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Interview of David Hill by Kenneth Ford on 1994 November 7,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Hill’s work with John Wheeler on fission dynamics in the late 1940s, and his collaborative work with Wheeler in 1949 on a paper that was to be co-authored by Bohr, Hill, and Wheeler (but appeared several years later without Bohr’s name on it).
David came to Princeton as a graduate student in September 1946 and left in June 1949, having finished his Ph.D. work except for some details on his thesis. He took up a faculty position at Vanderbilt, where he worked from September 1949 until June 1952. He spent the summer of 1950 at the Institute of Theoretical Physics in Copenhagen. There he and Bohr spent some time talking about nuclear physics, but mostly David served as an advisor to Bohr on a document that Bohr was working on, which became an Open Letter to the United Nations and in which Bohr argued for openness on nuclear matters.
David's Ph.D. degree was awarded in 1951. During his period at Vanderbilt, he began doing some consulting at Los Alamos. He recalls one trip to Los Alamos in December 1950 to work with Wheeler, and also remembers going up to Princeton from time to time to work with Wheeler there on the paper that was eventually published in 1953 under the title, "Nuclear Constitution and the Interpretation of Fission Phenomena." (He and Wheeler also gave a talk at an APS meeting in 1953 under the title, "Collective Model of the Nucleus.")
David's thesis was on a hydrodynamic analysis of fission. He used the liquid droplet model, pursuing dynamical features of the fission process. He carried out extensive calculations on the IBM SSEC at the IBM building in New York (and gained considerable public and press attention over this work, including a spread in Time magazine).
David does not remember any details concerning the draft paper written in 1949, which was intended to have, as its authors, Bohr, Hill, and Wheeler? — a draft that Wheeler carried with him to France in 1949. Nor does David remember the circumstances of Bohr's involvement in this draft paper. He assumes that Bohr and Wheeler corresponded regularly and saw each other from time to time before and during the period when this paper was being drafted (1948-49).
The papers of Mayer and Haxel, Jensen, and Suess that first made quite clear the independent-particle aspects of the nucleus were published in 1948. These must have triggered Wheeler's interest in uniting the liquid droplet and independent-particle aspects of the nucleus in what Hill and Wheeler later called the collective model and what Bohr and Mottelson called the unified model. David thinks that the term collective model was already in use by Wheeler in 1949, but he is not certain of this.
David can't remember whether the 1949 draft paper was focused mainly on fission or whether it concerned nuclear structure and nuclear behavior more broadly. He does recall that when he and Wheeler picked up this work again in 1950-52, there was an informal "pact" with Copenhagen that he and Wheeler would emphasize the vibrational modes of motion and the Copenhagen group would work on the rotational aspects. He notes that working with Bohr had some very positive features because Bohr was so prolific with good ideas, but that getting a paper out quickly was not in the cards in a collaboration with Bohr, whose style was very "deliberate."