Ralph P. Hudson

Ralph P. Hudson was born on October 14, 1924, in Wellingborough, Northamptonshire, in the United Kingdom, about 80 kilometers north of London.⁠[1][2]

In 1942 he won an open scholarship to Merton College at the University of OxfordUniversity of OxfordThe University of Oxford is a university in Oxford, England, where teaching existed in some form by 1096; it describes itself as the oldest university in the English-speaking world and is organised as a federal system of the university and dozens of self-governing colleges.Open the full entry, and he received his B.A. in 1944.⁠[1][2]

The obituary notes that Oxford was only about 60 kilometers from his home town.⁠[1]

After his B.A. he was assigned to “Britain’s Tube Alloy project.” In 1945 he became a Scientific Officer of the U.K. Ministry of Supply and spent two years overseas, in Montreal and at the Chalk River Laboratories in Ontario, Canada.⁠[1]

The National Institute of Standards and Technology’s biography gives his years as a scientific officer of the Ministry of Supply as 1944–1946.⁠[3]

The obituary says that after his B.A. he became a Junior Scientific Officer of the U.K. Department of Scientific and Industrial Research, in which capacity he was assigned to the Tube Alloy project.⁠[1]

After his service overseas he returned to Oxford, where he worked in the Clarendon Laboratory under Professor Nicholas Kurti, and in 1949 he received his M.A. and D.Phil.⁠[1][3]

He had three publications while at Oxford. The obituary says that an acquaintance, Ernest AmblerErnest AmblerErnest Ambler (1923–2017) was a British-born American physicist who joined the National Bureau of Standards in 1953 to work in low-temperature physics and was one of the four bureau physicists who carried out the cobalt-60 parity experiment of 1956–1957 with Chien-Shiung Wu. He became the bureau’s acting director in 1975 and its director in 1978, presided over its change into the National Institute of Standards and Technology in 1988 and retired in 1989.Open the full entry, was at Merton College too, following a similar path toward the D.Phil.; the White House release of May 28, 1976, has Ambler attending New College.⁠[1][4]

The obituary notes that Nicholas Kurti had worked on the Manhattan ProjectManhattan ProjectThe Manhattan Project was the United States program that developed the atomic bomb during the Second World War, managed from 1942 by the Manhattan Engineer District of the Army Corps of Engineers with British and Canadian participation. It built plants and laboratories at Oak Ridge, Tennessee, Hanford, Washington, and Los Alamos, New Mexico, among other sites, carried out the first nuclear test in 1945, and produced the bombs dropped on Hiroshima and Nagasaki, Japan, later that year; after the war its functions passed to the civilian Atomic Energy Commission.Open the full entry, and that the two degrees of 1949 closed seven busy years in which his studies had overlapped with non-academic work.⁠[1]

He then went to Purdue University in West Lafayette, IndianaIndianaIndiana is a state in the Midwestern United States; its capital and largest city is Indianapolis. It was admitted to the Union on December 11, 1816, as the 19th state, and its population in the 2020 census (April 1, 2020) was 6,785,528.Open the full entry, as a visiting lecturer in Pieter Keesom’s low-temperature physics group, and published three more papers before leaving.⁠[1]

Purdue University’s Department of Physics and Astronomy has him as a visiting lecturer in the department in 1949 and 1950; the National Institute of Standards and Technology’s biography says he taught physics at Purdue from 1949 to 1951.⁠[2][3]

Elsewhere the obituary has him an Assistant Professor in Purdue University’s physics department in 1951. In his second year there he received a letter from Ferdinand Brickwedde, who was contemplating an expansion of his division into deep cryogenics, had heard that he was well qualified in that field and asked whether he would come to Washington to talk about employment. He took a train to Washington, D.C., received and accepted an offer, and moved his family to the city.⁠[1]

Ferdinand Brickwedde, chief of the Heat and Power Division of the National Bureau of Standards, wrote to him, and in 1951 he joined the bureau’s Cryogenic Physics Section.⁠[1][3]

He worked with Dirk de Klerk, a docent of physics at Leiden University who came to the bureau on a one-year visit to supervise the installation of a magnetic cooling facility; the two published an adiabatic demagnetization experiment in 1953.⁠[1]

Soon after his own arrival he was instrumental in bringing his old acquaintance Ernest Ambler to the bureau.⁠[1][5]

The obituary names his colleagues of the time: Russell B. Scott, then chief of the Cryogenics Section, who was planning a liquid-hydrogen plant for Boulder, ColoradoColoradoColorado is a U.S. state classified as one of the Mountain states, with Denver as its capital. It was admitted to the Union on August 1, 1876, as the 38th state, and its population in the 2020 census (April 1, 2020) was 5,773,714.Open the full entry, with Brickwedde; John Pellam, an MIT graduate whose specialty was second sound in liquid helium; and Emanuel Maxwell, another MIT alumnus and a pioneer in studies of the isotope effect in superconductivity. Brickwedde encouraged his scientists to pursue their studies at the highest level, asking first-class science in return for flexible hours.⁠[1]

The magnetic cooling facility was installed in the Low Temperature building, a task that occupied the team for more than a year. The obituary says that a flood of papers followed in 1954 and that the laboratory became known for research below 1 K and for the thermometry it required.⁠[1]

The references of his own retrospective article give his paper with Dirk de Klerk, “Installation for Adiabatic Demagnetization Experiments at the National Bureau of Standards,” as published in the Journal of Research of the National Bureau of Standards, volume 53, pages 173–184, in 1954, and the paper by the two with J. R. Pellam, “Second sound propagation below 1 K,” as published in the Physical Review, volume 93, pages 28–37, in 1954.⁠[6]

David Lide’s remembrance says that he met him shortly after joining the bureau in August 1954 and that their friendship lasted 60 years; both were in the Heat and Power Division under Ferdinand Brickwedde, where, Lide writes, he headed the Cryogenic Physics Section and asked Lide to help with a nuclear alignment experiment by measuring the microwave frequency for a sample in a cryostat. Lide adds: “Ralph’s dry British wit was often displayed when something went wrong.”⁠[1]

In 1955 he became chief of the Cryogenic Physics Section.⁠[1]

His papers with Ernest Ambler and Georges M. Temmer, “Alignment of Cerium-141 and Neodymium-147 Nuclei” and “Alignment of Three Odd-A Rare-Earth Nuclei,” appeared in the Physical Review in 1955 and 1956; his later account cites them for the laboratory staff’s experience in the spatial orientation of atomic nuclei.⁠[6]

He wrote that Georges M. Temmer, first in the bureau’s Radioactivity Section and later at the Carnegie Institution’s Department of Terrestrial Magnetism, played an important part in establishing the Cryogenic Physics Section’s nuclear orientation program, and called him “a gifted scientist of infectious enthusiasm.” The references also list “Low-Temperature Alinement of Radioactive Nuclei,” NBS Technical News Bulletin, volume 40, pages 49–51 (1956).⁠[6]

The obituary says that Ferdinand Brickwedde left the bureau in 1956 to become dean of the College of Chemistry and Physics at Penn State, and that his successor, Charles M. Herzfeld, restructured the renamed Heat Division and served about five years before leaving for DARPA.⁠[1]

Early in 1956 Tsung-Dao LeeTsung-Dao LeeTsung-Dao Lee (1926–2024) was a Shanghai-born American physicist who taught for decades at Columbia University. In 1956 he and Chen Ning Yang proposed that parity might not be conserved in weak interactions, for which they shared the 1957 Nobel Prize in Physics; from the 1970s he helped advance high-energy physics and the training of physicists in China.Open the full entry and Chen Ning YangChen Ning YangChen Ning Yang (1922–2025) was a theoretical physicist born in Hefei, Anhui, China, who shared the 1957 Nobel Prize in Physics with Tsung-Dao Lee for their investigation of the parity laws. In 1954 he and Robert L. Mills formulated non-Abelian gauge theory (Yang–Mills theory), and he worked in turn at the Institute for Advanced Study, Stony Brook University and Tsinghua University.Open the full entry surveyed the experimental evidence on parity, concluded that it neither supported nor refuted parity conservation in weak interactions, and proposed experiments to test it, one of them a measurement of the beta radiation from oriented cobalt-60 nuclei.⁠[6]

They consulted Chien-Shiung Wu, a beta spectroscopist at Columbia UniversityColumbia UniversityColumbia University, formally Columbia University in the City of New York, is a private research university in New York City and a member of the Ivy League. Founded in 1754 by royal charter from King George II as King's College, it is the oldest institution of higher education in New York State and the fifth oldest in the United States. It was renamed Columbia College in 1784 and adopted the university name and moved to Manhattan's Morningside Heights in 1896. It has 17 schools and four affiliated colleges, with 35,978 students enrolled in fall 2025. Legal scholar Jennifer L. Mnookin became president on July 1, 2026.Open the full entry. She approached Henry Boorse of Columbia University and Mark W. Zemansky of the City College of New York, who suggested that she contact Ernest Ambler at the National Bureau of Standards, and arrangements to run the experiment in the bureau’s low-temperature laboratory were soon made.⁠[6]

Ralph P. Hudson later wrote that the laboratory was chosen for its research capability in the millikelvin region and its staff’s experience in orienting nuclei.⁠[6]

He was then chief of the Cryogenic Physics Section, in which Ernest Ambler worked, and shared with him the responsibility for the cryogenic side of the experiment. James Schooley’s obituary says the two agreed to “give it ‘the old college try.’”⁠[7][5][1]

Raymond W. HaywardRaymond W. HaywardRaymond W. Hayward (1921–2001) was a nuclear physicist at the National Bureau of Standards of the United States. In 1956–1957, with Chien-Shiung Wu, Ernest Ambler, Dale D. Hoppes and Ralph P. Hudson, he carried out the cobalt-60 beta-decay experiment that showed parity is not conserved in weak interactions.Open the full entry and his student Dale D. HoppesDale D. HoppesDale D. Hoppes (born 1928) was a nuclear physicist at the National Bureau of Standards of the United States (later the National Institute of Standards and Technology), where he later led the Radioactivity Group. In 1956–1957, with Chien-Shiung Wu, Ernest Ambler, Raymond W. Hayward and Ralph P. Hudson, he carried out the cobalt-60 beta-decay experiment that showed parity is not conserved in weak interactions.Open the full entry helped design and construct the coincidence system.⁠[7]

The work-up took about six months. About midway, outgassing problems judged insurmountable led the team to redesign the whole assembly from stainless steel to glass.⁠[6]

The National Institute of Standards and Technology’s page dates Lee and Yang’s survey of the evidence to the summer of 1956 and says the experiment was carried out in the bureau’s low-temperature laboratory at Chien-Shiung Wu’s suggestion.⁠[8]

He wrote that Henry Boorse and Mark W. Zemansky ran a modest cryophysics program at Columbia University and lacked the facilities for the experiment, but were active in the international low-temperature community, knew the bureau’s program and knew of Ernest Ambler’s recent move there from Oxford.⁠[6]

The obituary says that he and Ambler had done nuclear orientation work but had never detected beta particles inside the cryostat, that Raymond W. Hayward and Dale D. Hoppes, the bureau’s beta-decay experts, helped judge whether the experiment was feasible, and that the four-man team succeeded after much late-night work.⁠[1]

He recounted the unknowns at the outset: the beta source had to be in intimate contact with the cooling medium yet lie on the surface of the crystal so that beta particles could escape; it was unclear whether contact and refrigeration would be adequate or whether backscattering would be a major drawback; and the team had to decide whether to count the beta rays in situ or remotely, how to polarize the nuclei without heating the refrigerating salt, and what source activity would balance detection sensitivity against local heating.⁠[6]

By his account the cobalt-60 lay in a thin surface layer on a single crystal of cerous magnesium nitrate (CMN); the National Institute of Standards and Technology’s page gives the thickness of the layer as 50 micrometers. The plate-like crystal is strongly anisotropic magnetically, so the main cooling field was applied in its plane and the small polarizing field of the solenoid perpendicular to it, with negligible heating; the team worried that the torque exerted by the polarizing field might break the fragile thermally isolating mount.⁠[6][8]

A counter had to sit inside the evacuated flask, and the team used a thin anthracene crystal as a scintillation counter about 2 centimeters above the cobalt-60 source; its flashes passed through a glass window and a 120-centimeter lucite light pipe to a photomultiplier at the top of the flask, and the pulses were counted on a 10-channel pulse-height analyzer. Two sodium iodide gamma scintillation counters outside the flask measured the directional intensity of the gamma radiation, from which the degree of nuclear polarization was determined. Cooling was by adiabatic demagnetization from a field of about 2.3 tesla; once the exchange gas had been pumped out to isolate the specimen, the temperature fell to about 0.003 K.⁠[6]

The experiment compared the beta emission in the two directions by reversing the polarizing field of a solenoid. Emission proved greater in the direction opposite to the nuclear spin, showing that parity is not conserved in the beta decay of cobalt-60. His own account has the paramagnetic crystal containing the cobalt-60 cooled to within 0.003 K.⁠[6]

Page 90 of Ernest Ambler’s laboratory notebook records the measurements of December 27, 1956; Ralph P. Hudson later added “PARITY NOT CONSERVED!” at the top of the page.⁠[8]

Within a day or two Chien-Shiung Wu’s Columbia University colleagues R. L. Garwin, L. M. Lederman and M. Weinrich, working at the university’s cyclotron, demonstrated the parity effect in a pion–muon–electron decay experiment.⁠[6]

He wrote that the asymmetry parameter could have been anywhere from 0 to 1 and turned out to be maximal; that general opinion of Lee and Yang’s proposal, until then largely dismissive, changed overnight; and that the nuclear physics community quickly set about other feasible tests. The bureau–Wu team had at that point not yet completed the check experiments it expected skeptics to demand.⁠[6]

The notation “Field on” on the notebook page is also his and refers to the solenoid field; in his own article he explains that the comment at the top left of the page was added by him.⁠[8][6]

The National Academy of Sciences memoir of Chien-Shiung Wu gives the temperature of the crystal as 0.01 K and names the three experimenters at Columbia University’s Nevis cyclotron laboratory as Leon Lederman, Richard Garwin and Marcel Weinrich.⁠[9]

The paper on the experiment appeared in the Physical Review, volume 105, pages 1413–1415, in 1957. In a follow-up experiment with cobalt-58, a positron emitter, the team found positrons emitted preferentially along the nuclear spin.⁠[6]

Tsung-Dao Lee and Chen Ning Yang received the 1957 Nobel PrizeNobel PrizeThe Nobel Prize is an international award established under the will of Alfred Nobel, comprising five prizes in physics, chemistry, physiology or medicine, literature and peace, awarded since 1901; its funds are managed by the Nobel Foundation, whose Board is based in Stockholm. The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, established in 1968, is not a Nobel Prize.Open the full entry in Physics.⁠[1]

He wrote that the New York meeting of the American Physical Society in January 1957 saw “extraordinary jam-packed sessions.”⁠[6]

He also recounted that when Georges M. Temmer brought the result to Wolfgang PauliWolfgang PauliWolfgang Pauli (1900–1958) was a Vienna-born theoretical physicist who received the 1945 Nobel Prize in Physics for the discovery of the exclusion principle, also called the Pauli principle, and who in 1930 proposed the neutral particle later named the neutrino; he was professor of theoretical physics at ETH Zurich from 1928 until his death.Open the full entry, Pauli first said “That’s total nonsense” and then “Then it must be repeated!”⁠[6]

He wrote that Temmer, trying to point out at a colloquium in Switzerland that the work had been done at the National Bureau of Standards, was hooted down, and that afterwards hardly a speaker or writer referred to the event as anything but “the Wu experiment.”⁠[6]

In 1957 the Department of Commerce gave its Gold Medal, the Award for Exceptional Service, to the bureau’s parity experiment team.⁠[6][7]

The paper on the second experiment, “Further Experiments on β Decay of Polarized Nuclei,” by E. Ambler, R. W. Hayward, D. D. Hoppes, R. P. Hudson and C. S. Wu, appeared in the Physical Review, volume 106, pages 1361–1363, in 1957.⁠[6]

He wrote that some scientists passed from skepticism about the proposal to disbelief in the results that validated it, parity conservation having been an article of faith; that it was when the colloquium in Switzerland was interrupted to announce the “triumph at Columbia U.” that Temmer rose to correct the record; and that only Chen Ning Yang and Nicholas Kurti made efforts to set the record straight.⁠[6]

He wrote that later theoretical development and many follow-up experiments led to the unification of the weak and electromagnetic interactions, a history set out in the Nobel Prize lectures of Weinberg, Salam and Glashow.⁠[6]

At the end of the article he recorded what became of his collaborators: Chien-Shiung Wu returned full-time to beta-decay research and the training of graduate students at Columbia University, received the National Medal of Science and was elected president of the American Physical Society in 1975, received the Wolf Prize in Physics in 1978 and died in New York in February 1997 at the age of 84; Raymond W. Hayward went back to the Radioactivity Section under Wilfrid B. Mann, became chief of the new Nuclear Spectrometry Section, wrote a treatise on the dynamics of particles of higher spin, then turned to the study of gravitation and retired in 1980 at the age of 59; Dale D. Hoppes continued to study beta-particle distributions from oriented nuclei, took a Ph.D. at The Catholic University of America in 1961, became Radioactivity Group leader when Mann retired in 1981 and retired from the National Institute of Standards and Technology in 1992 at the age of 64.⁠[6]

He became a naturalized citizen of the United StatesUnited StatesThe United States is a federal country in North America made up of 50 states, the District of Columbia as the seat of government, and territories such as Puerto Rico and Guam; its capital is Washington, D.C. The Continental Congress adopted the Declaration of Independence on July 4, 1776. The 2020 census (April 1, 2020) counted a resident population of 331,449,281, and the 435 seats of the House of Representatives are apportioned among the states on the basis of the census.Open the full entry in 1960.⁠[1]

In 1961 Director Allen Astin appointed him chief of the Heat Division, and Ernest Ambler took his place as chief of the Cryogenic Physics Section.⁠[5][6]

The Heat Division had four sections: Low Temperature Physics, Heat Measurement, Equation of State and Statistical Physics. He headed it until 1978.⁠[1]

The first chapter of James F. Schooley’s history lists the sections of the Heat Division and their heads as heat measurements (Defoe C. Ginnings), cryogenic physics (James F. Schooley, temporarily), equation of state (Max Klein), statistical physics (Melville S. Green), temperature (Harmon H. Plumb) and radiation thermometry (Henry J. Kostkowski).⁠[10]

The history records that he and Robert S. Kaeser, measuring the internal energy of cerous magnesium nitrate against its entropy by magnetic cooling and gamma-ray heating, derived thermodynamic temperatures and built a magnetic temperature scale from 0.002 K to 2 K; their paper “Cerous magnesium nitrate: a magnetic temperature scale 0.002-2 °K” appeared in the journal Physics in 1967.⁠[10]

The obituary says that as division chief he went on studying, writing and serving the cryogenics community, and hired carefully to fill the places left by retirements, deaths and departures; in his own article he says that, as administrative preoccupations permitted, he continued research on cryothermometry and low-temperature magnetism.⁠[1][6]

B. W. Mangum’s remembrance says that at the bureau the two studied relaxation times of rare-earth compounds at low temperatures by magnetic susceptibility and by electron paramagnetic resonance of dilute rare-earth ions in lanthanum salts; when Mangum later studied the cooperative low-temperature behavior of pure rare-earth arsenates, phosphates and vanadates, he became interested too and they collaborated on a study of one of the compounds. Mangum had first met him at the Clarendon Laboratory, where Mangum was an NSF postdoctoral fellow.⁠[1]

James Schooley recalls that when he came to the bureau as a postdoc in 1960 he was somewhat intimidated by Hudson’s businesslike demeanor; asked whether Schooley should publish his first results right away, Hudson replied, “that depends on whether you have something useful to say.” Schooley also remembers his quip, drawn from his time at Purdue University, that people from Indiana should be regarded as speaking English only as a second language.⁠[1]

Norm Belecki recalls that when he was a graduate student in the George Washington UniversityGeorge Washington UniversityGeorge Washington University (officially The George Washington University) is a university in Washington, D.C., United States, whose forerunner was Columbian College.Open the full entry–NBS metrology program, the Heat Division staff who taught him held their division chief in unusually high respect both as a scientist and as a person.⁠[1]

David Lide writes that by the time he became division chief the division no longer included Power. Lide’s wife was English and, like him, had an Oxford background, and the two couples kept up a close social relationship for 20 years; he greatly enjoyed the annual Oxford-Cambridge Boat Race Dinners, formal affairs attended by many high-ranking figures in government, especially in the years of John F. KennedyJohn F. KennedyJohn F. Kennedy (1917–1963) was an American politician who represented Massachusetts in the U.S. House of Representatives and the U.S. Senate and served as the 35th president of the United States from 1961 to 1963. The youngest person elected president and the first Roman Catholic to hold the office, he was assassinated in Dallas on November 22, 1963.Open the full entry’s presidency.⁠[1]

Lide also writes that in the 1970s he organized a bridge group that lasted until about 2005; it met on Wednesday nights at the players’ homes on a rotating schedule he devised, with Hudson keeping score and specifying the food and drink, and its members included bureau colleagues such as Harmon Plumb, Jack Colwell, Billy Mangum, Martin Reilly and Hans Frederickse. It closed reluctantly when late-night driving became too hazardous for octogenarians with failing eyesight.⁠[1]

In 1962 Chien-Shiung Wu and the National Bureau of Standards team received the Franklin Institute’s John Price Wetherill Medal for the parity experiment.⁠[7][6]

In December 1964 the bureau named Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes and Ralph P. Hudson as recipients of that year’s Samuel Wesley Stratton Award; each was to receive a bronze plaque, and they shared a $5,000 honorarium equally.⁠[11]

The Physics Today item gives the grounds for the award as the four men’s part, with C. S. Wu, in the first experimental confirmation that parity is not conserved in weak interactions, and identifies him as then chief of the Heat Division.⁠[11]

In 1972 his monograph Principles and Application of Magnetic Cooling was published by North-Holland and American Elsevier as volume 2 of the North-Holland series in low temperature physics.⁠[12]

Bernard M. Abraham of Argonne National Laboratory reviewed the book in Physics Today in October 1974, noting that the author intended it as “a shop manual for the uninitiated,” that he had made the study of paramagnetic salts his specialty and that he was a principal contributor to the thermodynamic temperature scale based on the susceptibility of CMN.⁠[13]

The review’s heading gives the book as 230 pages, Elsevier, New York, 1972, $20.75, and prints the title as Principles and Applications of Magnetic Cooling. Bernard M. Abraham judged that graduate students would find much of value in the book but doubted that many would find it essential for their bookshelf; he also noted the omission of a calculation of a demagnetization schedule and the short treatment of the Casimir-du Pré technique.⁠[13]

In 1976 the review article “Recent Advances in Thermometry below 300 mK,” which he wrote with H. Marshak, R. J. Soulen, Jr., and D. B. Utton, received the bureau’s Edward U. Condon Award for distinguished authorship.⁠[6][1]

The review had appeared in the Journal of Low Temperature Physics, volume 20, pages 1–102, in 1975.⁠[6]

In the bureau’s 1978 reorganization the Heat Division was abolished and he became deputy director of the Center for Absolute Physical Quantities under Karl G. Kessler, with additional responsibility for managing the standards activity in mass and length.⁠[6][5][3]

By the time he left the bureau in 1980 he had a total of 80 publications.⁠[1]

In its list of the reorganized units James F. Schooley’s history shows him as head of the center’s division for length and mass measurements and standards; the obituary describes Karl G. Kessler as the former chief of the Atomic Physics Division.⁠[5][1]

In 1980 he resigned from the bureau and joined the Bureau International des Poids et Mesures at Sèvres, France, as Director of Publications and editor of the international journal Metrologia.⁠[6][1][3]

The organization’s staff list of January 1, 1983, places him among the “Physiciens et Métrologistes.”⁠[14]

The minutes of the 78th session of the Comité International des Poids et Mesures, held on September 26–28, 1989, record that D. A. Blackburn would replace him as editor of Metrologia in October 1989 after his retirement; the report in the same volume says the journal’s editor was due to retire on October 31, 1989.⁠[15]

The list of publications in the same volume includes, as in press, his “Thermometry” for the Encyclopedia of Physics.⁠[15]

The obituary says that it was the Bureau International des Poids et Mesures that asked him to become editor of Metrologia; he and his wife, Nancy, moved to Paris, where they were still living in 1985. He remained editor until 1989, when he reached the mandatory retirement age of 65.⁠[1]

David Lide writes that in those years his work for CODATA took him to Paris every two or three months and that he always saw the couple; Nancy served French cooking at their apartment, or they went to a neighborhood bistro whose chef greeted them enthusiastically.⁠[1]

The organization’s staff list of January 1, 1985, still places him among the “Physiciens et Métrologistes”; the staff list of January 1, 1989, at the front of the 1988 volume has “Dr R. P. Hudson” under the heading “Metrologia,” and the organization chart of June 1, 1989, likewise shows him under Metrologia.⁠[16][17][15]

The minutes of the 77th session of the Comité International des Poids et Mesures (1988) record that, because of his coming retirement, the bureau of the committee discussed the future of Metrologia at a meeting he attended; the French text of the minutes puts his retirement at the end of 1989, the English text at the end of October 1989.⁠[17]

The minutes of the 78th session note that the editor was paid entirely by the Bureau International des Poids et Mesures, one reason for examining the journal’s long-term future; the bureau of the committee favored having the journal published directly by the Comité International des Poids et Mesures rather than by Springer-Verlag and proposed that the director, “en accord avec MM. Blackburn et Hudson,” approach Springer-Verlag. The committee confirmed the engagement of D. A. Blackburn at grade 11 and decided that, if the negotiations with Springer-Verlag succeeded, the journal would be titled “Metrologia, the international journal of pure and applied metrology,” be published by the Bureau International des Poids et Mesures and remain a quarterly.⁠[15]

The section of the director’s report in the same volume headed “Metrologia (R. P. Hudson)” records that 52 manuscripts were submitted to the journal in 1988, of which 17 were published that year, 23 were scheduled for 1989, 4 were rejected and 8 were still under review on May 31, 1989, thermometry (14) and electricity (9) being the commonest subjects, and that 30 manuscripts were received from January 1 to September 30, 1989. It adds that the retiring editor helped the director select candidates for the succession and met some of them.⁠[15]

The list of travel in the volume shows him at the American Physical Society’s spring meeting in St. Louis on March 20–22, 1989, and visiting the National Institute of Standards and Technology in Gaithersburg on April 1.⁠[15]

Purdue University’s Department of Physics and Astronomy says he edited Metrologia for nine years and retired from the International Bureau of Weights and Measures in Paris, France.⁠[2]

After retiring in 1989 at the age of 65 he returned to the Washington area and took a three-year post at the National Science Foundation as Program Director for Low-Temperature Physics.⁠[6][1]

The National Institute of Standards and Technology’s biography dates the post to 1989–1992 and adds that he served intermittently afterward.⁠[3]

James Schooley’s obituary has him retiring from gainful employment for good in 1994.⁠[1]

He is listed on the first membership roster of the Standards Alumni Association. On October 11, 1990, he gave the association a talk on his life and work in Paris.⁠[1]

In 1995 the association’s president, Manny Horowitz, asked him to succeed John Bennett as editor of the SAA Newsletter, and he also took on the chairmanship of the Portrait Gallery committee.⁠[1]

He had himself been inducted into the gallery in 1988, its list giving his years at the bureau as 1951–1980, and with David Lide he helped the association draw up its selection criteria.⁠[18]

The obituary says that the Standards Alumni Association began in 1985 as the NBS Alumni Association. After retiring he became a regular at its meetings and often wrote them up for the newsletter, among them Bob Kamper’s autobiographical talk; John Bennett gave up the editorship because he was moving away and felt that editing at a distance was not a good idea.⁠[1]

As editor he intensified the reporting of the association’s activities, including talks by Sam Kramer, Bill Phillips, Jake Rabinow and Gordon Day, and a growing number of obituaries. In 2002, as age began to affect his energy, Norm Belecki became associate editor, and about eighteen months later succeeded him as editor; he went on attending board meetings, where, the obituary says, his “wit and wisdom continued to be most welcome.”⁠[1]

Norm Belecki says that he served about eighteen months as his apprentice, learned more English grammar from him than from two years of high-school German, and learned that “patience in the attention to details is essential”; he calls him “a consummate gentlemen, a rare trait indeed!” and says he never heard him say a bad word about anyone.⁠[1]

In 1998 he returned to the National Institute of Standards and Technology as a guest worker in its Fundamental Constants Data Center.⁠[1]

In January 1998 Physics Today published the obituary of Karl Gunther Kessler that he wrote with William C. Martin.⁠[19]

The authors’ note of that obituary gives the affiliation of both as the National Institute of Standards and Technology, Gaithersburg, MarylandMarylandMaryland is a Middle Atlantic state of the United States, deeply indented by Chesapeake Bay and bordered by Pennsylvania, Delaware, Virginia, the District of Columbia and West Virginia; its capital is Annapolis and its largest city is Baltimore. One of the original 13 states, it ratified the U.S. Constitution on April 28, 1788, as the seventh state to do so, and had a population of 6,177,224 in the 2020 census (April 1, 2020).Open the full entry.⁠[19]

In April 2001 Purdue University announced that it would award 15 honorary doctorates; his, a Doctor of Science, was to be conferred on May 12 at commencement in the Elliott Hall of Music on the West Lafayette campus.⁠[20]

The release gives his home at the time as Chevy Chase, Maryland.⁠[20][2]

The university’s Department of Physics and Astronomy says that Purdue was honored to recognize him for “a lifetime of achievement and contributions in science.”⁠[2]

The release says that thirteen of the fifteen honorary doctorates were to be awarded on the West Lafayette campus, at four ceremonies on May 11–13, his at the one beginning at 2:30 p.m. on Saturday, May 12. As to the decade of the parity research, the department’s page says the 1950s and the release the 1960s.⁠[20][2]

In 2009, acceding to his children’s wishes, he moved to Madison, WisconsinWisconsinWisconsin is a state in the north-central United States; its capital is Madison and its largest city is Milwaukee. Wisconsin was admitted to the Union on May 29, 1848, as the 30th state, and the 2020 census (April 1, 2020) counted 5,893,718 residents.Open the full entry.⁠[1]

He died on January 29, 2016, at the age of 91.⁠[1]

The Standards Alumni Association published an obituary by James Schooley and remembrances by several colleagues in its SAA Newsletter of March 2016.⁠[1]

The obituary says that he moved to Madison to be closer to his son Geoffrey and that after the move he still read the newsletter and followed the association’s activities. David Lide writes that he last saw him in September 2013, when, in Madison for an event of the University of Wisconsin’s physics department, he had breakfast with him at his assisted living facility, joined by Geoff and Carol; Lide found him in good spirits — he “appeared very content in this attractive home” — with a sharp long-term memory and eager for news of old colleagues.⁠[1][1]

A note at the end of the obituary gives its sources as the NIST Archives, issues of the SAA Newsletter, “A Unique Institution” by Elio Passaglia, “Responding to National Needs” by James Schooley, David Lide and Geoffrey Hudson.⁠[1]

In 1947 he married Nancy Brisby, a Canadian he had met at Chalk River, and they had a son, Geoff, and a daughter, Wendy. She died before him, after 61 years of marriage.⁠[1]

Ernest Ambler recalled that Ralph P. Hudson had been best man at his wedding.⁠[1]

His son Geoffrey was born on September 4, 1951, and his daughter Wendy in Washington in 1954. The obituary lists as survivors his son Geoff (Carol) of Madison, his daughter Wendy of Monmouth, OregonOregonOregon (officially the State of Oregon) is a state on the Pacific coast of the western United States; its capital is Salem and its largest city is Portland. It was admitted to the Union on February 14, 1859, as the 33rd state. Its population in the 2020 census (April 1, 2020) was 4,237,256.Open the full entry, and three grandsons: Keith and Nicholas of Madison and Matthew (Caroline) of Chicago.⁠[1]

Besides the awards shared by the parity team he received the Science Award of the Washington Academy of Sciences and a Guggenheim Fellowship. A remembrance by his colleague B. W. Mangum mentions that he held the Guggenheim Fellowship at the Clarendon Laboratory in Oxford.⁠[1]

NIST Special Publication 958, “A Century of Excellence in Measurements, Standards, and Technology: A Chronicle of Selected NBS/NIST Publications, 1901-2000,” edited by David R. Lide, contains his article “Reversal of the Parity Conservation Law in Nuclear Physics” on pages 111–115.⁠[21][6]

In December 1964 he published the piece “Cryogenics” in the reviews section of Physics Today under the name R. P. Hudson.⁠[22]

In October 2002 Physics Today published the obituary of Raymond W. Hayward that he wrote with Bert Coursey and Sydney Meshkov.⁠[7]

“Cryogenics” appeared in Physics Today, volume 17, number 12, pages 60–61, with his affiliation given as the National Bureau of Standards.⁠[22]

Purdue University’s 2001 release states: “He is highly respected in both the low-temperature physics and fundamental standards areas.”⁠[20]

James Schooley’s obituary says that many of the bureau’s staff members regarded him as “a superior administrator in his role as chief of the Heat Division.”⁠[1]

On leaving office in 1989 Ernest Ambler said that the “years working with Ralph were some of the happiest I have spent.”⁠[1]

The obituary calls him “devoted to scientific study.” James Schooley’s remembrance says that he ran a fine division, encouraging its staff to excel in research and giving them all the resources he could. Purdue University’s Department of Physics and Astronomy calls him “a key member” of the team that carried out the landmark research.⁠[1][2]

National Institute of Standards and Technology: Official website: https://www.nist.gov/ (opens in a new window).⁠[23]

Bureau International des Poids et Mesures: Official website: https://www.bipm.org/en/ (opens in a new window).⁠[24]

U.S. National Science Foundation: Official website: https://www.nsf.gov/ (opens in a new window).⁠[25]