John Riley Holt, FRS (15 February 1918 – 6 January 2009) was an English experimental physicist who played a part in the development of the atom bomb and later became one of the pioneers of elementary particle physics research.

Early life and education

Holt was born in Runcorn,

Cheshire Cheshire ( ) is a ceremonial and historic county in North West England, bordered by Wales to the west, Merseyside and Greater Manchester to the north, Derbyshire to the east, and Staffordshire and Shropshire to the south. Cheshire's county t ...

, England, in 1918, his father being a worker in a boat-building yard, and his mother the owner of a bakery and

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shop. He was educated in Runcorn and in 1934 at the age of 16 became an undergraduate in the physics department at the University of Liverpool. The following year James Chadwick was appointed Professor of Physics at the university, shortly after he had been awarded the Nobel Prize in Physics for proving the existence of the neutron. During the time that Holt was a student, Chadwick built a cyclotron, then a newly invented research tool, in the physics department. Holt graduated with first class honours in 1938 and won the Oliver Lodge Prize. Chadwick took him on as a research student describing him as "the best research student he had ever supervised".

Career and research

During the Second World War, Chadwick formed a team, which included Holt, to perform measurements, some of which involved the cyclotron, to confirm the findings in the

Frisch–Peierls memorandum The Frisch–Peierls memorandum was the first technical exposition of a practical nuclear weapon. It was written by expatriate German-Jewish physicists Otto Frisch and Rudolf Peierls in March 1940 while they were both working for Mark Oliphant a ...

relating to the critical mass required for an atomic bomb. Some of the experiments were performed in a Liverpool Underground station during the Liverpool blitz. This work led to Holt completing his

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in 1941. The thesis describes his work on

artificial radioactivity Induced radioactivity, also called artificial radioactivity or man-made radioactivity, is the process of using radiation to make a previously stable material radioactive. The husband and wife team of Irène Joliot-Curie and Frédéric Joliot-Curie ...

, but his findings on uranium, which related to the bomb, were not released for security reasons. Holt's work played a part in proving the feasibility of the production of a nuclear weapon. Following the war, Holt was appointed lecturer at the University of Liverpool in 1946 and Professor of Experimental Physics in 1966. He was involved with the design of a larger cyclotron and in 1949, with C. T. Young discovered low-energy deuteron stripping. Using the more powerful

synchrocyclotron A synchrocyclotron is a special type of cyclotron, patented by Edwin McMillan in 1952, in which the frequency of the driving RF electric field is varied to compensate for relativistic effects as the particles' velocity begins to approach the spe ...

, Holt's team carried out experiments on the weak interaction responsible for the decay of the

muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of , but with a much greater mass. It is classified as a lepton. As wi ...

, which played a large part in the current understanding of the

Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...

. In the early 1960s Holt was involved with the design of the electromagnets for the electron synchrotron at

Daresbury Laboratory Daresbury Laboratory is a scientific research laboratory based at Sci-Tech Daresbury campus near Daresbury in Halton, Cheshire, England. The laboratory began operations in 1962 and was officially opened on 16 June 1967 as the Daresbury Nuclear ...

and in 1964 he was elected a Fellow of the Royal Society. In the 1970s and 1980s he led the Liverpool group in the

European Muon Collaboration The European Muon Collaboration (EMC) was formed in 1973 to study the interactions of high energy muons at CERN. These experiments were motivated by the interest in determining the quark structure of the nucleon following the discovery of high level ...

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...

. This group investigated

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

structure and discovered that proton spin was not carried by the valence quarks, which overturned the previous predictions. Holt retired in 1983.

References

{{DEFAULTSORT:Holt, John (Physicist) 1918 births 2009 deaths English physicists British nuclear physicists People associated with CERN Experimental physicists Fellows of the Royal Society Alumni of the University of Liverpool Academics of the University of Liverpool People from Runcorn