John Holt (physicist)
Encyclopedia
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.
, Cheshire
, England, in 1918, his father being a worker in a boat-building yard, and his mother the owner of a bakery and confectionery
shop. He was educated in Runcorn and in 1934 at the age of 16 became an undergraduate at in the physics
department of Liverpool University
. 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".
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
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 PhD
in 1941. The thesis describes his work on artificial radioactivity
, 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 Liverpool University 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
, Holt's team carried out experiments on the weak interaction
responsible for the decay of the muon
, which played a large part in the current understanding of the Standard Model
. In the early 1960s Holt was involved with the design of the electromagnet
s for the electron synchroton at Daresbury Laboratory
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
at CERN
. This group investigated proton
structure and discovered that proton spin
was not carried by the valence quarks
, which overturned the previous predictions. Holt retired in 1983.
Royal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
(15 February 1918 – 6 January 2009) was an English experimental physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
who played a part in the development of the atom bomb
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
and later became one of the pioneers of elementary particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
research.
Early life and education
John Holt was born in RuncornRuncorn
Runcorn is an industrial town and cargo port within the borough of Halton in the ceremonial county of Cheshire, England. In 2009, its population was estimated to be 61,500. The town is on the southern bank of the River Mersey where the estuary narrows to form Runcorn Gap. Directly to the north...
, Cheshire
Cheshire
Cheshire is a ceremonial county in North West England. Cheshire's county town is the city of Chester, although its largest town is Warrington. Other major towns include Widnes, Congleton, Crewe, Ellesmere Port, Runcorn, Macclesfield, Winsford, Northwich, and Wilmslow...
, England, in 1918, his father being a worker in a boat-building yard, and his mother the owner of a bakery and confectionery
Confectionery
Confectionery is the set of food items that are rich in sugar, any one or type of which is called a confection. Modern usage may include substances rich in artificial sweeteners as well...
shop. He was educated in Runcorn and in 1934 at the age of 16 became an undergraduate at in the physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
department of Liverpool University
University of Liverpool
The University of Liverpool is a teaching and research university in the city of Liverpool, England. It is a member of the Russell Group of large research-intensive universities and the N8 Group for research collaboration. Founded in 1881 , it is also one of the six original "red brick" civic...
. The following year James Chadwick
James Chadwick
Sir James Chadwick CH FRS was an English Nobel laureate in physics awarded for his discovery of the neutron....
was appointed Professor of Physics at the university, shortly after he had been awarded the Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...
for proving the existence of the neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
. During the time that Holt was a student, Chadwick built a cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
, 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 WarWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
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
Frisch-Peierls memorandum
The Frisch–Peierls memorandum was written by Otto Frisch and Rudolf Peierls while they were both working at the University of Birmingham, England. The memorandum contained new calculations about the size of the critical mass needed for an atomic bomb, and helped accelerate British and U.S...
relating to the critical mass
Critical mass
A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...
required for an atomic bomb. Some of the experiments were performed in a Liverpool Underground station during the Liverpool blitz
Liverpool Blitz
The Liverpool Blitz was the heavy and sustained bombing of the British city of Liverpool and its surrounding area, at the time mostly within the counties of Lancashire and Cheshire but commonly known as Merseyside, during the Second World War by the German Luftwaffe.Liverpool, Bootle, and the...
. This work led to Holt completing his PhD
Doctor of Philosophy
Doctor of Philosophy, abbreviated as Ph.D., PhD, D.Phil., or DPhil , in English-speaking countries, is a postgraduate academic degree awarded by universities...
in 1941. The thesis describes his work on artificial radioactivity
Induced radioactivity
Induced radioactivity occurs when a previously stable material has been made radioactive by exposure to specific radiation. Most radioactivity does not induce other material to become radioactive....
, but his findings on uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, 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 Liverpool University 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
Stripping reaction
A stripping reaction is a term used to describe two separate physical processes:*In nuclear physics a stripping reaction is a nuclear reaction in which part of the incident nucleus combines with the target nucleus, and the remainder proceeds with most of its original momentum in almost its original...
. Using the more powerful synchrocyclotron
Synchrocyclotron
A synchrocyclotron is a cyclotron 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 speed of light...
, Holt's team carried out experiments on the weak interaction
Weak interaction
Weak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
responsible for the decay of the muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
, which played a large part in the current understanding of the Standard Model
Standard Model
The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
. In the early 1960s Holt was involved with the design of the electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
s for the electron synchroton at Daresbury Laboratory
Daresbury Laboratory
Daresbury Laboratory is a scientific research laboratory near Daresbury in Cheshire, England, which began operations in 1962 and was officially opened on 16 June 1967 as the Daresbury Nuclear Physics Laboratory by the then Prime Minister of United Kingdom, Harold Wilson...
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
European Muon Collaboration
The European Muon Collaboration conducted high energy particle physics experiments at CERN. In 1983, it discovered that nucleons inside a nucleus have a different distribution of momentum among their component quarks...
at CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
. This group investigated proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
structure and discovered that proton spin
Nucleon spin structure
Nucleon spin structure describes the partonic structure of nucleon intrinsic angular momentum . The key question is how nucleon spin 1/2 is carried by its constituents, say partons . It was originally expected before the 1980s that quarks carry all of the nucleon spin, but later experiments...
was not carried by the valence quarks
Quark model
In physics, the quark model is a classification scheme for hadrons in terms of their valence quarks—the quarks and antiquarks which give rise to the quantum numbers of the hadrons....
, which overturned the previous predictions. Holt retired in 1983.