James Chadwick The Nobel Prize in Physics 1935


Chadwick (1891-1974) was born in Bollington, 18 miles from Manchester, England; son of a cotton spinner, and thus raised on meager means. Being the best science and math student in town, he won scholarships to the University of Manchester. He intended to study math, but entered physics line by mistake in 1908, and ended up with a Master of Science, 1912. Thereupon he received a Research Student Fellowship, which led him to Berlin. There he worked with Geiger, whose famous Geiger counter Chadwick employed, within a few months of arriving, for his first important contribution to physics, one concerning the beta radiation spectrum. This discovery resulted in his most significant encounter with Einstein, in 1914, at the Reichsanstalt near Berlin. ..... Chadwick had been working in Hans Geiger's laboratory to determine the status of beta-particle emissions. Before Chadwick had turned twenty-three years old, he would publish a paper on how he was able to determine that there was a continuous beta spectrum (but "up to a certain limit") rather than a set of discrete lines, as had been heretofore accepted, due to work by Meitner and Hahn; this discovery, would have given him a place in physics history had he done nothing thereafter. Other physicists would miss its significance, but not Einstein. That Spring, he visited the lab to hear Chadwick explain in German his findings, at which time Einstein responded "I can explain either of these things, but I can't explain them both at the same time," referring to the spectrum vs. the "certain limit." This discovery has been called a "turning point" in modern physics (see Burton Feldman letter below).

Months later, after Britain declared war on Germany, Chadwick was interned as an enemy alien in racehorse stables west of Berlin; throughout this ordeal he suffered from malnutrition, leaving him in poor health for much of the rest of his life. The Germans did allow him to continue his research, and he employed, among other things, German radioactive toothpaste! Besides, he did thus escape the fate of many in his generation, who had to endure the horrors of trench warfare; he would feel some guilt for gaining this bit of luck, such as it was. ....

Liberated after the 1918 armistice, he was swiftly hired by Rutherford at the Cavendish Laboratory, Cambridge. There Chadwick succeeded in proving the correctness of Rutherford's theory, that an element's atomic number is equal to the charge of its nucleus, ie. that protons exist. He received his Ph.D. in 1921, and that year brought his second major contribution, when he and E.S. Bieler determined that some "strong force" holds the nucleus together, a force distinct from the electromagnetism which had been up until then presumed to be achieving this holding effect; the search since WWII for a "theory of everything" tries to account for the relationship between this force, "the weak force," gravity, and electromagnetism. This achievement is considered one of the few dozen milestones in the history of quantum physics. (Again, see Feldman letter) ....

In 1923 Chadwick was named Cavendish's (first ever) Assistant Director of Physics Research, becoming the de facto Director as Rutherford aged. In 1925 he married Aileen Stewart-Brown, daughter of a prominent stockbroker on the Liverpool exchange; in 1927 were born twin daughters, with Chadwick earning a reputation as a committed father, balanced with his growing responsibilities to science and society. After searching eight years, and, in 1932, "working day and night for three legendary weeks," (as put by the official historian of the British Atomic Energy Authority) he discovered the neutron in 1932, and, largely for this achievement, would always be known as the ideal experimentalist; this discovery is generally considered to be one of the 100 most significant events in the history of science, and made Page One of the New York Times. Madame Curie's daughter might have preceded Chadwick in this, but she incorrectly interpreted her results. (see Special Section "Significance of a Discovery of Neutron in 1932, later" below.) He was renowned, with all at Cambridge who assisted him, for being meticulous in sharing credit for this achievement. He obtained a patent for this discovery, but would allow governments and universities use the neutron for free, but his estate gets a penny for every 1020> neutrons used by commercial reactors to create fission. As it was, this discovery is understood to have transformed physics, since subsequently, protons and neutrons came to be seen as being held together by a newly understood force, the Strong Force. ....

His Nobel Prize was presented only three years after the discovery which it honored; only a handful of physics Nobels were ever awarded so soon after the feats for which the Prizes were earned. The family's trip to Stockholm for the ceremony, as one might expect, put all members "in a state of high excitement." In 1935 Chadwick left Cambridge for the University of Liverpool, where he used his Nobel Prize money toward buying a cyclotron. This machine, invented at Berkeley, U.S.A. by his friend, Ernest Lawrence, could accelerate sub-atomic particles much faster than was heretofore possible; Chadwick hoped that this device, ready in July 1939, might facilitate efficient reduction of tumors. Neutron therapy against cancer was always close to his heart, a fact verified to us at Outstanding Awards by his daughter Judith in a March 2000 letter. He already was, as of February 1938, one of a six-man Liverpool Cancer Commission.

After the start of WWII, he was asked, by the Secretary of the U. K. Department of Scientific and Industrial Research, to explore the possibility of building an A-bomb; Chadwick thus became chief scientific advisor to the group of British officials weighing the option of investing much of Britain's limited resources in development of a Bomb. He would work on Bomb-related matters for the rest of the war, initially under unheard-of conditions by contemporary scientific standards. .... While Einstein deserves to be seen as the great-grandfather of the Bomb, (owing to e=mc2) Chadwick should be seen as the grandfather or (according to "How the Bomb's creator learned to love the United States," a British review of Dr. Andrew Brown's major biography of Chadwick, The Neutron and the Bomb) the father; Oppenheimer, known in the U.S. as the father of the Bomb, would have remained unknown but for Chadwick's MAUD Report , before which, Oppenheimer later conceded, the U.S. program was a series of desultory committees (which could not make a case to FDR sufficient to persuade him to authorize the massive expenditure required to bring the Manhattan Project to fruition). As pointed out by the "Manhattan Project" page of the web site of the American Museum of Natural History in New York's Einstein exhibit, Einstein was excluded from the Project due to security concerns arising from his Leftist views, so his famous1939 letter to FDR would be the extent of his contribution to the Project; probably Einstein's love for interacting with the media also increased the security risks of his possible inclusion. (His Nobel Prize and other important objects are being exhibited in conjunction with the Hebrew University of Jerusalem.) Actually, even this Einstein contribution is overrated; this 1939 letter led only to the formation of a Uranium Committee chaired by a bureaucrat, Lyman Briggs, whose knowledge of physics would be quite inadequate. Moreover, the venerable McGeorge Bundy agrees with ace American physicist Arthur Compton that "things would have gone faster if Einstein had never written ..." to FDR; this view owes to the fact that the U.S. uranium committee, set up by FDR after Einstein's letter, valued security over scientific progress, and thus excluded foreign-born physicists, including Einstein, and led native-born physicists to presume that all that could be done was being done. . All in all, British contributions to the Manhattan Project are not given their due in the U.S., as far as British writers are concerned; this much is conceded by Ferenc Szasz of the U. of New Mexico, who, in British Scientists and the Manhattan Project, argues that the significance of this contribution was matched only by the significance of 1): U.S. money, 2) Oppenheimer's ability to inspire, and 3) Project commander Gen. Leslie Groves' drive. The only U.S. statesman to give the British their due was Bundy, particularly in his chapters on "How the Americans Went First" and "The Americans and Their Wartime Allies" in his book Danger and Survival: Choices about the Bomb in the First Fifty Years, which makes fascinating reading; these chapters would be worth reproducing in full here were this web page not devoted so specifically to Chadwick, who Bundy called "preeminent among British nuclear physicists" in WWII. The only major aspect of Chadwick's reputation not referred to by Bundy was Chadwick's ability to set an example as a team player who avoided fame

Few stories, esp. in the history of science, combine such high stakes with such dramatic appeal. In what were up to that point the Experiments of the Century, Chadwick would research this Bomb issue in spring 1941 using his cyclotron, while his city, Liverpool, and indeed his Physics Department, were being hammered by the Luftwaffe; in one week 3,000 became casualties and more than 70,000 became homeless. The cyclotron was in the basement, and managed to avoid being hit. Occasionally he would step outside after a German bomb raid to check the city with a Geiger Counter for radioactivity, in case Hitler had already learned how to weaponize uranium. Important though his work was, resources in a Britain under siege were so scarce that he had to fight with the Ministry bureaucracy to get enough funds to be able to afford fuel to travel to even a town near Liverpool, in order to confer with personnel producing weaponizable uranium. He and his wife would move from Upstairs to sleep Downstairs, for safety's sake; the raids were so frequent that the Chadwicks stopped going to the bomb shelter, lest they get to do nothing else but go back and forth. Such conditions would make those encountered by physicists at Los Alamos seem to be blissful by comparison. Every night, the windows, and the cardboard which replaced them, would be blown out. (Their twin daughters had been sent to safety in Nova Scotia in July 1940.) . .... Of the other scientists involved in the U.K. Bomb project, the most experienced were not British citizens, so none could be given access to the big picture; thus Chadwick alone, in spring, 1941, became the first person with the burden of knowing, as he vividly recalled decades later, (in a passage often quoted in the literature about the Bomb, as moving a passage as any in the annals of science) that the human condition had reached a turning point:

"I remember the spring of 1941 to this day. I realized then 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 to action. And I had nobody to talk to. You see, the chief people in the laboratory were Frisch and Rotblat. However high my opinion of them was, they were not citizens of this country, and the others were quite young boys. And there was nobody to talk to about it. I had many sleepless nights. But I did realize how very, very serious it could be. And I had then to start taking sleeping pills. It was the only remedy, I've never stopped since then. It's 28 years, and I don't think I've missed a single night in all those 28 years."

.... His reputation in the U.S. for cautious judgement was such that, when, in October 1941, his "MAUD Report" on the Bomb's feasibility reached President Roosevelt, the report persuaded FDR to authorize the Manhattan Project even before Pearl Harbor was attacked; before FDR received this Report, Oppenheimer would later admit, the U.S. Bomb effort had floundered, despite Einstein's famous 1939 letter to FDR (see Special Section "Alerting FDR to Bomb's Feasibility," below). Suffice for now to say that the trust which Allied statesmen were putting in Chadwick and other physicists, to accurately assess the prospects of building a Bomb, was not matched by Hitler's (lack of) trust in his physicists, so that Churchill and FDR would authorize the unprecedentedly massive expenditures on and deployments toward such an undertaking, whereas Hitler would not. .... After the U.S. economy geared up for war, the gap between U.S. and U.K. resources was such that the U.S. was the clear senior partner, particularly since, as Mc George Bundy puts it, "the British at the political level were slow in understanding the difficulties in their own program in the year that followed the great intellectual achievement of the MAUD Report." Thus the U.S. effort became dominant, and the Manhattan Project was launched and placed under the direction of U.S. General Leslie Groves. Chadwick was viewed by H.M. Secret Service to be the physicist most likely to be able to persuade Niels Bohr to flee Nazi-occupied Denmark, so a message from Chadwick was smuggled to Bohr, who was thus persuaded to escape to Britain in the fall of 1943, thereafter coming to the U.S. to work with Chadwick, who was first sent to the U.S. in September 1943 as head of the U.K. Mission of scientists contributing to the Bomb Project, and as technical advisor to the U.K. members of the Combined Policy Committee which directed the Project. (He would return to Britain to meet Bohr, just escaped from Denmark, in late September, and then return to the U.S. in November.) As the leading figure in the MAUD saga, sending Chadwick made sense, but he had zero experience in international diplomacy strictly-defined, much less preparation for dealing with such a formidable person as Groves in such a crucial context as the Manhattan Project, the largest international scientific undertaking ever. His challenge was all the greater because of the decline in Anglo-U.S. relations after Britain had spurned the 1941 post-MAUD U.S. proposal for a joint Bomb Project; he would prove to be almost totally responsible for a startling improvement in this situation. .... Chadwick and wife set up residence in Los Alamos in January 1944, in a large log cabin, (one of the few with bathtubs) chosen for them by Groves; the daughters arrived from Canada in early summer. Generally, Chadwick spent most of his time in Washington, D.C., and other places where U.S. facilities and meetings were located, including in Chicago and New York. He had authority over all non-American physicists in the Project, (except Bohr) all of whom were desperately needed, because, as Groves put it, the small number of qualified experimental physicists in the U.S. meant that "we could not afford not to use everyone possible." It was Chadwick's job to persuade them to endure Groves' "dictatorial" rush to build a bomb at all costs, with none of the leaks of project secrets so feared by Groves; Chadwick's stature as a Nobel laureate was indispensable for this task. His expertise and apolitical bent won Groves' confidence, and Groves concluded that Chadwick's reports from Los Alamos would be more reliable than those presented by leftists like Oppenheimer; his loyalty not in question, Chadwick could persuade Groves to modify his tight-security policy somewhat, particularly as to Groves' desire to isolate physicists from engineers. Only Groves, his American scientific advisor, (not a Nobel laureate) and Chadwick would be privy to an overall perspective of the project, and thus of its various facilities across the U.S. Furthermore, as Groves later put it, "if Dr. Chadwick had been in charge of the British mission at that time [of Red spy Klaus Fuchs' joining the mission]...I am sure that no such deception [by Fuchs] would have been attempted." Such was Groves' trust in Chadwick that Sir James would thereafter be by far Groves' closest friend among the scientists; to Groves, Chadwick was "wholly straightforward and honest...a true gentleman." This confidence in Chadwick would result in his sway coming to pertain to, not just the foreigners, but almost the entire project; one student of the matter (in a review of Brown's biography of Chadwick) calls him "Groves' viceroy among the scientists." Chadwick's and Groves' friendship would be lifetime. .... To his scientific expertise he had to add diplomatic finesse, as when he managed to persuade his own government and French physicists of the error of their disputing Groves' veto of these physicists' wish to visit their homeland after the Liberation; the big secret did not leak to Hitler, and Chadwick got to see "his neutron" in action in the successful bomb test at Los Alamos. As described by William Lawrence, New York Times ace reporter, "Never before in history had any man lived to see his own discovery materialize itself with such telling effect on the destiny of man ..." Churchill, in his 6 August 1945 statement issued just after Hiroshima was devastated, would assess U.S.- British collaboration as follows: .

The smoothness with which the arrangements for cooperation which were made in 1943 have been carried into effect ... reflects great credit on all concerned - on the members of the Combined Policy Committee which we set up; on the enthusiasm with which our scientists and technicians gave of their best - particularly Sir James Chadwick who gave up his work at Liverpool to serve as technical advisor to the United Kingdom members of the Policy Committee and spared no effort ...

U.S. writer Stephane Groeff's 1967 book Manhattan Project (sponsored by Reader's Digest) would assert that "the contribution of the British mission was inestimable." .

..................................................... Post-WWII .... Chadwick flew to Britain in November 1945 to be knighted by King George VI, then returned to the U.S., representing the U.K. at the U.N. as both science advisor, and alternate representative, to the Atomic Energy Commission until summer 1946, when he tired of nuclear diplomacy and returned to Liverpool, only to return to the U.N. for two months early in 1947, before leaving the U.S. for good (see section below on visa rejection). He would continue to be a driving influence upon Britain's move to build a nuclear arsenal, succeeding in persuading the U.S. to honor its wartime agreement with the U.K. to share weaponizable uranium. He was named chairman of the new Royal Society Advisory Committee on the Nuclear Research Centre in January 1952. In 1948, he returned to Cambridge as Master of Gonville and Caius College, but later wearied of the politics there, leaving in 1958; it was during his Mastership at that Crick (with Watson) discovered the DNA double helix. He was offered the post of Vice-Chancellor of Cambridge, but declined for health reasons. Until his retirement in 1962, he continued to earn his reputation for being indefatigable by being immersed in the politics and diplomacy of nuclear weapons, serving as chair of the Nuclear Physics Sub-Committee of the U.K. Atomic Energy Advisory Committee, and as a member of the U.K. Advisory Committee on Atomic Energy. .... Chadwick preferred obscurity to glory, and refrained from public statements on the politics of the bomb; he held that such debates were for the public, not scientists, to dominate. However, after retiring, he did participate in interesting ways: in 1961 Pope John XXIII named him to join fifty-five others as a member of the Pontifical Academy of Science; this did not prevent Chadwick from joining 80 other Nobel Laureates' 1965 petition to the Vatican against the Pope's opposition to birth control. .... Chadwick can be said to have been the first, and greatest, scientist-diplomat Before Chadwick, science and statecraft were almost completely separate realms; after Chadwick's mission to the U.S., scientists would regularly be attached to diplomatic delegations in all conferences (esp. summit meetings) of real international importance. That his role has been so obscured is clearly due to the fact that his personal style was so opposite to the styles of Einstein and Oppenheimer, who enjoying the limelight; Chadwick's reputation with his colleagues for integrity, modesty, shyness and stiffness, was paralleled by a distant attitude toward the media, an attitude which almost certainly helped endear him to Gen. Groves.

.................. Significance of the Discovery of the Neutron in 1932, not later .... This discovery, while immediately seen to be important, has been particularly underrated from the standpoint of the significance of its timing, since subsequent history may have been quite different had the neutron been discovered even a year later than it was. The eventual invention of an A-bomb was inevitable, but its timing mattered greatly. Had the post-1932 breakthroughs in nuclear physics, such as the creation of the first chain reaction, been likewise delayed even a year, the A-bomb might have been ready for use, not in August 1945, but in August 1946, too late to have been used against Japan, which would probably have been conquered by then. As put by Kai Bird and Gar Alperovitz, in their assessment of physics' progress from 1905 (Einstein) through 1932 (Chadwick) to1938 (Fermi), .

It is rarely acknowledged that had this line of development not been moving at this particular rate we would never have gotten to ...the 1941 MAUD Committee report, and then to the Manhattan Project - to the point ... where large sums of money ... could have produced an atomic bomb by August 1945. .

.... The significance of this wartime first-use of the Bomb was described by Chadwick thusly: . It is ... fortunate that this weapon was developed during the war, firstly, because its development in time of peace would have occurred more or less concurrently in different countries and competition would thereby have been inevitable, and secondly, because the sufferings and havoc of the present war have branded into our minds the merciless nature of war and have made us long for peace as never before.

.... Without the memory of the horror of Hiroshima to deter war between the Soviets and the West, such a war probably would almost certainly have occurred, one way or the other, possibly with atomic weapons; the still-secret nature of this super-weapon (each superpower hiding Bomb-possession from the other until deciding to surprise the other with a devastating strike) would have had profound impact upon the strategic situation, with potentially fateful results. In the likely event that the U.S. finished building a Bomb before the Soviets, the U.S., in the event of war with the Soviets, would have faced a decision over Bomb-use even more momentous than that which Truman actually faced over Bomb-use against Japan, since he may or may not have been as confident of the lack of a Soviet retaliatory capacity as he actually was of the lack of a Japanese retaliatory capacity. At least the Soviets would have been less likely to miscalculate, had they produced a Bomb before the U.S. had revealed possession of such a device, in that their atomic capacity came (and would have come) partly from U.S. secrets delivered by pro-Soviet scientists working in the Manhattan Project almost from its inception; Soviet knowledge that the U.S. had a retaliatory capacity would likely have deterred the Soviets from striking first. In any case, such a war would have made the world a very different place than it is now.

James Chadwick was born in Cheshire, England, on 20th October, 1891, the son of John Joseph Chadwick and Anne Mary Knowles. He attended Manchester High School prior to entering Manchester University in 1908; he graduated from the Honours School of Physics in 1911 and spent the next two years under Professor (later Lord) Rutherford in the Physical Laboratory in Manchester, where he worked on various radioactivity problems, gaining his M.Sc. degree in 1913. That same year he was awarded the 1851 Exhibition Scholarship and proceeded to Berlin to work in the Physikalisch Technische Reichsanstalt at Charlottenburg under Professor H. Geiger. During World War I, he was interned in the Zivilgefangenenlager, Ruhleben. After the war, in 1919, he returned to England to accept the Wollaston Studentship at Gonville and Caius College, Cambridge, and to resume work under Rutherford, who in the meantime had moved to the Cavendish Laboratory, Cambridge. Rutherford had succeeded that year in disintegrating atoms by bombarding nitrogen with alpha particles, with the emission of a proton. This was the first artificial nuclear transformation. In Cambridge, Chadwick joined Rutherford in accomplishing the transmutation of other light elements by bombardment with alpha particles, and in making studies of the properties and structure of atomic nuclei.

He was elected Fellow of Gonville and Caius College (1921-1935) and became Assistant Director of Research in the Cavendish Laboratory (1923). In 1927 he was elected a Fellow of the Royal Society.

In 1932, Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. Chadwick in this way prepared the way towards the fission of uranium 235 and towards the creation of the atomic bomb. For this epoch-making discovery he was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935. He remained at Cambridge until 1935 when he was elected to the Lyon Jones Chair of Physics in the University of Liverpool. From 1943 to 1946 he worked in the United States as Head of the British Mission attached to the Manhattan Project for the development of the atomic bomb. He returned to England and, in 1948, retired from active physics and his position at Liverpool on his election as Master of Gonville and Caius College, Cambridge. He retired from this Mastership in 1959. From 1957 to 1962 he was a parttime member of the United Kingdom Atomic Energy Authority.

Chadwick has had many papers published on the topic of radioactivity and connected problems and, with Lord Rutherford and C. D. Ellis, he is co-author of the book Radiations from Radioactive substances (1930). Sir James was knighted in 1945. Apart from the Hughes Medal (Royal Society) mentioned above, he received the Copley Medal (1950) and the Franklin Medal of the Franklin Institute, Philadelphia (1951). He is an Honorary Fellow of the Institute of Physics and, in addition to receiving honorary doctorate degrees from the Universities of Reading, Dublin, Leeds, Oxford, Birmingham, Montreal (McGill), Liverpool, and Edinburgh, he is a member of several foreign academies, being Associ? oft he Acad?mie Royale de Belgique; Foreign Member of the Kongelige Danske Videnskabernes Selskab and the Koninklijke Nederlandse Akademie van Wetenschappen; Corresponding Member of the S?chsische Akademie der Wissenschaften, Leipzig; Member of the Pontificia Academia Scientiarum and the Franklin Institute; Honorary Member of the American Philosophical Society and the American Physical Society.

In 1925, he married Aileen Stewart-Brown of Liverpool. They have twin daughters, and live at Denbigh, North Wales. His hobbies include gardening and fishing.

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