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Holt, John Riley (1918–2009), experimental physicist, was born on 15 February 1918 at 2 Old Albert Terrace, Runcorn, Cheshire, the elder son of Frederick Holt, foreman shipwright, and his wife, Annie, née Riley, who ran a family bakery in the town during the later stages of Holt's childhood. He developed an early interest in physics at Runcorn secondary school, which encouraged the study of science and had a Wireless Society which gave him an early introduction to electronic techniques. He left school with an excellent school certificate and in 1934, at the age of sixteen, enrolled at the University of Liverpool. In 1938 he was awarded a first-class honours degree in physics.

In 1935 James Chadwick, winner of that year's Nobel prize for physics, became head of the Liverpool physics department and started making changes, beginning with the construction of a cyclotron, aiming to make the department an international centre for nuclear physics research. Holt was very impressed, so after graduation he enrolled as a research student and was given the task of designing and constructing Geiger counters to study the properties of artificially produced radioactive isotopes. He was awarded his PhD in 1941. However, the outbreak of the Second World War in 1939 completely changed the research priorities of the department. Chadwick had assembled an international team of nuclear physicists to make detailed measurements on neutron induced fission in uranium in order to investigate the feasibility of making an atomic bomb. Holt became a junior member of this team, designing and constructing apparatus, participating in the experiments, and operating the cyclotron. In 1942 he was appointed assistant lecturer at Liverpool. He and the junior members of the team continued with this work after the senior members left to join the Manhattan project in the USA. When the cyclotron was closed down in 1944 the whole group was transferred to Cambridge, where Holt set about designing experimental equipment for use in the post-war period.

Immediately after the war Holt accepted the post of lecturer at Liverpool. (He became a senior lecturer in 1953 and a reader in 1956.) He began a programme of research on the properties of nuclei using an 8 MeV deuteron beam produced by the cyclotron as a nuclear probe, employing a process known as ‘deuteron stripping’. Using a new type of particle detector, which could distinguish between protons and deuterons, he carried out a systematic investigation into the properties of a wide range of nuclei, producing results that strongly supported the shell model of the nucleus. Meanwhile, on 6 August 1949 he married Joan Silvester Thomas (1921–2001), daughter of William Eric Percy Thomas, marine engineer. They initially set up home in Birkenhead but in 1955 moved to a large house called Rydalmere in Higher Bebington, overlooking open country in the centre of Wirral, where they enjoyed entertaining his colleagues. Their sons, David and John Eric, were born in 1950 and 1953 respectively.

Post-war plans for the future of nuclear physics in the UK included building a 400 MeV synchro-cyclotron at Liverpool, which became operational in 1954. Holt then set up a small research team which began a programme to investigate proton structure using proton-proton and pion-proton scattering. However, in 1957 the first observation of parity violation in nuclear beta decay was made. Parity conservation, a fundamental conservation law, applies generally to elementary particle interactions and this immediately raised the question as to whether the violation also occurred in other interactions. Holt and his group immediately set up an experiment on muon decay, and after only ten months published the important result that confirmed parity violation in the weak interaction and later showed that this also applies to charge conjugation, a related conservation law.

In the late 1950s the National Institute for Research for Nuclear Science proposed that a 5 GeV electron synchrotron, called NINA (National Institute Northern Accelerator), be built at Daresbury in Cheshire. Holt was invited to set up and run a design team for the complex magnet system required to maintain the accelerated electrons in a circular orbit. A simple, elegant design was produced and construction began in 1962, with the first circulating beam obtained in 1966. Holt was elected a fellow of the Royal Society in 1964 and appointed to the chair of experimental physics at Liverpool in 1965.

When NINA became operational Holt formed a research group to investigate the structure of the proton via a process known as photo-production, using a high-energy photon beam. At a later stage, a collaboration was formed involving groups from other universities which extended the investigation into the effects of the spin of the particles involved, requiring measurements to be made using both a polarized photon beam and a spin polarized proton target. When the NINA programme ended in 1976 Holt with three of his colleagues joined the European Muon Collaboration at CERN (Conseil Européen de Recherches Nucléaires), near Geneva, to study spin effects in the high energy muon interaction with the quark substructure of the proton. He retired in 1983 before this experiment was completed, but nevertheless maintained a strong interest and was highly delighted when the unexpected and dramatic result was announced, that the spin of the proton was not attributable to the spins of its three constituent quarks.

John Holt was an outstanding experimental physicist who spent all his working life in the physics department of the University of Liverpool. He took a strong interest in the history of the department and wrote a number of articles on this topic. A modest, quiet, and unassuming man, he kept a relatively low profile within the wider physics community. His main interests outside work were gardening, photography, and painting. He looked after his wife when she became ill in later years. After her death he continued actively to cultivate his garden at Rydalmere until he died at Arrowe Park Hospital, Birkenhead, on 6 January 2009, of bronchopneumonia. He was survived by his two sons.

Geoffrey Court and Erwin Gabathuler

Sources  

A. Salam, ‘Non-conservation of parity’, Nature, 181 (1958), 447–9 · W. E. Burcham, ‘Nuclear physics in the United Kingdom, 1911–1986’, Reports on Progress in Physics, 52 (1989), 847–8 · J. R. Holt, ‘Reminiscences and discoveries: James Chadwick in Liverpool’, Notes and Records of the Royal Society, 48/2 (1994), 299–308 · A. Brown, The neutron and the bomb: a biography of Sir James Chadwick (1997) · Memoirs FRS [forthcoming] · John Holt papers, priv. coll. · John Holt papers, RS · WW (2009) · personal knowledge (2013) · private information (2013) [David Holt, son] · b. cert. · m. cert. · d. cert.

Likenesses  

obituary photographs · photograph, repro. in Memoirs FRS

Wealth at death  

£503,902: probate, 1 Oct 2009, CGPLA Eng. & Wales