Robert Vivian Pound and the Discovery of Nuclear Magnetic Resonance in Condensed Matter
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This paper is based upon five interviews I conducted with Robert Vivian Pound in 2006–2007 and covers his childhood interest in radios, his time at the Massachusetts Institute of Technology Radiation Laboratory during the Second World War, his work on the discovery of nuclear magnetic resonance in condensed matter, his travels as a professor at Harvard University, and his social interactions with other physicists.
KeywordsNicolaas Bloembergen Felix Bloch William W. Hansen Martin Packard Robert V. Pound Edward M. Purcell I. I. Rabi John T. Tate Henry C. Torrey John H. Van Vleck Harvard University Massachusetts Institute of Technology MIT Radiation Laboratory Stanford University University of Buffalo Nobel Prize in Physics molecular beams nuclear magnetic resonance history of physics
As a student of physics and history of science I became particularly attracted to the history of nuclear magnetic resonance (NMR) from its beginnings in molecular-beam physics to its present ubiquity in chemistry, materials science, and medicine.
The first detection of NMR in condensed matter occurred just weeks after the end of the Second World War, independently and nearly simultaneously by two teams of physicists on opposite coasts of the United States. Of the six physicists comprising the two teams—Felix Bloch, William W. Hansen, and Martin Packard at Stanford University, and Edward M. Purcell, Henry C. Torrey, and Robert V. Pound at Harvard University and the Massachusetts Institute of Technology (MIT)—only Pound is still living. I met and interviewed him five times during the academic year 2006–2007 at the Cadbury Commons nursing home, north of the Harvard campus. I provide excerpts of my interviews below, especially as they pertain to the early history of NMR.
Pound: The Halicrafters radio receiver was a familiar thing to me because I was an amateur radio person who invested much of my youth in that. That is why I became what I became; that is how I learned about electronics. (I 3, p. 31)
Pound: I was very grateful to him [George Pake] once because he wrote me a long letter to tell me how much he appreciated me as a physicist and not as an electronics expert. (I 1, p. 9)
Pound: It was impressive that the Queen Mary came in and docked down at the army base in South Boston. It was an image that was a large part of our horizon when we looked out of our windows there, from Atlantic Avenue. It was quite illegal to mention it in the newspapers. (I 2, p. 14)
Pound: The whole radar program is almost identical to the NMR problem. Namely, in both cases you apply a driving signal and look for its aftereffects. In the case of radar, you look for echoes, backscatter from whatever it is that is out there. And in NMR you activate it by applying a large RF [radio-frequency] signal, and it may have a persistence in response which you can see later. (I 2, p. 15)
Pound: The equipment we used in the NMR experiment were just common parts of an electronics laboratory that you would have had at that time. (I 3, p. 8)
They carried out their experiments in a run-down shed adjacent to Jefferson Physical Laboratory, home of the Harvard Physics Department, using some of Harvard’s and some of MIT’s equipment, while working under a contract from the US Navy. They should have begun by using pulsed radar techniques but instead used continuous-wave radar techniques, because these were what they had used at the MIT Rad Lab.
Pound: It [physics] is a social phenomenon. I have often emphasized the fact that the MIT Radiation Lab had a tremendous impact on the future of physics because so many people became such close collaborators and friends during that period. They would never have met each other [otherwise]. As Purcell pointed out, he had no concept of magnetic resonance before getting into the MIT Radiation Lab. (I 5, p. 23)
Pound: My book is called Microwave Mixers.3 That is the thing which you [use to] convert microwaves into ordinary radio frequencies, that could be amplified by conventional technology. (I 2, p. 18)
During the early 1940s, Pound and his colleagues went for lunch daily to a delicatessen in Central Square, where he would be served his favorite Boston Cream Pie with ice cream for the same price as that day’s 40-cent Special. Pound called this “The Waitress Effect.” The delicatessan also made its own molasses bread, which he regularly took home to his wife Betty.
Pound: We were happy that we did not have to do the kind of high-vacuum work and so forth that the molecular-beam people had to do. That is why this was a great simplification of the whole game. The idea of magnetic resonance was already well established by those molecular-beam experiments. (I 2, p. 10)
Pound: [It] was something entirely predictable, and if it had not been the way it is, if it had not worked, it would have been completely our fault because everything about it was calculable. All we did was dig it out of the noise. It was just as it should be. Sure enough, it was there.
As Ed [Purcell] has sometimes said, if we had not been able to find [NMR in condensed matter] that would have been a catastrophe, because everything was clearly calculable, and there is no way it could have failed. Now the only way it could have failed was by what is called saturation; overpowered by the RF field, so the absorption can be wiped out by being saturated. We knew enough about it; we kept it at a level so that it could not do that. … We were pretty clear about what we were doing. (I 1, pp. 20, 23)
Pound: We used to do that kind of thing—work all night. We not only did that in that case [of NMR], but we were quite used to it during the war years in the Radiation Lab. (I 1, p. 21)
Pound: Van knew all about what we were doing. He was a major reference with a background in the area that Purcell and I were up to…. [Van’s] subject was essentially the knowledge of ions in paramagnetic media. So, NMR was sort of the epitome of that kind of thing. And so Van was the person who knew the most about paramagnetism in materials. (I 5, pp. 8–9)
Pound: We discovered that quantitative aspects to study were things like relaxation times and line widths.
When I started studying nuclear magnetic resonance in crystals, and in solids and so forth, I began studying line shapes and structures. I soon realized that the nuclear quadrupole moment could be exploited. (I 1, p. 23)
Pound: We were used to thinking in terms of Fourier Transforms of the signals we were applying in time, and looking at the frequency distributions and so forth. It is just like a lot of the kind of thing we did anyway, not just to do with magnetic resonance, but with radio reception, microwave signal reception. (I 3, p. 8)
Back in December 1945, on the West Coast, Felix Bloch, William W. Hansen, and Martin Packard detected NMR in condensed matter independently and almost simultaneously using a slightly different method.6 Later, after both teams had published their results, Bloch approached Pound at a cocktail party at the home of physicist J.B.H. Cooper on 72nd Street in New York City, asking if the Harvard group would like to file a joint patent on NMR with the Stanford group. Pound and his coworkers declined to do so, and in fact could not have done so, because the two groups had not collaborated in making the discovery of NMR in condensed matter. According to Pound, it is even possible that Rabi had told the Stanford group of the Harvard group’s achievement and this helped Bloch’s team to the discovery. In any case, the leaders of the two teams, Bloch and Purcell, shared the Nobel Prize in Physics for 1952 “for their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith.”7
Pound: If anybody had invented the whole subject, it was Hansen…. Hansen came to MIT [in the fall of 1941] and gave lectures for about three years on the foundations of magnetic resonance and in technical aspects of solid-state physics. (I 5, p. 20)
Pound has a fond recollection of Hansen’s lectures.
Most of my interviews were focused on nuclear magnetic resonance, but in one I asked Pound about his and Glen Rebka’s gravitational-redshift experiments.9 He recalled that he went down in mineshafts and up in the Empire State Building in search of a good location for them before settling on a shaft in Jefferson Physical Laboratory.
Pound has had a full life as an experimental physicist. While never formally receiving a Ph.D. degree, he invented a device called The Pound Box2; he did experiments on a nuclear-spin system at negative temperature;10 and he invented “frequency locking.”
Immediately after the war, Pound was elected to the prestigious Harvard Society of Fellows which, he recalled, was like a fraternity with scholars in such diverse fields as Irish history and literature, botany, English, and physics who came together socially in the evenings. Then, in 1948, he was appointed as an assistant professor at Harvard, where he spent his entire career. The first course he taught was on signal-to-noise, building on books in the MIT Rad Lab series such as Threshold Signals and Vacuum Tube Amplifiers.11 He served as chair of the Harvard Physics Department for eight years, occasionally having to deal with eccentric behavior, for example, when one of the laboratory teaching assistants painted the NMR magnets in bright colors and named them after the wives of Henry VIII. He recalled that he was known among the Harvard faculty for his opposition to Harvard’s core curriculum.
Pound: I have always felt that it was a little bit unfortunate that the world bases all of its history on political and military frontiers and so forth, whereas such a formative aspect of the history of the world should be based on the advances of technology…. People do not recognize how much various technical advances have changed the world. (I 5, p. 15)
Pound: So many of them [nuclear moments] had already been observed in other ways by the time it [NMR] came along, that there was never much effort made to extend it into that use as a particular application…. [Instead, NMR] revealed all kinds of things about the interactions among nuclei and of the nuclei with their surroundings in materials. So that is what dominated the applications for many years. (I 3, pp. 10–11)
Later, when NMR found an increasing number of applications in medicine, the letter “N” was dropped and the technique was renamed magnetic resonance imaging, or MRI, and as such has become known worldwide.
During one of my last visits to Cadbury Commons, a pianist performed Mozart’s A-minor Sonata for its elderly residents. Pound was seated in the front row. Other people hummed along with the music; some moved their fingers as if playing a piano; still others tapped their hands on their knees. I sensed that Pound could not enjoy the performance as others did, which was confirmed when he left the room during the slow, sad, second movement. Pound’s wife Betty, a niece of the renowned Danish composer Carl Nielsen, is a gifted pianist. Their house in Arlington, which was designed by Bauhaus architect Karl Coke and an associate, was built as a homage to music: the living room has a special corner to accommodate their 5-foot 6-inch Steinway piano. They used to invite scientists for musical evenings. Physicists Otto Robert Frisch, Victor Weisskopf, and others would play the Steinway during their visits, but Pound recalled that his wife Betty was never satisfied with the quality of their performances. Once, on a return visit to Frisch’s home in Cambridge, England, Pound met Frisch’s aunt, Lise Meitner, there.
Pound remembers people fondly, and he is a good conversationalist. He eases smoothly from one story into another, from anecdotes to technical explanations. He does not repeat himself much; his thoughts, however, sometimes take him down avenues related only obliquely to his scientific work.
I got the impression that Pound pursued his research—on NMR, the gravitational redshift, and much more—aggressively, but that he did not wholly center his soul on his physics. It might be said that his colleagues, his secretaries, and others who were involved in his research projects formed the backbone of his scientific universe. He was known as an extraordinarily precocious and gifted experimental physicist, but he does not speak about his experiments or scientific instruments with anything like the love he manifests for the uniqueness and timeless worth of the people in his life. He and his wife read The New Yorker “religiously,” he said, and they used to talk about the articles in it even before they were married.
On one of my visits, when I told Pound that I am fascinated not only by scientific facts but also by scientific stories—that stories were what attracted me to physics in the first place—he replied, with a twinkle in his eyes, “Good, good, good.”
I thank Roger H. Stuewer for his thoughtful and careful editorial work on my article.
- 1.Robert V. Pound, an oral history conducted in 1991 by John H. Bryant, IEEE History Center, Rutgers University, New Brunswick, N.J. USA, p. 3.Google Scholar
- 2.Ibid., p. 5.Google Scholar
- 3.Robert V. Pound, Microwave Mixers. With a chapter by Eric Durand. Edited by C.G. Montgomery and D.D. Montgomery [Radiation Laboratory Series, No. 16] (New York and London: McGraw-Hill, 1948).Google Scholar
- 7.Felix Bloch, “The principle of nuclear induction” [Nobel Lecture, December 11, 1952], in Nobel Foundation, Nobel Lectures Including Presentation Speeches and Laureates Biographies. Physics 1942–1962 (Amsterdam, London, New York: Elsevier Publishing Company, 1964), pp. 203–216; Edward M. Purcell, “Research in nuclear magnetism” [Nobel Lecture, December 11, 1952], in ibid., pp. 219–231.Google Scholar
- 8.Luis W. Alvarez and F. Bloch, “A Quantitativbe Determination of the Neutron Moment in Absolute Nuclear Magnetons,” Phys. Rev. 57 (1940), 111–122.Google Scholar
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