AVS Historical Persons | Alfred O.C. Nier - 1991

Alfred O.C. Nier - 1991

Oral History Interview with Alfred O.C. Nier

Interviewed By Konrad Mauersberger, December 7, 1991
MAUERSBERGER: I'm Konrad Mauersberger, a professor of physics at the University of Minnesota. As part of the historical archive series, today I will be talking to Professor Emeritus Alfred Nier. It is December 7, 1991, and we are in Minneapolis, Minnesota. Professor Nier was born 80 years ago here in the Twin Cities area in St. Paul, Minnesota. Alfred has studied at the University. He received his Ph.D. 55 years ago in 1936. After two years at Harvard University, he returned to the University, became a professor, and started a very active and successful career in research and teaching. Professor Nier's work has involved mass spectrometer work, and he has done research in the area of space physics, geochronology, and many other ones. Let me ask you first, how did it all start some 60 years ago?

nier.jpgNIER: Well, it's quite a long story, Konrad. As you know, I was an undergraduate in electrical engineering. In fact, I got my undergraduate degree in electrical engineering and studied physics, as one does along the way. I was very fortunate in my first physics class that the instructor then was Professor Henry Erikson, who was also the head of the Physics Department. He was interested in helping young people, and he gave me a job as a research assistant, working for him on his own research, which was in several areas. So I was introduced to experimental work in physics at that time. Throughout my undergraduate career, I worked for him part-time, and then also Professor Valesek; X-rays1 was his field. So I had experience in optical spectroscopy, or the study of radioactive things and X-rays and so on. So I had a kind of general background in this.

MAUERSBERGER: When did you realize that you needed a very good vacuum in your research work?

NIER: Well, that came somewhat later. After I graduated in electrical engineering, I thought I would get a job for a while before going on to graduate work, but there were no jobs for electrical engineers in 1931. So I continued on as a graduate student here. I was helped on by Professor Henry Hartig2 from the Electrical Engineering Department, who discovered that I didn't have anything, so I was appointed a teaching assistant there. I did that for two years, got a master's degree, and then I came into physics, where I got my Ph.D. degree finally in 1936. Now, when I started as a graduate student here, at the time, the leading research advisor was Professor John Tate, who was also the editor of the Physical Review and who had studied under James Franck3 in Berlin just before World War I, or at least the beginning of World War I. And at that time, one of the fields of interest was energy levels in atoms and molecules. That was just coming out. Tate followed up that kind of work during the 1920s, so a program was developed here in that area, studying what happens when you bombard atoms and molecules with electrons. So I was one of a number of graduate students who worked in that, and I benefited, of course, by the ones who worked before me at the time. 

One of the things that I inherited from my predecessors there - one was Walker Blake, who's still living. He's now 90 years old and lives out in Santa Barbara. He was the one who perfected the cross-beam electron bombardment system, which made modern mass spectrometry possible. He was one of the early people, around 1929, who did this beautiful work with that. There were several others, and then I came along. So I sort of fell into this because this was the kind of thing the graduate students working under Tate were doing at the time.

MAUERSBERGER: When did you get your hands for the first time on a mass spectrometer?

NIER: Well, this would have been about 1934 was when I really started. I started in on this, planning to work on the bombardment of heavier molecules because I had perfected an instrument that had better resolution and better performance than others in existence then. One of the things you have to remember is that there were only a handful of people in the entire world who had ever worked or even seen a mass spectrometer, so it was kind of a wide-open field. But through my engineering background, I had an understanding of how feedback circuits worked and things like this, and I was able to put together an instrument which was more stable, and I could do things that couldn't be done before. But the thing that came up in the midst of all this was that Tate, who had been the leader in the electron impact work here, began to lose interest in the field because nuclear physics was just coming in in the 1930s, and he thought we ought to get into nuclear physics. So I found myself in the position of being a graduate student who was starting to work on something where my advisor was no longer interested. So I thought the sensible thing to do was just move in the nuclear physics direction. I said, “Well, this instrument that I have has got such beautiful performance. Why don't I see what I can do with isotopes?” Because at that time, isotopes had just been discovered, and there was a lot of uncertainty about the relative abundances and about rare isotopes existing, so this instrument lent itself just beautifully to this problem.

MAUERSBERGER: Now, that was a magnetic instrument 180 degrees?

NIER: Yes, 180-degree magnetic instrument.

MAUERSBERGER: So this old, classical instrument you teach to undergraduate students.

NIER: That is correct. It's the easiest one to explain. That is correct.

MAUERSBERGER: But then you must have become very soon aware that you needed a good vacuum to do all this work, because the nature of the mass spectrometer really requires that the gases are admitted to the instrument.

NIER: Yes, that's exactly right. And of course what we did at that time, we weren't thinking of a leak detector that would be applied to other things, but we would look for leaks in our system by tuning it to some peak that wouldn't normally be very abundant in air. For instance, if you tuned it to argon and there's only 1% argon in the atmosphere, if you went over the instrument with a nozzle with argon in it and you come to a leak, obviously, the argon peak would go way up. Or even oxygen, which is only 20% of the air. You could find things. So there were lots of techniques like that that you'd use. So we were really using a selective sort of device then, but not thinking of it as something that would be used really as a leak detector and such.

MAUERSBERGER: At that time, how good were the vacuum conditions inside your instrument?

NIER: Well, quite good. We used mercury diffusion pumps. That was the standard thing that was used. I didn't have any ionization gauges when I did the work. We used the McLeod gauge; detect with the McLeod gauge. And we had pressures better than 10-6 millimeters, probably 10-6 to 10-7. We'd bake the instrument. We had no grease joints, no wax joints. We'd bake them. So we probably had pretty good vacuums, aside from the mercury vapor. We used dry ice for cooling the traps because liquid nitrogen was expensive, and I had to go after it myself because we didn't have any on the campus, so I had to drive and we'd buy it by the quart in a picnic thermos bottle. That's the way we operated [laughs], but it worked. So you could do that.

MAUERSBERGER: Yeah. It is very interesting to realize all the tools, which we use today in everyday life on its routine, was really not available.

NIER: Oh, no. And there wasn't much money. We had very small budgets. I know when I needed a piece of glass tubing that was longer than six inches or a foot long, I would go down to the “morgue”. We had a “morgue” of old apparatus and I would go down there and cut off pieces of glass and attach them together, for example. So we worked on a shoe-string for much of this.

MAUERSBERGER: Al, you already mentioned the keyword - we'd like to hear more about it - and that would be the leak detector. How was it invented, when was it invented, and what was its impact?

NIER: Well, that came about really through the Manhattan Project. You see, when I came back here on the faculty in 1938, I started doing the same kind of work I'd been at Harvard, making lead isotope measurements, for instance. And building on the program that I had worked on at Harvard. In the meantime, I had gotten acquainted with John Dunning, who was the expert on neutron physics at Columbia University. He was one of the world's experts on it at the time. That was when Fermi4 was at Columbia University also. Nuclear fission, you see, was discovered just about the time I came here, so I became acquainted with all these people. I knew Dunning very well. I used to go back and forth to Columbia. I remember at the American Physical Society meeting in April, 1939 in Washington, I met Fermi through Dunning. And this is when there was uncertainty. This was just after fission was discovered just a few months before. Of course, at the American Physical Society meeting, the big topic was nuclear fission - could you get power from it? And the war was starting in Europe, you see, about that time. So there was an interest - possibly, could bombs be made? There was a lot of talk about it.

I was introduced to Fermi by Dunning, as I say. The question was the uncertainty. Which isotope of uranium was responsible? Dunning and Fermi figured out that, with the sensitivity they had with their ionization chambers that they measured these fission frags with, that if I could separate a small amount of U-235, they could probably tell the difference. They also encouraged (which I didn't know quite at the time) a group at GE5; Pollock6, I believe, worked on this also about the same time. They were encouraging anybody who they could encourage, you see. [Chuckles] So I proceeded on this and managed to separate some, and the group at GE did it within weeks or days after I did it. It was one of those crazy things that happens every once in a while - things happen about the same time in places. But anyhow, once this milestone was passed and it was clear it was the U-235, then, of course, the interest was, can you enrich this? Because the feeling was you had to enrich it to make use of it.

MAUERSBERGER: Enrich it considerably.

NIER: Considerably, yes. And how do you do it? And of course, there were various ways proposed; just having bigger and better mass spectrometers, which is what, later on, that group at Berkeley picked up - Ernest Lawrence. Dunning pushed on the idea of using gaseous diffusion, so we began working with them, analyzing their samples. They had these very small diffusing units. They had these little, porous diaphragms - if you wish to call them that - that were about the size of a nickel or a quarter that they sent the UF6 through and to see if there's isotopic separation. And they even cascaded some of those. So we worked with them very actively there for a few years and proved that, indeed, the diffusion method would work. Of course, this was then extrapolated in the big diffusion plan. But then one of the problems that came up was, since UF6 reacts with water, if you didn't have an absolutely dry atmosphere, the barriers would be plugged and the whole plant would be shot down as a result. So, one of the things that came up was, how can you make something like this vacuum tight? You have to remember that vacuum technology was really in a pretty crude state except for people who were doing research that involved high vacuum. Industrially it had not been applied, for instance.

MAUERSBERGER: Now, if we were to have built an apparatus, and we would like to leak-check our apparatus at that time, how would we have done it?

NIER: Well, there were various means, usually. The simplest thing was to have a separate pressure gauge, and if there was a leak in it, you watch the pressure gauge go up and wait overnight or something of that sort. Or you can use an ionization gauge to see if the currents changed in that if you introduce an organic gas or something through a leak. So there were techniques of that kind used. But the thing that was interesting was that, how could you get a much higher sensitivity, and therefore, you looked for something specific. It turned out as a result - I don't know who mentioned this first because I visited regularly with the Columbia group - but when we talked about this, the question came up. Could we maybe build a little mass spectrometer that you could tune to something like helium, and therefore use that for probing? Now, nobody had ever built a portable instrument that I know of to do this kind of thing, and what's more, mass spectrometers or devices like that were very large and cumbersome. 

I think, almost by coincidence, we worked on different kinds of instruments for the Manhattan Project. It wasn't called that in the early days; it was called the Uranium Project. It was only when the military got into it that it was called the Manhattan Project. But there was this activity in this general area, and we had built a small instrument - a little glass tube which had a permanent magnet. It's a magnetic deflection instrument, which had the magnets right inside. We had built this for hydrogen analysis for the heavy water plants that were planned for the uranium fission work, you see. It was kind of natural that one could adapt one of these little tubes and use it for a leak detector, so we proceeded to do this. One of my colleagues here, a man named Andrew Husterlet7 who was a professor of physics, he and I had been undergraduates and graduates together. He taught over on the St. Paul campus. When the war had started, there weren't too many students already, so these people were all anxious to do things. So he helped on this development here before we finally moved on to do it in the East.

MAUERSBERGER: And you selected helium as a possibility.

NIER: Yes, and I can't claim that I'm the one who selected helium. This came out of the discussions with the several people who were involved. I'm sure this came up in my discussions with John Dunning at Columbia; Eugene Booth, who was his right-hand man; and several of the other people. A. V. Grosse was a very, very good chemist who gave up his job with Universal Air Products to work on this and was at Columbia during that period. So they were a very interesting group that I worked with a lot there in the East. Also, another chap who was involved in this was Manson Benedict, who was the head designer of the diffusion plant. He worked for the M. W. Kellogg Company in Jersey City or Newark, wherever they're located. That company got the contract for building the big diffusion plant. Well, it turns out Manson Benedict was one of my dear friends from Harvard. He was a post-doc there the same time I was. We used to go to Harvard Square to have lunch together. So there was a group of us who knew each other at the time. In the meantime, Kellogg had hired another friend of mine, who I shared a lab with at Harvard - again a coincidence - who became head of the vacuum-testing thing for Kellogg, which was this subsidiary that built a diffusion plant. It was called the Kellox Corporation. So I worked with all these people, who, by coincidence, I'd known before, but they were very good friends and so on, so we all worked together and had a lot of fun doing this.

MAUERSBERGER: Now, when you then invented the leak detector, the impact must have been tremendous. It must have been obvious that you had an instrument that was many times more sensitive than what was available.

NIER: Yes, but the question was, how practical would it be to use it? And maybe I should show you one of the original instruments. We have one of the glass versions, and you begin to wonder how practical it would be to use on a large scale. I should show you that. [He shows a 60 degree glass instrument, with 2 arms about 40 cm and 30 cm long with the magnets at the junction] I have before me now a mass spectrometer tube, as we called it, which is very, very similar to the original leak detector tube that we had when we started the work using the leak detector for testing purposes. This particular instrument was built in 1942 - it just happened to survive - and it was used for hydrogen analyses. When we talked about the problem of leaks, the question of having something that was specific, such as a mass spectrometer tuned to something like helium, it became obvious that an instrument like this could do the job. So we made some specially for the hydrogen work, and I'll show you that in a moment, too. But this just gives you some idea of the size of this. It was a magnetic deflection instrument with some little horseshoe magnets in here for bending the ions. There's an ion source up in this region, a collector system over here, and then there was, of course, the electronics and the pumps and everything that went with this. I have here the picture also, and I can show you how the original instrument looked that we built for the purpose.

MAUERSBERGER: Is that an instrument - there's a famous Nier ion source?

NIER: Yes, that has a source very similar to the ones that we used during that whole period.

MAUERSBERGER: And an electron impact source.

NIER: An electron impact source, which was based on the earlier Blakeney8 type of source that should have been here before.

MAUERSBERGER: And the small magnet is located here.

NIER: In here. So the ions come down through here, are deflected 60 degrees here. We, in the meantime, had gotten away from the 180 degrees because you can do the same job with a smaller magnet and it'd be a more efficient system. So all this subsequent instruments were built were either 60 degrees or 90 degrees for the turn.

MAUERSBERGER: And that instrument was tuned to helium.

NIER: It was tuned to helium specifically, yes.

MAUERSBERGER: And the early instruments, as you built them, were also located in a glass envelope.

NIER: In a glass envelope, yes. Yes, that's right.

MAUERSBERGER: You also have some pictures to show us.

NIER: I have some pictures and I can show you this. This is a picture of one of these tubes. [He shows the photo of the glass instrument] Again, very similar to what I just showed you. The instrument had to be useful for the work for the Manhattan Project. The instrument had to be portable so you could wheel it to wherever it was needed in the plant, or when they were manufacturing components by the various vendors that provided things. So we put one of these in wheels, and here you can see that. I don't know how well this will show up, but here is the entire instrument in a case. [Shows a photo of a cart with wheels and the glass components visible] You can see the wheels at the bottom and some mercury vacuum pumps that were part of it, gas introduction system. And if you look carefully, you can see the glass tube there, but that gives you a feeling of how it was constructed.

MAUERSBERGER: How long did it take from your invention of the leak detector in the laboratory to apply that to the industry?

NIER: Well, we built four glass instruments, such as this, for test purposes. Three of them were sent to various places where they were needed, like at Columbia University, and one went to the General Electric Company in Schenectady, which had the contract with the Manhattan Project for the various instruments that we needed for the gaseous diffusion plant. I moved from Minnesota to New York in the summer of 1943, and we continued development on the instrument and started working with the General Electric people at the time. We changed the glass tube to a metal tube, and then General Electric, of course, applied various engineering methods that were consistent with their manufacturing techniques, so they came up with a more rugged, reliable instrument than we had, which was just a prototype for starting out.

MAUERSBERGER: So, in everyday life in such a plant, where they had the diffusion process, the leak detector was always there, although many of them were there in order to detect potential troubleshooting.

NIER: Yes, that's right. I don't know the exact number that were manufactured. It was in excess of 500. There were several hundred in Oak Ridge, and then they were farmed out to the various vendors that built components for the plant. So, there was something like between 500 and 1,000 of these manufactured, as far as I know.

MAUERSBERGER: I see you have also some other pictures.

NIER: Yes. Here is the commercial version, which General Electric manufactured, as I say. [Shows photo of metal unit, with ventilation slots on the side and sloped control panel with 3 dials] They manufactured something between 500 and 1,000 of these. They worked very successfully. They used oil diffusion pumps. The instruments, as they produced them, still have the kind of methods we used in some cases, that we used for heating the filaments. I think we used automobile storage batteries because we knew they were the most reliable. We used radio B batteries to get the high voltage. So, you had really reliable things. This is before you went in for all the electronic gadgetry, which came along later, of course.

MAUERSBERGER: Would they become available at the time for other research labs, and how much would it cost you to buy a leak detector?

NIER: I've forgotten what they charged for these. It wasn't that very high by present-day standards and what the inflation has been. It was a number of thousands of dollars. It was certainly under ten. Some higher number, like $4,000 or $5,000 comes to mind, as I recall what it cost to make these.

MAUERSBERGER: What was the development of the leak detector then after the war? I mean, they played a major role in the Manhattan Project.

NIER: Yes. Well, after the war, of course, many people learned about instrumentation and electronics during the war - the radar, sonar, and all of the other things in the Manhattan Project. So, I would say that there were probably...well, just the number of technicians. If you have 500 instruments being used, you have a number of people associated with each one. There were a number of thousands of people who became intimately connected. And, of course, many of the young people working on these things saw the opportunities to do other things with them and apply them to other devices and so on, so there was quite an interest in it. General Electric manufactured these for a number of years, I think. It was not the kind of business they would normally do because it wasn't that big a business, so I think the main instruments that were sold after the war were the Consolidated Electrodynamics in Pasadena, which had been making mass spectrometers for the oil industry and got into this business. And then one of the people who worked on the Manhattan Project, Al Nerken, together with several others, started the Veeco Company. Nerken had worked with us in our development laboratory in New York when I went to work for Kellox during the war period, and he became acquainted with these instruments. He did a very good job in providing service along with it, showing people how to use them, because he was involved in the testing of many of the components and because there was the group that we worked with, headed by my friend Bob Jacobs, a friend of mine from Harvard days, who was in charge of the leak technology for the work, so there these people who got acquainted with it. And I as I say, this gradually spread to many other people, so the result is that a lot of people became acquainted with it. It was just such a nice thing to use. And as a result of the experience gained during the war, these people learned how to use these things reliably.

I have to story about this type of instrumentation. When I was employed by the Kellox people in the summer of 1943, I could have gone to Berkeley, I could have gone to Chicago to work with Arthur Compton and the group there, I could have gone to Los Alamos because Oppenheimer offered me a job there, but I thought I would stick with my old friends from Columbia because it seemed a place where there was a need for something with somebody who would work with the industry, especially because of the leak problem, and also the whole analyses of the uranium and so on. So that's they happened to set up this development laboratory in Kellox, who I worked for, for doing this development. Well, when I arrived in New York in July (I guess it was) 1943, I took time to set up the laboratory. We were in a building called the Nash Building, which had been the warehouse for the Nash Motor Company up on Broadway by the 133rd Street, I think it was, or 130th Street. 

I had time to go to the library because we didn't even have a shop to work with, and I spent a lot of time figuring out, how could you do some of these analyses and avoid a mass spectrometer, because of the complexity of all this apparatus and all these that could go wrong, because it was in many respects more of an art than a science to use instruments like this. So I spent a lot of time figuring ways of getting around. But every time I'd get to a point, you discover that, for instance in the case of the diffusion plant, they were going to introduce another kind of refrigerant, which if that leaked, you wouldn't know what you had. So you had to have something that was very versatile, and what is more versatile than a mass spectrometer? So finally, the man who - don't I think I know what his title was - who was a project manager or whatnot, he was directly under the president of the Kellox Corporation. He was a radio amateur and had great faith in electronic things, and he knew about mass spectrometers when he heard it from me. He said, “For goodness sake, Nier, we hired you because you're supposed to know something about mass spectrometers, and here you're trying to avoid using them.” [Laughter] So from then on, I had a very green light to pass an order to do what I was supposed to know what to do, and so we worked very hard on these developments. And, of course, like all these things, it looked so difficult at first. You learn how to do them better and better and better. So, pretty soon, you had these things operating routinely with a downtime that wasn't too bad. Not much worse than an automobile or other complicated devices.

MAUERSBERGER: Well, it's my impression that as time went by on your research, if you go to today's research, you are still concerned very much with very good vacuum condition. As a matter of fact, I think you are even more concerned. Maybe you can tell us a little bit how excellent vacuum conditions really influence your research today.

NIER: When I left the Manhattan Project and my employment with the Kellox Corporation in October 1945 and came back here, they had promoted me to be a full professor in my absence and when I was away, so I came back to a full professorship in 1945 at the age of 34 and picked up research that I had done before the war and gotten into various things involving space physics, sending mass spectrometers off to Mars, for instance. We were involved in that and a whole variety of related things. More recently, since I've been retired, I've discovered that so many have gotten into this act now that it's kind of hard to find things to do that are unique. So what you have to do is find problems that other people don't work on, sometimes because they maybe think they're not that important, or sometimes because they're too difficult to do. So many people do things with instruments that are commercial instruments built for particular jobs, so if you do something that's a little bit offbeat, they can't do them quite as well as you can do with a custom-made instrument. So that's the sort of things I worked on. What I've been doing recently is looking at the helium and neon in interplanetary dust particles, which are collected in the stratosphere by high-flying airplanes like U-2 planes. Put flypaper on the wings - effectively flypaper - and then they collect the dust.

MAUERSBERGER: What is the size of these particles?

NIER: The sizes of typical particles are, like, 20 microns in diameter. They're very small. You can't see them except with a microscope. They're very precious because there aren't many collected. We get these and we ask for them, and a committee decides whether you can have some. I've had 38 or 39 in my lifetime, in recent years. And we analyze them one at a time with an instrument. Of course, there isn't much gas in a particle that size, you can imagine, so we naturally have to have systems that are very vacuum-tight. So our mass spectrometers that we use are extremely tight, and we do everything we can. I don't know the exact vacuum, but it's down to 10-11, 10-12 Torr, numbers like that. We're accustomed to having it. The thing we specialized on, which other people haven't, is a measure of the helium-3 to helium-4 ratio in these extraterrestrial particles. We work with a small sample that we will have in the instrument because the gas is so small. We trap it there and we use it. The instrument is in what's called the static mode, and we will have, like, 100,000 helium-3 atoms that bounce around in there - numbers like that - we work with. And so we've tried to learn something about the ratio of the helium-3 to helium-4, the ratio of the neon isotopes. That has to do with such things as where the particles come from. There are different theories that some of those dust particles come from asteroids bumping into each other, and the dust just falls into the Earth's atmosphere and is collected in the stratosphere. Some probably come from comets. As they come near the sun, the water vapor and other volatiles come off and dust is left behind. So, you have that. It's kind of an interesting thing to do. You have to keep in mind that I don't have to produce anything. There's no promotion on the job that makes any difference. It's sort of like having a post-doc or a fellowship without having to worry about a job when the fellowship expires.

MAUERSBERGER: Yeah, but you can worry about messengers from outer space.

NIER: Yes, yes. I could do that, of course. [Laughs] So that's the kind of thing we're doing these days. I don't know how much longer I'll keep this up, but I'm having fun doing it. I have an excellent full-time assistant, Dennis Schlutter, who works for me, as you know. I lend him to you folks every once in a while. So, we're getting along fine. And as I say, I come and go. I'm not tied down by classes and things like this, so I have a pretty good time doing that now.

MAUERSBERGER: Well, I think you should keep it up as long as possible. I'd like to thank you very much for coming today and contributing to this archive series. Thank you again.

NIER: Thank you.

1. J. Valesek
2. Henry E Hartig
3. James Franck, Nobel Prize 1925
4. Enrico Fermi
5. General Electric Company
6. Herberet C Pollock
7. Spelling uncertain
8. H. K. Blakeney

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