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Born in Bollington, England. Master of Science from University of Manchester, 1912. Thereupon he received a Research Student Fellowship, which led him to Berlin. There he worker with Geiger, whose famous Geiger counter Chadwick employed, within a few months of arriving, for an important discovery concerning the beta radiation spectrum, at age 23. This discovery was doubted by almost all physicists but (Rutherford and) Einstein, who found the discovery quite important and enigmatic, after Chadwick explained it to him in German. Chadwick was interned months later, after the start of WWI, throughout which 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 examined, among other things, German radioactive toothpaste.

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 the charge of a nucleus is equal to its atomic weight, ie. that protons exist. He discovered the neutron in 1932, after a search lasting eight years, and, largely for this achievement, would always be known as the ideal experimentalist ; Madame Curie's daughter might have preceded Chadwick in this, but she incorrectly interpreted her results. This discovery, while immediately seen to be important, has been particularly underrated from the standpoint of its timing, since subsequent history may have been quite different had the neutron been discovered even a year later than it was. Had the resultant subsequent

breakthroughs in nuclear physics, such as the creation of the first chain reaction, been likewise delayed even a year, the A-bomb might havebeen ready for use, not in August 1945, but in August 1946, too late to have been used against Japan. Without the memory of the horror of Hiroshima to deter war between the Soviets and the West, such a war probably would have occurred; one way or the other, such a war would have made the world a very different place than it is now. In 1935 Chadwick left Cambridge for the University of Liverpool, where he used his Nobel Prize money to buy a cycletron, and, after the start of WWII, he explored the possibility of building an A-bomb; his motivation was a concern that the Allies would be naked if Heisenberg etc. could build a bomb for Hitler.

After the outbreak of WWII, he was chief advisor to the group of British officials weighing the option of investing much of Britain's limited resources in development of an atomic bomb. His reputation in the U.S. for cautious judgement was such that, when his"MAUD Report" reached the U.S., the report persuaded administration officials of the feasibility of a fission device even before Pearl Harbor. As the British official history later put it, in Spring 1941,U.S. officials "urged that Chadwick, with his great prestige, should go to America. 'Send Chadwick' was the call from Washington --a call that was to be repeated to great effect in 1943". H.M. Government prefered to retain Chadwick to keep alive the native bomb program in the U.K., a decision later regretted; by the time Chadwick arrived in the U.S, the need for his expertise and stature had become less desperate.

Chadwick After

After the U.S. economy geared up to a war footing, the gap between U.S. and U.K. resources was such as to make the U.S. the clear senior partner, so the Manhattan Project was placed under the direction of U.S. General L. Groves, who was obsessed with the fear that the Axis might learn of the project. In the meantime, Chadwick was considered by H.M. Secret Service to be the physicist most likely to be able to persuade Niels Bohr to flee Nazi-occupied Denmark, so it was a message from Chadwick which was smuggled to Bohr, who managed to escape to Britain in the fall of 1943, thereafter coming to the U.S. to work with Chadwick, who had been sent to the U.S. as head of the U.K. delegation of scientists for the bomb project.

Chadwick had authority over all non-American
scientists in the project, (except Bohr) all of whom were desperately needed, because, as Groves put it, the small number of qualified atomic scientists in the U.S. meant that "we could not afford not to use everyone possible." It was Chadwick's job to persuade them to tolerate Groves' "dictatorial" rush to build a bomb at all costs, with no leaks of the secrets of the project ; Chadwick's stature as a Nobel laureate was indispensible for this task.
His expertise and apolitical bent won Groves'
confidence that Chadwick's reports from Los Alamos would be more reliable than those delivered by leftists like Oppenheimer; his loyalty not in question, Chadwick could persuade Groves to modify his tight-security policy somewhat, particularly respecting 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