James Chadwick Sir James Chadwick ( 20 October 1891 – 24 July 1974 ) was an English physicist who was awarded the 1935 Nobel Prize in physics for his discovery of the neutron in 1932 . He was the head of the British scientists who worked on the Manhattan Project during World War II . He was knighted in 1945 for achievements in physics . A graduate of the University of Manchester , where he studied under Ernest Rutherford , Chadwick was awarded an 1851 Exhibition Scholarship , and elected to study beta radiation under Hans Geiger . Using Geiger ' s recently developed Geiger counter , he was able to demonstrate that beta radiation produced a continuous electromagnetic spectrum , and not discrete lines as had been thought . Still in Germany when World War I broke out in Europe , he spent the war in the Ruhleben internment camp . After the war , Chadwick followed Rutherford to the Cavendish Laboratory at the University of Cambridge , where Chadwick earned his Doctor of Philosophy degree at Gonville and Caius College , Cambridge . 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 , Norman Feather , and Mark Oliphant . In 1932 , Chadwick pursued a line of research that led to his discovery of the neutron . He went on to measure its mass . Chadwick left the Cavendish Laboratory in 1935 to become a professor of physics at the University of Liverpool , where he overhauled an antiquated laboratory and , by installing a cyclotron , made it an important centre for the study of nuclear physics . During the Second World War , he carried out research as part of the Tube Alloys project to build an atomic bomb . When the Quebec Agreement merged his project with the American Manhattan Project , he became head of the British Mission , and worked at the Los Alamos Laboratory . In July 1945 , he viewed the Trinity nuclear test . Uncomfortable with the trend toward Big Science , Chadwick became the Master of Gonville and Caius College , Cambridge , in 1948 . He retired in 1959 . Education and early life . Chadwick was born in Bollington , Cheshire , on 20 October 1891 , the first child of John Joseph and Anne Mary Knowles Chadwick . He was named after his paternal grandfather . In 1895 , his parents moved to Manchester , leaving him in the care of his grandparents . He went to Bollington Cross Primary School , and was offered a scholarship to Manchester Grammar School , 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 for two university scholarship examinations , and was offered both . Chadwick chose to attend Victoria University of Manchester , which he entered in 1908 . 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 , 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 , a unit of measurement which would become known as the Curie . Unfortunately , Rutherford ' s suggested approach was unworkable — something Chadwick knew but was afraid to tell Rutherford — so Chadwick pressed on on his own , 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 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 only . He was awarded his Master of Science ( MSc ) degree in 1912 , and was appointed a Beyer Fellow . The following year he was awarded an 1851 Exhibition Scholarship , which allowed him to study and research at a university in continental Europe . He elected to go to the " Physikalisch - Technische Reichsanstalt " in Berlin in 1913 , to study beta radiation under Hans Geiger . Using Geiger ' s recently developed Geiger counter , which provided more accuracy than the earlier photographic techniques , he was able to demonstrate that beta radiation produced a continuous electromagnetic spectrum , and not discrete lines as had previously been thought . The reason for this would remain unexplained for many years . Chadwick was still in Germany at the start of World War I , and was interned in the Ruhleben internment camp 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 D . Ellis , he worked on the ionisation of phosphorus , and the photochemical reaction of carbon monoxide and chlorine . He was released after the Armistice with Germany 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 of platinum , silver , and copper , and experimentally found that this was the same as the atomic number within an error of less than 1 . 5 percent . In April 1919 , Rutherford became director of the Cavendish Laboratory at the University of Cambridge , 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 ( PhD ) student at Gonville and Caius College , Cambridge . The first half of his thesis was his work with atomic numbers . In the second , he looked at the forces inside the nucleus . His degree was awarded in June 1921 . In November he became a Fellow of Gonville and Caius College . Research . Cambridge . 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 , 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 , Norman Feather and Mark Oliphant , 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 would also edit 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 . They had twin daughters , Joanna and Judy , who were born in February 1927 . In his research , Chadwick continued to probe the atomic nucleus . In 1925 , the concept of spin had allowed physicists to explain the Zeeman effect , but it also created unexplained anomalies . At the time it was believed that the nucleus consisted of protons and electrons , so nitrogen , for example , with a mass number of 14 , was assumed to contain 14 protons and 7 electrons . This gave it the right mass and charge , but the wrong spin . At a conference at Cambridge on beta particles and gamma rays in 1928 , Chadwick met Geiger again , who brought with him a new model of his Geiger counter , which had been improved by his post - doctoral student Walther Müller . This was something that Chadwick had not used since the war , and the new Geiger - Müller counter was potentially a major improvement over the scintillation techniques then in use , which relied on the human eye for observation . The major drawback with it was that it detected alpha , beta and gamma 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 is an alpha emitter , and Lise Meitner sent Chadwick about 2 millicuries from Germany . In Germany , Walter Bothe and his student Herbert Becker used polonium to bombard beryllium , 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 , a theoretical nuclear particle with no electric charge . Chadwick dropped all his other responsibilities to concentrate on the neutron , 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 a material such as paraffin wax and the particles displaced , which were protons , would go into a small ionisation chamber where they could be detected with an oscilloscope . In February 1932 , after only about two weeks of experimentation with neutrons , Chadwick sent a letter to " Nature " titled " Possible Existence of a Neutron " . He communicated his findings in detail in " The Existence of a Neutron " in May . His discovery was a milestone in understanding the nucleus . Reading Chadwick ' s paper , Robert Bacher and Edward Condon realised that anomalies in then - current theory like the spin of nitrogen would be resolved if the spin of the neutron was ½ and a nitrogen nucleus consisted of 7 protons and 7 neutrons . The theoretical physicists Niels Bohr and Werner Heisenberg became convinced that the neutron must be a nuclear particle , and not a proton - electron pair . Chadwick and Maurice Goldhaber , a refugee from Nazi Germany , determined the mass of the neutron experimentally , and found that it was greater than that of the proton , thereby confirming this theory . For Chadwick ' s discovery of the neutron , he was awarded the Hughes Medal by the Royal Society in 1932 , the Nobel Prize in Physics in 1935 , the Copley Medal in 1950 , and the Franklin Medal in 1951 . Chadwick ’ s discovery of the neutron also made it possible to produce elements heavier than uranium in the laboratory , by the capture of slow neutrons followed by beta decay . Unlike the positively - charged alpha particle s , which are repelled by the electrical forces present in the nuclei of other atoms , neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and enter the nuclei of even the heaviest elements such as uranium . His discovery of the neutron inspired Enrico Fermi , the Italian physicist and eventual Nobel Prize winner , to investigate the nuclear reactions brought about by collisions of nuclei with slow neutrons . The continuous spectrum of beta radiation , which Chadwick had reported in 1914 , was explained by Wolfgang Pauli by recourse to another hypothetical neutral particle , which Fermi christened the neutrino . Liverpool . Rutherford succeeded McCormick as Chairman of the Advisory Council of the Department of Scientific and Industrial Research in 1930 . With the onset of the Great Depression in the United Kingdom , the government became more parsimonious with funding for science . At the same time , Ernest Lawrence ' s recent invention , the cyclotron , promised to revolutionise the experimental nuclear physics , and Chadwick felt that the Cavendish laboratory would fall behind unless it also acquired one . Chadwick therefore chafed under Rutherford , who clung to the belief that good nuclear physics could still be done without large , expensive items of equipment . In March 1935 , Chadwick received an offer of the Lyon Jones Chair of physics at the University of Liverpool , in Aileen ' s home town , in succession to Lionel Wilberforce . The university was something of a backwater , and the laboratory was so antiquated that it still ran on direct current , 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 . 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 by Metropolitan - Vickers , 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 Nobel Prize money . Second World War . Tube Alloys . In January 1939 , Meitner and her nephew Otto Frisch created an uproar with a paper that explained how uranium atoms , when bombarded by neutrons , broke into two roughly equal fragments , a process they called fission . They calculated that this would result in the release of about 200 MeV , implying an energy release orders of magnitude greater than chemical reactions . It was soon noted by Otto Hahn and Fritz Strassmann that if neutrons were released during fission , then a chain reaction was possible . French scientists , Pierre Joliot , Hans von Halban and Lew Kowarski , soon verified that more than one neutron was indeed emitted per fission . Neils Bohr theorised that fission was more likely to occur in the uranium - 235 isotope , which made up only 0 . 7 percent of natural uranium . He published this in a paper co - authored with the American physicist John Wheeler . 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 therefore came as a shock . Determined not to spend another war in an internment camp , Chadwick made his way to Stockholm 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 . When he reached Liverpool , Chadwick found Joseph Rotblat , a Polish post - doctoral fellow who had come to work with the cyclotron , who 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 atomic bomb . Chadwick responded cautiously . He did not dismiss the possibility , but carefully went over the large number of theoretical and practical difficulties involved . Chadwick decided to investigate the properties of uranium oxide further with Rotblat . However , in March 1940 , Otto Frisch and Rudolf Peierls at the University of Birmingham re - examined the theoretical issues involved in a paper that became known as the Frisch – Peierls memorandum . Instead of looking at uranium metal , they considered what would happen to a sphere of pure uranium - 235 , and found that not only could a chain reaction occur , but it might require as little as of uranium - 235 , and unleash the energy of tons of dynamite . As a result , a special subcommittee of the Committee for the Scientific Survey of Air Warfare ( CSSAW ) known as the MAUD Committee was created to investigated 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 techniques , Chadwick ' s team at Liverpool concentrated on determining the nuclear cross section of uranium - 235 . By April 1941 , it had been experimentally confirmed that the critical mass of uranium - 235 might be or less . When George Pegram and Harold Urey visited Britain to see how the project , now known as Tube Alloys , 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 . " Manhattan Project . Owing to the danger from aerial bombardment , the Chadwicks sent Julie and Joanna to Canada as part of a government evacuation scheme . However , Chadwick was reluctant to move Tube Alloys thither , believing that the United Kingdom was a better location for the isotope separation plant , but as the enormous scope of the effort became more apparent in 1942 , it became clear that 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 , and would have to be built in America . But at the same time that the British became convinced that a joint project was necessary , the progress of the American Manhattan Project was such that British cooperation seemed less essential , although the Americans were eager to utilise Chadwick ' s talents . The matter of cooperation had to be taken up at the highest level . In September 1943 , Prime Minister Winston Churchill and President Franklin Roosevelt negotiated the Quebec Agreement , which reinstated cooperation between Britain , the United States and Canada . As a result , Chadwick , Oliphant , Peierls and Simon were summoned to the United States by the director of Tube Alloys , Sir Wallace Akers , to work with the Manhattan Project . The Quebec Agreement established a new Combined Policy Committee to direct the joint project , but the Americans disliked Akers , and 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 , which he was not allowed to see . Observing the work on the K - 25 gaseous diffusion facility at Oak Ridge , Tennessee , he realised how wrong he had been about building the plant in wartime Britain . In early 1944 , he moved to Los Alamos , New Mexico with Aileen and the 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 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 project that Chadwick was committed to . 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 . Although he had more knowledge about the project that 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 in the New Years Honours on 1 January 1945 . 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 in April 1945 . He was present at the meeting of the Combined Policy Committee on 4 July when Field Marshal Sir Henry Maitland Wilson gave Britain ' s agreement to use the atomic bomb against Japan , and at the Trinity nuclear test on 16 July , when the first atomic bomb was detonated . Inside its pit was a polonium - beryllium modulated neutron initiator , a development of the technique that Chadwick had used to discover the neutron over a decade before . Later life . Shortly after the war ended , Chadwick was appointed to the Advisory Committee on Atomic Energy ( ACAE ) . He also appointed the British scientific advisor to the United Nations Atomic Energy Commission . He clashed with fellow ACAE member Patrick Blackett , 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 . In 1948 , Chadwick accepted an offer to become the Master of Gonville and Caius College . The job was a prestigious but ill - defined one ; 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 . Bauer was subsequently involved in what became known as the Peasants ' Revolt , in which fellows led by Patrick Hadley voted an old friend of Chadwick ' s off the council and replaced him with the younger Bauer . More friends of Chadwick ' s were removed over the following years . He retired in November 1958 . Over the years , Chadwick received many honours , including the Medal for Merit from the United States , and " Pour le Mérite " from Germany . He was made a Companion of Honour in the New Year Honours on 1 January 1970 for " services to science " , and went to Buckingham Palace for the investiture ceremony . He died in his sleep on 24 July 1974 . His papers are held at the Churchill Archives Centre in Cambridge , and are accessible to the public .