Oral History Transcript — Dr. John Carpenter
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Interview with Dr. John Carpenter
John Carpenter; December 17, 2008
ABSTRACT: In this interview, John Carpenter discusses topics such as: his graduate school work in nuclear engineering; his early professorship at the University of Michigan; going to the Reactor Testing Station in Idaho to learn about neutron scattering; beginning work at Argonne National Laboratory; developing the first-ever pulsed spallation neutron sources equipped for neutron scattering, ZING-P and ZING-P'; development and implemention of the intense pulsed neutron source (IPNS); becoming an advisor at Oak Ridge National Laboratory; spallation neutron source (SNS); his retirement; slow neutron scattering; Motoharu Kimura and winning the Clifford G. Shull prize.
TranscriptSession I | Session II | Session III
Westfall:This is Catherine Westfall. I'm speaking with Jack Carpenter. It's the 17th of December 2008. We're at the Guest House at Argonne National Lab. So what I would like to ask you, Jack, is to start with first how you got to the University of Michigan, and then how you got from there to Argonne, and then step us through the ZING series and how that became the Intense Pulsed Neutron Source (IPNS).
Carpenter:How did I get to the University of Michigan? I went there as a graduate student. I started my college education at Penn State in 1953 where I began in mechanical engineering so that, like my dad, I could design airplane engines, the kind with pistons that I've always loved. After the first semester, I had a very high average and I examined out of the usual math course (but didn't substitute another math course, although I probably should have.) But the good grades put me into an experimental curriculum called Engineering Science in which those running the program, Warren Wilson and Jack Mentzer chose 25 top students to enter a special program together. The curriculum was heavier on sciences than on the engineering, heavy on math, heavy on physics, not so much on chemistry, some engineering electives. So that was the atmosphere at Penn State, and I managed to excel, even though semester to semester I kept telling myself, “Oh my God, I survived the last one. I have to really buckle down for the next one.” I came out well: some of my classmates said that it seemed to them that only I understood everything. In the senior year, I took an elective course in nuclear engineering, which was really in a very primitive state at that time as education goes. Alan Jacobs, who had studied at Oak Ridge National Laboratory, led the course. It was an elementary nuclear engineering course that probably evolved from the Oak Ridge School of Reactor Technology and it fascinated me. It came time to decide what I would do with myself. I had always intended to go to graduate school, so Al said, “You should go to Michigan because there's a great teacher who joined the Nuclear Engineering program there and used to teach at the Oak Ridge school. His name is Dick Osborn. You should go to Michigan.” I applied, received a three-year fellowship from the Oak Ridge Institute for Nuclear Studies, and went to Michigan in the fall of 1957. That's how I got to Michigan. There, I was always breathlessly working toward the next semester, thinking, “Oh my God, I survived that one, I really have to buckle down ….” I did reasonably well except for one period when my personal affairs went awry: A girlfriend not very committed to the relationship that I ended up marrying anyway. That’s another story. We had four wonderful children, though the marriage, not made in heaven, didn’t last.
Westfall:That was just the prelude to marrying your current wonderful wife.
Carpenter:Yes. That earlier marriage was an important learning experience. I loved her, but she didn't seem to understand that. I spent some time in depression, but that’s getting ahead of our story. At any rate, I did reasonably well in my studies. I started out thinking I would become a theorist because I really liked math. I was pretty good and took math or mathematical physics courses every semester except my first semester at Penn State. So I was aiming for being a theorist. After my course work I hooked up with a mathematical physicist named Paul Zweifel. He had the idea to take part in a neutron scattering instrumentation program that was forming up around the nuclear reactor at Michigan, which was just in formation when we first arrived. It was one of the Atoms for Peace reactors, the 2-MW Ford Nuclear Reactor.
Westfall:What year is this?
Carpenter:This is 1957.
Westfall:Okay. That makes sense, because the Atoms for Peace, I think, was '55 and '56; they had the big meetings.
Carpenter:A lot of small reactors were built in those days. So there was a faculty initiative to build up an experimental program in neutron scattering around the Ford reactor, and Paul Zweifel managed to get a grant from the AEC (now the Department of Energy) to build a 4-rotor neutron chopper spectrometer. Paul was a theoretical physicist, but he didn't know much about practical things. I was to be the theory guy on the team, and there were a couple of other students who were to be the practical people and eventually carry out scientific measurements. About that time, the department hired a real experimentalist, Dietrich (Dieter) Vincent, to the faculty. It turned out that the student experimentalist-designate on the spectrometer was Ed Klevans, a very good friend of mine I had known from Penn State, who came to Michigan at the same time and with the same scholarship as I. He was my roommate during the early years in Ann Arbor. Ed was supposed to be the experimentalist, designer, and so on, on the spectrometer project. He stuck with it for a little while, but I don't remember when he decided that this was going to take too long. He wanted his degree and to get out of there. So he changed his field of study, became a plasma physicist, and went off in that direction.
Westfall:At that time, what did you consider your field to be?
Carpenter:I was having problems defining myself. I thought I was an engineer. I came out of an engineering family where topics at the breakfast table were engines and stuff, how things work. I came out of high school with an inclination this way. In 1952 I wrote a high school English paper on Peaceful Uses of Atomic Energy. I think I still have a copy of it. So now you see, it's not only an engineering and nuclear inclination, but peaceful uses. Somewhere along the line, I made a vow that I was going to work on peaceful applications of nuclear phenomena and never take a job on weapons systems. Anyway, I began to work on this chopper spectrometer that Paul Zweifel had a grant to build and, maybe by default, became the designer and builder.
Westfall:Now, what would this spectrometer have been used for?
Westfall:Part of what I'm pushing at you here is that you have something related to materials science that starts to come together at this time, with nuclear engineering being one of the threads and metallurgy being kind of another.
Carpenter:That’s right, materials science, but not necessarily metallurgy.
Carpenter:Neutron scattering is an interesting, very general business, devoted to fundamentals of materials science, taken broadly.
Westfall:Neutron scattering, what kind of materials? Was it condensed matter or what used to be called solid-state physics?
Carpenter:In those days, neutron scattering focused mostly on basic physics questions.
Westfall:So it would have been what they called at the time solid-state physics? Possibly?
Carpenter:Maybe, but we didn't think of it that way.
Westfall:You just thought of it as physics.
Carpenter:It was science and materials. As well as physics, thinking of a general term, we could say that we belonged in the Materials Science Department of the University. They had such a department.
Westfall:It was coming together at this point, the whole notion of materials science.
Carpenter:The focus of the neutron scattering research at the time was really basic physics. Fundamental science always on the material side. Where was I? Ed Klevans decided he would go off and be a good plasma physicist, and Paul Zweifel said, “Now, Jack, you become the experimentalist.” So I took it up. Somewhere in there we began to buy equipment, and we bought some very fancy rotating equipment, choppers that had been designed by Peter Egelstaff while he was at Harwell Laboratory in England. We ordered some these of these, they were on their way, and I had to learn to maintain them. So I went to Canada for a month where they had a chopper spectrometer of the type that was built up with these choppers, and I learned how to run them and maintain them and came back. They were delivered, we built a spectrometer, and we began to work with it. Dieter Vincent directed the program and became my PhD thesis advisor.
Westfall:And this spectrometer would have been used with a research reactor?
Carpenter:Yes, it was a 2-megawatt research reactor, the Ford Nuclear Reactor. It wasn't really a very hotshot spectrometer as an inelastic scattering instrument goes, but as a part of the instrumentation program that the department had undertaken, it was one of the types to be built. John King was a very close colleague. He built a triple-axis spectrometer that was used for spectroscopy and was the traditional instrument for many research purposes, especially single crystals. Everybody loved triple-axis spectrometers, invented by Bertram Brockhouse, for which he was the Nobel Prize winner in 1994. So we worked in this field, and I made it the topic of my doctoral thesis, basically just to analyze its performance having built it. I wouldn't say my thesis is any kind of hotshot thesis. They certainly tolerated my writing, whatever I would write, and they said, “Okay, you're a doctor.” I don't know how many events you would like me to include in this interview. [Chuckles]
Westfall:We can do a second part of the interview next, so say everything you want.
Carpenter:There are funny stories I recall. Before my preliminary exam, which was about the time when I had this personal disappointment, I didn't study for the prelims at all. I didn't really get the grade that they expected me to get. They expected me to do better. I didn't do particularly well, but didn't turn out to be total buffoon either, so they let me take the oral exam, and it was a pretty thorough exam. Four or five faculty members questioned me for hours. At the end, Paul Zweifel said, “Please write Poisson's equation,” a well-known equation in mathematical physics. And I did. And he said, “There's something fishy about that.” I was very much taken aback: I looked at the blackboard at what I had written and it looked like Poisson's equation to me. So he let me stew. The people in the examination room were silent and let me simmer for about five minutes. Zweifel said, “That's okay. ‘Poisson’ means fish. Please go outside.” He meant in French, of course. Well, I knew that Paul Zweifel had supported himself teaching French as graduate student at Duke. I should have thought of this, but I was too serious to take that into account and recognize his joke. They let me in after a bit and said, “Okay, you passed. Go on.” He was justified to pick on me. Although I passed the German language exam that was required as a graduate student at the time (I passed the German exam with flying colors), I was not very good at French. I passed the French exam, but not with flying colors. So I should have known. I still can't speak much French. In the end Dieter Vincent became my thesis adviser because Paul Zweifel was no experimentalist; he's a mathematical physicist of considerable reputation. Anyway, Dieter was a real physicist, and an experimental physicist, so that was a good alliance. He let me do whatever I pleased. He is a very nice man. He's still among us, and we see each other once in a while. I finished my degree. I didn't know what I was going to do. After the spectrometer was built and operating and we began doing measurements, it was a natural thing to apply for a post-doc at the Institute for Science and Technology at the University of Michigan. The central building of that Institute was across the street from the Phoenix Memorial Laboratory where I worked — I didn't have to move my office. I stayed there and ran the spectrometer and began to gather a little research group and had some graduate students hanging on. The post-doc went on for a year, and there was an opportunity to apply for a faculty position, so I did. I was allowed to join the faculty as an assistant professor. My duties then were to teach introductory nuclear engineering courses and run the Nuclear Reactor Laboratory course, NE 445, which I had inherited. I had taught this a couple of times as a graduate student and a post-doc and made it into a fantastic course. It was offered twice a year, maybe sometimes also during the summer. I really enjoyed doing that course. I worked those students to the bone, the intellectual and sometimes physical bone. We all had fun, and the experience helped connect the students to their theory courses. We always did something new, invented some new experiment to do on the reactor or a reactor-related subject. It was my main course the whole time that I was a professor there. One of my doctoral students, Ronald Fleming, helped me in essential ways as my teaching assistant in NE 445, and we worked together in a collaboration that has lasted many years. From time to time, I taught the introductory Nuclear Reactor Theory course and Glenn Knoll’s Radiation Detection course, from which I learned a great deal. Also, I enjoyed a close collaboration and personal friendship with Louis Hamilton, who joined the NE faulty from UC Berkeley. We devised some pool boiling and flow boiling experiments for the Reactor Laboratory course. I had graduate students, some of whom did work on the spectrometer, which we converted into a 2-rotor diffraction instrument because, as a spectrometer, it wasn't going to make many marks, but it was pretty effective as a diffraction instrument, providing access to higher wave vectors than was available in those days, a range that is still respectable. The DOE bailed out, having supported this as a spectrometer until the NSF picked it up. So I worked with the NSF. Half my students did reactor physics for their thesis and half did neutron scattering. As a young professor, I took on what, at the time, were some of the older students, senior to me but still working on their degrees. My first student was Wayne Lehto. He did an experiment with reactor noise, which was an interesting phenomenon that was of current interest at the time. He went to work for Argonne National Laboratory, Argonne West in Idaho, and retired a few years ago.
Westfall:Did any of the professors from the Michigan Physics Department work on that research reactor?
Carpenter:I won't say that none did because there were activities there that I was not aware of. Among more pure physicists was a colleague of mine, actually a cohort in grad school, Sam Werner. He did fundamental neutron physics work on a beam that he had developed there, working with Tony Arrott and Al Overhauser, physicists at the Ford Scientific Laboratory. They did real physics, fundamental stuff: dynamical neutron diffraction studies, perfect-single-crystal interferometry. Sam has made a big name for himself with very clever interferometry work. I must mention that during the time that I was a graduate student and later, we had a long-running series of seminars on neutron scattering. Zweifel and Vincent. And John King, who was very close during my student years and as a professor colleague. He's the one who built the triple-axis spectrometer. He also built a double-axis crystal-based diffractometer. So we had quite a number of neutron scattering instruments that John King had taken up with the crystal-based instruments. Chihiro Kikuchi was a materials physicist from the nearby Willow Run Laboratory who came into the faculty because of his outstanding reputation. (Some say that Kikuchi narrowly missed a Nobel Prize for his work on Microwave Amplification by Stimulated Emission of Radiation, the Ruby MASER.) Along this line, I had for a while, with one of my students, David Mildner, a collaborative program with Ed Hucke, of the Materials Science Department, we studying the structures and he preparing samples of glassy carbon. I still have frequent collaborations with David.
Westfall:Brought him into the nuclear engineering faculty?
Carpenter:Yes. So these were key people. Another who joined the growing faculty was George Summerfield, a theorist. We became close friends. George worked productively with John King on small-angle neutron scattering using instruments elsewhere. Kikuchi and Summerfield also took part in the neutron scattering seminars.
Westfall:So there's an interesting overlap there between physics and nuclear engineering in materials science.
Carpenter:Now that you mention it, this was no engineering department. I was the only person on the faculty except one who even had the least idea what a heat exchanger did. At Penn State, I had learned how to design heat exchangers and had a summer job at Westinghouse Bettis Atomic Power Laboratory in Pittsburgh, where I worked on fluid flow and heat transfer problems. I was the only engineer except for Fred Hammitt, a mechanical engineer who had a half-time appointment in the NE department and a half-time appointment in the mechanical engineering department. Fred knew about heat exchangers and more, and directed a respected program of research in heat transfer, fluid flow, and cavitation. I served on some of Fred’s students’ doctoral committees. This is just an example of something that nuclear engineers should know about. But hardly any of the people in the department knew anything about heat transfer, which is basic to power plant engineering.
Westfall:So most of them were really material scientists, is what you’re saying.
Carpenter:This was more an applied physics department; it was not so much a nuclear engineering department.
Westfall:It was just so called.
Carpenter:We gave a lot of attention to reactors, of course, but not so much attention to reactor plant engineering. Of course, there was some, but it was really an applied physics department. Materials science and neutron scattering fit well into nuclear engineering because nuclear phenomena, calculational techniques, and radiation detection are fundamentally important to both fields.
Westfall:And because you had had so much physics in your training, you fit there.
Carpenter:I've always been curious how things work. It's natural to me to ask how things work. I understand how things work up to a point. If I had really studied about it, I'm ready. It's natural to me. How do things work? Yes, that’s me. This neutron scattering seminar went on for years and met every couple of weeks. Students and faculty would prepare presentations and deliver them to those present for discussion, and the students would flow through and get degrees. New people would come. It was the basis for a neutron scattering concentration in the department. Real science. Not that we were a particularly outstanding group; we weren't recognized, really. We taught ourselves pretty much without connection to earlier famous workers in the fields of neutron scattering and materials science. Here’s a good place for me to admit that the teaching experience and my years on the NE faculty were my most intense learning experiences. I firmly believe that teaching is the best way to learn.
Westfall:It's this kind of background; I can see looking ahead, which allows you to build, to know what kind of instrument to build for physicists.
Carpenter:Yes, because I knew what they would be used for.
Westfall:Exactly. So for device builders such as yourself, really it's valuable to have that kind of experience.
Carpenter:Yes, by now I have had 40 years of experience in how neutron sources and instruments will be used.
Westfall:You knew the science issues that people were interested in and you could think about it, okay, well what's the way to get them those neutrons they want?
Carpenter:Yes. And we weren't neutron physicists; we were users of neutrons for materials science.
Carpenter:So that was the topic of the neutron scattering seminars, and they went on for years. I thought as a young professor, I should gain experience outside, so I arranged for six months’ leave in 1965. I finished my PhD in 1963 and had a faculty position in the fall of 1964, so in the fall of 1965 I arranged to go to Idaho. It's now the Idaho National Engineering Lab (it was called the National Reactor Testing Station at the time), where the MTR reactor was, then the world’s highest-flux research reactor, which I thought would be a good place to go. I packed up my two-child family, and we went to Idaho Falls. And I'd get on the bus in the morning and ride 40 miles out to the reactor site. They had a small group of physicists working there with a number of spectrometers. My interest was to do experiments on the chopper spectrometer, the same class of instrument that I had built in Michigan. So I did some sort of shake-out measurements to measure the phonon dispersion relation in beryllium oxide single crystal, and I did some inelastic scattering measurements on molecular gases, which, I guessed, were pretty much interesting topics at that time. I met some of the people there who were doing neutron scattering. One of them, Tom Worlton, worked at this time in Idaho and eventually was my colleague here at Argonne Lab. He was a diffractionist at the time. It wasn't because I came here or he came here; we just happened to land together at Argonne. He worked at Argonne’s CP-5 reactor; he was originally a diffractionist, but later gravitated to computer science, where he prospered. A very fascinating and brilliant man, Rex Fluharty, a physicist who headed the small group at MTR. The group, as a neutron scattering group, really never distinguished itself. I think the reason; I found out later, is that although the local people were good scientists, they were isolated. Not many people wanted to come to Idaho. It was just not a place where people would go, although some very good ones did carry out important experiments there. So mostly only foolish people like myself went there. It wasn't so foolish because I did learn a lot, but that was not where it was at. Really good physicists were working in strong groups at Argonne, Brookhaven, and Oak Ridge at that time. So that was not really the place to go to advance my career except it was a learning experience, but I had a very valuable acquaintance with Rex Fluharty. He was the sort of person in conversation with whom you had to have patience while he decided what it was he was going to say next. So you had to wait. It was not appropriate to interrupt. He was a gentle man, understand. You could sense always to wait until he was ready to speak. Many other people couldn't talk with Rex Fluharty, but, although he was reticent in this way, he and I could communicate well. Rex had an interest in developing next-generation neutron sources and pulsed neutron sources at the time. He thought that solid methane would be a good moderator. So he arranged some tests at Rensselaer Polytechnic Institute (RPI) with the electron linac neutron source there. He had two theorists in his group working on the dynamics of solid methane. So there was a considerable concentration of effort on solid methane. The thinking was that the high density of protons was very desirable, and the molecules were free to rotate and take up small amounts of energy that efficiently thermalized neutrons at low temperatures in solid methane. I learned a little about solid methane at that time. Rex and his team used the straightforward chopper technique to determine the time-dependent shapes of moderated neutron pulses from the moderator. But what you called the resolution in such an instruments is not very good for the purpose — they always produce a fuzzed out version of the answer we wanted. I knew that. Later, in 1967 when I was back at Michigan, we had a neutron scattering meeting in Ann Arbor that brought us focus: We invited, along with other people, Rex Fluharty to give a talk about solid methane. Paul Zweifel was present during Rex Fluharty's talk. When Rex was finished, Zweifel woke up and asked, “What happens when you lower the temperature?” Rex answered, “That's what my entire talk is about.” Zweifel had slept through the talk. He probably asks this, which is usually a very good question, in every seminar. So that same year another student older than I, Kingsley F Graham (F with no period because it didn't stand for anything. It is a little fetish.), came to ask whether I had any ideas for a thesis project, and I suggested, “Why don't we look at solid methane?” So we thought we'd do some measurements on solid methane, but how could we do that better? We had some ideas based on some time-focusing features that I had incorporated into my chopper spectrometer for characterizing the chopper spectrometer for my thesis. So I thought time focusing would allow us to measure moderated-neutron pulse shapes. Kingsley and I worked out what a focused arrangement of moderator, crystal, and detector would look like. The NE Department had a 300-kilovolt Texas nuclear Cockroft-Walton DT neutron generator, a moderately powerful device commercially available at the time. The basis for our pulse measurements would be to operate the DT generator in a pulsed mode to excite a moderator and erect a focused crystal-detector arrangement to look at it. Most people didn't believe that this would work, but of course it did, and we made some outstandingly precise measurements. It worked in no small measure because of Kingsley’s extensive experience in electronics. The measurements we made covered the whole time distribution with many points for each wavelength. We could measure for three or four wavelengths, but they were done with precise resolution. We carried out systematic studies of pulse shapes of solid methane and slabs of polyethylene. Using similar, simpler apparatus, we measured the neutron spectral distributions absolutely normalized to the number of incident fast neutrons. This enterprise was really a wonderful success, and Kingsley won the competition for the best nuclear engineering thesis of the year, the American Nuclear Society’s Mark Mills Award. We began to build a database on pulsed moderators. As we went along, we found that neutrons from the walls come back and contaminate the measurements, so we had to reduce the effects of these neutrons, the room-return neutrons. We had started out using cadmium shielding for this purpose, as is conventional. But cadmium is transparent to neutrons with energies above a half an electron volt, and many neutrons returned after long times with energies higher than that. We needed a better shield, so we made a box about an inch thick of boron carbide, which is opaque to thousand-volt neutrons. It's thought of as a pure absorber, only absorbing neutrons, which is what we wanted. When we put this box around the moderator, we were much less bothered by the room-return neutrons. What we didn't understand at the time was that with this boron carbide box around the moderator, the intensity went up. That was left for us to understand later. Kingsley went on and got his degree and the Mark Mills Award and spent his career in the instrumentation section of Westinghouse. Now I'm at Michigan teaching NE courses, with a few graduate students doing diffraction with my diffractometer and seeing other students through some reactor-related experiments. In 1967 the A2R2 research reactor was under construction at Argonne Lab. Sam Werner and I and others like Lyle Schwartz from Northwestern University, along with Argonne scientists who had experience in the instrumentation business, were named to a group commissioned to devise neutron scattering instruments for the A2R2 . We met once at Argonne, in January of 1968 I think, and maybe we met again the following month, and we went off to think up stuff and gather information. An International Agency for Atomic Energy (IAEA ) symposium on neutron scattering was scheduled for Copenhagen in the summer of 1968. I was supposed to go to learn what I could about the computer systems that they were constructing for instruments at the Institut Laue-Langevin (ILL) High Flux Reactor under construction at that time in Grenoble. Heinz Maier-Leibnitz, pre-eminent leader of European neutron scattering, was the spark plug, one of the principle motivators for the ILL. I was to meet with Maier-Leibnitz to ask about computer systems and to report any other things I might learn. In April, before that meeting took place, an announcement came out: The A2R2 project was canceled — no more A2R2. By then I had already made my travel arrangements, and I ended up going to this meeting anyway. I think I did meet Maier-Leibnitz, a great privilege for a young scientist to meet a great man. But I didn't find out much because I was too stupid to ask many questions, especially in the circumstances. But it was good to get acquainted in the larger community. That was the end of A2R2. But then, still in 1968 Argonne leadership formed a committee on Advanced Neutron Sources, the “what are we going to do now?” committee. This group included some accelerator physicists, some who don't do slow neutron scattering for material science, but Lowell Bollinger in the Argonne Physics Division —
Westfall:And he was a neutron physicist.
Carpenter:Yes. He did nuclear physics studies using fast neutrons.
Westfall:But he was studying neutrons?
Carpenter:He was studying nuclei using fast neutrons. Not neutron scattering in the sense that material scientists do. Others on this committee were Argonne chemists Selmer Peterson in the Chemistry Division, and Mel Mueller. And Lyle Schwartz from Northwestern University. The committee, the Committee on Intense Neutron Sources (CINS), was to think about what Argonne should do for neutrons now that the prospect for A2R2 was gone: the “what are we going to do now” committee. Lowell Bollinger ended up chairing the committee. Other people who were very influential included Bruce Cork, head of the High Energy Physics Division, and Ron Martin, who is still around at Argonne Lab.
Westfall:Worked on the Zero Gradient Synchrotron (ZGS).
Carpenter:That's right. Ron was head of the Accelerator Research Facilities Division. He came back from a meeting in Russia with an idea that he explained to CINS: to use a high-emittance, high-efficiency negative hydrogen ion (H-) source with stripping injection into the synchrotron. This source had been developed in Russia. The source would be powerful enough to serve as an effective injector to increase the intensity of the ZGS. So that was a possibility for a high-power proton-based neutron source. It was already clear that a great advantage accrued from pulsed operation, because all the energy deposited in the target is dissipated in the long interval between pulses, while the maximum slow neutron flux is proportional to the energy delivered in the pulse. This indicated that the accelerator should be a synchrotron, which inherently delivers pulsed beams of short duration (< 1 microsecond). Where are we now? I want to throw in the ideas that join us to the rest of the story. Ron Martin brought the H-minus source and the stripping injection idea, which he delivered to the CINS. I happened to have a copy of the proceedings of the Seminar on Intense Neutron Sources that had taken place in Santa Fe in 1966. There, workers presented all sorts of ideas, some crazy, some practical reactors pulsed and steady, accelerators, bombs, nuclear fountains, fusion devices... It was a marvelous conference. Gil Bartholomew’s seminar paper referred to another, “Neutron Production in Thick Targets Bombarded by High Energy Protons” by John Fraser and several colleagues, motivated by the Canadian Intense Neutron Generator Project (ING) Project, pursued in the early ’60s at Chalk River and carried out at the Brookhaven Cosmotron, provided very crucial information about the absolute yield of neutrons from bombardment of various materials by protons of various energies. Now you could design something and know how many fast neutrons you would get out. I had made absolutely normalized measurements of moderated neutron intensities with Kingsley Graham in which we measured the absolute low-energy neutron yield for given high-energy neutron input for moderators appropriate for pulsed sources. We knew the numbers and could put them together. We could conceive an accelerator that would produce a proton beam of given intensity, because high-current synchrotrons of appropriate energy (~ 1 GeV) had recently been demonstrated. We could calculate the fast neutrons generated from targets by this proton beam. And then we could compute how many slow neutrons you would get from the fast neutrons that you produced. And, at least for certain moderating materials, we already knew the shapes of the slow neutron pulses, which allowed estimating the resolution of neutron scattering instruments. But when we did the numbers, they were a little disappointing. More on this later. With all these considerations, Lowell Bollinger and I went around to different places and talked to people about their ideas for neutron scattering with powerful neutron sources. After about a year’s intermittent activity, the committee reported, “The best idea we saw was a proton-driven pulsed spallation source.” So there remained the question on how effective such a source would be. I continued as a professor at Michigan and consulted frequently at Argonne. Finally I managed to arrange a sabbatical leave at Argonne in 1971-1972, and the story continues. I came to Argonne partly to do some measurements on the new chopper spectrometer at the CP-5 reactor, and I brought some of my students to do that. We were guinea pigs (politely called “friendly users”), but we went away with good measurements. The other part of my goal was to further look into the pulsed spallation source, which Oliver Simpson, the head of the Solid State Sciences Division at the time, strongly urged me to do. We had marvelous conversations because he was a real physicist of the old school.
Westfall:By the way, the Solid-State Sciences Division was relatively new at that time. As I mentioned to you, I talked with Frank Fradin about this, and Frank came from metallurgy and they had combined a variety of different preexisting groups to form this division. It included some people like Frank Fradin who had come from metallurgy. Some people had come from different types of physics, and I believe that some like Simpson had come from physics, and other people who had come from nuclear engineering. Some people had come from chemistry.
Carpenter:Yes. I just jumped in and worked with them for a while. Central to my own activities was Don Connor, who headed the neutron scattering group working at the CP-5 reactor. He, too, encouraged me to work on the spallation source. So part way through the year, I observed that we needed to verify experimentally our calculations of neutron intensities from a pulsed source. Then my idea gelled about the reflector as I recalled the unexplained intensity increase in the Kingsley Graham measurements. Boron carbide is not just a black absorber of neutrons. It also scattered the faster neutrons back into the moderator, no doubt increasing the efficiency of converting fast neutrons into slow neutrons. That's why intensity went up with the B4C “shield” in place! So I announced, “I'd like to build a prototype, a mockup of this. I’ll need a pile of beryllium,” the best stuff for a reflector that I could think of. “I’ll need a strong, absolutely-calibrated fast neutron source and I’ll need special detectors.” Because the neutron counting rates would be mighty, mighty low. A2R2 was shut down. They had piles of beryllium blocks that had been intended to mock up the neutron source for A2R2. I got some of that and I piled it up in some space that Connor arranged for the purpose. The pulsed-source mockup had an oversize space for the neutron source, about the size of a neutron-producing spallation target. The moderator was a block of polyethylene decoupled from the reflector by a thin cadmium sheet and viewed through a cadmium-lined channel, all of sizes that approximated our best guess as to the appropriate size, 10-cm square. I borrowed calibrated isotope-driven neutron sources from Alex DeVolpi, a neutron physicist, so I knew how many neutrons they emitted. And they were also well characterized as to the mean energy of the neutrons. One was an americium-241-beryllium source (neutron energy ~ 5 MeV), the other a californium-252 spontaneous fission source (neutron energy ~ 2 MeV). Alex brought them to me in his coat pocket. You'd get in trouble these days if you did that. I handled them gingerly.
Westfall:You would get in trouble because they were radioactive?
Carpenter:Yes. They were pretty powerful little neutron sources. Exposing yourself to these sources was not a good idea even in those days, but we did it anyway because it was convenient. As for neutron detectors, again Don Connor arranged for someone to teach me how to do track-etch detection of neutrons using a uranium foil in front of a piece of mica, I believe. The fission fragments from the neutron capture in U-235 formed tracks in the mica. You etch these to enlarge the tracks and make holes. Then under a microscope, count the density of holes, and then from that you determine the number of neutrons that hit the uranium foil. It was a calibrated detector technique, and it worked out well for the application, although you needed to be patient. So I learned how to do track-etch counting of neutrons and did various measurements with and without the beryllium reflector and with different neutron sources. The net conclusion was that the reflector improved the neutron flux in the neutron beam by a very substantial factor, about 10. But it was not appropriate to advertise that at that time because a practical reflector needs more than one beam opening, and operating with that arrangement is costly of neutrons. So in end we obtained only a factor of 3 or 4. That's enough to put it over the top, however. Now it became interesting. This was in early 1972. Then we could say, “Well, we have an idea.” I worked with Bob Kleb, who was Solid State Science’s best engineer — he was a real engineer. Very clever gadget man. He builds it; it works. So with Bob Kleb, we worked out a conceptual design for a proton-driven pulsed spallation neutron source. We called it ZING, the ZGS Intense Neutron Generator. With laboratory encouragement, I prepared a patent application based on the beryllium reflector principle, which was granted Dec. 11, 1973: “High Intensity, Pulsed Thermal Neutron Source,” Patent No. 3,778,627, assigned (per contract) to the AEC. I received $1.00 for the patent and $25.00 for my trouble. The basic idea is to make use of the “room return” neutrons that come back quickly from the reflector, but to exclude with a cadmium “decoupler” the long-lived slow neutrons returning from the reflector.
Westfall:And this is kind of playing off the ING to get ZING?
Carpenter:Acknowledging the significance of the ING neutron yield data and the ZGS, yes, that's right. So with others encouraging us, David Price, an influential member of the SSS neutron scattering group, and I convened a workshop to evaluate ZING. I've forgotten how many people came — like 20 or 30 people. We had a three- or four- day meeting in late April 1973 to discuss what you could do with a pulsed spallation neutron source with performance parameters that we could now estimate with some confidence. Among the attendees was Motoharu Kimura, who ran an electron-linac-driven pulsed neutron source in Tohoku, Japan. He stated he was really skeptical of ZING at first. He didn't believe the measurements Graham and I had done. He said, “When I heard about those measurements, I didn't believe them. I didn't think anybody could do that.” But at this point he said, “I’m convinced. You did it after all. Furthermore, you should build a prototype of your neutron source.” It was just keen advice. At that stage he said, “And I will help.” So he returned later to stay through the fall. He said, “I want to help in the design of the neutron source. I will bring my protégé, Noboru Watanabe,” who was a student working with him at Tohoku. Tohoku is the province of Sendai, Japan, and Tohoku is the main university. “To” (pronounced “tow”) means “east” and “hoku” means “north”, so it’s Northeastern University in Japan. The Tohoku linac was a really powerful neutron source for the day, but it was an electron-driven source and it, like others, worked at the limit of what could be done with that technology. I went back to Michigan to finish the semester and, after a one-month stay at Los Alamos working with Rex Fluharty, continued commuting to Argonne.
Westfall:This was an electron pulsed source.
Carpenter:This was an electron-linac-driven pulsed source. You couldn't make a more powerful one profitably because the beam would just melt the target. It was at the limit of the technology, which was generally acknowledged at the time. Kimura having said, “You should build a prototype. I will help,” brought Watanabe to work with us on instruments. I arranged a semester’s leave from the university for fall, 1973 and brought my family to Chicago. Watanabe and Kimura arrived, and they and I worked with Bob Kleb to design the prototype, ZING-P. The prototype consisted of one-half of a lead brick for a target with a soldered-on copper water-cooling tube, surrounded with a beryllium reflector, lead brick shielding, two polyethylene moderators, two vertical neutron beam tubes, and a shielded house for the scattering instruments above the earth-shielded beam transport tunnel to the ZGS. The neutron beams were vertical. Though totally unconventional, this was a prototype — it didn't matter if they were awkward to use for neutron scattering instruments. Noboru and I worked out a concept for a diffraction instrument. We requested money from the laboratory to build the ZING prototype. It was October or so that Kimura and Watanabe had to return to Japan, and Kimura left expressing disappointment because here's this great idea that he had worked on and the laboratory didn’t say yes. Around that time, our group, including Kimura, met to discuss project organization. Masao Atoji, a prolific scientist also present, suggested that he should head the project. David Price told him no, he could be Kimura’s chauffeur. Funked, Atoji hoisted himself onto the conference table and sat, cross-legged and silent for the rest of the session. Very shortly after Kimura left, the laboratory provided $30,000 to us and Bob Kleb and his great sidekicks, Tom Erickson and Bob Stefiuk, and appointed Tom Banfield, then CP-5 reactor manager, to head the project.
Westfall:For the ZING Prototype.
Carpenter:ZING Prototype, yes, ZING-P. So we had the Watanabe diffractometer and a spectrometer (for inelastic scattering measurements) based on a time-focused crystal array designed by Kurt Sköld, a Swede who worked in the Solid Sciences Division. We also had some other instruments for characterizing the neutron beam. We ran ZING-P for three several-month periods of time in 1974 and 1975. It worked, and we could verify our numbers, and that was the basis for the proposal for IPNS that was originally called ZING. We had marvelous support at high levels in the laboratory. Important in that respect was Michael Nevitt, the deputy laboratory director. He was instrumentally helpful. Halfway through the construction of the ZING prototype, we were installing some massive steel shielding. All the accelerator activities in the country used to collect decommissioned battleship armor for shielding purposes. So we had some at Argonne Lab. We would stack up these slabs of steel, 4 feet square and up to 8 inches thick, lowering them down into the concrete-lined pit. That's the shielding for ZING-P. While we were lowering the steel plates down in there with a big crane, I brought Mike Nevitt over to show him what we were doing, and he looked down into the hole at the steel plates, where he saw “BB-58” written on the steel. He exclaimed, “That's my ship! The battleship Indiana! That was my ship. I was Fire Control Officer on the battleship Indiana in the Second World War.” That was just one of many incidents that endear me to Mike Nevitt. A marvelous supporter. I just received a Christmas card from him, now living in Minnesota, and I see him and his wife, Jean from time to time at their summer home in Door County, Wisconsin.
Westfall:Do you have time to tell us about ZING-P'?
Carpenter:Yes. The ZING-P Prototype was a success not so much that it did science, although it did some science. In fact, one of my doctoral students carried out some of the measurements for his doctoral thesis there. We reported our experience with ZING-P at the 1975 Neutron Diffraction Conference in Petten, Netherlands. ZING-P was really intended only to demonstrate the numbers and that you could build some effective instruments, which in that scale were effective. But the accelerator that drove ZING-P, Booster-1, was a prototype accelerator in its own right: the retired 2-GeV electron synchrotron brought from Cornell University to demonstrate the high-energy H- injection principle delivered only about 200 watts of 200-MeV proton beam power. Booster-1 shut down in 1975 to be replaced with what is now called the Rapid Cycling Synchrotron, and then called Booster 2, which was a full-blown, 500-MeV implementation of the high-energy H- injected synchrotron. Booster-2 took a couple of years to build, and we aimed to build on the basis of it another prototype, a proper one with three horizontal holes and two vertical holes. With a proper target, not a half of a lead brick like we used for ZING-P. So we got some money from the laboratory to build ZING-P’, a second-round prototype, at the same location. It started operation in 1977 when Booster 2 came on. So it had better instruments and better moderators and better targets. We ran ZING-P’ a fairly large fraction of the time between 1977 and 1980. At that same time, we were developing the proposal for IPNS. We completed the proposal and got some kind of (then ERDA) approval for IPNS in 1978.
Westfall:Okay, tell the story of how IPNS got changed from ZING.
Carpenter:Well, ZING-P was a prototype. The neutron business end was an assembly of targets and moderators and shielding in a tunnel that led from Booster 2 to ZGS, and we built the experimental enclosure in a small steel building there on top of a mound of dirt. We had to scale a muddy bank to get up to do the experiments. This was not a proper place for a target, but was okay for the purpose. IPNS was supposed to be really much more properly done: a separate place where there was a room full of instruments, 12 beams from each of two separately shielded targets.
Westfall:So that it could really be used by users.
Carpenter:Yes. IPNS was to be a proper facility. Still built out of recycled accelerators, materials, buildings, and infrastructure, junk — we built all of this out of junk with great savings in capital expense. But the location of the ZING-P and the ZING-P’ target was just not appropriate for large scale, although it was appropriate for testing instruments, and you could do some science, and we even did some science. A doctoral student of mine, John Gunning, did his thesis on the basis of diffraction measurements done at ZING-P and ZING-P’. He looked like Santa Claus. No, he looked more like the author of The Old Man and the Sea, Ernest Hemingway. Still does.
Westfall:Well, I must say Hemingway looks a little bit like Santa Claus, so I know what you mean.
Carpenter:I thought he was a little bit of a lazy student, and I probably was right, but he did an OK thesis and went off on his a career. I am really proud of him now. He has spent years working on the nuclear disarmament activities in Russia.
Westfall:Well, it's almost time for you to leave, but maybe you could just do a brief explanation of how you put in a proposal while you're still doing your running for this ZING-P’. You put in your proposal to DOE or the IPNS? And they tell you, as you've told me before, that ZING was too cute a name.
Carpenter:There were a number of aspects to this. We got some money from what is now DOE in 1975 for the initial design of IPNS. It was to be a half-megawatt version of a pulsed spallation source: a justifiable but ambitious extrapolation from the prototypes. I resigned my professorship at the University of Michigan in January 1975 and moved with my family to Chicago. Argonne gave me a full-time position to direct this project. The laboratory knew that to build big things like we proposed required a big-time manager. When the money came in mid-1975, the laboratory brought Norm Swanson from Argonne West in Idaho, naming him manager of the construction project. We began to develop the proposal for the IPNS. We were still calling it ZING. Paul McDaniel, head of Argonne Universities Association, had an office on the site at the time, and he also was interested in this potential major facility here. One time, as Paul and I were walking from the 223 building to the cafeteria, he said, “You know, you're pushing this big project and you call it ZING.” He said, “You have to start it right. It's too cute. It's not believable. You shouldn't do that.” He told a story about when he was earlier a proponent for a large reactor at Argonne called Mighty Mouse, a predecessor to A2R2. It failed, and he said, “I was testifying before the congressional committee about Mighty Mouse. The senator evaluating the testimony said, 'You want $50 million for a thing called Mighty Mouse?' He said, 'No suh!' And that was the end of it.” Paul told me that story. “Don't do that. Don't use a cutesy name. Use a name that forces people to think what it means. So make it unpronounceable.” I easily conceded that that's what to do, and we called it Intense Pulse Neutron Source, IPNS, from then on.
Westfall:Okay. This might be a good time to stop until next time, do you think?
We can continue, yes. Sure.