Wednesday, January 20, 2021

Sir Arnold Wolfendale obituary | Particle physics


Sir Arnold Wolfendale, the 14th astronomer royal, who has died aged 93, did much to advance understanding of cosmic rays, the stream of charged particles from outer space that continuously bombard the Earth’s atmosphere. For this purpose he assembled a strong team at Durham University, making it one of Britain’s leading centres for research in this field. In 1956 he joined the physics department as a lecturer, and during his time as professor (1965-92) established a highly regarded astronomy division.

Secondary cosmic rays result from primary rays impacting on the Earth’s atmosphere. Among the secondary particles found at ground level are muons, one of the fundamental particles of the standard model of particle physics.

In the 1960s and 70s Arnold spearheaded measurements of the number of these particles as a function of their energy, using an electromagnet and an array of Conversi neon-tubes, the performance of which he greatly improved. His measurements gave information on the energy spectrum of primary cosmic rays at what were then extreme energies, with the data also of importance for testing theories then current in particle physics.

One of Arnold’s outstanding achievements was to collaborate with scientists from India and Japan in searching for the related particles known as muon neutrinos, produced within the atmosphere simultaneously with the muons, using Conversi tubes located in the Kolar Gold Fields, Karnataka, southern India, at depths of 2,300 metres. The rock above the laboratory, in which the detectors operated with great difficulty because of the high temperatures in the mine, acted as a shield against the ubiquitous muons. Data on the muon background measured in the mine was later used in the analysis of results from the famous solar-neutrino experiment of the Nobel laureate Ray Davis in the Homestake Mine in South Dakota.

Arnold Wolfendale, left, with fellow physicists GD Rochester and John Cockcroft, in the early 1960s.
Arnold Wolfendale, left, with fellow physicists GD Rochester and John Cockcroft, in the early 1960s

About this time, a near-fatal accident with a power supply turned Arnold’s interests to the more phenomenological aspects of cosmic rays, testing theory – particularly the particle-physics connections and origin theories – against experimental data. From then on he mainly used data gathered by the large international collaborations then emerging.

Arnold was born in Rugby, to where his Lancastrian parents, Arnold and Doris (nee Hoyle), had moved for work. Soon afterwards the family returned to the Manchester area, where his father worked as an engineering draughtsman at Metropolitan Vickers Electrical Company in Trafford Park. He won a scholarship to Stretford grammar school and in 1945 entered the physics department of Manchester University. PMS Blackett (later Lord Blackett), his head of department there, sparked his interest in cosmic rays. Arnold had approached him with a request to research on oxide-coated cathodes, only to be told: “You will research on cosmic rays.” He obeyed, and a distinguished career was launched.

In 1951 Arnold married Audrey Darby. Blackett sent him, still a graduate student and without Audrey, who was then pregnant with their twin sons, to work in Colombo with Arumugam Mailvaganam, one of Blackett’s former students and the first non-white professor of physics there. This visit led to Arnold’s lifelong desire to help science prosper in places out of the mainstream, and to a love of travel.

He developed many international links, in particular with scientists from the eastern bloc, Japan, China and India, many of whom worked for short periods in Durham. In the 1960s George Wdowczyk (from Poland) and Hannis de Beer (from South Africa) spent time in Durham developing methods to interpret information about the highest-energy cosmic rays, including some obtained at the British project at Haverah Park in North Yorkshire. After his collaborators returned home, the fact that the notes on the work were in a mixture of Polish and Afrikaans created some problems.

With the Polish scientist Wlodzimierz Zawadksi, Arnold founded the European Cosmic Ray Symposiums, a series of biennial meetings that in pre-glasnost years were excellent occasions for east to meet west. The inaugural meeting in Łódź, in 1968, of fewer than two dozen scientists, was one of the most productive I ever attended. With collaborators, Arnold also made significant contributions to the astrophysical implications of cosmic rays, exploiting particularly the gamma-ray data from the European Space Agency’s COS-B satellite, showing, among other things, the important result that there was a gradient of cosmic rays across the galaxy.

Arnold could be a fierce critic and I recall, as a young man, trembling when he raised his hand after I had given a talk. But his bark was much worse than his bite.

As Arnold’s interests in astrophysics grew, so did his recognition that the Durham department was too small to sustain experimental activities in particle physics, and he persuaded colleagues to transfer their skills to observational astronomy and astronomical instrumentation. His success in doing so was a factor in his appointment as astronomer royal in 1991.

The appointment surprised many – including Arnold – since he was not a mainstream astronomer. Furthermore, he was the first to hold this 350-year-old office who had not been educated at the universities of Oxford or Cambridge and, with Lancastrian directness, used his position to harangue government on science funding very effectively. Perhaps because of this tenacity, the traditional knighthood did not come until the day of his retirement from the role.

He was elected to fellowship of the Royal Society in 1977 (and awarded its Bakerian medal in 2002), to foreign fellowships of the Indian and Polish academies of science; and to a foreign associateship of the Royal Society of South Africa. At the Royal Institution he was professor of experimental physics (1996-2002), and he served as president of the European Physical Society (1999-2001).

He chaired the Cabinet Office committee on the public understanding of science, engineering and technology leading to the Wolfendale Report (1995), which urged that more attention be given to the shortage of science teachers and to the popular dissemination of the results of scientific research, a forerunner of today’s move towards outreach.

Arnold remained emeritus professor at Durham, and the 40th anniversary of the astronomy division in 2015 saw the foundation of a Centre for Extragalactic Astronomy. He continued his researches in cosmic rays into his late 80s, working with a Russian colleague, Anatole Erlykin. With Terry Sloan (of the University of Lancaster) he did definitive work to debunk overstated claims that low-energy cosmic rays might affect cloud formation and thus enhance global warming.

Beyond science, Arnold had many interests. As president of the Antiquarian Horological Society (1993-2014) he arranged for a plaque to John Harrison, solver of the “longitude problem”, to be placed in Westminster Abbey. He was a man of ready wit and an entertaining after-dinner speaker. The Wolfendale home, where he and Audrey entertained frequently, was a welcoming place and, even after Audrey’s death in 2007, Arnold thought nothing of preparing lunch for 30 people.

In 2015 he married the anthropologist Dorothy Middleton. She survives him, along with his sons, Colin and David, and five grandchildren.

Arnold Whittaker Wolfendale, physicist, born 25 June 1927; died 22 December 2020

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