Oral History Transcript — Robert V. Pound
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Interview with Robert V. Pound
Robert Pound; November 18, 2006The 50th anniversary celebration of the discovery of NMR. On NMR amplifier. On book, “Microwave Mixers.” Amateur radio in Pound’s childhood and later. Year spent in The Netherlands. On the prestige of Nuclear Physics. NMR magnets used. Dominance of NMR in Materials Science.
TranscriptSession I | Session II | Session III | Session IV | Session V
Pound:He [Purcell] said, if it had not worked, it would have been a bad show for what we understood, because everything about it was completely predictable from what we understood at the time. Most physicists of the era could have anticipated everything that happened. So, to call it [the detection of NMR] a discovery is kind of strange.
Pavlish:[In your article] You have a picture here of resonant the 30 Megahertz resonant cavity. This is the original one you used?
Pound:That is right.
Pavlish:It says it is held at The Smithsonian.
Pound:That is right. We borrowed it back at the time of an NMR reunion that they held in the 1990s. It was organized by Dudley Hirschbach originally. Dudley thought that there had to be some kind of ceremony celebrating the 50th anniversary of the detection of Nuclear Magnetic Resonance. It was 50 years after 1945.
Pavlish:Were the three of you there — Purcell, Torrey, and you?
Pound:We had Torrey come up from Rutgers in order to be present at that affair. There is a picture of Purcell, Torrey, and me. I guess it is in my bedroom at home now. There was a poster that came out for the celebration, and that picture of the three of us is on that poster.
Pavlish:In this paper from April 1st, 1948, there is a diagram of your experimental apparatus.
Pound:So complicated, yes.
Pavlish:This is complicated?
Pound:I was teasing.
Pavlish:I was wondering how much of this had been in place already in 1945.
Pavlish:You used the same apparatus in those first few years?
Pound:No, we fabricated the same things. They were commonplace things — nothing special there. There is an SCR radio receiver, a Halicrafter’s radio receiver, which formed one of the principal amplifiers for the signal. The detector at the far-end of it was put in after its previous use, which had been in a crystal test set that I had in my laboratory, at my desk in the Radiation Lab. My function in the Radiation Lab was testing and developing mixers for microwave receivers. I wrote a book called Microwave Mixers as you may know. This was used in the test set for operation. It belonged to MIT, or to the Radiation Laboratory. I brought it to Harvard in order to have it available when I was developing some other things. So I always say that I stole it from MIT. There was a cabinet in the room next to my office up on the third floor of Lyman Lab. I always say, I stole that from MIT. It was on a shelf in the back of a cabinet there. I would always say, “I stole that from MIT.” It was called a Halicrafter’s S-36. The reason it was special, is that it was designed before the war and it was an uncommon thing in those days because it was an FM radio receiver and FM radio did not exist. Halicrafters built special electronics for amateur radio people. That is why I had it. I acquired it to use in this test operation at the MIT Radiation Lab. Not only did I, but all the people who worked developing crystal mixers, like Henry Torrey, my co occupant of an office at MIT. He had one too, but I do not think he stole his. The other person who had things like that was Bob Dickey who went on to Princeton. 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. It was derived from my background in amateur radio. By the time I got to formal education in the field, like as a physics student, I was way ahead because I had done much more in my career in amateur radio, even by the time I was in high school. I attribute a lot of that background to my spending time with these people who ran a radio store in the basement of a house on the street where I lived. I lived in Amherst, New York. The township was Amherst, but my family had moved from the city to the suburbs. There were two villages. One called Eggertsville [sp?], the other called Snyder. Going East from Buffalo toward. Eggertsville was where a certain road crossed Main Street going east from Buffalo towards Albany. Snyder was where the Harlem Road crossed Main Street going east.
Pavlish:There was an amateur radio store on your street in Eggertsville?
Pound:Yes, and it became DIMAC radio. Dimac was short for the names of the two proprietors. One was called Tony Dibousky and the other was MacArthur. The person I was particularly fond of and knew there was called Larry Cane [sp?]. Larry Cane was the amateur radio operator. They had one of the most elegant amateur radio stations that I ever encountered, because they had all the materials and the parts and the machinery for making everything they needed. They had this big wooden relay rack full of the equipment for the high-powered amateur radio station there in that basement. I used to go there every day when I came home from high school. I would go down the street to DIMAC, and help them build things. They built their own transformers and they made their own quartz crystals and various things. They were quite technologically educated. That gave me a leg-up in everything that I got into later. I knew more about those things from that background than I ever learned in technical school.
Pavlish:Was it through that store that you became aware of amateur radio?
Pound:I first became aware of amateur radio through a friendship with my next-door neighbor on that street. He was what they call a short-wave listener. He listened to the radio. He was also a broadcast listener. They had a very expensive, fancy, multi-band radio set in his family. He could pick up these things on that. I had started building radio receivers on my own by this time. I was maybe 12 years old by this time. I started adjusting the radios that I built, in order to listen in on the short wave bands, listening to amateur radio things. Bob House, which was the name of my next door neighbor. Along with him, we started looking into getting amateur radio licenses. In those days you had to be able to copy Morse code. The main test for an amateur radio license was the Code Test. We went and took our code test exams in the spring of that year, in March or so. I failed the first test. The first test I ever failed, as far as I know. Oh, no, I also failed in motorcycling. I tried to get my license as a motorcyclist and my inspector did not like that it that I was so nervous in doing U turns in a narrow street. I tended to want to put my foot down. He failed me on that.
Pavlish:Did you retake that test to become a motorcyclist?
Pound:No, but I kept riding a motorcycle with my learner’s permit.
Pavlish:Was your friend Bob House your age?
Pound:He was three or four years older than I. I got to know Bob House when I went back into amateur radio. I discovered that he still operated. The trouble is, that that area of the city of Buffalo had changed its regional call letters. He was W8JPE. I was W8JKCH. I knew that he could not be an eight anymore because Buffalo had become a part of the same district as New York City, which is W2. I did not know if he could be JPE, because these call letters are always taken up, you see. But he did become W2JPE, so I got to know him again when I got back into this thing.
Pavlish:When was that? While you were still teaching?
Pound:I was at Harvard. It was in 1984. When I went to the Netherlands in 1982, my host there, Hendrik Tithard [sp?] was a very active amateur radio operator. PA0ZX. Zulu X-ray is the alliteration for understanding ZX. He would say in the European, or British manner, Zed. They say Zed in England of course. I said Zed also as a Canadian. PA0 is the prefix for Dutch radio. PA0ZX. I always think of that because I spent so much time calling on the radio “Papa Alfa Zero Zulu X-ray.” That is what I would say. An old friend. I think he is still alive. I visited him there in Kroeningen [sp?] which is in the north-east corner of the Netherlands. We spent a year there one year.
Pavlish:Do you have concrete thoughts on the relationship between theory and experiment in Magnetic Resonance, how the two interacted? This paper was a theoretical foundation for further studies, but it also summarized your experimental work. You have these really nice figures from your experiment. This one is especially nice.
Pound:That is “the wiggles,” as we called it.
Pavlish:Yes, it says here, “The wiggles occur after the magnetic resonance field has passed through resonance.” The wiggles are these?
Pound:It is a transient, because passing through the magnetic resonance produces an activation of the resonance phenomenon. The precessing signal beats with the continuing driving signal. That is what the wiggles are. It is a heterodyne beat.
Pavlish:This is the resonance here?
Pound:The first bump is the time it’s passing through, yes. The ones after that are because that activates the precession. Then that precession beats against the continuing driving signal, so you get the heterodyne beats between the two. Heterodyne beats, that means they get out of phase with each other as the magnetic field sweeps through one frequency compared with the other. The driving signal of course, stays at one frequency. But the precessing signal follows the magnetic field so it beats at different rates as time goes on.
Pavlish:What do you change in the apparatus to get the wiggles versus a clean signal?
Pound:Well, in order to avoid the wiggles, we had to transit that resonance quasi-statically; that is, very slowly. The signal damped out by the time we got to the frequencies where the beats would have been.
Pavlish:When you thought about magnetic resonance, how much did you think in terms of these images and how much in terms of equations? Was there a dominant mode of thought?
Pound:Well, I do not know. I think 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. So, it is just like the kind of thing we did anyway, not just to do with magnetic resonance, but radio reception and microwave signal reception. Microwaves are the same kind of thing, by the way. Radio behaves in the same way. You could get the beats of that kind of thing.
Pavlish:You could get the same kind of image?
Pavlish:Do you mean in radar?
Pound:Yes, you could produce that in radar.
Pavlish:What would you say if I present a historian of science’s take of magnetic resonance in the early days? What if I interpret it in the framework of scientific objects? The magnet, the oscilloscope, might be thought of as scientific objects, and you put them together in this way to form a congregate scientific object.
Pound:The equipment we used in the NMR experiment are just common parts of an electronics laboratory that you would have had at that time. In that era you had oscilloscopes; you had magnets. Well, magnets were the objects that were more special. The magnet that I used first was built back in the 1930s or first had been used by a man named Ivan Getting [sp?], who just died last year, by the way. He was at Berkeley in California, in recent years. He was the director of an organization supported by the United States Air Force. Its main purpose was to support people working in electronic communication.
Pavlish:He had used this magnet in his own work and then he gave it to you?
Pound:He did not give it to me personally. No, it was left behind. He had gone off to MIT during the war years and it was something that he used. Actually, I think it kicked around in the lab before him anyway. It was a little electromagnet with an iron frame. I built a bigger magnet. I built a permanent magnet. There had been a permanent magnet that Purcell had built. There was a former student of his who went to Berkeley, later. He used this permanent magnet in his thesis with Purcell. Then, I built a bigger one. Also, I had three other ones built for the teaching laboratories at Harvard. Those permanent magnets were made by Indiana Steel; I think they called themselves, a company in Indiana I guess it must have been who manufactured them. In those days, the principal source of permanent magnetism was an alloy of Iron, Nickel, Cobalt, Cadmium, and some other things. They later went into the business of selling magnets. When I first wanted to make a magnet of this kind, they would not make it and magnetize it themselves because they would not trust themselves. They thought that it would decay, that it would not hold. They were wrong. We already knew that these magnets could be magnetized and demagnetized without any problem. So, we got into the business of making them. These magnets are still kicking around at Harvard. There are some in that storage space associated with the teaching laboratories. I thought that Nuclear Magnetic Resonance would be a way (with the background that I had, with my particular expertise being in the electronics world) it would let me get into Nuclear Physics. But the word ‘nuclear’ never really worked out that well because the nuclear aspect was already satisfied. One of the ideas is that you can measure and observe the nuclear magnetic moments of various nuclei. But, so many of them had already been observed in so many other ways by the time it came along that way, that there was never much effort made to extend it into that use as a particular application. You had to have access to the place that produced these special isotopes. That meant cyclotrons and other types of accelerators in those days. So, it never really got exploited in that way. By that time the nuclear aspect had been forsaken. It turned out to be a much more rewarding way of studying Materials Science. It 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 in the beginning. I was somewhat disappointed that it did not give me a leg up in nuclear physics which was the frontier of physics at that time. I never got much profit from that.
Pavlish:Was it Rabi who named the technique ‘Nuclear Magnetic Resonance’?
Rabi had started it in the sense of doing it in atomic and molecular beams, yes. His group included Ramsey and a lot of people. In fact, Henry Torrey had been a student of Rabi’s and did his thesis work on nuclei of some kind at Columbia.