national programme there were three sun-stabilised Skylark rounds, one to study X-rays from quiet and active regions of the sun, and Lyman-alpha radiation, and two to study the solar extreme ultra-violet spectrum, and ionospheric processes in E and lower F-regions, and one moon-pointing Skylark round to study ultra-violet fluxes from hot stars, and stellar atmospheres, all fired from Woomera; five Skua 2 rounds to study the correlation between lower ionospheric electron temperature and geomagnetic fluctuations based on ground magnetometer measurements, and four Petrel rounds to study ionospheric parameters in D and lower E-regions over the twilight period, all fired from South Uist.

Solar X-ray and Ultra-Violet Astronomy

The OSO-D satellite was launched on 18 October 1967 as OSO-4. The UCL/Leicester experiment designed to measure the total X-ray intensity in the 1.3-18 Å and 44-70 Å wavelength bands, using proportional counters developed from those used in Ariel 1, was successful, X-ray emission from the full disc of the sun being observed throughout the seven-year life of the satellite. X-ray bursts associated with solar flares were found to be of two kinds, one impulsive and the other showing a relatively gradual rise and fall. The X-ray flux usually provided the first indication of the start of a solar event, but there was, on average, a delay of two minutes between the peaks of the corresponding microwave and X-ray bursts, the delay being longer the softer the X-radiation. However many X-ray events were found to have precursors and there was evidence that some X-ray activity preceded the microwave. The first evidence for the cooling of flare plasmas by thermal conduction was obtained, a theory of conductive cooling of plasmas in loops being developed by Culhane, K. J. H. Phillips and J. F. Vesechy.
ESRO II, the first satellite constructed under the management of ESRO, was launched on 29 May 1967, but did not attain orbit owing to a failure of the Scout rocket launcher. The back-up satellite, renamed Iris, was launched on 16 May 1968 and carried into orbit a UCL/Leicester proportional counter spectrometer to measure the solar flux in the 1-20 Å wavelength band. After some trouble during the initial switch-on period, the apparatus was switched off until 14 July, when it started to work correctly. Later it continued working in its low sensitivity mode, the high sensitivity mode being affected by ambient plasma conditions at certain parts of the orbit.
OSO-F, later to become OSO-5, was launched on 22 January 1969, carrying into orbit the first of its kind, proportional counter detector, X-ray spectroheliograph. A 3-9 Å counter detecting radiation gathered by a pair of slits, and a 8-12 Å counter, mounted at the focus of a grazing incidence paraboloidal mirror, were used in the scan of the solar disc. This UCL/Leicester instrument performed well and provided data from which the first daily graphs of solar X-ray activity were published by the World Data Centre C at Boulder until January 1973, when they were superseded by higher resolution data becoming available with the launch of OSO 7. The instrument still functioning well, was switched off in July 1975.
The opportunity to improve the space, time and wavelength resolution in order to study individual solar flares in detail came with the opportunity to participate in the Solar Maximum Mission (SMM) planned by NASA to study solar flares during the maximum of the solar cycle in 1979-80. An MSSL group, led by Culhane, in collaboration with an Appleton Laboratory group, led by an old departmental student, A. H. Gabriel, and the USA Lockheed Palo Alto Research Laboratory (LPARL) designed and constructed an X-ray polychromator for one of the two UK experiments accepted for SMM. The polychromator comprised two instruments, namely, a flat crystal spectrometer with fine collimation scanning all atomic transitions important for flare and plasma diagnostics in the wavelength range 0.15 to 2.5 nm, and a bent crystal spectrometer providing simultaneous fixed coverage of the wavelengths in certain important spectral intervals with very good time and wavelength resolution at the cost of broader collimation. SMM was launched on 14 February 1980 and over 50 major flares and many more minor ones were observed by the polychromator until the fine pointing control of the satellite failed in November 1980. Following the in-orbit repair by the crew of the Space Shuttle, Challenger, in April 1984, observations were resumed and continued until the re-entry of SMM after almost ten years in orbit.
In an early sun-pointing Skylark rocket launched on 5 May 1966, K. Evans, Pounds and Culhane measured the intensities of 28 identified and 4 unidentified solar X-ray emission lines in the wavelength band 11-22 Å with two slitless crystal spectrometers. It was possible to derive information about temperatures both in the quiet corona and in active regions from these results, some of the first obtained in this spectral region. This rocket also carried a proportional counter spectrometer placed at the focus of a parabolic mirror to obtain X-ray pictures of the sun in the 8-18 Å wavelength band, as did another rocket, launched on 8 August 1967. Contour maps of the intensity of solar X-radiation made from these spectral heliographic observations showed that, during the interval between the flights, the sun, which had been active in the northern hemisphere only, became active in the southern hemisphere also. The use of proportional counters enabled information to be gained on the change of intensity of the radiation with wavelength for each emitting region on the sun. D. H. Brabben and W. M. Glencross measured spectra in the wavelength band 10-24 Å from three active solar regions with a collimated crystal spectrometer flown on a Skylark rocket, launched on 10 December 1971; strong lines of Fe XVIII, Ne IX, O VII and O VIII were readily identifiable. A more advanced spectrometer was flown on a Skylark rocket launched on 26 October 1972. Instead of using a fixed collimator defining a small area of the solar disc, it used a rotating collimator before the crystal, whose rocking curve defined a strip across the disc, the rotating collimator then locating each emitting region within the strip. The crystal was rotated slowly throughout the flight to explore the whole of the observable corona in the spectral range 6-25 Å. During the flight a small flare commenced in the McMath calcium plage region 12094 and the emission from this provided the major contribution of the observed spectrum in the wavelength range 14.5-17.1 Å. Spectral and spatial observations from a group of active regions in the S W and the small McMath region 12094 were combined to investigate the conditions in both active regions and flare plasmas. Culhane in collaboration with LPARL used a collimated Bragg crystal spectrometer to study the X-ray line spectrum of the solar corona. The first flight of the instrument took place in an Aerobee 170 rocket from White Sands, USA. Temperatures and differential emission functions were obtained for the general corona and for six active regions, and electron densities both in the general corona and the active regions were shown to be less than 5 x 10⁹ cm³. The intensities of the principal satellite lines of O VII or Ne IX were measured and used to obtain the coronal temperature, and the satellite wavelengths were measured more precisely than theretofore. In a further MSSL collaboration with LPARL, a Skylark rocket launched on 30 January 1976, carrying an instrument containing three plane Bragg crystal spectrometers designed to investigate the temperature and emission measure distributions in quiet coronal structure typical of solar minimum, developed a fault in flight preventing the payload achieving fine stabilization.
The UCL, small grazing incidence, monochromator on OSO-4 monitored variations in the absolute intensity of a 10 Å wavelength band of the solar extreme ultra-violet spectrum centred on the He II Lyman-alpha line at 304 Å during periods, October to December 1967 and June 1968 to December 1969. Measurements were also made during these periods of the absolute intensity of the solar H Lyman-alpha line at 1216 Å. The intensity of the He II line revealed long-term variations of up to 20% from the mean value and short-term flux increases of up to 25%, but that of the H line remained essentially constant. Solar activity, measured from the ground, was found to be a poor indicator of the level of the solar extreme ultra-violet flux, the general level of the observed He II Lyman-alpha line intensity following most closely variations in the relative sunspot number.
OSO-G was launched on 9 August 1969, becoming OSO-6. It carried into orbit the extreme ultra-violet polychromator to measure absolutely the total ultra-violet flux of important solar lines from H, He, C, N, O and Fe. During the first six months of the flight, results were obtained for four lines, 304, 537, 584 and 1216 Å; mean fluxes, and daily variations were given and compared with corresponding variations of the 10.7 cm radio flux and Zurich sunspot number.
A grazing incidence spectrograph with a concave grating stigmatised by a grazing incidence toroidal mirror was designed for one of the two ESRO small stabilized, satellites, TD-2. The instrument had a wavelength resolution of 1 Å and spatial resolution of 1' arc and was intended to observe 27 solar lines from 150-600 Å. It was planned to use a small on-board digital computer for data processing, experiment control and the interpretation of telecommands. However in 1968 when it became clear that the completion of both TD-1 and TD-2 would be too expensive, the latter was dropped.
The first experiment involving the simultaneous measurements of related ionospheric and solar ultra-violet parameters in relation to ionospheric theory in the 150-200 km range was carried out by MSSL and Birmingham University in a sun-stabilized Skylark rocket flown on 3 April 1969, an account of the experiment being given on pp.99-100 of the Geophysics section. A joint experiment planned with the Appleton Laboratory involved a Skylark rocket payload consisting of a grazing incidence grating spectrograph designed to determine the He/H abundance ratio in the solar corona as a function of height. The intensities of selected wavelengths in the range 150-1335 Å were to be recorded so that measurements could be made of the resonant scattering from the corona of the Lyman-alpha of H I at 1216 Å and He II at 304 Å. The rocket, the last Skylark launched from Woomera, was flown on 12 May 1978, good observations being obtained with the spectrograph. The experiment was rebuilt in an enhanced payload for the systematic study of hydrogen and helium abundances, temperatures and densities in coronal structures during the second flight of Spacelab in 1985.

Cosmic X-ray and Ultra-Violet Astronomy

Before any evidence of the existence of observable cosmic X-ray sources, the UCL group under Boyd and Willmore had started to design a telescopic system using grazing incidence parabolic reflectors with proportional counters at the foci for inclusion in a satellite to observe cosmic X-rays. They also considered the design of detectors for use in Stage 3 stabilised Skylark rockets as announced in their research plans to the British National Committee in January 1962. Later that year, Scorpio X-1, the first powerful X-ray source, was discovered, and encouraged development in the field. Boyd and Willmore's proposal to include their telescopic system in the payload of the third US astronomical satellite OAO-3, as an auxiliary system to the main ultra-violet observing system, was accepted in 1963, but the satellite was not launched until 21 August 1972. Meanwhile the US satellite Uhuru, the first devoted to cosmic ray astronomy, had been launched in December 1970, leading to the discovery of many new sources, including extended ones, particularly from clusters of galaxies. Thus the launching of OAO-3, thenceforth known as Copernicus, was most propitious, giving MSSL a unique and powerful means for the observation of X-ray sources, galactic and extragalactic, with high space and time resolution. The X-ray telescope, c. 90 cm long, consisted of three reflecting mirror systems, a collimated proportional counter and a star tracker to measure any gross misalignment of the instrument relative to the axis of the spacecraft. Observations were made over the waveband 1-20 Å, the background count, despite care being taken to make it tolerable, prevented them in the range, 20-100 Å. The fields of view of the mirrors could be varied by changing the aperture at each focus. For the 1-3 Å waveband, the field of view of 3 deg was fixed by the collimators, but for 6-18 Å it could be selected to be 2, 6 or 10 min, and for 3-9 Å, 1, 2, or 10 min, the large aperture generally being used for studying time variations in the intensity emitted from a particular source. The initial allocation of 10% of Copernicus's time to X-ray observation was increased to 20% in 1973. Operations from Copernicus were ended at the end of 1980 after 7¹/₂ years of very successful observations.
Copernicus was the first satellite to include an X-ray instrument which could be pointed with high accuracy for extended periods at selected sources. The first observations located the source GX2 + 5 more accurately than theretofore. The second observations were directed to Cygnus X-3, since in 1972 a nearby, weak radio source had suddenly flared up to many times its original strength. No corresponding increase in X-ray emission was found, but it was discovered that the X-ray intensity varied with a period of c. 5 h. The form of the X-ray light curve differed from those of other periodically varying sources in that it was smooth, with the minimum flux near zero, whereas, for example, Hercules X-1 exhibited sharp transitions from high to low with no residual flux at the minima (F. J. Hawkins, K. O. Mason and P. W. Sanford) .
Following on the discovery of compact objects in binary systems by the Uhuru satellite, Hawkins, Mason and Sandford showed that absorption features or 'dips' in the X-ray intensity of Cygnus X-1 occurred at times when the secondary of the HDE226868 binary system was at superior conjunction. These observations confirmed the identity of the X-ray source with the binary system and pointed to the existence of a black hole.
The first detailed maps of the X-ray emission from supernova remnants were obtained by the MSSL reflectors on Copernicus. The structure of Cassiopeia-A was resolved for the first time and maps of the older remnant Puppis-A showed the interaction of the expanding shock with interstellar clouds. X-ray emission was detected in a broken ring at a radial distance of 4 arc min from the centre of the Crab nebula, the origin of the emission, shock heated gas or a halo from scattering by interstellar gas, not being established (P. A. Charles, J. L. Culhane, A. C. Fabian and J. C. Zarnecki).
Many observations were made of extragalactic sources, the most exciting being those of Centaurs-A in 1975, which was found to have increased its X-ray emission by more than a factor of four since its first observation from Uhuru. This was the first discovery of a variable extragalactic X-ray source. Its emission was monitored every few weeks and it gradually settled back towards the original intensity observed from Uhuru (P. J. H. Davison, Culhane, Fabian and R. J. Mitchell).
The first proposal for a cosmic X-ray payload in the Ariel series was made to NASA through the SRC in July 1968. After several revisions, an agreement was reached in 1970 for a satellite code named UK-5, which became Ariel 5 on launching into orbit on 15 October 1974. It contained two experiments devised by Boyd and Willmore, namely, measurement of source positions and X-ray sky survey in the energy range, 0.3 to 30 keV, and study of the spectra of discrete sources in the energy range, 2 to 30 keV. In the former experiment a rotation-modulation collimator was aligned along the spin axis of the satellite. With a known X-ray source in the field of view as a reference, position was determined to 1 min of arc, otherwise the accuracy was c. 10 min of arc. A time resolution of 0.5 min was obtained in the energy range 1.9-18 keV using proportional counter detectors, this being raised to c. 1 min for the low-energy range 0.6-6 keV using electron multipliers as detectors. In the spectral energy range 1.4-30 keV, a multi-wire proportional counter with a beryllium window was used to obtain the best possible spectral resolution for sources in directions close to the satellite axis; the time resolution was 1 min, but it was reducible to a few milliseconds by means of a 'pulsar' mode of operation.
During the first year of operation of Ariel 5, the MSSL rotation collimator experiment observed 8-9 transient sources, many more than expected. They were generally very bright at maximum, Tau-XT (A 0535 + 26), very close to the galactic anti-centre, being the second brightest source observed up to that time, and A 0620-00 in Monoceros being the strongest source in the sky for several weeks. During a transient flaring stage of Cygnus X-1 in May 1975, a phase difference was found between variations of high and low energy flux. Tau-XT, the second brightest source of soft and medium energy X-rays, proved to be the strongest hard X-ray source observed.
The first transient sources observed, lasting weeks to months, were all located close to the galactic plane; later several brief or fast transients, visible for hours or less, were found. The rotation collimator instrument found amongst the first transients observed, one modulated with a period of 6.75 min and a second of period 1.7 min. These were the first slow rotators observed, probably being characteristic of neutron stars in binary systems as distinct from single stars responsible for radio pulsations.
The multi-wire proportional counter experiment obtained X-ray spectra of the supernova remnants, Cassiopeia-A and Tycho, showing emission lines of Fe XXV and allowing estimates to be made of both the ion abundance and the temperature of the shock-heated gas. X-ray bursters, discovered in 1976, were soon observed by the rotation collimator instrument, bursts being seen on every occasion in 1976 when the instrument was pointed close to the galactic centre. High-time resolution studies made on the very strong burster, MXB 1930-335, showed that the bursts, each a few seconds long, came in pulse trains, the pulses within each train having some periodicity, typically of period 15 to 20 s.
Using both the rotation-modulation collimator and multi-wire proportional counter experiments, detailed studies were made of the emissions from some extragalactic sources, including the quasar 3C 273, the strongest extragalactic source, M 87, the Seyfert Galaxy, NC-C4151, and the four bright clusters of galaxies, Virgo, Perseus, Coma and Centaurus. A feature of the spectrum of the Perseus cluster near 7 keV was identified as arising from the K emission lines of Fe XXV and Fe XXVI; similar weaker features were also identified in the spectra of the Centaurus cluster and the source 0627-544. The existence of these lines supported the view that the X-rays arose from a hot plasma, at temperatures of the order of 5 x 10⁷ K. Two X-ray spectra of NGC 415 were obtained one year apart, the second showing a substantial increase in the quantity of absorbing material surrounding the active nucleus of the galaxy; an Fe-K absorption edge was detected for the first time.
Ariel 6, the last spacecraft in the Ariel series, was planned in 1972 mainly to meet the needs of cosmic ray scientists. However it included two X-ray experiments capable of extending the scope of the observations made by Ariel 5. The UCL experiment of Boyd and Willmore was designed to observe very soft X-ray emissions. The satellite was launched on 2 June 1979 but the operation of the X-ray experiments were seriously upset by spurious switching, and inadequate thermal control resulting in the satellite operating outside the expected range of high accuracy attitude sensors for most of the mission.
MSSL was involved with the Cosmic Ray Working Group of the Huygens Laboratory, Leiden and the Laboratory for Space Research, Utrecht in providing the payload for the ESA Exosat satellite. It was responsible for the X-ray detectors for the low energy experiments. Two interchangeable detectors were required to be placed at the focus of each of two Wolter Type I mirrors, one being a position-sensitive proportional counter and the other a position-sensitive channel-multiplier array detector. The resistive-disc readout system developed at MSSL was incorporated in both detectors. It was also involved with the Space Science Division of ESTEC and the Institutes for Cosmic Physics in Milan and Palermo to build a gas scintillation proportional counter (GSPC) as a small 'add-on' experiment for Exosat. The same instrument was also developed for the first flight of Spacelab. The effective aperture was 200 cm2, and the energy range, 2.0-30 keV, with an integrated energy resolution at 6 keV of c. 10%.
MSSL flew two proportional counters of 1000 cm² collecting area on a stabilized Skylark rocket on 11 November 1970 in a successful survey of the centre of the galaxy, the large and small Magellanic clouds and several pulsars for X-ray sources in the energy range, 0.5 to 12 keV. This flight was related to three unstabilized Skylark flights, two in 1970, one on 14 July carrying a rotation collimator, the other on 14 October carrying a rotation collimator and proportional counters, and the third on 7 October 1971 carrying a rotation collimator, so that a large area of sky could be surveyed with good space and wavelength resolution.
The application of lunar occultation methods in determining source positions with high precision was made by both the Leicester and MSSL groups in 1971 when the occultation of the source GX 3+1 was observed by equipment flown on a stabilized Skylark on 27 September (Leicester) and on an unstabilized Skylark on 24 October (MSSL). The source was located to ± 0.5", the most precise location of any cosmic X-ray source.
The first flight of a low-energy X-ray detector, a large thin window, proportional counter, was flown on an unstabilized Skylark on 4 February 1974 by MSSL. A highly sophisticated control system was used to maintain the gas density in the detector within the range, ± 0.15%. The flight established Gould's belt as an X-ray absorbing region and also discovered an absorbing ridge in Hydra.
MSSL also made the first high-resolution detection of an X-ray line from a cosmic source by means of a Bragg crystal spectrometer flown on a high accuracy Skylark, directed to the supernova remnant Puppis A, on 4 October 1974, this being the O VIII Lyman-alpha line at 19 Å (Zarnecki and Culhane). A comparison of this result with a later observation by Ariel 5 allowed a new determination to be made of the distance to this source.
A position-sensitive detector was flown for the first time in a Skylark rocket launched from Woomera on 12 May 1976 to obtain a high-resolution, two-dimensional, X-ray map of Puppis A, this being a collaborative study with Birmingham University and the NASA Marshall Space Flight Centre. A Skylark rocket, launched from the Arensillo range in Spain on 17 July 1976, carried two sets of reflecting crystals feeding one-dimensional, position-sensitive detectors to measure the strengths of the sulphur (2.6 keV) and iron (6.8 keV) lines in Cas A, this being a collaboration with the University of Tubingen. A further collaboration involved LPARL and ESTEC in the construction of an imaging X-ray telescope for a flight in a NASA Aries rocket. The two-dimensional, position-sensitive proportional counter was to be carried at the focal plane of the telescope, with its associated gas system, electronics and ground support equipment, two further models of the GSPC being incorporated.

Involvement in UV Satellites (M & R pp. 146-161 & 355-360)

The Solar and Stellar Astronomy Working Group (SASA) of the British National Committee for Space Research, formed in 1958, was soon involved with the RAE, Farnborough in the design of a satellite with a payload consisting of an ultra-violet spectrometer operating in the wavelength range 1200 to 3000 Å with a spectral resolution of 1 Å. The RAE programme was directed by A. W. Lines, who later became Technical Director of ESRO. By 1962 the attention was directed towards the ESRO programme involving the large astronomical satellite (LAS). By October 1964 the specification of the first primary instrument covering the wavelength range 3500 to c. 1100 Å, extending if possible to 912 Å, was prepared, no details being given about a second smaller primary instrument to make broad band X-ray observations. The UCL group under Boyd and the Culham group under R. Wilson were both well equipped and keen to join the project. As soon as it was clear that proposals for carrying out primary experiments on the LAS would be requested, Massey called a meeting in his room at UCL to initiate concerted action on the matter. It was agreed that a proposal should be submitted to ESRO, involving the Wilson group concentrating on the design of the instrumentation for ultra violet astronomy, with Boyd and Boksenberg at UCL providing the design for a detector for the main payload as well as the instruments for the subsidiary X-ray experiment. The UK consortium presented its proposal to ESRO before the required 15 December 1964, as did a German-Dutch group, both meeting the scientific requirements laid down. A French-Belgian-Swiss proposal was also submitted, but departing from the specification. However it was agreed that contracts should be placed with all three groups to produce detailed designs within six months of February 1965. After some delay in placing the contracts because of uncertainty concerning the launch vehicle, the three groups submitted their final design reports by 31 January 1966, and on 9 May 1966 it was recommended that the UK design be adopted for the first LAS instrumental package with one back-up unit. However by the end of 1966 it was clear that the project would not go ahead on financial grounds, and apparently the scientific and technical effort expended on the payload design would be wasted.
A UK Project Study Group, including Bokensberg, set up under Wilson's leadership, produced a new overall design, the Ultra-Violet Astronomy Satellite (UVAS), with substantial savings. Its scientific aim was restricted to the primary objective of the LAS, namely, high-resolution spectroscopy of bright stars. The 80 cm Cassegrain telescope feeding a Paschen-Runge spectrometer operating in the spectral range 900-3000 Å, in the LAS design was replaced by a 45 cm Cassegrain telescope feeding an echelle spectrograph which was 10-20 times more powerful spectroscopically, thereby permitting relaxed tolerances in the pointing, mechanical and thermal satellite sub-system. The reduction of telescope aperture followed from Bokensberg's proposal to use a television camera as detector; however it would be necessary to develop rugged image tubes operating at ultra-violet wavelengths. The new optical system would only operate efficiently down to 1200 Å. Further economy in design was achieved by eliminating stars of magnitude 8 and 9 from the observing programme thereby saving observing time and reducing the accuracy of the coarse guidance systems from 1' to 10'. The UVAS proposal, when submitted to ESRO in 1968, received a very favourable report, but it was not finally accepted, again on financial grounds.
Wilson then wrote privately to L. Goldberg, Chairman of the USA Space Science Board, outlining the UVAS proposal. The Board passed it on to the Goddard Space Flight Centre for detailed evaluation. Wilson visited Goddard spending a week there in detailed discussions of the project. The Americans proposed that the satellite should be launched into a geosynchronous orbit so that it could be operating more or less in real time as an observatory for the whole astronomical community. It was also proposed to include facilities which, through degradation of the spectral resolution when required to 6 Å instead of the usual 0.1 Å, would permit the observation of faint objects.
Wilson returned, proposing that the UK should join the USA in the new project, then referred to as SASD in the American small astronomical satellite programme. Although a decision was not required until late 1971, the SRC allocated at the end of 1970 £137,000 for participation in full design studies. ESRO joined the project, agreeing to supply the solar paddles and the European operation ground station. NASA undertook to provide the spacecraft, the optical and mechanical components of the scientific instrument, and the US ground observatory and spacecraft control software, while the SRC in co-operation with UCL would provide the television cameras and baffles to record the spectroscopic data, and also for acquisition. The image processing software would be developed jointly by the Appleton Laboratory and NASA. The satellite was to be placed in a geosynchronous orbit over the Atlantic Ocean and operated 16 hours a day from the US ground observatory at the Goddard Space Flight Centre for US sponsored observers, and 8 hours a day for UK and ESRO sponsored observers from a ground station at Villafranca in Spain.
The co-operation between the SRC and UCL had to be a very special one since, just before the project was accepted in all three participating agencies, the senior College administration decreed that no further large grants could be accepted by departments from the research councils owing to the load thrown on the administration in processing and supervising the large expenditures involved. The need to supply Boksenberg, the project scientist for the UK side of the programme, with supporting manpower and expensive sophisticated research equipment was met by Massey making special arrangements with J. F. Hosie of the SRC and J. Saxton of the Appleton Laboratory for the secondment of staff and the loan of the equipment to UCL, no large grants ever being necessary. The only problems were those of shortage of working space, but the overcrowding was suffered owing to appreciation of the importance of the project by all concerned.
The project was approved in the US Presidential Budget of 1973/4, its name having been changed to the International Ultra-Violet Explorer (IUE); the SRC and ESRO also approved it at about the same time. In May 1975 Wilson, then Perren Professor of Astronomy, was appointed project director of the UK side of the IUE, nominally on a half-time basis, with the full-time assistance of P. Baker of the Appleton Laboratory. The SRC management team under Wilson took over the responsibility for the assessment and measurement of the properties of the ultra-violet to visible converters, delivered from ITT in the USA, for the bonding of the converters to the Videon tube, and for their delivery to MSDS, a branch of GEC at Portsmouth, with a list of the optimal operation parameters. In 1975 a further SRC grant of £658k was allocated to the IUE work, the contributions from NASA, ESA and SRC being £36m, £9.5m and £4m respectively. By the introduction of three shifts a day, seven days a week working at MSDS, the flight cameras were delivered to NASA by 30 November 1976, and IUE was launched successfully on 12 January 1978. The excellent facilities for astronomical research provided by IUE was soon appreciated, astronomers from 27 different countries using them during its first three years of operation.
The ultra-violet scan experiment, proposed by the Royal Observatory Edinburgh and the Institut d'Astrophysique of the University of Liege, as a major experiment for the first three-axis stabilised ESRO satellite, TD-1, involved operation of the satellite in full sunlight, and this required the design of a baffle system reducing the intensity of sunlight at the detector by a factor of 10¹⁷. ESRO placed a contract with a small company, formed by some members of the UCL physics department, of which Boksenberg was chairman. A Monte Carlo method of ray tracing was devised and used to work out a suitable design. The entire success of the project depended on this work, which could not be checked in the laboratory; in the event it proved completely successful, thanks especially to Esten's contribution. The design, development and production of the main scientific payload was far behind schedule in 1968, so Wilson, Boksenberg and others, involved in the planning of the LAS and engaged in other ultra-violet astronomical activities, were called in to restore the position. The spectrometry was improved by Boksenberg's suggestion that simply by opening up the entrance slit of the spectrograph, advantage could be taken of the passage of the stellar image across the slit due to the satellite motion to cover the 1350-2550 Å wavelength range by observation in effectively 61 rather than 3-4 channels, thereby greatly increasing the wavelength resolution. When TD-1 was successfully launched on 9 March 1972, the now joint UK-Belgium experiment functioned very well.
The first record of ultra-violet radiation from stars in the Southern sky by Heddle and his collaborators at UCL in 1961 has been described on p 90. Further unstabilized rocket flights were carried out by the UCL group, the last broad band observations being made on 14 July 1965. The equipment comprised a cluster of three photomultipliers, each sensitive to a different band in the region 1,450 to 2,800 Å, set at the focus of a 13_ inch telescope mirror aligned along the rocket axis. Aspect data were provided by a highly redundant system of moon detectors, airglow horizon detectors and magnetometers. Thereafter work commenced on a telescope-spectrometer aiming at a resolution of 0.1 Å in the region between 2,000 to 3,000 Å carried by Skylark moon pointing stabilized rocket. The work then entered a new phase, involving collaboration with the SRC Astrophysics Research Unit (ARU), Culham Laboratory. Two forms of instrumentation were planned, one for the observation of single stars and the other for observation of star fields. The former was based on a Cassegrain telescope, employing a large, forward-viewing primary mirror, fitting into the Skylark conical nosecone. The optical design of a spectrometer with a resolution capability of 0.1 Å was carried out at UCL using a computer ray tracing programme. The spectrometer used an echelle grating of high dispersion crossed with a conventional grating of low dispersion to produce a cyclic spectrogram in a rectangular format covering the range 2,000 to 3,000 Å, the spectrogram being detected by the EMI 9677 UV vidicon tube. The latter used a concave grating in a Wadsworth mounting operating as a dispersing objective to obtain star spectra in the range 900 to 1400 Å over a field of 2 deg x 2 deg. A ray-trace computation showed that the inherent resolution capability of an instrument using a 600 lines per mm, 10 cm by 10 cm grating of 2 m radius of curvature was better than 1 Å over the wavelength range and angular field considered, a pointing noise of 10 arcsec degrading this to c. 2 Å. Two star-stabilized Skylark rockets were launched from Woomera, one on 11 February 1970 for ESRO and the other on 16 June 1970 in the national programme, each payload comprising a cluster of three objective grating spectrographs covering the range 900 to 2300 Å with a spectral resolution of c. 0.5 Å. Each spectrograph had a 2400 lines per mm concave grating in a Wadsworth mounting, the optical design being optimised by the computer ray-tracing technique, and used photographic recording.

Geophysics

OGO-5, the Orbiting Geophysical Observatory, was launched into a highly elliptical orbit on 4 March 1968, MSSL providing one of the twenty-six experiments on board. It was designed to measure the electron temperature and concentration within the magnetosphere, and in the solar wind when the concentration was high enough, by means of a spherical Langmuir probe on an extendable boom, two metres from the main body of the spacecraft. The probe, of greatly increased sensitivity, was operated in the a.c. mode, measuring electron densities in the range from 10 to 5 x 10⁴ cm^-3, and electron temperatures from 10³ to 2.5 x 10⁴ K.
ESRO I, renamed Aurora, was launched on 3 October 1968 and its performance was so satisfactory that the back-up model for ESRO I, renamed Boreas, was launched on 1 October 1969 with a similar payload. They carried out the first satellite study of the anisotropy of the velocity distribution over auroral regions, and indeed globally, due to the presence of the earth's magnetic field.
ESRO TD-2 was cancelled, but the intended further version of the experiments, carried out on Explorer XXXI, were undertaken on the rescue satellite, ESRO IV, launched on 22 November 1972.
The electron temperature probe, modified to operate in the very low electron densities in and beyond the plasmasphere, worked satisfactorily after its deployment on OGO-5 on 7 March 1968. Within the plasmasphere, where the Debye length was short compared with the distance between probe and spacecraft, the properties of the ambient plasma could be measured, but when the electron density fell below 10 cm^-3 the current to the probe was predominantly due to secondary electrons from the probe and spacecraft surface. An analysis of the probe response outside the plasmasphere, with other measurements on the spacecraft, produced good results on the interaction of the spacecraft with its environment and the population of energetic electrons within the magnetosphere. They indicated that photoemission from the probe itself dominated when it was in direct sunlight, but when it was shadowed by other parts of the spacecraft the electrons reaching the probe were secondaries from the impact of higher energy electrons on the spacecraft surface, the secondary electron flux correlating well with incident electron energies in the 0.5-1 keV range.
The energy distribution of electrons from the gold surface of the probe was measured and found to correspond approximately with a Maxwellian distribution of most probable energy, 1.1 eV, but with a significantly higher energy tail. Measurements were made of the distribution of electrons in the outer magnetosphere, particularly those with energies less that 1 keV, and the convection pattern of low energy particles. They were extended to include the connection between the changes which occurred during magnetic storms and observations of ground-based magnetograms; in particular, a good correlation was obtained between thinning of the plasma sheet and the onset of magnetic substorms. Other studies included the variation of spacecraft potential within the magnetosphere, the properties of thermal electrons within the plasmasphere at altitudes above 1000 km, and the mapping of the plasmapause boundary.
The Boyd-Willmore a.c. probes were flown in seven satellites launched during the 1962-72 decade, namely Ariel I (26 April 1962), Explorer 20 (25 August 1964), Explorer 31 (29 November 1965), OGO 5 (4 March 1968), ESRO IA (3 October 1968), ESRO IB (1 October 1969) and ESRO 4 (22 November 1972), as well as in many rockets. Wrenn, D. H. Clark, Raitt and H. C. Carlson made a comparative study of ionospheric electron temperatures measured by the a. c. (modulation) Langmuir probes on Explorer 31 and ESRO IA and various incoherent backscatter radar stations and found good agreement between them. Previous comparisons by Carlson and J. Sayers between satellite d.c. (slow-sweep) probe, T_es, and radar, T_er, electron temperature measurements had fitted the simple linear relationship:-

T_er = 5/6 T_es - 400 K.
The discrepancy between modulation and slow-sweep probes, typically 20% on Explorer 31, could be due to work-function drift during a slow sweep. Differences of 50-80% observed in electron temperatures measured by slow-sweep probes and incoherent scatter radars suggested additional sources of discrepancy, such as, temperature anisotropy, effect of fine structure, and a possible non-Maxwellian distribution function for the electrons.
The Langmuir probe technique was frequently applied to study the morphology of electron temperature in the topside ionosphere. Clark, Raitt and Willmore were the first to report a synoptic study of results taken near the sunspot maximum and providing new evidence on night-time heating effects, and day-time heating at high latitudes by low energy particles penetrating the clefts in the dayside magnetosphere. It was based on measurements from the a.c. probe experiment of the magnetically orientated, ESRO IA, taken between October 1968 and April 1969. During this period, over one million independent temperature estimates were obtained, and then used to determine variations of temperature with geomagnetic latitude, local solar time, altitude, and magnetic activity condition. The probe experiment used two plane circular collectors, one remaining parallel, and the other perpendicular, to the direction of the local magnetic field. The observed anisotropy of electron temperature, measured parallel and perpendicular to the magnetic field, most pronounced near local midnight, was strongly influenced geomagnetically; no theory fitting the geometry of the observations in the two hemispheres was given. The study of Wrenn, Clark, Raitt and H. C. Carlson showed that the electron temperatures measured perpendicular to the magnetic field were in essential agreement with radar measurements, whereas those measured parallel to the field significantly exceeded them.
Raitt presented measurements of thermospheric electron temperatures made by the probe experiment on ESRO IA before, during, and after the large geomagnetic storm of 31 October to 1 November 1968. The data covered a complete time sequence over a period of nine days while the satellite covered the altitude range 280-1500 km and remained in the noon/midnight local time zones. They clearly showed the development of enhanced temperatures at mid-latitudes associate with stable auroral red arcs in the midnight time zone, traced the latitude dependence of the heating during the progress of the storm, and showed the persistence of the zone of elevated temperatures after the magnetic activity had declined. The heating of electrons in the noon time zone was not observed to follow the same pattern as that in the midnight time zone.
The ESRO-4 satellite was launched into a near polar orbit (88.9 deg) of apogee 1177 km, perigee 245 km on 22 November 1972 and yielded excellent ionospheric measurements until its re-entry on 15 April 1974. It carried six experiments, including the MSSL one to measure the temperature and density of the major thermal ions in the topside ionosphere up to 1100 km, and in addition the thermal electron density and temperature, and fluctuations in the total ion density. A three-probe system was used, namely, a major spherical gridded probe, with swept potential, collecting positive ions; a subsidiary Langmuir probe measuring electron temperature and vehicle potential; and a subsidiary, fixed potential, spherical probe collecting positive ions.
Dorling and Raitt used the thermospheric electron temperature measurements at altitudes between 250 and 1100 km to derive model functions of electron temperature in terms of altitude, magnetic latitude and local time for the periods November 1972 to June 1973, and March to October 1973. They were compared with those obtained from similar instruments on Ariel-1 in 1962, ESRO-1A in 1968-69, and from ground-based observatories. The models reproduced the major features of topside electron distributions, namely, midday temperatures exceeding midnight temperatures by c. 500 K, dawn enhancement leading to peak temperatures greater than midday values particularly around 50 deg magnetic latitude, and temperatures increasing with altitude at all latitudes and with latitude at all altitudes. The daytime mid-latitude temperature was used to complete a series of observations by various techniques over a solar cycle and thereby confirmed the sense and degree of solar cycle control on the thermospheric electron temperature predicted by theoretical considerations.
The most comprehensive study of topside ionospheric irregularities from direct probe measurements revealing new evidence on possible production mechanisms was carried out by Clark and Raitt. The total ion current probe monitored thermal plasma density variations in the range ± 30% of ambient density with a spatial resolution of about 1.5 km. Latitudinal, diurnal, and altitudinal characteristics of density irregularities in the topside ionosphere were investigated using the 2 x 10⁸ total ion current values recorded during the lifetime of the satellite. The morphology of topside irregularities was dominated by the high-latitude zone evident throughout the day, with the appearance of a distinct sub-auroral zone at night. Significant mid-latitude irregularity occurred at low altitudes at night.
Raitt and Dorling used the data from the thermal plasma probe to study the altitude, latitude, local time variations of H⁺ density during the northern hemisphere summer of 1973. The form of the latitudinal variation was interpreted in terms of one region of H⁺ inflow and outflow within the plasmasphere dependent on local time, and another region of continuous outflow polewards of the plasmasphere, and the role of O⁺ density, as an additional control of H⁺ density, was discussed. The observed variations of H⁺ density in the altitude/latitude plane were used to show the latitudinal transition from low to high speed flow, and the location of the mean plasmapause was defined in terms of the physical processes equatorwards and polewards of the plasmapause.
Raitt collaborated with U. von Zahn (Bonn University) and P. Cristopherson (Kiruna Geophysical Institute) in a study of the magnetosphere-ionosphere-atmosphere interaction at middle and high-latitudes during magnetic storms. Three main effects were observed during increased magnetic activity, namely, a general increase of N2 density over the whole polar cap, but with no clear ionospheric effect; an enhancement of N2 density in the region of the nightside mid-latitude trough with an abrupt termination of the trough on the poleward side by local ionization due to to measured low energy electrons; and the formation of a narrow region of enhanced electron temperature and N2 density, with reduced electron density, in the vicinity of the dayside cusp region. Further collaboration with Bonn involved the depletion of F-region ionospheric density and its relation to the enhancement of N2 densities measured by the Bonn instruments. The reduced data from the MSSL ionospheric instruments on ESRO-4 continued to be the primary source of thermal plasma measurements for an on-going programme of research mainly directed to studies of magnetosphere-ionosphere-atmosphere coupling. Global models of electron temperature and density were developed providing realistic average properties of the electron component of the topside ionospheric plasma, the lower boundary of interactions between the solar wind and the earth's immediate environment, acting through the magnetosphere.
Adrienne and J. G. Timothy and Willmore, with J. H. Wager of Birmingham, studied the ion chemistry and thermal balance of the E and lower F-regions of the daytime ionosphere in a sun-pointing Skylark rocket launched from Woomera on 3 April 1969. Although the importance of simultaneous measurement of related ionospheric and solar parameters was realized by that time, this experiment was the first one to attempt such measurements relating to ionospheric theory in the 150-200 km range. The payload was designed to measure (i) absolute solar flux in the waveband 80-1050 Å with a resolution of 10 Å by a scanning extreme ultra-violet spectrometer, (ii) atmospheric extinction profiles of five strong lines in the solar extreme ultra-violet spectrum by a fixed extreme ultra-violet spectrometer, (iii) the electron temperature by spherical and plane Langmuir probes operated in the a.c. mode, (iv) the total positive ion density by a fixed potential spherical probe, (v) the ambient electron density by a capacitance probe. MSSL provided the instruments in (i) to (iv), Birmingham that in (v). Good agreement was obtained from electron density measurements by the capacitance probe and a ground-based ionosonde close to the launch site. Neutral atmospheric densities and temperatures were derived from the spectrometric data, and ion production rates were obtained from the absorption of solar EUV radiation in the 100-270 km range. Individual ion densities and ambient electron temperature were then calculated on the assumption of quasi-static equilibrium. The effective loss coefficient over that altitude range was 1 x 10^-7 cm³ sec^-1 at 120 km and 2.2 x 10^-3 cm³ sec^-1 at 270 km. Above 130 km the calculated total ion density agreed with the measured density to 30%, but below this altitude it diverged, becoming twice as low at 120 km. The measured electron temperature was greater than the neutral temperature at all altitudes in the 120-270 km. range. The thermal imbalance was explicable on the basis of the measured solar EUV heat input at all altitudes above c. 140 km; an additional heat source was necessary to account for the thermal anomalies at lower altitudes.
Following the observation of a narrow shelf of ionization at an altitude near 100 km due to the presence of sporadic E ionization in the fifth Skylark rocket fired from Woomera on 19 June 1958, much effort was devoted to exploring the phenomenon. UCL introduced a simple fixed potential, positive ion probe, which was flown as a 'piggy-back' experiment on many occasions. Measurements of wind shear, and electron temperature by means of the type of probes developed for Ariel 1, to look for the effect of electric fields, were also included. A collaborative payload of a Skylark rocket fired from Woomera on 2 March 1971 contained two MSSL positive ion probes, a Radio and Space Research Station (RSRS) rubidium vapour magnetometer, RSRS and Birmingham electric field probes, and UCL barium and trimethyl aluminium (TMA) release canisters. The rocket was fired at twilight so that the drift of the vapour trail from the TMA could be photographed from the ground. Ion density profiles on the upward and downward trajectories of the flight clearly showed a sporadic E layer, with peak near 10⁷ km altitude. The vertical ion velocity calculated from the wind velocity, observed from the TMA trail, showed a minimum close to 10⁷ km, but no change of sign. However the electric field, obtained from barium release observations and concordant measurements by the two electric field probes, contributed significantly to the vertical velocity of the ions, the combined effect of wind and electric field showing zero vertical velocity at 107.6 km, and hence the necessity of taking into account both the effects of electric fields and neutral winds.
Following work on the detection and measurement of low energy suprathermal electrons by means of magnetically screened hemispherical analysers, a Skylark rocket was launched from Kiruna on 13 October 1972 into a strong aurora to investigate particle fluxes in the energy range 2-30 eV and resulted in the successful detection of fine structure in the electron flux. There followed three co-ordinated Skylark flights from Andoya forming part of the UK High Latitude Campaign in October-November 1973 to gain a better understanding of the mechanism of the auroral substorm, the range of the analysers being extended to 500 eV. J. J. Sojka and Raitt obtained calibrated energy spectra in all three flights over the range 5-500 eV. These were compared with values calculated from their production as secondaries by the energetic electrons measured in the same flights by RSRS and Southampton University and good agreement was obtained for primary electrons of energy greater than 1 keV. Strongly field-aligned pitch angle distributions were seen on the first flight at altitudes from 200-27 km and energies from 5-500 eV. Four improved detectors measuring electrons and positive ions in the energy range 5-500 eV were flown on the first three-stage Skylark 12 ever launched, and it achieved an altitude of 715 km over Andoya on 24 November 1976, covering an altitude and latitude range normally only associated with satellites while retaining the much greater spatial and temporal resolution of sounding rockets. The flight crossed a stable auroral arc, approximately 100 km thick, just before apogee. A substantial amount of diffuse aurora was crossed before the arc was reached, and after emerging from the arc on the poleward side intense bursts of suprathermal electrons were encountered. The detectors were flown later on the ESA magnetospheric observatory satellites, GEOS I and II, launched on 27 April 1977 and 14 July 1978 respectively.
Finally it should be recorded that Prof. Boyd was created Knight Bachelor in the Queen's Birthday Honours in 1983.

Space Science & Atmospheric Structure Group

As recorded above, almost the entire staff of the department concerned with space research in 1962 co-operated in the development of the grenade programme. Groves then took over the responsibility for the whole programme to determine the temperature, pressure, density and wind speeds in the atmosphere at heights up to c. 85 km at Woomera (31degS), the programme benefiting "very much from his skill both in theory and in the analysis of complicated and extensive data, as well as his ability to plan and carry through the technological side of the work" (M & R, p.273).
He built up a thriving group in the mainstream of research into atmospheric structure, making major contributions both on the experimental and theoretical sides, and carrying out pioneering work in the deduction of data on atmospheric properties from the analysis of satellite orbits. Groves also played a full part in the international organisation of space research and was one of those who produced the first International Reference Atmosphere through the Committee on Space Research CIRA).
He also introduced a course for the College Diploma in Space Science (one year full-time, two years part-time). All postgraduate students joining the group took the course in their first year. It was in two parts:-
General: atmospheric structure, ionosphere, magnetosphere, solar-terrestrial relations,
meteors, interplanetary space, moon and planets, stellar and planetary orbits.
Theoretical and Research: numerical analysis and computer programming, satellite dynamics,
gravitational fields, charged particle motion, selected research topics.
A dissertation on a selected topic was prepared during the third.
28 grenade experiments using the Skylark rocket were carried out at Woomera with the co-operation of members of the Australian Weapons Research Establishment (WRE). The results of a series of 21 of these experiments during 1957-63 were collected together and the variations in temperature, pressure, density and wind velocity were analysed and shown at height levels of 30(10)80 km by Groves. Seasonal variations in W-E wind, in pressure and in density from 30 to 80 km, and in temperature from 30 to 50 km were compatible with a general seasonal model (evaluated for latitude 31degS), apart from the autumn and winter months where slightly larger temperature variations were found at 40 and 50 km, apparently owing to the model being based on measurements taken at different times and different sites, thereby leading to a smoothing of the seasonal effects. The scatter in measurements of all parameters increased with height, a similar increase in the four measurements made on the night of 15-16 October 1963 (see below) indicating some diurnal origin. Measurements of the S-N wind showed a positive bias at 50 and 60 km from October to May, general considerations suggesting a diurnal origin. This was investigated by examining summer S-N flow in 938 launchings mostly carried out within the USA Meteorological Rocket Network. It was found that a diurnal variation with local time was present with a maximum S-N component of c 8 m s-1 occurring at 50 km and close to local noon. An analysis of seasonal variations between 30 and 80 km was prepared for the CIRA.
Height profiles both of temperature and wind speed derived from seven grenade flights during 5 March to 4 December 1962 showed oscillations particularly at the higher altitudes. These were important in connection with diurnal and semi-diurnal variations associated with atmospheric tidal phenomena, and led to experiments being undertaken at closer intervals of time and with successive explosions as near as possible. During the night of 15-16 October 1963 four rockets were successfully launched at local times of 19.21, 21.16, 00.39 and 04.52 hr, the first and last firings being timed for twilight conditions. The use of double grenade bays and some smaller grenades enabled the average spacing between explosions to be reduced to c. 4 km. This remarkable achievement resulted in height profiles of the S-N and W-E wind components showing a clear oscillatory character particularly above 50 km and exhibiting a regular change with local time. Finally on the night of 29-30 April 1965 seven Skylark rockets were launched each containing 36 grenades programmed for ejection at c. 3 km. Although the first and last, launched at local twilight and dawn, were unsuccessful, good results of winds and temperatures were obtained from the other five. The resultant height profiles of temperature, except that from the second flight, were all of the characteristic form showing oscillations becoming more marked at the higher altitudes and varying with time in at least a semi-regular way. Height profiles of the components of wind speed obtained from acoustical observations below 88 km and glow cloud tracking between 90 and 140 km were oscillatory in character, the amplitude of oscillation being much greater above 90 km.
To elucidate the regular features of the upper atmosphere such as the general circulation and tidal oscillations many more launchings were required at different locations. Groves and his group were involved in launchings at Sonmiani in Pakistan in a collaborative programme between NASA, the British National Committee for Space Research (BNCSR) and the Pakistan Space and Upper Atmosphere Committee (SUPARCO) during the International Quiet Sun Year; at Thumba in India as part of the Commonwealth Collaboration; and at the ESRO ranges at Sardinia and Kiruna in Sweden. The rockets involved varied from the Petrel, capable of reaching c. 150 km, to the Skylark and Nike-Tomahawk, capable of achieving an apogee greater than 300 km. The work included payload preparation and testing, development of ground observational equipment, complex data handling and computer analysis, and extensive collaboration with research groups in the various countries concerned. At Sonmiani, for example, the group provided all the special ground equipment, including microphones, cameras and flash detectors, and trained the Pakistan personnel in the acquisition and reduction of the meteorological data and in the operation and maintenance of the equipment, and provided continuing technical assistance in such operation and maintenance.
Although the group contributed to the study of atmospheric tidal oscillations by grenade firings at many geographical locations, they only provided a small fraction of the data required. However Groves undertook the task of analysing a much greater volume of data, discussing his results in a Royal Society review lecture of atmospheric tides (Proc. Roy. Soc., 351, 437-469, 1976). Data from the co-ordinated series of grenade flights carried out by NASA at Wallops Island, Natal (Brazil), and Kourou ( French Guiana), and the greater volume of Meteorological Rocket Network data provided by observations of wind speeds up to 60 km above North America and adjacent oceanic areas were included with particular reference to tidal theory. He also worked on the vertical structure of atmospheric oscillations formulated by classical tidal theory, including the effect of heat sources and gravity. "As a result, a much more detailed and reliable understanding of the phenomena which, though studied in some detail as early as 1898, presented difficult problems of interpretation which still remained until information from space techniques has been forthcoming" (M & R, p. 277).
The first two grenade experiments at Somniani were carried out on 29 and 30 April 1965, Nike-Apache rockets carrying payloads manufactured in the USA; 9 out of 12 grenades were ejected and flashes recorded at four stations in the first experiment, but only two flashes were recorded in the second. A payload containing 25 grenades designed by AWRE, Aldermaston, together with a parallel payload section designed by the Air Force Cambridge Research Laboratories for generating a trail release of trimethyl aluminium (TMA), was used on the next 3 launchings carried out on 24, 27 March and 26 April 1966. Chemiluminescent reactions between TMA and the ambient atmosphere produced a glow enabling measurements to be made of winds and temperature, the analysis of which provided some information on the near equatorial atmosphere, for example, the altitude profile of atmospheric temperature showed two maxima in Spring and changed markedly during a 72-hour period; the meridional component of wind speed above 55 km showed marked diurnal changes confirming earlier observations; and the principal maximum in wind speed occurred at 105 ± 5 km, being a little less than 100 m s^-1 towards NW in Winter and near 118 m s^-1 towards E or NE in Summer at that altitude. "This campaign showed that the combined grenade-TMA technique could be used very effectively in a co-operative programme" (M & R, p.171).
The first grenade experiments at Sardinia were carried out on 30 September and 2 October 1965 after Groves and his group had prepared the ground equipment. Two boosted Skylarks were launched, glow clouds and TMA trails being photographed against the background of stars of Canis Major and Orion to determine camera orientation.
The multiplex system for acoustical recording in which signals from a widely-spaced array of hot-wire microphones were transmitted to a central recording point proved to be one of the most accurate methods of measuring wind velocity and temperature in the upper atmosphere below 100 km. A technique for achieving minimum line noise was developed by R. W. Procunier; each microphone was associated with a control frequency in the range 595 to 2975 Hz, amplitude modulated by the pressure variations. Tests of the prototype equipment at the USA Eglin Air Force Base and at the ESRO range in Sardinia in 1965, where detection was extended to 107 km, led to the development of a unit for extended use at the ESRO range at Kiruna.
The first grenade experiments at Kiruna took place on 1 and 4 February 1968, Groves organizing the supply of the ground equipment. Two Centaure launchings with TMA release were successful, wind velocity and temperature measurements being made up to 90 km acoustically and up to 150 km optically. Although the ground temperature fell to -45 C no major operating problems arose. However the performance of the acoustical recording system deteriorated over three weeks, leading to modification of the system involving component substitution and improved heat insulation for the second two launchings at twilight on 15 October and 1 November 1968. The experiments were carried out in collaboration with ESLAB, the launch times being co-ordinated with NASA grenade launchings at Wallops Island, Fort Churchill and Point Barrow.
Four Nike-Cajun rockets carrying grenade and TMA payloads were launched between 17 and 25 January 1969 from Kiruna to measure wind and temperature profiles in the stratosphere and mesosphere during a stratospheric warming. A stratalert had declared a stratospheric warming over central and south eastern Europe on 16 January and a weak warming still existed over central Asia on 25 January. A cooling of about 45 K at 40 km was observed as anticipated, but at 70 km a warming of about 50 K was noted. Thus a mesospheric warming appeared to follow a stratospheric warming with little variation of temperature occurring at 65 km. Wind speeds of 220 m s-1were observed on 19 January, some of the highest ever recorded in the stratosphere. These launchings were made in collaboration with the Meteorological Institute of the University of Stockholm and the Swedish Space Technology Group and were co-ordinated with six other grenade launchings from northern hemisphere locations, two each from Wallops Island, Fort Churchill and Point Barrow, and three meteorological sonde launchings from South Uist, Hebrides. A. F. D. Scott was in charge of this investigation.
The most effective method of studying the temperature, density and wind structure of the atmosphere above 100 km involved ground-based observations of glow clouds produced at chosen altitudes. A good illustration of the method was provided by the launch of two Skylark rockets from Woomera under twilight conditions on the morning and evening of 31 May 1968. Chemiluminescent reactions between TMA released as a trail between 80 and 140 km in the Earth's shadow enabled the trail to be photographed, its drift giving the atmospheric wind profile, and high resolution photography of the lower trail yielding information on atmospheric turbulence. Four standard 0.45 km grenades were released in succession in the trail, and charges of 5, 25 and 45 kg of high explosive were detonated on the ground, about 1 km downrange of the launcher, at such times that the shock waves produced by them reached the trail shortly after it was formed at altitudes near 100 km, the velocity of the shock waves produced by them giving the temperature of the ambient atmosphere. This was the first time that the propagation of shock waves from grenade detonations in the 90-130 km region was studied optically to derive the temperature from the sonic velocity. Standard aluminised grenades were released at intervals between 150 and 240 km above the Earth's shadow, multiple releases above 190 km maintaining a nearly constant surface intensity; the AlO produced resonantly scattering the sunlight. Time-sequenced photographs of the AlO clouds enabled the diffusion coefficient and neutral winds to be determined, spectroscopic observations of the band structure of the resonant radiation at c. 2 Å resolution enabling the temperature to be determined. A dynamic picture of the interactions of atmospheric structure was constructed from the co-ordinated series of measurements of neutral atmospheric wind velocity, turbulent structure, temperature and density made during each launch between 90 and 250 km altitude. D. Rees collaborated with Messrs. R. G. Roper, K. H. Lloyd and C. H. Low (WRE) in this work, applying different observational methods and experimental techniques developed by their groups (Phil. Trans., Roy. Soc., Vol. 271. 631, 1972).
In a collaboration with workers from the Appleton Laboratory, WERE and the University of Brisbane, Rees and M. P. Neal showed in 1972 that a lithium glow cloud could be used to determine the wind distribution in sunlight. A Skylark rocket released the lithium at an altitude of c. 200 km, daylight observations of the glow being made by a differential photometer and also by a Fabry-Perot plate with a resolution of 1.0 Å together with an interference filter of 3.0 Å band pass around the lithium resonance line. The glow cloud was observed for 20 minutes and from its motion the wind speed of 32 ± 2 km s-1 in a direction specified by an azimuthal angle of 221 ± 2 deg was measured at 202 km. Frequent applications of the lithium glow technique followed this successful flight. A notable example involving the group, under the leadership of Rees since 1974, took place at Thumba during February 1975 in which it was planned to launch 12 rockets in one day between dawn and dusk to investigate atmospheric and ionospheric processes including neutral winds and the equatorial electrojet. In the event five Petrels were launched on 9 February, four being successful, the fifth only partially so. Measurements were made of neutral winds and temperature at dawn by means of TMA trails and in daytime using lithium vapour trails; of electron density and temperature; and of electric fields. On 19 February two further Petrel flights measured wind distribution at dusk and daytime, and two Centaure flights, one completely successful, measured electron density and temperatures, and electron currents using a scalar magnetometer, and the other, mainly successful, measured electron currents with a vector magnetometer. Rees collaborated with scientists from the Indian Space Research Organisation and the University of Birmingham in these experiments. (M & R, p. 175 ).
To extend measurements of night-time winds above 150 km, the normal limit of a TMA trail, the group in collaboration with the Appleton Laboratory developed a mobile tuned dye laser radar system for tracking sodium clouds. It was first operated successfully by Rees and M. C. W. Sandford, of the Appleton Laboratory, during the High Latitude Campaign at Andenes, Norway in October and November 1973, the experiments indicating that the laser radar system could obtain wind profiles from sodium clouds at over 300 km, the predicted design limit.
Rees developed an ultra-stable single etalon, Fabry-Perot interferometer to make direct observations of the line profiles of airglow emissions in order to obtain wind speeds and temperatures in the thermosphere. A successful trial in a balloon experiment observing atmospheric absorption lines of H2O and O2 led to the etalons being incorporated in an instrument developed with the University of Michigan and launched on 3 August 1981 as part of the NASA Dynamics Explorer mission (M & R p. 280).

Ultra-violet and Optical Astronomy Group

Boksenberg's involvement in ultra-violet astronomy, with the instrumentation of the UV scan experiment on TD-1 and as project scientist for the UK side of the IUE programme, has already been referred to on pp. 96-97. In 1969 he collaborated with Wilson in writing a comprehensive review of ultra-violet astronomy (Ann. Rev. Astron. Astrophys. 7, pp. 421-472, 1969). On 16 June 1973 they collaborated with the Culham Laboratory in a successful launching from Woomera of a Skylark rocket for high resolution UV spectroscopy of the bright stars, g² Velorum and z Puppis (see pp.106-107). Meanwhile Boksenberg had established his own group which, with substantial SRC funding, proceeded to work on three main fronts: satellite UV astronomy; balloon UV astronomy; and optical astronomy.

Satellite UV astronomy

The group participated in the scientific analysis and interpretation of data from TD-1 which was launched from Western Test Range, California at 1.55 hr GMT on 12 March 1972, the orbit being circular, sun synchronous, and nearly polar. Although the onboard tape recorders ceased functioning ten weeks after launch, some 60% of the data were soon being recovered in real time and by January 1973 this had been steadily increased to over 95%. Some 30,000 stars down to the ninth visual magnitude were scanned in two six-monthly sky scans. The sky surveys provided broadband ultra-violet spectra of many stars for the first time, making possible the determination of extinction as a function of wavelength in different directions within the galactic plane. One of the main achievements was the first analysis of the chemical composition of Wolf-Rayet stars.
The largest of the seven experiments on board TD-1, namely the UV scan experiment covering the wavelength range 1350-550 Å in 60 channels with a grating spectrophotometer, and a single photometric channel with peak response at 2740 Å and bandwidth near 300 Å became fully operational on orbit 107. The results obtaned during the first few weeks after launch covering stellar observations, interstellar extinction, Wolf-Rayert stars and the Large Magellanic Cloud soon appeared in Nature, Vol. 238, 34, 1972 and Mon. Not. R. Ast. Soc., Vol. 163, 291, 1973 (Boksenberg, Wilson & their colleagues from the UK and Belgium).
Boksenberg and J-C. Gerard of the University of Liege while carrying out their main function of observing stars, reported incidental observations of equatorial ultra-violet dayglow above 540 km. The main features of the dayglow were explicable on the basis of resonance scattering of sunlight by Mg⁺ ions.
He and D. Carnochan with J. Cahn and S. P. Wyatt of the Department of Astronomy, University of Illinois, obtained the far ultra-violet spectrum (1350-2550 Å) of the central star of the planetary nebula, NGC 6543. The adopted temperature and angular radius were (40,000 ± 4000) K and (2.5 ± 0.5) x 10^-11 rad. respectively. The temperature and range of likely luminosities of the central star placed it near the beginning of the Harman-Seaton evolutionary sequence, consistent with an enveloping planetary nebula that was young and optically thick.
The group's main research involvement in the IUE was the development of the television detector system, and the design of the sun baffle to allow the observation of stars 10¹⁵ times fainter than the sun. IUE was launched on 12 January 1978, the onboard instruments functioning well from the start.

Balloon UV astronomy

The group collaborated with the University of Belfast in a programme of spectral observations of stars and interstellar gas in the balloon ultra-violet. Spectral observations at a resolution of 0.1 Å covering the region 2730-2880 Å were made with an objective grating spectrograph mounted on the UCL balloon-borne, star-stabilised system. Of particular interest were the interstellar lines of Mg II at 2795.53 and 2802.70 Å and Mg I at 2852.13 Å, the two important astrophysical reasons being: (i) since Mg is predominantly in the Mg⁺ state in the general interstellar medium, the interstellar abundance of Mg can be determined directly from the measured widths of the Mg II doublet lines, thus avoiding the difficult problem of allowing for atoms in unobserved states by consideration of the ionization balance, which is encountered in the optical region for Na and Ca; (ii) observation of both Mg⁺ and Mg^o gives information on the ionization balance, and values for the interstellar electron density can be derived using estimates of the interstellar radiation density. 5.7 x 10⁵ m³ capacity balloons were launched from the National Centre for Atmospheric Research Balloon Flight Station, Palestine, Texas reaching a float altitude of c. 40 km at which the zenith atmospheric transmission is in the region of 50% for the range of wavelengths concerned.
During 4/5 October 1972 spectral observations were made of the interstellar lines of Mg II and Mg I in the directions of stars in Orion and Cassiopeia from which the interstellar Mg column density and interstellar electron density were derived.
For the two coolest stars studied (b Orion and a Lyra) wavelengths of all spectral features in the aforesaid range were obtained with an accuracy of c. ± 0.04 Å. From these results the velocity field in the atmosphere of b Orion was investigated and evidence found for an outward motion in the higher layers and a pulsation-type motion in the deepest layers. The strength of the Mg⁺ resonance and subordinate lines near 2800 A for all the stars observed was compared with non-l.t.e. calculations, good agreement between observation and theory being found for main sequence stars, but the stronger lines in the super giants implying microturbulent velocities greater than 10 km s^-1.
Spectral observations of interstellar Mg in the Mg II doublet lines at 2795.5 Å and 2802.7 Å and Mg I at 2852.1 Å in the directions of stars in Orion, Scorpius and Virgo enabled values for the interstellar Mg abundance and electron density to be derived for the gas in the directions observed. The results indicated that the predominant ionizing mechanism in cool clouds is photoionization by starlight.
During 19/20 1974 May the spectra of nine stars were obtained covering the region 2870-2740 Å with an accuracy better than 0.1 Å. The discussion of the analysis of the spectra was presented in three papers. In the first, concerning four, nearby, unreddened stars, namely a Leo, h UMa, s Sgr and a Vir, values were derived for the interstellar Mg abundance and electron density for the gas in those directions. In the second, concerning the more reddened stars, namely, b, d, t Sco and b Cep, it was found from the relative Mg/H abundances that Mg was depleted by a factor of approximately ten for the moderately reddened stars, b and d Sco, E(B-V) about 0.2, while for t Sco and b Cep, E(B-V) about 0.5, the Mg/H abundance was closer to the solar value in accord with earlier studies of Orion stars of similar reddening. A comparison of the results and those obtained for Orion with interstellar Na observations gave a constant Na/Mg abundance ratio indicating similar depletion factors for Na and Mg over the range of E(B-V) studied. There being no evidence in the spectrum of d Sco for the high velocity gas components reported by Hicks et al, the third paper considered several physical conditions in an attempt to explain the anomalously low Mg^o:Na^o ratio implied by the observations. It was concluded that if the features were not of a time-dependent nature, then Mg is underabundant with respect to Na by at least an order of magnitude in the high-velocity components in contrast with the previous general findings.
Members of the group associated with Boksenberg in this work were B. Kirkham, Elizabeth Michelson and M. Pettini; also involved were W. A. Towlson and T. E. Venis, who with H. S. Tomlinson, designed and developed the UCL balloon platforms for infrared and ultraviolet astronomy (see p.108).

Optical astronomy

A new type of detection system for optical astronomy, known as the UCL Image Photon Counting System (IPCS), was conceived by Boksenberg in 1968 and thereafter developed with SRC funding. In essence, a high gain image intensifier capable of registering single photons was optically coupled to a television camera, which was interfaced to an on-line computer. The system was capable of photon counting in at least 10⁵ image elements simultaneously, so behaving as a vast bank of photomultipliers operating in the counting mode. Because of the on-line processing, noise pulses were largely rejected, storage capacity was essentially unlimited and signal integration was linear. Another feature was the capability of time resolution in increments of a few milliseconds per frame. The President of the International Astronomical Union at the Conference on Auxiliary Instrumentation for Large Telescopes, held in Geneva in 1972, stated: "The photon event counting system of Boksenberg of University College London is the purest answer to the questions of recording information in astronomy". It was to become used on most of the world's largest telescopes, attracting the foremost astronomers to collaborate with Boksenberg in studying outstanding astronomical problems, including those related to cosmology.
Instances of its use with the 98-in Issac Newton telescope (INT) at the Royal Greenwich Observatory (RGO), Herstmonceux and with the 200-in Hale telescope (HT) on Mount Palomar in California in the first half of the seventies follow. During the observation of spectra of faint objects with the HT, at a resolution (0.7 Å) theretofore unprecedented, priority was given to the quasar, PKS 0237-23; an analysis of the 75 absorption lines obtained, combined with 26 from other sources, posed a number of intriguing questions, particularly the strange doublet behaviour of the redshifts, and the possibility that absorption line-locking played some role in determining the actual distribution of redshifts ( Boksenberg & W. L. W. Sargent of the Hale Observatories). A systematic spectrometric study of the brightest quasar, 3C 273, covering a range of dispersions between 30 and 210 A mm^-1, yielded improved spectra, particularly of the blue region, showing previously undetected features. Emission line widths were compared with photoionization models (Boksenberg & K. Shortridge with R. A. E. Fosbury, M. V. Penston & A. Savage using the INT at the RGO). Spectral observations with the IPCS on the HT covering the wavelength region 3300-6500 Å of the object associated with the unusual variable radio source 2005 + 403 near the galactic plane showed it to be a QSO with an emission redshift of 1.736 (Boksenberg, S. A. Briggs & R. F. Carswell with M. Scmidt of the Hale Observatories & D. Walsh of the Nuffield Radio Astronomy Laboratories, Jodrell Bank); those covering the range from c. 3300 to over 7000 Å of the red stellar object associated with the highly asymmetric double radio source, 3C 68.1, showed it to be a QSO with red shift 1.238, the spectral index of the optical continuum being c. 6, a value considerably steeper than that previously found for QSOs (Boksenberg & Carswell with J. B. Oke of the Hale Observatories).
Spectral observations of Seyfert galaxies included new observations of the optical spectrum of NGC 4151 with the IPCS mounted at the camera focus of the Unit Spectrograph at RGO; two spectra with resolution 1 Å covering the spectral regions 3727 to 4363 Å and H g to 5007 Å spanned the blue region and one spectrum covered the red region from H b to c. 8000Å with 5 Å resolution; and scans covering the wavelength region from 3240 to 11240 Å were obtained using the MultiChannel Spectro-Photometer (MCSP) at the Cassegrain focus of the HT. The underlying broad line spectrum in NGC 4151 was similar in nearly all respects to that of 3C 273, and the similarity of the ratio of broad-to-narrow line intensities of H beta and He I (5876 Å) suggested that the low-density gas in the galaxy was excited by radiation with much the same spectrum as that exciting the high-density region nearer the nucleus. (Boksenberg & Shortridge with Messrs. D. A. Allen, Fosbury, Penston, & Savage of RGO). Further ultra-violet spectral observations of NGC 4151 with the INT at the RGO were obtained by Boksenberg and Penston, namely at 1.3 Å resolution from the short-wavelength atmospheric cut-off to 4000 Å, since studies by previous workers had been most detailed at wavelengths longward of the O II lines at 3727 Å. The identifications, equivalent widths and intensities of emission lines in the wavelength range 3130 to 3966 Å were given. Observations of the spectrum of the nucleus of NGC 3516 yielded accurate measurements of emission-line intensities and profiles (INT); an explanation of the emitted spectrum with the aid of a photoionization model; and a correlation of the emission-line variability with physical conditions in the nucleus (Boksenberg & H. Netzer of the Department of Physics and Astronomy, Tel-Aviv University and the Wise Observatory). Spectra, scans and a direct electronograph were obtained of Markarian 231, using respectively the INT at Herstmonceux, the MCSP on the HT on Mount Palomar, and the RGO electronograph camera on the 40-in telescope at the Wise Observatory, Israel; these gave rise to two interpretations of the continuum, each placing the galaxy among the quasars in optical luminosity; a synthesis of the observed emission spectrum; the structures of three absorption line redshifts; and two possible configurations for the nuclear components of the galaxy (Boksenberg & Carswell with Messrs. Allen, Fosbury, Penston & Sargent).
Spectra of three Wolf-Rayet stars in M33 covering the wavelength range 3450-5150 Å were obtained with the HT; one object, WR-13, was found to be a WN star, probably WN5 or WN6; the second, WR-16, was confirmed to be a WC star, although, contrary to previous contention, its spectrum in the aforesaid range was consistent with a Galactic WR classification of WC7; and a third object, previously unclassified, in the H II IC 132 was found to be a WN4 star. (Boksenberg & A. J. Willis with L. Searle of the Hale Observatories).
Spectra of the nucleus and plates of the galaxy NGC 5506, suggested as the X-ray source, 3U 1410 - 03, were obtained with the INT and the Anglo-Australian telescope. Photographs showing it to be a highly elongated system, crossed by dust lanes and possessing a prominent nucleus, supported its classification as an irregular Type II, morphologically superficially resembling M 82. The nuclear spectrum implied that the object was active, greatly enhancing the probability of association with the X-ray source (A. S. Wilson of the Astronomy Centre, University of Sussex with Messrs. Boksenberg, Fosbury, & Penston).
A study of the rotation and gravitational redshift in some dozen hydrogen-atmosphere DA white dwarfs with the Palomar coude image tube and the IPCS implied that degenerate stars have low specific angular momentum and since, they have lost most of their mass, transport of angular momentum across molecular-weight barriers must be an efficient process (J. L. Greenstein of the Hale Observatories with Boksenberg, Carswell and Shortridge).
Boksenberg became a Fellow of the Royal Society in 1978, the same year that he was appointed Professor. In 1981 he was appointed Director of the RGO, but retained a position as Visiting Professor at UCL.

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