John Cockcroft

Sir John Douglas Cockcroft (27 May 1897 – 18 September 1967) was a British experimental physicist who shared the 1951 Nobel Prize in Physics with Ernest Walton for their splitting of the atomic nucleus, which led to the development of nuclear power and weapons.

After service on the Western Front with the Royal Field Artillery during the Great War, Cockcroft studied electrical engineering at Manchester Municipal College of Technology whilst he was an apprentice at Metropolitan Vickers Trafford Park and was also a member of their research staff. He then won a scholarship to St John's College, Cambridge, where he sat the Tripos exam in June 1924, becoming a Wrangler. Ernest Rutherford accepted Cockcroft as a research student in the Cavendish Laboratory, and Cockcroft completed his doctorate under Rutherford's supervision in 1928. With Walton and Mark Oliphant, he built what became known as a Cockcroft–Walton generator. Cockcroft and Walton used this to perform the first artificial disintegration of an atomic nucleus, a feat popularly known as "splitting the atom."

During the Second World War, Cockcroft became assistant director of scientific research in the Ministry of Supply, working on radar. He was also a member of the committee formed to handle issues arising from the Frisch–Peierls memorandum, which calculated that an atomic bomb could be technically feasible, and of the MAUD Committee which succeeded it. In 1940, as part of the Tizard Mission, he shared British technology with his counterparts in the United States. Later in the war, the fruits of the Tizard Mission came back to Britain in the form of the SCR-584 radar set and the proximity fuze, which were used to help defeat the V-1 flying bomb. In May 1944, he became director of the Montreal Laboratory, and oversaw the development of the ZEEP and NRX reactors, and the creation of the Chalk River Laboratories.

After the war Cockcroft became the director of the Atomic Energy Research Establishment (AERE) at Harwell, where the low-powered, graphite-moderated GLEEP became the first nuclear reactor to operate in western Europe when it was started on 15 August 1947. This was followed by the British Experimental Pile 0 (BEPO) in 1948. Harwell was involved in the design of the reactors and the chemical separation plant at Windscale. Under his direction it took part in frontier fusion research, including the ZETA program. His insistence that the chimney stacks of the Windscale reactors be fitted with filters was mocked as Cockcroft's Folly until the core of one of the reactors ignited and released radionuclides during the Windscale fire of 1957.

From 1959 to 1967, he was the first master of Churchill College, Cambridge. He was also the chancellor of the Australian National University in Canberra from 1961 to 1965.

Early life and education

thumb|upright=1.2|right|The house in [[Walsden, Todmorden, where Cockcroft lived from the age of two until he was 28-years-old.]]

John Douglas Cockcroft was born on 27 May 1897 in Todmorden, England, the eldest son of John Arthur Cockcroft, a mill owner, and Annie Maude Fielden. He had four younger brothers; Eric, Philip, Keith and Lionel. His early education was at the Church of England school in Walsden from 1901 to 1908, at Todmorden Elementary School from 1908 to 1909, and at Todmorden Secondary School from 1909 to 1914, where he played football and cricket. Among the girls at the school was his future wife, Eunice Elizabeth Crabtree. In 1914, he won a County Major Scholarship, West Riding of Yorkshire, to the Victoria University of Manchester, where he studied mathematics.

After the war ended, Cockcroft was released from the Army in January 1919. He elected not to return to the Victoria University of Manchester, but to study electrical engineering at Manchester Municipal College of Technology. Because he had completed a year at Victoria University of Manchester, he was allowed to skip the first year of the course. He received his B.Sc. in June 1920. Miles Walker, the professor of electrical engineering there, persuaded him to take up an apprenticeship with Metropolitan Vickers. He obtained a 1851 Exhibition Scholarship from the Royal Commission for the Exhibition of 1851, and submitted his M.Sc. thesis, Harmonic Analysis for Alternating Currents, in June 1922.

Walker then suggested Cockcroft sit for a scholarship to St John's College, Cambridge, Walker's alma mater. Cockcroft was successful, winning a £30 scholarship and a £20 bursary awarded to undergraduates of limited means. Metropolitan Vickers gave him £50 subject to his returning after completing his degree. Walker and an aunt made up the balance of the £316 fee. As a graduate of another university, he was allowed to skip the first year of the tripos. He sat the tripos exam in June 1924, achieved a B* as a wrangler, and was awarded his B.A. degree.

Cockcroft married Elizabeth Crabtree on 26 August 1925, which was published in the Proceedings of the Royal Society. He was awarded his doctorate on 6 September 1928. During this time he was an assistant to the Russian physicist Peter Kapitza, who was working on the physics of magnetic fields in extremely low temperatures. Cockcroft helped with the design and construction of helium liquefiers.

Cockcroft was elected a Fellow of St John's College on 5 November 1928. He and Walton began operating their accelerator in March 1932, bombarding lithium and beryllium with high-energy protons. They expected to see gamma rays, which French scientists had reported, but none were found. In February 1932, James Chadwick demonstrated that what had been observed were actually neutrons. Cockcroft and Walton then switched to looking for alpha particles instead. On 14 April 1932, Walton bombarded a lithium target and noticed what he thought might be alpha particles. Cockcroft and then Rutherford were summoned, and confirmed that this was indeed the case. That evening, Cockcroft and Walton met at Rutherford's home and produced a letter for Nature in which they announced their results, the first artificial disintegration of an atomic nucleus, which can be described thus:

: + → 2 + 17.2 MeV

This feat was popularly known as "splitting the atom." For this accomplishment, Cockcroft and Walton were jointly awarded the Hughes Medal in 1938, and the Nobel Prize in Physics in 1951. They went on to disintegrate carbon, nitrogen and oxygen using protons, deuterons and alpha particles. They demonstrated that they had produced radioactive isotopes, including carbon-11 and nitrogen-13.

thumb|left|Cockcroft–Walton voltage multiplier circuit

In 1929, Cockcroft was appointed a Supervisor in Mechanical Sciences at St John's College. He was appointed a Supervisor in Physics in 1931, and in 1933 became the junior bursar, making him responsible for the upkeep of the buildings, many of which were suffering from neglect. The college gatehouse had to be partly taken down in order to repair damage done by deathwatch beetles, and Cockcroft supervised rewiring of the electrics. In 1935, Rutherford appointed him the director of research at the Mond Laboratory after Kapitza, who had returned to the Soviet Union. He supervised the installation of new cryogenic equipment, and supervised low temperature research. He was elected a Fellow of the Royal Society in 1936,

World War II

thumb|right|[[GL Mk. III radar ]]

On the outbreak of World War II, Cockcroft took up the post of assistant director of scientific research in the Ministry of Supply, working on radar. In 1938, Sir Henry Tizard showed Cockcroft Chain Home, the ring of coastal early-warning radar stations built by the Royal Air Force (RAF) to detect and track aircraft. Now, he helped deploy scientists to help get the system fully operational. In 1940, he became part of the Advisory Council for Scientific Research and Technical Development. In April 1940, along he became a member of the Committee for the Scientific Study of Air Warfare formed to handle issues arising from the Frisch–Peierls memorandum, which calculated that an atomic bomb could be technically feasible. This committee was succeeded by the MAUD Committee, of which Cockcroft was also a member, in June 1940. This committee directed the ground-breaking early research in Britain.

In August 1940, Cockcroft travelled to the United States as part of the Tizard Mission. Because Britain had developed many new technologies but lacked the industrial capacity to fully exploit them, it was decided to share them with the United States, although that nation was not yet at war. The information provided by the Tizard Mission contained some of the greatest scientific advances made during the war. The shared technology included radar technologies, in particular the greatly improved cavity magnetron designed by Oliphant's group at Birmingham, which the American historian James Phinney Baxter III described as "the most valuable cargo ever brought to our shores," the design for the proximity fuze, details of Frank Whittle's jet engine and the Frisch–Peierls memorandum describing the feasibility of an atomic bomb. Though these may be considered the most significant, many other items were also transported, including designs for rockets, superchargers, gunsights and submarine detection devices. He returned to Britain in December 1940.

Soon after his return, Cockcroft was appointed Chief Superintendent of the Air Defence Research Development Establishment (ADRDE) at Christchurch, Hampshire.

In August 1943, the Quebec Agreement subsumed the British Tube Alloys project into the Manhattan Project, and established the Combined Policy Committee to control the Manhattan Project. A final agreement was spelt out on 20 May 1944. Under it, the Americans would assist with the construction of a heavy water-moderated nuclear reactor in Canada, and would provide technical assistance with matters such as corrosion and the effects of radiation on materials. They would not provide details about plutonium chemistry or metallurgy, although irradiated uranium slugs were made available for the British to work it out for themselves. A sticking point was the director of the Montreal Laboratory, Hans von Halban, who was a poor administrator, did not work well with the Canadians, and was regarded as a security risk by the Americans. In April 1944 a Combined Policy Committee meeting at Washington agreed that Montreal Laboratory scientists who were not British subjects would leave, and Cockcroft would become the new director of the Montreal Laboratory in May 1944.

thumb|right|[[ZEEP reactor in February 1954 with NRX and NRU (under construction, in background).]]

On 24 August 1944, the decision was taken to build a small reactor in order to test the Montreal Laboratory's calculations relating to such matters as lattice dimensions, sheathing materials, and control rods, before proceeding with the full-scale NRX reactor. This was named ZEEP, for Zero Energy Experimental Pile. Building reactors in downtown Montreal was out of the question; the Canadians selected, and Groves approved, a site at Chalk River, Ontario, on the south bank of the Ottawa River some north west of Ottawa. The Chalk River Laboratories opened in 1944, and the Montreal Laboratory was closed in July 1946. Originally designed in July 1944 with an output of 8 MW, the power was raised to 10 MW through design changes such as replacing uranium rods clad in stainless steel and cooled by heavy water with aluminium-clad rods cooled by light water.

Cockcroft was shocked when he was informed on 10 September 1945 that the British physicist Alan Nunn May, who worked at the Chalk River Laboratories, was a Soviet spy. In August 1947, Cockcroft was one of the scientists who signed a petition urging that Nunn May's ten-year prison sentence be reduced, an act he later regretted.

Post-war

In April 1945, Cockcroft and Oliphant scouted a site for a similar establishment in Britain, settling on RAF Harwell. Cockcroft was offered the directorship of the Atomic Energy Research Establishment (AERE) at Harwell on 9 November 1945. The official announcement was made on 29 January 1946, but the news leaked two months before the announcement, and before the Canadian government was informed, creating a diplomatic incident. It was agreed that Cockcroft would not depart until a successor was found, and he did not depart Chalk River for Harwell until 30 September 1946. In the meantime he recruited staff for the new laboratory. Klaus Fuchs from the Manhattan Project's Los Alamos Laboratory became head of the Theoretical Physics; Robert Spence, Cockcroft's deputy at Montreal Laboratory, became head of Chemistry; H.W.B. Skinner, of General Physics; Otto Frisch, of Nuclear Physics; and John Dunworth, of Reactor Physics. Fuchs was later arrested as a Soviet spy on 3 February 1950.

The low-powered, graphite-moderated GLEEP, which stood for Graphite Low Energy Experimental Pile, was designed by the Montreal Laboratory, and became the first nuclear reactor to operate in Western Europe when it was started on 15 August 1947. This was followed by BEPO, a 6 MW research reactor designed by AERE, on 3 July 1948. Because heavy water was unavailable in Britain, BEPO was designed and built as a graphite-moderated reactor. Harwell was involved in the design of reactors at Windscale, and the chemical separation plant there.

Under Cockcroft's direction, AERE took part in frontier fusion research in the post-war years, including the ZETA program. Sir George Paget Thomson began research in nuclear fusion at Imperial College London in 1946. This was subsequently transferred to the Associated Electrical Industries Laboratory at Aldermaston, under Allibone's direction. Research independently began at Oxford University under Peter Thonemann. In 1951, Cockcroft arranged for the Oxford group to be transferred to Harwell. Cockcroft approved the construction of ZETA (Zero Energy Thermonuclear Assembly) by the Thonemann's Harwell group, and the smaller Sceptre by Allibone's AEI group. James L. Tuck's group at the Los Alamos Laboratory was also researching fusion, and Cockcroft struck an agreement with the Americans that they would release their results together, which was done in 1958. Despite Cockcroft's perennial optimism that a breakthrough was imminent, fusion power remained an elusive goal.

Cockcroft's Folly

thumb|upright=1.2|The two chimney stacks of the [[Windscale Piles|Windscale reactors, with the visible swellings to house Cockcroft's filters.]]

As director of the AERE, Cockcroft famously insisted that the chimney stacks of the Windscale plutonium production reactors be fitted, at great expense, with high-performance filters. That was in response to a report that uranium oxide had been found in the vicinity of the X-10 Graphite Reactor in Oak Ridge, Tennessee. Because it was decided to fit them after the stacks had been designed, the filters became pronounced lumps at the top of the chimneys.

The reactors had been designed to remain clean and uncorroded during use, so it was thought there would be no particulate for the filters to catch. As well, the uranium oxide at Oak Ridge turned out to be from the chemical plant and not the reactor. The filters therefore became known as "Cockcroft's Folly". However, when the core of one of the two reactors ignited the Windscale fire of 1957, the filters prevented a far worse release of radioactive material. Terence Price, future scientific advisor at the Ministry of Defence in the 1960s, noted that "the word folly did not seem appropriate after the accident".

Later life

On 24 January 1959, Churchill College, Cambridge, was formally recognised by the university. Two days later, the trustees announced that Cockcroft would be its first master. Although it would also teach the humanities and social sciences, 70 percent of the student body would study science and technology-related subjects. He nominated the first fellows, and he oversaw the initial construction. Controversy arose over the chapel. A 1961 plan to build it at the entrance to the college, as was traditional at Cambridge, led to the immediate resignation of Francis Crick, a staunch atheist, as a fellow. The first undergraduates arrived in 1961, and the college, still incomplete, was formally opened by Prince Philip, Duke of Edinburgh, on 5 June 1964.

thumb|upright=1.2|left|[[Churchill College, Cambridge, in 2005]]

Cockcroft was president of the Institute of Physics from 1954 to 1956, and of the British Association for the Advancement of Science. He served as chancellor of the Australian National University in Canberra from 1961 to 1965, a largely symbolic post that involved a visit once a year for degree conferring ceremonies. He delivered the Rutherford Memorial Lecture in 1944. He was the British delegate on the Council of CERN as well as Chairman of the Nuclear Physics Sub-Committee of the Department of Scientific and Industrial Research.

Awards

{| class="wikitable"

! Year

! Organisation

! Award

! Citation

| 1938

| Royal Society

| Hughes Medal

| "For their discovery that nuclei could be disintegrated by artificially produced bombarding particles."

| 1951

| Royal Swedish Academy of Sciences

| Nobel Prize in Physics

| "For their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles."

| 1955

| Institution of Electrical Engineers

| Faraday Medal

| 1958

| Danish Society of Engineers

| Niels Bohr International Gold Medal

| 1961

| Austrian Trade Association

| Wilhelm Exner Medal

| 1961

| Atoms for Peace Award

Chivalry

{| class="wikitable"

! Year

! Head of state

! Title/Order

| 1944

| George VI

| Commander of the Order of the British Empire

| 1952

| Vincent Auriol

| Knight of the Legion of Honour

| 1953

| Elizabeth II

| Knight Commander of the Order of the Bath

| 1957

| Elizabeth II

| Order of Merit

Commemoration

Several buildings in the United Kingdom are named after him: the Cockcroft building at the New Museums Site of the University of Cambridge, comprising a lecture theatre and several hardware laboratories; the Cockcroft Institute at Daresbury Laboratory in Cheshire; the Cockcroft building of the University of Brighton; and the Cockcroft building of the University of Salford. The oldest building at the Research School of Physical Sciences and Engineering, Australian National University, the Cockcroft building, is named after him.

Cockcroft's papers are held at the Churchill Archives Centre in Cambridge, and are accessible to the public. They include his lab books, correspondence, photographs (with dozens depicting the construction of Chalk River, CKFT 26/4), theses and political papers.

Notes

References

External links

Oral history interview transcript with John Cockcroft on 2 May 1963, American Institute of Physics, Niels Bohr Library & Archives
Oral history interview transcript with John Cockcroft on 28 March 1967, American Institute of Physics, Niels Bohr Library & Archives
Biography from Churchill Archives Centre
Another Nobel biography
1958 visit at the Joint Institute for Nuclear Research (Объединённый институт ядерных исследований) in Dubna (UdSSR)