James Chadwick
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Sir James Chadwick, (20 October 1891 â€“ 24 July 1974) was an English
physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...
who was awarded the 1935
Nobel Prize in Physics ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
for his
discovery of the neutron The discovery of the neutron and its properties was central to the extraordinary developments in atomic physics in the first half of the 20th century. Early in the century, Ernest Rutherford developed a crude model of the atom, based on the go ...
in 1932. In 1941, he wrote the final draft of the MAUD Report, which inspired the U.S. government to begin serious
atom bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb ...
research efforts. He was the head of the British team that worked on the
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. He was
knighted A knight is a person granted an honorary title of knighthood by a head of state (including the Pope) or representative for service to the monarch, the Christian denomination, church or the country, especially in a military capacity. Knighthood ...
in Britain in 1945 for his achievements in physics. Chadwick graduated from the
Victoria University of Manchester The Victoria University of Manchester, usually referred to as simply the University of Manchester, was a university in Manchester, England. It was founded in 1851 as Owens College. In 1880, the college joined the federal Victoria University. Afte ...
in 1911, where he studied under
Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 â€“ 19 October 1937) was a New Zealand physicist who came to be known as the father of nuclear physics. ''Encyclopædia Britannica'' considers him to be the greatest ...
(known as the "father of nuclear physics"). At Manchester, he continued to study under Rutherford until he was awarded his MSc in 1913. The same year, Chadwick was awarded an 1851 Research Fellowship from the
Royal Commission for the Exhibition of 1851 The Royal Commission for the Exhibition of 1851 is an institution founded in 1850 to administer the international exhibition of 1851, officially called the Great Exhibition of the Works of Industry of all Nations. The Great Exhibition was held ...
. He elected to study
beta radiation A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β∠...
under
Hans Geiger Johannes Wilhelm "Hans" Geiger (; ; 30 September 1882 â€“ 24 September 1945) was a German physicist. He is best known as the co-inventor of the detector component of the Geiger counter and for the Geiger–Marsden experiment which discover ...
in Berlin. Using Geiger's recently developed
Geiger counter A Geiger counter (also known as a Geiger–Müller counter) is an electronic instrument used for detecting and measuring ionizing radiation. It is widely used in applications such as radiation dosimetry, radiological protection, experimental ph ...
, Chadwick was able to demonstrate that beta radiation produced a continuous spectrum, and not discrete lines as had been thought. Still in Germany when
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
broke out in Europe, he spent the next four years in the
Ruhleben internment camp Ruhleben internment camp was a civilian detention camp in Germany during World War I. It was located in Ruhleben, a former ''Vorwerk'' manor to the west of Berlin, now split between the districts of Spandau and Charlottenburg-Wilmersdorf. The ...
. After the war, Chadwick followed Rutherford to the Cavendish Laboratory at the
University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledge. , established = , other_name = The Chancellor, Masters and Schola ...
, where Chadwick earned his
Doctor of Philosophy A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin: or ') is the most common Academic degree, degree at the highest academic level awarded following a course of study. PhDs are awarded for programs across the whole breadth of academic fields ...
degree under Rutherford's supervision from
Gonville and Caius College, Cambridge Gonville and Caius College, often referred to simply as Caius ( ), is a constituent college of the University of Cambridge in Cambridge, England. Founded in 1348, it is the fourth-oldest of the University of Cambridge's 31 colleges and one of th ...
, in June 1921. He was Rutherford's assistant director of research at the Cavendish Laboratory for over a decade at a time when it was one of the world's foremost centres for the study of physics, attracting students like
John Cockcroft Sir John Douglas Cockcroft, (27 May 1897 â€“ 18 September 1967) was a British physicist who shared with Ernest Walton the Nobel Prize in Physics in 1951 for splitting the atomic nucleus, and was instrumental in the development of nuclea ...
,
Norman Feather Norman Feather FRS FRSE PRSE (16 November 1904 – 14 August 1978), was an English nuclear physicist. Feather and Egon Bretscher were working at the Cavendish Laboratory, Cambridge in 1940, when they proposed that the 239 isotope of element ...
, and
Mark Oliphant Sir Marcus Laurence Elwin Oliphant, (8 October 1901 – 14 July 2000) was an Australian physicist and humanitarian who played an important role in the first experimental demonstration of nuclear fusion and in the development of nuclear weapon ...
. Chadwick followed his discovery of the
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
by measuring its
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
. He anticipated that neutrons would become a major weapon in the fight against cancer. Chadwick left the Cavendish Laboratory in 1935 to become a professor of physics at the
University of Liverpool , mottoeng = These days of peace foster learning , established = 1881 – University College Liverpool1884 – affiliated to the federal Victoria Universityhttp://www.legislation.gov.uk/ukla/2004/4 University of Manchester Act 200 ...
, where he overhauled an antiquated laboratory and, by installing a
cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Janu ...
, made it an important centre for the study of
nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies the ...
. During the Second World War, Chadwick carried out research as part of the
Tube Alloys Tube Alloys was the research and development programme authorised by the United Kingdom, with participation from Canada, to develop nuclear weapons during the Second World War. Starting before the Manhattan Project in the United States, the Bri ...
project to build an atom bomb, while his Manchester lab and environs were harassed by
Luftwaffe The ''Luftwaffe'' () was the aerial-warfare branch of the German ''Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the ''Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabtei ...
bombing. When the
Quebec Agreement The Quebec Agreement was a secret agreement between the United Kingdom and the United States outlining the terms for the coordinated development of the science and engineering related to nuclear energy and specifically nuclear weapons. It was s ...
merged his project with the American Manhattan Project, he became part of the British Mission, and worked at the
Los Alamos Laboratory The Los Alamos Laboratory, also known as Project Y, was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II. Its mission was to design and build the first atomic bombs. Ro ...
and in Washington, D.C. He surprised everyone by earning the almost-complete trust of project director Leslie R. Groves, Jr. For his efforts, Chadwick received a knighthood in the New Year Honours on 1 January 1945. In July 1945, he viewed the
Trinity nuclear test Trinity was the code name of the first detonation of a nuclear weapon. It was conducted by the United States Army at 5:29 a.m. on July 16, 1945, as part of the Manhattan Project. The test was conducted in the Jornada del Muerto desert abo ...
. After this, he served as the British scientific advisor to the United Nations Atomic Energy Commission. Uncomfortable with the trend toward Big Science, he became the
Master Master or masters may refer to: Ranks or titles * Ascended master, a term used in the Theosophical religious tradition to refer to spiritually enlightened beings who in past incarnations were ordinary humans *Grandmaster (chess), National Master ...
of Gonville and Caius College in 1948. He retired in 1959.


Education and early life

James Chadwick was born in
Bollington Bollington is a town and civil parish in Cheshire, England, to the east of Prestbury. In the Middle Ages, it was part of the Earl of Chester's manor of Macclesfield and the ancient parish of Prestbury. In 2011, it had a population of 8,310. B ...
,
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 ...
, on 20 October 1891, the first child of John Joseph Chadwick, a cotton spinner, and Anne Mary Knowles, a domestic servant. He was named James after his paternal grandfather. In 1895, his parents moved to
Manchester Manchester () is a city in Greater Manchester, England. It had a population of 552,000 in 2021. It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. The t ...
, leaving him in the care of his maternal grandparents. He went to Bollington Cross Primary School, and was offered a scholarship to
Manchester Grammar School The Manchester Grammar School (MGS) in Manchester, England, is the largest independent school (UK), independent day school for boys in the United Kingdom. Founded in 1515 as a Grammar school#free tuition, free grammar school next to Manchester C ...
, which his family had to turn down as they could not afford the small fees that still had to be paid. Instead he attended the Central Grammar School for Boys in Manchester, rejoining his parents there. He now had two younger brothers, Harry and Hubert; a sister had died in infancy. At the age of 16, he sat two examinations for university scholarships, and won both of them. Chadwick chose to attend
Victoria University of Manchester The Victoria University of Manchester, usually referred to as simply the University of Manchester, was a university in Manchester, England. It was founded in 1851 as Owens College. In 1880, the college joined the federal Victoria University. Afte ...
, which he entered in 1908. He meant to study mathematics, but enrolled in
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
by mistake. Like most students, he lived at home, walking the to the university and back each day. At the end of his first year, he was awarded a Heginbottom Scholarship to study physics. The physics department was headed by
Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 â€“ 19 October 1937) was a New Zealand physicist who came to be known as the father of nuclear physics. ''Encyclopædia Britannica'' considers him to be the greatest ...
, who assigned research projects to final-year students, and he instructed Chadwick to devise a means of comparing the amount of radioactive energy of two different sources. The idea was that they could be measured in terms of the activity of of
radium Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather t ...
, a unit of measurement which would become known as the
curie In computing, a CURIE (or ''Compact URI'') defines a generic, abbreviated syntax for expressing Uniform Resource Identifiers (URIs). It is an abbreviated URI expressed in a compact syntax, and may be found in both XML and non-XML grammars. A CURIE ...
. Rutherford's suggested approach was unworkable—something Chadwick knew but was afraid to tell Rutherford—so Chadwick pressed on, and eventually devised the required method. The results became Chadwick's first paper, which, co-authored with Rutherford, was published in 1912. He graduated with
first class honours The British undergraduate degree classification system is a grading structure for undergraduate degrees or bachelor's degrees and integrated master's degrees in the United Kingdom. The system has been applied (sometimes with significant variati ...
in 1911. Having devised a means of measuring gamma radiation, Chadwick proceeded to measure the absorption of gamma rays by various gases and liquids. This time the resulting paper was published under his name alone. He was awarded his
Master of Science A Master of Science ( la, Magisterii Scientiae; abbreviated MS, M.S., MSc, M.Sc., SM, S.M., ScM or Sc.M.) is a master's degree in the field of science awarded by universities in many countries or a person holding such a degree. In contrast to ...
(MSc) degree in 1912, and was appointed a Beyer Fellow. The following year he was awarded an
1851 Exhibition Scholarship The 1851 Research Fellowship is a scheme conducted by the Royal Commission for the Exhibition of 1851 to annually award a three-year research scholarship to approximately eight "young scientists or engineers of exceptional promise". The fellowship ...
, which allowed him to study and research at a university in continental Europe. He elected to go to the
Physikalisch-Technische Reichsanstalt The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of the Federal Republic of Germany, with scientific and technical service tasks. It is a higher federal authority and a public-law institution directly under fed ...
in Berlin in 1913, to study
beta radiation A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β∠...
under
Hans Geiger Johannes Wilhelm "Hans" Geiger (; ; 30 September 1882 â€“ 24 September 1945) was a German physicist. He is best known as the co-inventor of the detector component of the Geiger counter and for the Geiger–Marsden experiment which discover ...
. Using Geiger's recently developed
Geiger counter A Geiger counter (also known as a Geiger–Müller counter) is an electronic instrument used for detecting and measuring ionizing radiation. It is widely used in applications such as radiation dosimetry, radiological protection, experimental ph ...
, which provided more accuracy than the earlier photographic techniques, he was able to demonstrate that beta radiation did not produce discrete lines, as has been previously thought, but rather a continuous spectrum with peaks in certain regions. On a visit to Geiger's laboratory,
Albert Einstein Albert Einstein ( ; ; 14 March 1879 â€“ 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
told Chadwick that: "I can explain either of these things, but I can't explain them both at the same time." The continuous spectrum would remain an unexplained phenomenon for many years. Chadwick was still in Germany at the start of the
First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, and was interned in the
Ruhleben internment camp Ruhleben internment camp was a civilian detention camp in Germany during World War I. It was located in Ruhleben, a former ''Vorwerk'' manor to the west of Berlin, now split between the districts of Spandau and Charlottenburg-Wilmersdorf. The ...
near Berlin, where he was allowed to set up a laboratory in the stables and conduct scientific experiments using improvised materials such as radioactive toothpaste. With the help of
Charles Drummond Ellis Sir Charles Drummond Ellis (b. Hampstead, 11 August 1895; died Cookham 10 January 1980) was an English physicist and scientific administrator. His work on the magnetic spectrum of the beta-rays helped to develop a better understanding of nuclea ...
, he worked on the
ionisation Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecu ...
of
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, and the
photochemical reaction Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ...
of
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and
chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
. He was released after the
Armistice with Germany The Armistice of 11 November 1918 was the armistice signed at Le Francport near Compiègne that ended fighting on land, sea, and air in World War I between the Entente and their last remaining opponent, Germany. Previous armistices ...
came into effect in November 1918, and returned to his parents' home in Manchester, where he wrote up his findings over the previous four years for the 1851 Exhibition commissioners. Rutherford gave Chadwick a part-time teaching position at Manchester, allowing him to continue research. He looked at the
nuclear charge In atomic physics, the effective nuclear charge is the actual amount of positive (nuclear) charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevent ...
of
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...
,
silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
, and
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, and experimentally found that this was the same as the
atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
within an error of less than 1.5 per cent. In April 1919, Rutherford became director of the Cavendish Laboratory at the
University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledge. , established = , other_name = The Chancellor, Masters and Schola ...
, and Chadwick joined him there a few months later. Chadwick was awarded a Clerk-Maxwell studentship in 1920, and enrolled as a
Doctor of Philosophy A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin: or ') is the most common Academic degree, degree at the highest academic level awarded following a course of study. PhDs are awarded for programs across the whole breadth of academic fields ...
(PhD) student at
Gonville and Caius College, Cambridge Gonville and Caius College, often referred to simply as Caius ( ), is a constituent college of the University of Cambridge in Cambridge, England. Founded in 1348, it is the fourth-oldest of the University of Cambridge's 31 colleges and one of th ...
. The first half of his thesis was his work with atomic numbers. In the second, he looked at the forces inside the
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
. His degree was awarded in June 1921. In November, he became a Fellow of Gonville and Caius College.


Researcher


Cambridge Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge bec ...

Chadwick's Clerk-Maxwell studentship expired in 1923, and he was succeeded by the Russian physicist Pyotr Kapitza. The Chairman of the Advisory Council of the
Department of Scientific and Industrial Research Department of Scientific and Industrial Research, abbreviated DSIR was the name of several British Empire organisations founded after the 1923 Imperial Conference to foster intra-Empire trade and development. * Department of Scientific and Industria ...
, Sir William McCormick arranged for Chadwick to become Rutherford's assistant director of research. In this role, Chadwick helped Rutherford select PhD students. Over the next few years these would include
John Cockcroft Sir John Douglas Cockcroft, (27 May 1897 â€“ 18 September 1967) was a British physicist who shared with Ernest Walton the Nobel Prize in Physics in 1951 for splitting the atomic nucleus, and was instrumental in the development of nuclea ...
,
Norman Feather Norman Feather FRS FRSE PRSE (16 November 1904 – 14 August 1978), was an English nuclear physicist. Feather and Egon Bretscher were working at the Cavendish Laboratory, Cambridge in 1940, when they proposed that the 239 isotope of element ...
and
Mark Oliphant Sir Marcus Laurence Elwin Oliphant, (8 October 1901 – 14 July 2000) was an Australian physicist and humanitarian who played an important role in the first experimental demonstration of nuclear fusion and in the development of nuclear weapon ...
, who would become firm friends with Chadwick. As many students had no idea what they wanted to research, Rutherford and Chadwick would suggest topics. Chadwick edited all the papers produced by the laboratory. In 1925, Chadwick met Aileen Stewart-Brown, the daughter of a Liverpool stockbroker. The two were married in August 1925, with Kapitza as Best Man. The couple had twin daughters, Joanna and Judith, who were born in February 1927. In his research, Chadwick continued to probe the nucleus. In 1925, the concept of spin had allowed physicists to explain the
Zeeman effect The Zeeman effect (; ) is the effect of splitting of a spectral line into several components in the presence of a static magnetic field. It is named after the Dutch physicist Pieter Zeeman, who discovered it in 1896 and received a Nobel prize ...
, but it also created unexplained anomalies. At the time it was believed that the nucleus consisted of
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 ...
s and electrons, so
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
's nucleus, for example, with a
mass number The mass number (symbol ''A'', from the German word ''Atomgewicht'' tomic weight, also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approxima ...
of 14, was assumed to contain 14 protons and 7 electrons. This gave it the right
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
and charge, but the wrong spin. At a conference at Cambridge on beta particles and gamma rays in 1928, Chadwick met Geiger again. Geiger had brought with him a new model of his Geiger counter, which had been improved by his post-doctoral student
Walther Müller Walther Müller (6 September 1905, in Hanover – 4 December 1979, in Walnut Creek, California) was a German physicist, most well known for his improvement of Hans Geiger's counter for ionizing radiation, now known as the Geiger-Müller tube. ...
. Chadwick had not used one since the war, and the new
Geiger–Müller counter A Geiger counter (also known as a Geiger–Müller counter) is an electronic instrument used for detecting and measuring ionizing radiation. It is widely used in applications such as radiation dosimetry, radiological protection, experimental phy ...
was potentially a major improvement over the scintillation techniques then in use at Cambridge, which relied on the human eye for observation. The major drawback with it was that it detected
alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...
,
beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
and
gamma Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter re ...
radiation, and radium, which the Cavendish laboratory normally used in its experiments, emitted all three, and was therefore unsuitable for what Chadwick had in mind. However,
polonium Polonium is a chemical element with the symbol Po and atomic number 84. Polonium is a chalcogen. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character ...
is an alpha emitter, and
Lise Meitner Elise Meitner ( , ; 7 November 1878 – 27 October 1968) was an Austrian-Swedish physicist who was one of those responsible for the discovery of the element protactinium and nuclear fission. While working at the Kaiser Wilhelm Institute on rad ...
sent Chadwick about 2 millicuries (about ) from
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. In Germany,
Walther Bothe Walther Wilhelm Georg Bothe (; 8 January 1891 – 8 February 1957) was a German nuclear physicist, who shared the Nobel Prize in Physics in 1954 with Max Born. In 1913, he joined the newly created Laboratory for Radioactivity at the Reich Physi ...
and his student Herbert Becker had used polonium to bombard
beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
with alpha particles, producing an unusual form of radiation. Chadwick had his Australian 1851 Exhibition scholar, Hugh Webster, duplicate their results. To Chadwick, this was evidence of something that he and Rutherford had been hypothesising for years: the
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
, a theoretical nuclear particle with no electric charge. Then in January 1932, Feather drew Chadwick's attention to another surprising result.
Frédéric Frédéric and Frédérick are the French versions of the common male given name Frederick. They may refer to: In artistry: * Frédéric Back, Canadian award-winning animator * Frédéric Bartholdi, French sculptor * Frédéric Bazille, Impress ...
and
Irène Joliot-Curie Irène Joliot-Curie (; ; 12 September 1897 – 17 March 1956) was a French chemist, physicist and politician, the elder daughter of Pierre and Marie Curie, and the wife of Frédéric Joliot-Curie. Jointly with her husband, Joliot-Curie was award ...
had succeeded in knocking protons from
paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and begins to m ...
using polonium and beryllium as a source for what they thought was gamma radiation. Rutherford and Chadwick disagreed; protons were too heavy for that. But neutrons would need only a small amount of energy to achieve the same effect. In Rome,
Ettore Majorana Ettore Majorana (,, uploaded 19 April 2013, retrieved 14 December 2019 ; born on 5 August 1906 – possibly dying after 1959) was an Italian theoretical physicist who worked on neutrino masses. On 25 March 1938, he disappeared under mysteri ...
came to the same conclusion: the Joliot-Curies had discovered the neutron but did not know it. Chadwick dropped all his other responsibilities to concentrate on proving the existence of the neutron, assisted by Feather and frequently working late at night. He devised a simple apparatus that consisted of a cylinder containing a polonium source and beryllium target. The resulting radiation could then be directed at a material such as paraffin wax; the displaced particles, which were protons, would go into a small ionisation chamber where they could be detected with an
oscilloscope An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
. In February 1932, after only about two weeks of experimentation with neutrons, Chadwick sent a letter to ''
Nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
'' titled "Possible Existence of a Neutron". He communicated his findings in detail in an article sent to ''
Proceedings of the Royal Society A ''Proceedings of the Royal Society'' is the main research journal of the Royal Society. The journal began in 1831 and was split into two series in 1905: * Series A: for papers in physical sciences and mathematics. * Series B: for papers in life s ...
'' titled "The Existence of a Neutron" in May. His
discovery of the neutron The discovery of the neutron and its properties was central to the extraordinary developments in atomic physics in the first half of the 20th century. Early in the century, Ernest Rutherford developed a crude model of the atom, based on the go ...
was a milestone in understanding the nucleus. Reading Chadwick's paper, Robert Bacher and
Edward Condon Edward Uhler Condon (March 2, 1902 – March 26, 1974) was an American nuclear physicist, a pioneer in quantum mechanics, and a participant during World War II in the development of radar and, very briefly, of nuclear weapons as part of the ...
realised that anomalies in the then-current theory, like the spin of nitrogen, would be resolved if the neutron has a spin of 1/2 and that a nitrogen nucleus consisted of seven protons and seven neutrons. The theoretical physicists
Niels Bohr Niels Henrik David Bohr (; 7 October 1885 â€“ 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. B ...
and
Werner Heisenberg Werner Karl Heisenberg () (5 December 1901 – 1 February 1976) was a German theoretical physicist and one of the main pioneers of the theory of quantum mechanics. He published his work in 1925 in a breakthrough paper. In the subsequent series ...
considered whether the neutron could be a fundamental nuclear particle like the proton and electron, rather than a proton–electron pair. Heisenberg showed that the neutron was best described as a new nuclear particle, but its exact nature remained unclear. In his 1933
Bakerian Lecture The Bakerian Medal is one of the premier medals of the Royal Society that recognizes exceptional and outstanding science. It comes with a medal award and a prize lecture. The medalist is required to give a lecture on any topic related to physical ...
, Chadwick estimated that a neutron had a mass of about . Since a proton and an electron had a combined mass of , this implied the neutron as a proton–electron composite had a binding energy of about , which sounded reasonable, although it was hard to understand how a particle with so little binding energy could be stable. Estimating such a small mass difference required challenging precise measurements, however, and several conflicting results were obtained in 1933–4. By bombarding
boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
with alpha particles, Frédéric and Irène Joliot-Curie obtained a large value for the mass of a neutron, but
Ernest Lawrence Ernest Orlando Lawrence (August 8, 1901 â€“ August 27, 1958) was an American nuclear physicist and winner of the Nobel Prize in Physics in 1939 for his invention of the cyclotron. He is known for his work on uranium-isotope separation fo ...
's team at the
University of California The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco, ...
produced a small one. Then
Maurice Goldhaber Maurice Goldhaber (April 18, 1911 – May 11, 2011) was an American physicist, who in 1957 (with Lee Grodzins and Andrew Sunyar) established that neutrinos have negative helicity. Early life and childhood He was born on April 18, 1911, in ...
, a refugee from
Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
and a graduate student at the Cavendish Laboratory, suggested to Chadwick that
deuteron Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one n ...
s could be photodisintegrated by the 2.6 MeV gamma rays of 208Tl (then known as thorium C"): : An accurate value for the mass of the neutron could be determined from this process. Chadwick and Goldhaber tried this and found that it worked. They measured the kinetic energy of the proton produced as 1.05 MeV, leaving the mass of the neutron as the unknown in the equation. Chadwick and Goldhaber calculated that it was either 1.0084 or 1.0090 atomic units, depending on the values used for the masses of the proton and deuteron. (The modern accepted value for the mass of the neutron is .) The mass of the neutron was too large to be a proton–electron pair. For his discovery of the neutron, Chadwick was awarded the
Hughes Medal The Hughes Medal is awarded by the Royal Society of London "in recognition of an original discovery in the physical sciences, particularly electricity and magnetism or their applications". Named after David E. Hughes, the medal is awarded with ...
by the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
in 1932, the
Nobel Prize in Physics ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
in 1935, the
Copley Medal The Copley Medal is an award given by the Royal Society, for "outstanding achievements in research in any branch of science". It alternates between the physical sciences or mathematics and the biological sciences. Given every year, the medal is t ...
in 1950 and the
Franklin Medal The Franklin Medal was a science award presented from 1915 until 1997 by the Franklin Institute located in Philadelphia, Pennsylvania, U.S. It was founded in 1914 by Samuel Insull Samuel Insull (November 11, 1859 – July 16, 1938) was a Bri ...
in 1951. His discovery of the neutron made it possible to produce elements heavier than
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
in the laboratory by the capture of slow neutrons followed by
beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
. Unlike the positively charged
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...
s, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any
Coulomb barrier The Coulomb barrier, named after Coulomb's law, which is in turn named after physicist Charles-Augustin de Coulomb, is the energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a ...
, and can therefore penetrate and enter the nuclei of even the heaviest elements such as uranium. This inspired
Enrico Fermi Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...
to investigate the nuclear reactions brought about by collisions of nuclei with slow neutrons, work for which Fermi would receive the Nobel Prize in 1938.
Wolfgang Pauli Wolfgang Ernst Pauli (; ; 25 April 1900 – 15 December 1958) was an Austrian theoretical physicist and one of the pioneers of quantum physics. In 1945, after having been nominated by Albert Einstein, Pauli received the Nobel Prize in Physics fo ...
proposed another kind of particle on 4 December 1930 in order to explain the continuous spectrum of beta radiation that Chadwick had reported in 1914. Since not all of the energy of beta radiation could be accounted for, the law of
conservation of energy In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be ''conserved'' over time. This law, first proposed and tested by Émilie du Châtelet, means th ...
appeared to be violated, but Pauli argued that this could be redressed if another, undiscovered, particle was involved. Pauli also called this particle a neutron, but it was clearly not the same particle as Chadwick's neutron. Fermi renamed it the
neutrino A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
, Italian for "little neutron". In 1934, Fermi proposed his theory of beta decay which explained that the electrons emitted from the nucleus were created by the decay of a neutron into a proton, an electron, and a neutrino. The neutrino could account for the missing energy, but a particle with little mass and no electric charge was difficult to observe.
Rudolf Peierls Sir Rudolf Ernst Peierls, (; ; 5 June 1907 – 19 September 1995) was a German-born British physicist who played a major role in Tube Alloys, Britain's nuclear weapon programme, as well as the subsequent Manhattan Project, the combined Allied ...
and
Hans Bethe Hans Albrecht Bethe (; July 2, 1906 – March 6, 2005) was a German-American theoretical physicist who made major contributions to nuclear physics, astrophysics, quantum electrodynamics, and solid-state physics, and who won the 1967 Nobel ...
calculated that neutrinos could easily pass through the Earth, so the chances of detecting them were slim.
Frederick Reines Frederick Reines ( ; March 16, 1918 – August 26, 1998) was an American physicist. He was awarded the 1995 Nobel Prize in Physics for his co-detection of the neutrino with Clyde Cowan in the neutrino experiment. He may be the only scientist in ...
and
Clyde Cowan Clyde Lorrain Cowan Jr (December 6, 1919 – May 24, 1974) was an American physicist, the co-discoverer of the neutrino along with Frederick Reines. The discovery was made in 1956 in the neutrino experiment. Frederick Reines received the Nobel P ...
would confirm the neutrino on 14 June 1956 by placing a detector within a large antineutrino flux from a nearby nuclear reactor.


Liverpool Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...

With the onset of the
Great Depression in the United Kingdom The Great Depression in the United Kingdom also known as the Great Slump, was a period of national economic downturn in the 1930s, which had its origins in the global Great Depression. It was Britain's largest and most profound economic depress ...
, the government became more parsimonious with funding for science. At the same time, Lawrence's recent invention, the
cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Janu ...
, promised to revolutionise experimental nuclear physics, and Chadwick felt that the Cavendish laboratory would fall behind unless it also acquired one. He therefore chafed under Rutherford, who clung to the belief that good nuclear physics could still be done without large, expensive equipment, and turned down the request for a cyclotron. Chadwick was himself a critic of Big Science in general, and Lawrence in particular, whose approach he considered careless and focused on technology at the expense of science. When Lawrence postulated the existence of a new and hitherto unknown particle that he claimed was a possible source of limitless energy at the
Solvay Conference The Solvay Conferences (french: Conseils Solvay) have been devoted to outstanding preeminent open problems in both physics and chemistry. They began with the historic invitation-only 1911 Solvay Conference on Physics, considered a turning point i ...
in 1933, Chadwick responded that the results were more likely attributable to contamination of the equipment. While Lawrence rechecked his results at Berkeley only to find that Chadwick was correct, Rutherford and Oliphant conducted an investigation at the Cavendish that found that deuterium
fuses Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protec ...
to form
helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the ...
, thereby causing the effect that Lawrence had observed. This was another major discovery, but the Oliphant-Rutherford
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...
was an expensive state-of-the-art piece of equipment. In March 1935, Chadwick received an offer of the Lyon Jones Chair of physics at the
University of Liverpool , mottoeng = These days of peace foster learning , established = 1881 – University College Liverpool1884 – affiliated to the federal Victoria Universityhttp://www.legislation.gov.uk/ukla/2004/4 University of Manchester Act 200 ...
, in his wife's home town, to succeed Lionel Wilberforce. The laboratory was so antiquated that it still ran on
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
electricity, but Chadwick seized the opportunity, assuming the chair on 1 October 1935. The university's prestige was soon bolstered by Chadwick's Nobel Prize, which was announced in November 1935. His medal was sold at auction in 2014 for $329,000. Chadwick set about acquiring a cyclotron for Liverpool. He started by spending £700 to refurbish the antiquated laboratories at Liverpool, so some components could be made in-house. He was able to persuade the university to provide £2,000 and obtained a grant for another £2,000 from the Royal Society. To build his cyclotron, Chadwick brought in two young experts, Bernard Kinsey and Harold Walke, who had worked with Lawrence at the University of California. A local cable manufacturer donated the copper conductor for the coils. The cyclotron's 50-ton magnet was manufactured in
Trafford Park Trafford Park is an area of the Metropolitan Borough of Trafford, Greater Manchester, England, opposite Salford Quays on the southern side of the Manchester Ship Canal, southwest of Manchester city centre and north of Stretford. Until the l ...
by
Metropolitan-Vickers Metropolitan-Vickers, Metrovick, or Metrovicks, was a British heavy electrical engineering company of the early-to-mid 20th century formerly known as British Westinghouse. Highly diversified, it was particularly well known for its industrial el ...
, which also made the vacuum chamber. The cyclotron was completely installed and running in July 1939. The total cost of £5,184 was more than Chadwick had received from the University and the Royal Society, so Chadwick paid the rest from his (£8,243) Nobel Prize money. At Liverpool the Medicine and Science faculties worked together closely. Chadwick was automatically a committee member of both faculties, and in 1938 he was appointed to a commission headed by
Lord Derby Edward George Geoffrey Smith-Stanley, 14th Earl of Derby, (29 March 1799 – 23 October 1869, known before 1834 as Edward Stanley, and from 1834 to 1851 as Lord Stanley) was a British statesman, three-time Prime Minister of the United Kingdom ...
to investigate the arrangements for cancer treatment in Liverpool. Chadwick anticipated that neutrons and radioactive isotopes produced with the 37-inch cyclotron could be used to study biochemical processes, and might become a weapon in the fight against cancer.


Second World War


Tube Alloys and the MAUD Report

In Germany,
Otto Hahn Otto Hahn (; 8 March 1879 – 28 July 1968) was a German chemist who was a pioneer in the fields of radioactivity and radiochemistry. He is referred to as the father of nuclear chemistry and father of nuclear fission. Hahn and Lise Meitner ...
and
Fritz Strassmann Friedrich Wilhelm Strassmann (; 22 February 1902 – 22 April 1980) was a German chemist who, with Otto Hahn in December 1938, identified the element barium as a product of the bombardment of uranium with neutrons. Their observation was the ke ...
bombarded uranium with neutrons, and noted that
barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...
, a lighter element, was among the products produced. Hitherto, only the same or heavier elements had been produced by the process. In January 1939, Meitner and her nephew Otto Frisch astounded the physics community with a paper that explained this result. They theorised that uranium atoms bombarded with neutrons can break into two roughly equal fragments, a process they called fission. They calculated that this would result in the release of about 200
MeV In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacu ...
, implying an energy release orders of magnitude greater than chemical reactions, and Frisch confirmed their theory experimentally. It was soon noted by Hahn that if neutrons were released during fission, then a chain reaction was possible. French scientists,
Pierre Joliot Pierre Adrien Joliot-Curie (born 12 March 1932) is a noted French biologist and researcher for the CNRS. A researcher there since 1956, he became a Director of Research in 1974 and a member of their scientific council in 1992. He was a scientifi ...
,
Hans von Halban Hans Heinrich von Halban (24 January 1908 – 28 November 1964) was a French physicist, of Austrian- Jewish descent. Family He was descended on his father's side from Polish Jews, who left Kraków for Vienna in the 1850s. His grandfather, Hei ...
and
Lew Kowarski Lew Kowarski (10 February 1907, Saint Petersburg – 30 July 1979, Geneva) was a naturalized French physicist. He was a lesser-known but important contributor to nuclear science. Early life Lew Kowarski was born in Saint Petersburg to Nicholas K ...
, soon verified that more than one neutron was indeed emitted per fission. In a paper co-authored with the American physicist John Wheeler, Bohr theorised that fission was more likely to occur in the
uranium-235 Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exis ...
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
, which made up only 0.7 percent of natural uranium. Chadwick did not believe that there was any likelihood of another war with Germany in 1939, and took his family for a holiday on a remote lake in northern Sweden. The news of the outbreak of the
Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
therefore came as a shock. Determined not to spend another war in an internment camp, Chadwick made his way to
Stockholm Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...
as fast as he could, but when he arrived there with his family, he found that all air traffic between Stockholm and London had been suspended. They made their way back to England on a
tramp steamer A boat or ship engaged in the tramp trade is one which does not have a fixed schedule, itinerary nor published ports of call, and trades on the spot market as opposed to freight liners. A steamship engaged in the tramp trade is sometimes called ...
. When he reached Liverpool, Chadwick found
Joseph Rotblat Sir Joseph Rotblat (4 November 1908 – 31 August 2005) was a Polish and British physicist. During World War II he worked on Tube Alloys and the Manhattan Project, but left the Los Alamos Laboratory on grounds of conscience after it became ...
, a Polish post-doctoral fellow who had come to work with the cyclotron, was now destitute, as he was cut off from funds from Poland. Chadwick promptly hired Rotblat as a lecturer, despite his poor grasp of English. In October 1939, Chadwick received a letter from Sir Edward Appleton, the Secretary of the Department of Scientific and Industrial Research, asking for his opinion on the feasibility of an
atom bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb ...
. Chadwick responded cautiously. He did not dismiss the possibility, but carefully went over the many theoretical and practical difficulties involved. Chadwick decided to investigate the properties of
uranium oxide Uranium oxide is an oxide of the element uranium. The metal uranium forms several oxides: * Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende) * Diuranium pentoxide or uranium(V) oxide (U2O5) * Uranium trioxide o ...
further with Rotblat. In March 1940, Otto Frisch and
Rudolf Peierls Sir Rudolf Ernst Peierls, (; ; 5 June 1907 – 19 September 1995) was a German-born British physicist who played a major role in Tube Alloys, Britain's nuclear weapon programme, as well as the subsequent Manhattan Project, the combined Allied ...
at the
University of Birmingham , mottoeng = Through efforts to heights , established = 1825 – Birmingham School of Medicine and Surgery1836 – Birmingham Royal School of Medicine and Surgery1843 – Queen's College1875 – Mason Science College1898 – Mason Univers ...
re-examined the theoretical issues involved in a paper that became known as the Frisch–Peierls memorandum. Instead of looking at unenriched uranium oxide, they considered what would happen to a sphere of pure uranium-235, and found that not only could a chain reaction occur, but that it might require as little as of uranium-235, and unleash the energy of tons of dynamite. A special subcommittee of the Committee for the Scientific Survey of Air Warfare (CSSAW), known as the
MAUD Committee The MAUD Committee was a British scientific working group formed during the Second World War. It was established to perform the research required to determine if an atomic bomb was feasible. The name MAUD came from a strange line in a telegram fro ...
, was created to investigate the matter further. It was chaired by Sir George Thomson and its original membership included Chadwick, along with Mark Oliphant, John Cockcroft and Philip Moon. While other teams investigated
uranium enrichment Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...
techniques, Chadwick's team at Liverpool concentrated on determining the
nuclear cross section The nuclear cross section of a nucleus is used to describe the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a large ...
of uranium-235. By April 1941, it had been experimentally confirmed that the
critical mass In nuclear engineering, 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 (specifically, its nuclear fissi ...
of uranium-235 might be or less. His research into such matters was complicated by all-but-incessant
Luftwaffe The ''Luftwaffe'' () was the aerial-warfare branch of the German ''Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the ''Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabtei ...
bombings of the environs of his Liverpool lab; the windows were blown out so often that they were replaced by cardboard. In July 1941, Chadwick was chosen to write the final draft of the MAUD Report, which, when presented by
Vannevar Bush Vannevar Bush ( ; March 11, 1890 – June 28, 1974) was an American engineer, inventor and science administrator, who during World War II headed the U.S. Office of Scientific Research and Development (OSRD), through which almost all wartime ...
to
President President most commonly refers to: *President (corporate title) *President (education), a leader of a college or university *President (government title) President may also refer to: Automobiles * Nissan President, a 1966–2010 Japanese ful ...
Franklin D. Roosevelt Franklin Delano Roosevelt (; ; January 30, 1882April 12, 1945), often referred to by his initials FDR, was an American politician and attorney who served as the 32nd president of the United States from 1933 until his death in 1945. As the ...
in October 1941, inspired the U.S. government to pour millions of dollars into the pursuit of an atom bomb. When George B. Pegram and
Harold Urey Harold Clayton Urey ( ; April 29, 1893 – January 5, 1981) was an American physical chemist whose pioneering work on isotopes earned him the Nobel Prize in Chemistry in 1934 for the discovery of deuterium. He played a significant role in the d ...
visited Britain to see how the project, now known as
Tube Alloys Tube Alloys was the research and development programme authorised by the United Kingdom, with participation from Canada, to develop nuclear weapons during the Second World War. Starting before the Manhattan Project in the United States, the Bri ...
, was going, Chadwick was able to tell them: "I wish I could tell you that the bomb is not going to work, but I am 90 per cent sure that it will." In a recent book about the Bomb project, Graham Farmelo wrote that "Chadwick did more than any other scientist to give Churchill the Bomb. ... Chadwick was tested almost to the breaking point." So worried that he could not sleep, Chadwick resorted to sleeping pills, which he continued to take for most of his remaining years. Chadwick later said that he realised that "a nuclear bomb was not only possible—it was inevitable. Sooner or later these ideas could not be peculiar to us. Everybody would think about them before long, and some country would put them into action". Sir
Hermann Bondi Sir Hermann Bondi (1 November 1919 – 10 September 2005) was an Austrian- British mathematician and cosmologist. He is best known for developing the steady state model of the universe with Fred Hoyle and Thomas Gold as an alternative to the ...
suggested that it was fortunate that Chadwick, not Rutherford, was the doyen of UK physics at the time, as the latter's prestige might otherwise have overpowered Chadwick's interest in "looking forward" to the Bomb's prospects.


Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

Owing to the danger from aerial bombardment, the Chadwicks sent their twins to Canada as part of a government evacuation scheme. Chadwick was reluctant to move Tube Alloys there, believing that the United Kingdom was a better location for the isotope separation plant. The enormous scope of the effort became more apparent in 1942: even a pilot separation plant would cost over £1 million and strain Britain's resources, to say nothing of a full-scale plant, which was estimated to cost somewhere in the vicinity of £25 million. It would have to be built in America. At the same time that the British became convinced that a joint project was necessary, the progress of the American
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
was such that British cooperation seemed less essential, although the Americans were still eager to utilise Chadwick's talents. The matter of cooperation had to be taken up at the highest level. In September 1943, the
Prime Minister A prime minister, premier or chief of cabinet is the head of the cabinet and the leader of the ministers in the executive branch of government, often in a parliamentary or semi-presidential system. Under those systems, a prime minister is not ...
,
Winston Churchill Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 Winston Churchill in the Second World War, dur ...
, and President Roosevelt negotiated the
Quebec Agreement The Quebec Agreement was a secret agreement between the United Kingdom and the United States outlining the terms for the coordinated development of the science and engineering related to nuclear energy and specifically nuclear weapons. It was s ...
, which reinstated cooperation between Britain, the United States and Canada. Chadwick, Oliphant, Peierls and
Simon Simon may refer to: People * Simon (given name), including a list of people and fictional characters with the given name Simon * Simon (surname), including a list of people with the surname Simon * Eugène Simon, French naturalist and the genus ...
were summoned to the United States by the director of Tube Alloys, Sir
Wallace Akers Sir Wallace Alan Akers (9 September 1888 – 1 November 1954) was a British chemist and industrialist. Beginning his academic career at Oxford he specialized in physical chemistry. During the Second World War, he was the director of the Tube Al ...
, to work with the Manhattan Project. The Quebec Agreement established a new
Combined Policy Committee The Quebec Agreement was a secret agreement between the United Kingdom and the United States outlining the terms for the coordinated development of the science and engineering related to nuclear energy and specifically nuclear weapons. It was ...
to direct the joint project. The Americans disliked Akers, so Chadwick was appointed technical advisor to the Combined Policy Committee, and the head of the British Mission. Leaving Rotblat in charge in Liverpool, Chadwick began a tour of the Manhattan Project facilities in November 1943, except for the
Hanford Site The Hanford Site is a decommissioned nuclear production complex operated by the United States federal government on the Columbia River in Benton County in the U.S. state of Washington. The site has been known by many names, including SiteW a ...
where plutonium was produced, which he was not allowed to see. He became the only man apart from Groves and his second in command to have access to all the American research and production facilities for the uranium bomb. Observing the work on the
K-25 K-25 was the codename given by the Manhattan Project to the program to produce enriched uranium for atomic bombs using the gaseous diffusion method. Originally the codename for the product, over time it came to refer to the project, the prod ...
gaseous diffusion Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride (UF6) through semipermeable membranes. This produces a slight separation between the molecules containing uranium-235 (235U) and uranium-2 ...
facility at Oak Ridge, Tennessee, Chadwick realised how wrong he had been about building the plant in wartime Britain. The enormous structure could never have been concealed from the Luftwaffe. In early 1944, he moved to
Los Alamos, New Mexico Los Alamos is an census-designated place in Los Alamos County, New Mexico, United States, that is recognized as the development and creation place of the atomic bomb—the primary objective of the Manhattan Project by Los Alamos National Labora ...
, with his wife and their twins, who now spoke with Canadian accents. For security reasons, he was given the cover name of James Chaffee. Chadwick accepted that the Americans did not need British help, but that it could still be useful in bringing the project to an early and successful conclusion. Working closely with the director of the Manhattan Project,
Major General Major general (abbreviated MG, maj. gen. and similar) is a military rank used in many countries. It is derived from the older rank of sergeant major general. The disappearance of the "sergeant" in the title explains the apparent confusion of a ...
Leslie R. Groves, Jr., he attempted to do everything he could to support the effort. He also endeavoured to place British scientists in as many parts of the project as possible in order to facilitate a post-war British nuclear weapons project to which Chadwick was committed. Requests from Groves via Chadwick for particular scientists tended to be met with an immediate rejection by the company, ministry or university currently employing them, only to be overcome by the overriding priority accorded to Tube Alloys. As a result, the British team was critical to the Project's success. Although he had more knowledge of the project than anyone else from Britain, Chadwick had no access to the Hanford site. Lord Portal was offered a tour of Hanford in 1946. "This was the only plant to which Chadwick had been denied access in wartime, and now he asked Groves if he could accompany Portal. Groves replied that he could, but if he did then 'Portal will not see very much'." For his efforts, Chadwick received a
knighthood A knight is a person granted an honorary title of knighthood by a head of state (including the Pope) or representative for service to the monarch, the church or the country, especially in a military capacity. Knighthood finds origins in the Gr ...
in the New Year Honours on 1 January 1945. ''Knight Bachelor'' He considered this to be a recognition of the work of the whole Tube Alloys project. By early 1945, Chadwick was spending most of his time in Washington, D.C., and his family relocated from Los Alamos to a house on Washington's
Dupont Circle Dupont Circle (or DuPont Circle) is a traffic circle, park, neighborhood and historic district in Northwest Washington, D.C. The Dupont Circle neighborhood is bounded approximately by 16th Street NW to the east, 22nd Street NW ...
in April 1945. He was present at the meeting of the Combined Policy Committee on 4 July when
Field Marshal Field marshal (or field-marshal, abbreviated as FM) is the most senior military rank, ordinarily senior to the general officer ranks. Usually, it is the highest rank in an army and as such few persons are appointed to it. It is considered as ...
Sir
Henry Maitland Wilson Field Marshal Henry Maitland Wilson, 1st Baron Wilson, (5 September 1881 – 31 December 1964), also known as Jumbo Wilson, was a senior British Army officer of the 20th century. He saw active service in the Second Boer War and then during the ...
gave Britain's agreement to use the atom bomb against Japan, and at the
Trinity nuclear test Trinity was the code name of the first detonation of a nuclear weapon. It was conducted by the United States Army at 5:29 a.m. on July 16, 1945, as part of the Manhattan Project. The test was conducted in the Jornada del Muerto desert abo ...
on 16 July, when the first atom bomb was detonated. Inside its pit was a polonium-beryllium
modulated neutron initiator A modulated neutron initiator is a neutron source capable of producing a burst of neutrons on activation. It is a crucial part of some nuclear weapons, as its role is to "kick-start" the chain reaction at the optimal moment when the configuration i ...
, a development of the technique that Chadwick had used to discover the neutron over a decade before. William L. Laurence, ''
The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'' reporter attached to the Manhattan Project, wrote that "never before in history had any man lived to see his own discovery materialize itself with such telling effect on the destiny of man."


Later life

Shortly after the war ended, Chadwick was appointed to the Advisory Committee on Atomic Energy (ACAE). He was also appointed as the British scientific advisor to the
United Nations Atomic Energy Commission The United Nations Atomic Energy Commission (UNAEC) was founded on 24 January 1946 by the very first resolution of the United Nations General Assembly "to deal with the problems raised by the discovery of atomic energy." The General Assembly asked ...
. He clashed with fellow ACAE member
Patrick Blackett Patrick Maynard Stuart Blackett, Baron Blackett (18 November 1897 â€“ 13 July 1974) was a British experimental physicist known for his work on cloud chambers, cosmic rays, and paleomagnetism, winning the Nobel Prize for Physics in 1948. ...
, who disagreed with Chadwick's conviction that Britain needed to acquire its own nuclear weapons; but it was Chadwick's position that was ultimately adopted. He returned to Britain in 1946, to find a country still beset by wartime rationing and shortages. At this time, Sir James Mountford, the Vice Chancellor of the University of Liverpool, wrote in his diary "he had never seen a man 'so physically, mentally and spiritually tired" as Chadwick, for he "had plumbed such depths of moral decision as more fortunate men are never called upon even to peer into ... nd sufferednbsp;... almost insupportable agonies of responsibility arising from his scientific work'." In 1948, Chadwick accepted an offer to become the
Master Master or masters may refer to: Ranks or titles * Ascended master, a term used in the Theosophical religious tradition to refer to spiritually enlightened beings who in past incarnations were ordinary humans *Grandmaster (chess), National Master ...
of Gonville and Caius College. The job was prestigious but ill-defined; the Master was the titular head of the College, but authority actually resided in a council of 13 fellows, of whom one was the Master. As Master, Chadwick strove to improve the academic reputation of the college. He increased the number of research fellowships from 31 to 49, and sought to bring talent into the college. This involved controversial decisions, such as hiring in 1951 the Chinese biochemist Tien-chin Tsao and the Hungarian-born economist Peter Bauer. In what became known as the Peasants' Revolt, fellows led by
Patrick Hadley Patrick Arthur Sheldon Hadley (5 March 1899 â€“ 17 December 1973) was a British composer. Biography Patrick Sheldon Hadley was born on 5 March 1899 in Cambridge. His father, William Sheldon Hadley, was at that time a fellow of Pembroke Co ...
voted an old friend of Chadwick's off the council and replaced him with Bauer. More friends of Chadwick's were removed over the following years, and he retired in November 1958. It was during his mastership that
Francis Crick Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist. He, James Watson, Rosalind Franklin, and Maurice Wilkins played crucial roles in deciphering the helical struc ...
, a PhD student at Gonville and Caius College, and
James Watson James Dewey Watson (born April 6, 1928) is an American molecular biologist, geneticist, and zoologist. In 1953, he co-authored with Francis Crick the academic paper proposing the double helix structure of the DNA molecule. Watson, Crick and ...
discovered the structure of DNA. Over the years, Chadwick received many honours, including the
Medal for Merit The Medal for Merit was, during the period it was awarded, the highest civilian decoration of the United States. It was awarded by the President of the United States to civilians who "distinguished themselves by exceptionally meritorious conduct i ...
from the United States, and the ''
Pour le Mérite The ' (; , ) is an order of merit (german: Verdienstorden) established in 1740 by Frederick the Great, King Frederick II of Prussia. The was awarded as both a military and civil honour and ranked, along with the Order of the Black Eagle, the Or ...
'' from Germany. He was elected a
Fellow of the Royal Society Fellowship of the Royal Society (FRS, ForMemRS and HonFRS) is an award granted by the judges of the Royal Society of London to individuals who have made a "substantial contribution to the improvement of natural science, natural knowledge, incl ...
in 1927, and in 1946 he became foreign member of the
Royal Netherlands Academy of Arts and Sciences The Royal Netherlands Academy of Arts and Sciences ( nl, Koninklijke Nederlandse Akademie van Wetenschappen, abbreviated: KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands. The academy is housed ...
. He was made a Companion of Honour in the New Year Honours on 1 January 1970 for "services to science", ''Companion of Honour'' and went to
Buckingham Palace Buckingham Palace () is a London royal residence and the administrative headquarters of the monarch of the United Kingdom. Located in the City of Westminster, the palace is often at the centre of state occasions and royal hospitality. It ...
for the investiture ceremony. He became more frail, and seldom left his flat, although he travelled to Liverpool for celebrations of his eightieth birthday. A lifelong atheist, he saw no reason to adopt religious faith in later life. He died in his sleep on 24 July 1974. His papers are held at the
Churchill Archives Centre The Churchill Archives Centre (CAC) at Churchill College at the University of Cambridge is one of the largest repositories in the United Kingdom for the preservation and study of modern personal papers. It is best known for housing the papers of ...
in Cambridge, and are accessible to the public. The Chadwick Laboratory at the University of Liverpool is named after him, as is its Sir James Chadwick Chair of Experimental Physics, which was named after him in 1991 as part of celebrations of the centenary of his birth. A crater on the moon is also named after him. The James Chadwick Building, which houses part of the School of Chemical Engineering and Analytical Sciences, University of Manchester is named in his honour. He was described by the
United Kingdom Atomic Energy Authority The United Kingdom Atomic Energy Authority is a UK government research organisation responsible for the development of fusion energy. It is an executive non-departmental public body of the Department for Business, Energy and Industrial Strategy ...
official historian Lorna Arnold as "a physicist, a scientist-diplomat, and a good, wise, and humane man."


Notes


References

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Further reading

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External links


Oral history interview transcript with James Chadwick on 15 April 1969, American Institute of Physics, Niels Bohr Library & Archives
– Session I
Oral history interview transcript with James Chadwick on 16 April 1969, American Institute of Physics, Niels Bohr Library & Archives
– Session II
Oral history interview transcript with James Chadwick on 17 April 1969, American Institute of Physics, Niels Bohr Library & Archives
– Session III
Oral history interview transcript with James Chadwick on 20 April 1969, American Institute of Physics, Niels Bohr Library & Archives
– Session IV * {{DEFAULTSORT:Chadwick, James 1891 births 1974 deaths 20th-century British physicists Academics of the Victoria University of Manchester Alumni of Gonville and Caius College, Cambridge Alumni of the Victoria University of Manchester English atheists English nuclear physicists English Nobel laureates Experimental physicists Fellows of Gonville and Caius College, Cambridge Fellows of the Royal Society Knights Bachelor Manhattan Project people People from Los Alamos, New Mexico Masters of Gonville and Caius College, Cambridge Medal for Merit recipients Members of the Order of the Companions of Honour Members of the Royal Academy of Belgium Members of the Royal Netherlands Academy of Arts and Sciences Nobel laureates in Physics Recipients of the Copley Medal Recipients of the Medal of Freedom Recipients of the Pour le Mérite (civil class) Academics of the University of Liverpool People from Bollington World War I civilian detainees held by Germany People associated with the nuclear weapons programme of the United Kingdom People from Dupont Circle