00:00:00NIER: [ . . . ] When I got your note, I did a little looking around to see where things were, and I got out a number of things, reprints, that were, sort of, significant, some of which you may want to take.

GRAYSON: Yes, any copies of reprints that we can have would be great.

NIER: Yes, and I have some photographs. I don't know whether I have duplicates 00:01:00of these. I could lend them to you or let you know which they are and have copies made.

GRAYSON: Well, I have arrangements in St. Louis [Missouri] for making copies of photographs.

NIER: Okay, there may be a few here that I don't want to give up.

GRAYSON: I understand.

NIER: So, we'll have to negotiate that; whatever's most convenient for everybody. Also, since you raised the question about early meetings, were you acquainted with this 1951 conference held at the Bureau of Standards [Symposium on Mass Spectroscopy, National Bureau of Standards, 1951]?

GRAYSON: No.

NIER: That's the first meeting on mass spectrometry I ever attended. [The 1951 National Bureau of Standards meeting]

GRAYSON: Oh really?

NIER: I have a picture of the people at the meeting here, there was a group picture taken at the steps. John Hipple arranged that. He was the guy who had been at Westinghouse with Ed Condon and then went on to the Bureau of Standards. 00:02:00He was head of the section there; then he went to North American-Phillips, and was at Penn State [University] for a while.

GRAYSON: But you say Hipple was at Westinghouse at the time?

NIER: Yes.

GRAYSON: Okay.

NIER: Well, no, he moved to the Bureau of Standards.

GRAYSON: I see.

NIER: He had been at Westinghouse, and then Ed Condon became Director of the Bureau of Standards, and brought Hipple with him. Condon had been director of research for Westinghouse. But Hipple arranged this conference. It was a very nice group picture. I bet, there aren't many of the groups in existence any more.

GRAYSON: Is it in the book anywhere?

NIER: I don't think the picture's there, but I have an eight-by-ten of it. It's a very good one.

GRAYSON: That would be very excellent to go with the interview.

NIER: As a historical thing.

GRAYSON: Yes, and to identify the individuals that were there.

NIER: I have a standing list of these people. There were a lot. There were a hundred or so people. It was a very nice conference.

GRAYSON: This work is referenced in your publication list, is that correct?

00:03:00NIER: Yes, because I gave a talk there. Maybe two talks.

GRAYSON: Yes, I believe there are two. Okay.

NIER: It's referenced there. I thought you ought to know about that.

GRAYSON: Yeah, that is an excellent point. Well, how do you want to proceed here?

NIER: Well, you're the one in control! [laughter]

GRAYSON: I have a number of questions . . . [laughter]

NIER: Well, why don't you go ahead, and then we'll have to pick up loose ends, maybe.

GRAYSON: I understand.

NIER: Well, now, tell me what's going to happen so we can see if that'll help us decide how you're going to do it.

GRAYSON: Okay. The immediate plan with this recording is to have it transcribed. And then, of course, you'll get a chance to edit . . .

NIER: Or censor . . .

GRAYSON: Yes, censor it, yes. I'm presently negotiating to arrange for the Society [American Society for Mass Spectrometry] to become a partial affiliate with the National Foundation for the History of Chemistry [NFHC, now the Chemical Heritage Foundation], and I feel that eventually at some time or 00:04:00another, hopefully soon, this material will then be archived with the NFHC. And, so doing, thus make it available, essentially to scholars and people doing history of science work. So, that is the plan, and I believe, indeed, that's what will happen. It's a matter of timing as to when it would happen.

NIER: So, it should be reasonably well-organized.

GRAYSON: Well yes, it should be, on the other hand, I think the important thing here is to explore a lot of little nuggets that you don't get an opportunity to explore in some of the review papers.

NIER: Since nowadays, you put these things on word processors, you can move things around.

GRAYSON: Yes; the way these usually work is the transcripts are abstracted in terms of titles of subjects, and so if a particular tape is of interest, that 00:05:00could be found out fairly rapidly. So, rather than worrying too much about the organization, we might just kind of free run . . .

NIER: Alright.

GRAYSON: . . . because if we spend a whole lot of time on how it's organized we may end up missing the point. Well, what if we start with the very first question I have here; how old are you now?

NIER: I'll be seventy-eight in May [of 1989].

GRAYSON: That's in a month. Then, can you recall your initial interest in the areas of science; just when, how soon, how early in your life did that actually become an interest?

NIER: Well, that's hard to answer because I don't think there was any really definite time. The only thing I could point to is that I had done well in 00:06:00arithmetic in grade school. In high school, I was interested in the science courses. I took physics and chemistry there, and I took all the math that was available. And also, I took shop courses and drawing courses, which at that time were things that were kind of standard for people. I entered high school and you had to choose what kind of curriculum you were in. I went into the college preparatory curriculum, because my parents felt that I should go on to college and university.

GRAYSON: That was not common at that time, was it, for a young person to go on to college?

NIER: No, I'm trying to think. One time, I was wondering how many of my graduating class in high school, went on to higher education. [I graduated in 1927.] It turned out to be more than I thought it was after I looked at what had 00:07:00happened to some of the people. But I suppose a third, something like that. But of course, as may be pointed out in some of the things I've written already, my parents were immigrants. My mother had come as a ten-year-old, with her family from Germany, and my father came as a teenager. They met, because he lived in a rooming house next door to where they lived in St. Paul [Minesota]. Father had gone to a trade school--he was a machinist by trade. My mother, I don't think had much formal education. I would say the equivalent of grade school probably was all that she had. But they were, like immigrant families, very interested that their kids should get an education, and this was characteristic. This is just a standard thing, if you look at the whole record. My wife came from a 00:08:00Norwegian family in upper Minnesota, and the same kind of attitude prevailed among these people, too.

Keep in mind, my mother came in 1880s and my father came in 1890s. So this was sort of the opportunity. I was always steered in that direction. In high school, that was the time when radio was a coming thing. Keep in mind, this was the middle 1920s and people built their own radio sets, and I had friends who did this sort of thing. You could buy parts and tubes and crystals and whatnot, and so I got into that kind of thing. By the time I graduated from high school in 1927, it was understood that I would go into electrical engineering, which I 00:09:00did, and I came here to the University [of Minnesota]. Unfortunately my folks really didn't have much money, I carried newspapers when I was in high school to help some, and I rode the streetcars dutifully, everyday, back and forth from the other side of St. Paul over to here and back. I knew every bump on the streetcar tracks. I continued for four years here, and graduated in electrical engineering. That, sort of, seemed to be the direction I was going to go.

GRAYSON: Well, then, I gather that mass spectrometry interrupted that somewhere along the way.

NIER: Well, I want to give you another thing I wrote. I received an honorary degree here in 1980, and I wrote a blurb which I hadn't realized I'd written. It 00:10:00told a little bit about historical things. I made a copy of it, which you may want as part of the interview.

GRAYSON: Excellent, yes.

NIER: But, the story's a kind of an interesting one, because it shows you how you never know what's going to happen. All engineering students took physics in their sophomore year. That was the standard thing, at that time. This department was organized such that one person taught mechanics, another taught heat, another taught electricity, and so on . . . this was the style of many places at that time. Anyhow, the guy who taught the mechanics course was also the head of the department. His name was Henry [A.] Erikson, and he was one of these very tall, dignified sort of persons. I was in this class of probably two hundred 00:11:00students or something like this, and in those days, they kept track of your attendance in class, and if you missed classes too often, you failed the course. This was the standard thing that went on then. So, for these big classes we had numbered seats in this big auditorium, and they had somebody going around five minutes after the class started and seeing which seats were vacant. The instructor knew where everybody sat. Well, after the third quiz just before the class, this very dignified professor came up the middle of the room--I sat a few seats from the aisle--and said he'd like to see me. He didn't ask what my name was or anything else, he just came and said he'd like to see me. Well, then he turned around and went back. He asked me at my convenience to come to his 00:12:00office. I didn't know what this was all about, and, the people around me began to buzz. They wondered if I'd been caught cheating or something like that. But, anyhow, I went to his office, and made sure he was talking to the right person. And what had happened was I had gotten hundred's on the first three tests in the physics course, so he raised the question, "Had I considered becoming a physicist?" I said, "Well, no, I really hadn't." But he said I really ought to consider it, and what's more, he gave me a job, working as an assistant, doing some experiments. So this was my real introduction to physics as such.

GRAYSON: This gentleman's name?

NIER: Henry Erikson.

GRAYSON: Erikson.

NIER: It's spelled with an E- [the Norwegian spelling] R-I-K-S-O-N

GRAYSON: Okay.

00:13:00NIER: He did this for a lot of young people. It was really an introduction to science on a hands on sort of basis. For an undergraduate, it was quite a break. Besides, I got fifty cents an hour, which was the going rate then, which was high in 1935.

GRAYSON: That was high. I didn't earn that when I started working.

NIER: So, I did this and in the last summer I was an undergraduate, he got me a job full-time with somebody else, working in X-rays. Professor [Joseph] Valasek. V-A-L-A-S-E-K. By the way, he's the guy who discovered ferro-electricity. Didn't get credit for it for decades, but he's been recognized since. [J. H.] Van Vleck has officially given him credit for this. The J. H. Van Vleck. They had a symposium in Valasek's honor some years ago. Valasek's still living--he's about 00:14:00ninety years old. But anyhow, I worked for him full-time in the summertime, and part-time during the school year; so I saw a lot of what went on. Well, Professor Erikson wanted me to continue on as a graduate student in physics, and I said, "Gee, [this was my senior year] I wanted to really get out on the job for a while, and I wasn't thinking of graduate work so I think I'll pass it up." Well this was 1931, and jobs were not available for engineers. So, I estimate, I think about five people out of our graduating class of eighty got jobs.

GRAYSON: But why? Was it because of the Depression then?

NIER: Yes, the Depression, people were being laid off right and left and companies were not hiring. And there weren't many opportunities locally; there was probably a job for one or two electrical engineers at the power company and the telephone company and that was it, there was no industry. Honeywell 00:15:00[International] was still making dampers for stoves and things like that and 3M wasn't interested in scientists. So, the jobs were with Westinghouse, GE, Bell Labs, and so on and they just weren't hiring.

GRAYSON: But I would've thought . . . you probably graduated with good grades and you were a pretty good student.

NIER: Yes. But I didn't have all the other things they wanted, so . . .

GRAYSON: What other things were they interested in?

NIER: Well, I mean, that you'd been active in school activities and things like this. They were looking for these management types; leadership assistants, and so on. The research opportunities were very limited so people who had that sort of talent were very limited. Well, it turned out I was rescued, luckily, by a man in electrical engineering who was really outstanding. His name is Henry Hartig, who himself was a physicist and had come back to Minnesota. He had worked at AT&T sometime before he came back on the faculty here in our 00:16:00electrical engineering department. This is, by the way, mentioned in my honorary degree talk. And so, he rescued me and got me a teaching assistantship in the electrical engineering department.

GRAYSON: So your good qualities, your good record was recognized by someone.

NIER: Oh yes, he knew who I was. He saved me when he found out I didn't even have a job when I graduated. I spent two years there and got a master's degree in electrical engineering. But they had so few courses available in engineering departments in those days, that one took the courses in physics and math and so on. So, except for having taken one course in electrical engineering in circuit theory or something like that, I took just standard physics courses. It was just as if I'd stayed in physics as far as my coursework and that's all you did the 00:17:00first two years anyhow. But I did spend two years there, and that was valuable experience. I was always interested in instrumentation. As you can see the thread of engineering runs through this. When I finished up in 1933 with a Master's degree, Professor Erikson again offered me a teaching assistantship. There weren't things like research assistantships in those days. The only avenue was a teaching assistantship. So, he again offered one to me, which I accepted then because I was now on the way. That's the history of that time.

GRAYSON: In these teaching assistantships were you actually teaching courses or doing lab . . . ?

NIER: Lab--teaching labs. I think we had the standard load, which was called a 00:18:00half-time position. A standard load was four two-hour labs a week plus grading the papers that went with these.

GRAYSON: And these typically had twenty or thirty students in each?

NIER: Well, probably less than that in our case, more like fifteen, or sixteen, or something like that. You had so many stations they worked in pairs in many experiments. I think it hasn't changed that much since.

GRAYSON: No.

NIER: So, that was, kind of, the way it was. I did that in electrical engineering and it was very valuable. I taught a lot of different things, a radio lab, and a transient lab where you did experiments with an oscilloscope. This was one that had to be pumped down, crazy thing, never worked right; but that was the one for doing high-speed transient phenomena, stuff like that. That was kind of an interesting experience. Much more interesting than the run-of-the-mill thing. It was quite valuable and the communications lab I taught there was, kind of, fun.

00:19:00GRAYSON: To a large degree then, you had a foundation in electronic instrumentation that you could carry with you into mass spectrometry.

NIER: Yes. Which most physics majors didn't have, by the way.

GRAYSON: Yes. It turned out to be an extremely valuable background.

NIER: A very valuable background, that's right.

GRAYSON: So, a little fortuitousness there.

NIER: That's right. As I say, you have to be in the right place at the right time.

GRAYSON: So, mass spectrometry. We were trying to get to the point where you first became aware that such an activity existed and was worth pursuing or looking into. When did you really . . .

NIER: Well, I had been in and out of the physics department for years since I'd worked here as an undergraduate and the electrical engineering department was just across the street. I'd gone back and forth and I was more at home in the physics department actually, than I was in electrical engineering. Because I'd 00:20:00spent so much time here. I knew what the graduate students were doing. It was a very interesting time; this place excelled in the study of the electron impact of gases, thanks to John Tate. He was not head of the physics department. He never wanted to be head of it. He was editor of the Physical Review for twenty-four years. He got the job very young and he died quite young--he was only sixty when he died. But, he was the leader of that enterprise which was the largest research enterprise in the department here. A few students went into theoretical physics, which this department pioneered because we had Van Vleck on 00:21:00the faculty at that time. He turned out some of the first students in quantum mechanics in the country. Professor Valasek, in his work in X-rays and other related things had students, but otherwise, it was mainly Tate who had students. And they all worked on something related to electron impact and gases. There was a real break-through at the time. There were several students who were very, very good, they were predecessors of mine.

One that's really outstanding is Walter Bleakney, who was the man who first recognized the importance in electron-impact studies of separating the 00:22:00acceleration of the electrons from the acceleration of the ions. (Figure 1) Keep in mind that quantum mechanics was just coming in. It was the 1920s and there was an interesting thing that people called the critical potential. It was an interesting subject in the late 1920s. To do this quantitatively, you have to know how fast the electron has to go to make an ion. You see, it isn't just any old energy, you have to have a minimum energy or it doesn't ionize. Well, that wasn't very well understood, and if you did it the way the conventional spectrometers of the 1920s did it, where you accelerated the electrons in one direction and used the same field to accelerate the ions in the opposite direction, you got all mixed up and couldn't determine the potential of the electron when it made the ion, because it wasn't a sharply defined thing. So, 00:23:00Bleakney came up with the idea of having the electrons go at right angles to the ions. I wrote to him a few years ago--he's still living, well up into his eighties--about what the history of that was. He says yes, he was the one who really came across this idea. So, what you do is collimate an electron beam with a magnetic field, so you get a tight pencil of electrons. You can control their speed accurately by sending them through suitable diaphragms--a suitable gun arrangement--so, when they come out, they're going at a very definite speed, very sharply defined. Then you send them into a region where there is a small cross-field, and draw the ions out at right angles. Then you can do tricks with them, accelerate them, and so on.

00:24:00GRAYSON: So, this is essentially the beginnings of the electron-impact ion source that everybody uses.

NIER: Everybody's used since. It was Bleakney's doing.

GRAYSON: I see.

NIER: And this was about 1929.

GRAYSON: But his primary interest was this very fundamental phenomenon related to the ionization energy for different gases.

NIER: That's right, and he was the one who discovered quantitatively the formation of multiply charged ions. Before that, it was a big mixed-up business. His first study was on mercury, because we had mercury diffusion pumps and you just adjusted the trap temperature to get mercury vapor. He determined the ionization potential for singly charged mercury. He could tune to the mass 200 position and gradually increase the electron energy. You couldn't resolve the isotopes with those early machines, so it was just about 200.

00:25:00GRAYSON: He was just looking at this lump in the vicinity of mass 200, a single lump.

NIER: Lump, that's right, the single charged mercury, around 200. And you got nothing until the electrons were going 10.4 eV, or something like that. Then you began to see the onset and generally reached a maximum around 100 volts or so. You tuned to the position of doubly charged, like mass-100 m/e, and you didn't get anything till you got to, I don't know what the number was, 35 or 40 eV something like that.

GRAYSON: Yes, noticeably higher . . .

NIER: Then you turned to a third of 200, and you began to see those at sixty, seventy or eighty or whatever it was, I think he observed up to quintuply charged; that was the first time anybody had done that quantitatively. And this guy was just a graduate student, you understand. Then, the other thing he's responsible for is molecular ionization studies, which everyone's forgotten 00:26:00since. It really was a most amazing time. I was an undergraduate then and coincidentally, Bleakney was my lab instructor. I never knew that I would follow in his footsteps, but he was the teaching assistant in my first course in physics; just a coincidence.

But anyhow, Ed Condon, who was one of the pioneers in what might be called "chemical physics," especially the application of quantum mechanics to chemical problems, was here a year or two on the faculty as a theoretical physicist teaching quantum mechanics. I think he's one of the true pioneers of the middle 1920s, and he came here when Van Vleck left to go to [University of] Wisconsin. And that was when he worked on this problem of what happens when you hit a molecule, like a diatomic molecule, with electrons--what happens to the 00:27:00molecule? He was studying the quantum mechanics of this business, when either he or somebody else, came up with this idea, that if you raised the molecule to a higher energy level that it would fly apart. It doesn't start flying apart, you have to go to the right energy and then it flies apart. And you have excess 00:28:00energy over what would be in the state of the particle, so the thing would fly apart with energy. And so, if you take a neutral molecule, I think they worked with nitrogen, or carbon monoxide and hit it with electrons that were going at fast enough . . . you raise its energy up to the point where the ion and the neutral fly apart. And so, he pointed out that you ought to be able to observe these kinetic energy ions.

GRAYSON: Now, you said the second thing Bleakney was not known for was this business with Condon and molecular ionization/fragmentation.

NIER: Yes, Bleakney was a graduate student here, and he knew Condon . . . of course, everybody knew Condon. He was described like an old pair of pajamas: one of the most friendly, wonderful guys that you ever wanted to meet and a wonderful storyteller, just a terrific guy. Anyhow, he knew that Bleakney had this spectrometer that could do these tricks, you see? So, Condon told Bleakney, "Why don't you go downstairs and play with the apparatus, I'll teach your lab 00:29:00this afternoon." Or something like that. Well, Bleakney did essentially that, and sure enough, found the energetics of hydrogen fragmentation.

GRAYSON: So, this represented additional work in molecular ionization, fragmentation and so on as opposed to just the elemental ionization.

NIER: That's right. These were the two important things that Bleakney was involved in. And then he got a National Research Council Fellowship, and went on to Princeton [University]. There were two other guys who followed him shortly who also were very good, P.T. Smith, who very few people ever heard of. He was the most wonderful apparatus-builder, and my hero of those days.

GRAYSON: He was on staff here?

NIER: No, he was a graduate student, at my time. He had done this nice work, and knew how to build instruments nicely.

GRAYSON: When you say, "he knew how to build instruments nicely," can you explain?

NIER: Well, he knew how you fabricate this stuff; making electrodes and so on, 00:30:00and putting them in a vacuum system. He had a real appreciation.

GRAYSON: He had a way of going from an idea on a piece of paper to something that actually worked; that was a talent that some people had.

NIER: Yes. He had this peculiar sort of a talent, and he followed up things that Bleakney had done; measuring total cross-sections, without a spectrometer, just measuring the ions coming off, without trying to separate them by mass. And the work that he did, about 1931 . . . people still, very proudly point out that they checked Smith's values of l931. [1] That's how good he was. I'm sure that there've been improvements, but in general, these guys did things well.

GRAYSON: Yes

NIER: The other guy, Wally Lozier, L-O-Z-I-E-R also had a National Research Council Fellowship--there weren't many, maybe about two in all of physics and 00:31:00these guys got them and went off to Princeton. They followed Bleakney to work with him. I knew them all, because I'd been around for a year. So, after they were all gone I was casting around for something to do. I think I told this in my reminiscences about geology or something. I thought the last thing in the world I wanted to do was to work in that field. I thought I would do something else, so I considered various things, I thought of working in microwaves, because at that time, people were talking about the ultra-high frequency things you could send through lenses made out of "pitch" and stuff like that. It sounded like an interesting thing. And they talked about "plasma oscillations;" 00:32:00interesting discharges in gases.

So, I started out and set up the standard discharge tube where you have the striations in it and stuff like that. Tate, was a very systematic guy, and the students had great respect for him because he was so good, so you were sort of afraid of him. He was so busy, he was then instrumental in setting up the American Institute of Physics. He was editor of the Physical Review, the Review of Modern Physics, and he commuted all of the time to New York [New York] to set these things up. Remember you went by train, and it took two days each way, so, he wasn't around that much, plus his editorship . . .

GRAYSON: We'll have to continue on another tape . . .

[END OF AUDIO, FILE 1.1]

00:33:00GRAYSON: Okay, we're on Side B of Tape 1, interviewing Al Nier. Tom Krick and Mike Grayson are doing it. I meant to say that on Side A of Tape 1, but at any rate, we've got it on Side B, and he was telling us about Tate's activities. [laughter]

NIER: Tate, while he was the advisor for most of the experimental graduate students, he never spent much time with them. In particular, he didn't really spend much time with you unless you were getting results. It was really a rugged existence for people. I was batting around here, trying to work on something that he wasn't particularly interested in, and he would come and see me once in a while, and he'd look at the glow discharge and say "So, what're you going to do with that?" and so on. I wasn't quite sure what I was going to do with it; then finally, onetime he came down, and said "Gee, sounds a little like you're working on something that General Electric did years ago and never bothered to publish."

GRAYSON: Real helpful!

00:34:00NIER: Real helpful! But, it was helpful. There was a message there. I batted around a little more, and he suggested I might work with a guy by the name of John Williams, who had just come here as a post-doc to act as an assistant to Tate. Tate had prestige, he had money, so he could hire people full time as post-doc assistants. John Williams, whose whole background was in X-rays, had been with Sam [Samuel K.] Allison at [University of California] Berkeley and then at [University of] Chicago. He came here, and was supposed to work on electron impact, but by that time, the field was really drying up in the sense that it wasn't terribly exciting for physicists to continue in the field. 00:35:00Chemists hadn't quite caught on, and couldn't build instruments, even though it would turn into more of a chemical field; the study of the structure of molecules and so on. Tate had lost interest. He, sort of, had a short interest-span anyhow, because as editor of the Physical Review he knew everything that was going on, and nuclear physics was just coming in. He had Williams working with him, and they were going to build up a mass spectrometer, sort of, picking up where P.T. Smith had left off.

Well, Williams barely got here and nuclear physics began to break forth, and people were able to do nuclear disintegrations with relatively low voltages, a few hundred kilovolts. You could perform reactions on the light elements like lithium and boron. We had a 300,000 volt X-ray set here in the department, which 00:36:00really had never been used for anything before. So, Williams was encouraged to go into nuclear physics and of course, he was anxious to do that anyhow. He dropped out of the mass spectrometry entirely, and I was left alone; all on my own.

Well, in the meantime, I'd built an instrument taking advantage of all of the work of my predecessors. All the early instruments that we're talking about were 180 degree mass spectrometers, and you had a solenoid that enclosed the whole instrument. You accelerated electrons along the solenoid, because the magnetic field collimated them and you drew out the ions sideways. You had a long glass tube, which would be on one side of the hole in the solenoid, and a horseshoe-shaped glass tube would come off it, which contained a 180 degree 00:37:00analyzer, Bleakney's instruments were housed entirely in glass, using a four-inch diameter glass tube. (Figure 2) Smith came up with the idea of just having an arm on the side for housing the magnetic ion analyzer, so you didn't need the great big glass tube. You didn't have to have wax ends on it, so you could seal it all up. And I should mention also that the thing that was remarkable here was that they used ultra-high vacuum techniques in the sense that there were no grease joints, no stop-cocks, no nothing else. They used mercury pumps, and so you could pump down, bake the apparatus, and so on. You didn't have all of the impurity problems, because many of the early people who played with electron beams, had water present, and you formed hydrides and had all kinds of stuff that led to confusion in your results.

GRAYSON: So, these were glass-sealed systems?

NIER: Pyrex glass-sealed, the electrical leads were tungsten, which you could seal into the glass.

GRAYSON: So, you had to have some glass-blowing technology?

NIER: That's right. We had a very good glass-blower. But you also had to be able 00:38:00to do some of your own glass-blowing; I became a pretty good glass-blower.

GRAYSON: So, even as we're talking about the early 1930s, you're saying that the vacuum technology that was being used in these experiments was comparable to vacuum technology that was available many, many years later in other parts of the country.

NIER: In most places. Except that the people who manufactured electron-tubes had known this for decades, like GE, Westinghouse, Bell Labs and so on.

GRAYSON: Then, in 1930, electron tubes had been manufactured for how long?

NIER: Ten or fifteen years--1920 thereabouts. The good vacuum technology was standard in factories, in places like General Electric.

GRAYSON: So, in a way, better vacuum practice was being done in industry.

NIER: Industry, but not in the universities.

GRAYSON: Not in academia, I see. That's interesting.

NIER: And very few people in the academia had good vacuums. There wasn't 00:39:00anything mysterious about it; it just was the way it was.

KRICK: They just worked with grease-seals in those days, and just did it that way.

GRAYSON: Yeah.

NIER: So, anyhow, that was the kind of tube I inherited. I didn't work on electron impact on gases. Although I had the first spectrum of benzene that anybody ever had, and I was never encouraged to publish it. (Figures 3, 4)

GRAYSON: Really?

NIER: Mass 78, 77, 76 and then, finally . . .

GRAYSON: Where is it? [laughter]

NIER: I have it around. I have a copy of it.

GRAYSON: You have it around?! [laughter]

NIER: But it was never published. I made a slide of it once and showed it at a meeting, but that's as far as it ever got. The thing I missed the boat on was the metastables because as you got down in the 20s, and you had some fractional 00:40:00mass numbers. I didn't try to interpret them. It wasn't until later, when Hipple--John Hipple was at Westinghouse--and Condon, who had been interested at the time, published something on the interpretation of these fractional mass peaks--26.3 or there abouts.

GRAYSON: When did you put benzene in the mass spectrometer? I mean, that would have been what year?

NIER: 1934 or 1935.

GRAYSON: Okay. What prompted you to put benzene in?

NIER: Well, it sounded like fun. The instrument I had was a larger solenoid than people had used before. It was supposed to be part of a big electromagnet to be used with a cloud chamber for some nuclear studies, but the electromagnet was never completed, so there was a solenoid available with a seven-inch hole in it; about so long. It weighed 500 pounds or thereabouts. I have a picture of it, by the way.

00:41:00GRAYSON: Yes, we can hopefully get a picture or get a copy.

NIER: So, I had a larger magnetic field and a larger radius than had been used before. A five-kilowatt generator was used to power it. I could get resolution up to a hundred or so. I worked with the cadmium isotopes for instance, and so, to work at mass 78 wasn't all that hard. I looked in the literature of the chemists who had tried to build instruments in the 1920s. They had built instruments and done some work on electron impact, but with their greasy, watery systems, they found all kinds of crazy stuff. Also they didn't have nearly the resolution I had. At that moment, I had the highest resolution mass spectrometer in existence. There was nothing going on in Europe along this line, and there 00:42:00were a few places in America. Princeton and Chicago did some work in the chemistry department. But nobody had as good an instrument as I had with this solenoid that I'd inherited when Williams started out. There was a real break. Again, it shows you what happens to people. One of the problems we had was, you had to run the solenoid, which took a lot of power, five kilowatts, off a motor generator. And motor generators weren't exactly the most stable things; armatures would wander back and forth on the shaft, and the output voltage changes a volt or two in 110, or there abouts.

GRAYSON: Sounds like mass spectrometry in China today [1989].

NIER: [laughter] Yeah. Right. So, the question is, what to do about it, and it was at this point that my engineering background and connections came in. To me 00:43:00it seemed hopeless to control the output voltage of the generator, because it required stabilizing so much power. So why not be more subtle? It occurred to me that, since the mass that you collect is proportional to the square of the magnetic field divided by the accelerating voltage, why don't you fool the instrument by monitoring the magnetic field, and changing the ion accelerating voltage so that you stay on the peak. I went to talk to Dr. Hartig, who I'd known so well, and who'd been my savior a couple of years before, about this. Could we use a vacuum tube as a magnetron, and put it on the axis of the solenoid, outside of the instrument, pick up the fluctuations, and modulate the 00:44:00high voltage in such a way that if, for example, "B" went up by 1 percent, the accelerating voltage went up by 2 percent. B-squared over V. The result was, the ions didn't know the difference, so the trajectory was stable. I could work with heavy ions where you needed high resolution. It was my first publication, a little note in RSI [Review of Scientific Instruments]. [2]

GRAYSON: Yes, I noticed that.

NIER: As far as I know, only one person elsewhere ever used the idea--someone at Columbia. One of the guys there used the idea but I don't know whether it was successful or not, because they had other instrument troubles. Anyhow, it was the thing that got me started, because it made it possible for me to work with our cumbersome apparatus. The magnetron gave us the stability we needed. To tune up this apparatus you sat it on the side of a peak, and tuned the gain of the 00:45:00magnetron. You moved the position of it, with a slider. You slid it in and out of the magnetic field, to get it so that it would just balance, so that it didn't overdo it or didn't under do it, and you could sit there all day, on the side of a peak.

GRAYSON: What you were really doing was taking the fundamental concepts in electrical engineering such as feedback control . . .

NIER: That's right. That's what it was. Feedback control.

GRAYSON: And using it in the physics experiment to make the thing work.

NIER: To make it work, that's right. That is why it's so interesting how these things overlap. It isn't quite clear which is which, you see.

GRAYSON: Well then, how does one get a spectrum with this machine?

NIER: Well, we changed the accelerating voltage. We had decade boxes, which was all you had then, and put-and-take boxes, because it was just a potentiometer arrangement. We used a put-and-take box so you didn't change the resistance of the string; you just changed the tap on it, and you did it in a precise way. You sit there, and turn the nobs, and follow the galvanometer spot that you had to 00:46:00look at . . .

GRAYSON: So, now, we're saying that taking a spectrum represented a day-long proposition?

NIER: Well, hours.

GRAYSON: Hours long?

NIER: Originally. And another great break came. Being born at the right time and being around at the right time helped. The electrometer tube had just been invented. One of the other graduate students had built, for a master's degree, an amplifier using an electrometer tube. My first work was done with a quadrant electrometer, where you have a little piece of aluminum foil shaped like a four-blade outboard motor propeller hanging on a metallized-quartz fiber in a hollow round metal box cut in quadrants, opposite quadrants tied together. A potential difference between the pairs of quadrants sets up an unbalanced force which rotates the little propeller-shaped object, which in turn twists the fiber and attached mirror. You passed a current you wanted to measure through a 00:47:00resistor mounted between quadrant pairs. You couldn't buy commercial high-impedance resistors then, so you took a pencil and a piece of insulating material, such as fiberboard, and put pencil marks on it. You rubbed the pencil on the insulator, and that was the resistor. If you got the resistance too low, you erased some of the graphite. You adjusted this to get the amount of resistance you wanted. And that was standard in those days. Everybody was doing this in the 1920s and early 1930s. But I came in just at the tail end of the quadrant electrometer era, so I had the privilege, if you want to call it that, of working for only a short time with a quadrant electrometer!

GRAYSON: And so, basically, you adjusted the put-and-take box, as you call it, to move to different portions of the peak, and . . .

NIER: That's right, and you would go over the whole mass spectrum, dot by dot.

GRAYSON: Okay, then the job of the operator constituted recording the information at each point.

NIER: On a piece of paper.

00:48:00GRAYSON: Did you stay at a particular spot on the potentiometer for a minute, or did you collect data?

NIER: Well, what one generally did was probably not much different from what one might do today. You went over the whole spectrum to see what it looked like, and then you went back and did peak-stepping.

GRAYSON: Okay. The mass scale was assigned in what way then?

NIER: Yes, inversely proportional to the accelerating voltage.

GRAYSON: So, if you knew the mass of a prominent ion, you could compute the others as well.

NIER: Then you could predict every other one.

GRAYSON: And this was on a machine that had a resolving power, you say, of about a hundred.

NIER: Yes.

GRAYSON: And the peak shape looked like?

NIER: Well, not as sharp as nowadays, but not bad.

GRAYSON: Not bad. Do you have any data from those early experiments?

NIER: Yes, yes.

GRAYSON: Could we get copies of that kind of information?

NIER: Yes. You better write that down so that we remember to do all these things I'm promising you. [laughter]

00:49:00GRAYSON: So, the benzene . . . you just put that in as, kind of as a lark.

NIER: Yes, but I said, "Look, my advisor isn't interested in this anymore, so I better get in something to do with nuclear physics." And I said, "Gee, if I can do benzene, I could do such things as argon." Argon-38 had just been discovered, spectroscopically by some people in Holland, if I remember correctly, but the exact amount of argon-38 wasn't known. Argon-36 had been known before that. [Francis William] Aston may have even seen the argon-36 along with argon-40, the most abundant isotope. We had standard gas we bought them from Linde or from Air Products. Sure enough, when we introduce argon, there were three isotopes. without any question. So I made the first measurements on argon-38 that showed 00:50:00the five-to-one ratio from argon-36 to argon-38, I did that in a half an hour one afternoon. (Figure 5)

GRAYSON: This was with the machine that had the feedback control.

NIER: And the stability, so you could work effectively on isotopes.

GRAYSON: Then that represents really the, the discovery of the isotopes of argon; all of them.

NIER: Not quite, they'd been known, but I made the first quantitative measurements on all three.

GRAYSON: So you made accurate abundance determinations of the argon isotopes. I noticed in some of the early papers the references to a "spectrograph" in the title.

NIER: Yes, we were loose, everybody used the word "spectrograph" because that's what Aston had invented. But that was wrong; and later that was corrected. But I used it for a long time, I didn't know any better. And a lot of other people didn't know any better either, but that was corrected some time down the road and instruments which use electrical detection are now called mass spectrometers.

GRAYSON: In essence then, you really never did any work with spectrographs. 00:51:00Could that be said?

NIER: That's correct.

GRAYSON: So, it was always been electrical detection.

NIER: It was always electrical measurement. That is correct.

GRAYSON: Okay. That's interesting. Even in your Mattauch-Herzog instruments, you still were doing electrical detection.

NIER: Always.

GRAYSON: It's occurred to me, and this is just an aside, that you see "spectrometrists" used some times but I haven't found that word in the dictionary. You see "spectroscopists," but I don't know if I've seen "spectrometrists."

NIER: I may have. But it isn't common apparently.

GRAYSON: No, but I think most mass-spec people think of themselves as a "mass spectrometrist" as opposed to a "mass spectroscopist."

NIER: Yes, of course. But you see, "mass spectroscopy" is broader. It would include either spectrography or spectrometry; so that gives you more prestige in this instance. [laughter]

GRAYSON: Well, now that we have those little nomenclature details taken care of, 00:52:00we do have a promise that you are going to supply us with a copy of your raw data, right?

KRICK: Right, benzene and other point-by-point measurements.

NIER: Right.

GRAYSON: That would be excellent, because I think, as you're well aware, with instruments today, and computers and so on, so much of this type of activity is just taken for granted and people don't even think about it.

NIER: Oh, yeah. Well, the strip-chart recorders of those days were very primitive . . .

GRAYSON: Oh yes!

NIER: Even during the war, when we were building instruments for the Manhattan Project. Electronic chart recorders were not yet available, at least at the time when we needed them. So, we employed the old Leeds & Northrup devices where you had a galvanometer and a needle that went back and forth and something bit down on the needle. They were quite precise. Amazing instruments, by the way, but terribly slow by modern standards.

GRAYSON: I just finished listening to a reminiscence from John [H.] Beynon who 00:53:00described a high-speed recorder they had in England. He said, at that time, which I don't recall when it was, if the damping was a problem, you had to stay away from it because it spread ink all over the place. [laughter]

NIER: I believe that. That's right.

GRAYSON: Well, I posed this question to you earlier; if you look at the mass spectrometer as a series of different systems: a sample inlet system and an ionization system, an analyzer, detector, data system and vacuum system, starting back from when you first became involved, each of these systems were kind of fundamental and basic, and today we have tremendous advances in each of these. Why don't we just explore each of them with your early instruments. Like sample inlet. Obviously, when you say "put benzene into this machine", how did 00:54:00you do that? How did you put samples in that early machine?

NIER: Well, we had all-glass systems. And, we didn't use stop-cocks and such. I don't remember exactly, but we had a bottle of benzene--I still remember the little bottle. We got it from somebody in organic chemistry, and it was very pure stuff; that was part of it. I suppose I put a small amount in a glass tube, froze it in there, and then sealed that onto the manifold system. This probably had a u-tube. You could feed mercury into the bottom of a u-tube, a y-shaped one, and you could seal it off that way. And I suppose that's what we probably 00:55:00used in place of stopcocks. The leak system at that time, the standard thing was to send gas through a glass capillary. It was an art form to make the capillaries. You took a piece of 8 millimeter Pyrex tubing, heated it locally with a torch, and then drew out the tubing to a capillary. We worked entirely with Pyrex, so it was easy in that sense. Then you broke off, say, six inches from that part of the tube; and you hoped you'd drawn it at the right rate. If you pulled very fast, you'd make a very small tube. If you wait long enough, till it's just about ready to harden, you can make kind of a heavy walled tube. 00:56:00There was a lot of technique involved. You got pretty good at this. After you broke it off, you would test it by putting pressure behind and putting the end underwater to see if it bubbled. If it bubbled, it probably was too fast. So, you threw it away. Then, if it was too slow, you'd break off some more. So you got pretty good at this. Then you sealed it into a tube, which covered the capillary, so there was a ring-seal connecting it and protecting it. You ended up with a continuous length of, 8-millimeter tubing, with a barrier in it, and the capillary sticking in one part. That was how you admitted the sample into your spectrometer.

00:57:00We didn't worry much about fractionation, what it did to the sample. You were so happy to get something going, so you didn't worry much about that then. This was all sealed onto the apparatus, you pumped with the mercury pumps. In those days, we couldn't afford liquid nitrogen, except in special experiments. We used dry ice in alcohol or acetone for cooling. We got liquid oxygen in those days from the Air-Reduction people who had a plant over here in southeast Minneapolis [Minnesota], not far from the hotel you're staying in. I used to go over in my own car and buy it by the liter. I would take a quart thermos bottle, and go over there, and they'd fill it for me and I'd bring it back, and you nurse it along. It would last you about 24 hours or so, and I would go back the next day 00:58:00and get another liter if I needed more. The department owned some dewar flasks that would hold a couple liters. They were used for demonstration purposes, in standard-run physics experiments.

GRAYSON: Do you have any feeling for the level of vacuum that was actually achieved?

NIER: Yes, we used a McLeod gauge. We didn't use ionization gauges; some people did. In a McLeod gauge, you trapped a known amount of gas in a bulb and squeezed it up into a capillary where its pressure could be measured using pV=p'V'. Pressure was measured beyond the trap, because you didn't want mercury in the system. We had a very good glass-blower. He made these McLeod gauges with a sensitivity such that the first millimeter of the capillary was equivalent to 00:59:00about 2 x 10 -6 torr. So you had a 500cc bulb with a capillary that was about a half a millimeter in diameter. And of course, there was the matter of selecting capillaries that were uniform. But, since it was a squared scale, it didn't have to be that accurate anyhow. But we didn't really use that very quantitatively, the amount, it was just an indication that . . . .

GRAYSON: Essentially the vacuum system was usable.

NIER: . . . it was good. You could sense when the vacuum was good, because if there was no air in there, the mercury would bang against the end and stick. So you had what you called a "sticking vacuum," meaning that there was very little 01:00:00gas in there. That was like 10-7 [torr] or so, and I suppose that's as good as we ever got.

GRAYSON: And so, this would be between the trap and the mercury diffusion pump.

NIER: That's correct, that's right.

GRAYSON: Then basically, with your trap you were pulling out the mercury so you had a quite good vacuum.

NIER: I think we always worked with better than 10-6. But I don't think we ever got down to 10-8 or lower. The mercury vapor pressure was enough, first of all, that it would probably be around this range . . .

GRAYSON: Sure.

NIER: . . . and there must've been a little water. But it was certainly orders of magnitude better than what most people were doing then. And, as I say, that was standard technique in this lab.

GRAYSON: Okay. Now, if you were introducing a sample for isotope analysis, there were two problems. One was getting the sample into the gas phase, and the other was the problem of getting it inside the instrument. I guess getting it inside the instrument would be similar to the way you would do for benzene.

NIER: Yes. Well, argon was a cinch.

GRAYSON: Oh, yes.

NIER: You just trapped some of it, that was easy.

01:01:00GRAYSON: Yes, gases would be somewhat easy. Now, for instance, for some of these other isotopes . . . ?

NIER: Well, that took a little more technique.

GRAYSON: Did you have a chemist assist you in some of these.

NIER: No, not in those days. [laughter] But I stuck to things I learned to work with . . . you see, the next thing I did after argon was potassium. (Figure 6)

GRAYSON: Okay

NIER: That was interesting, and it really fit into the nuclear physics picture because at the time there was a big argument about which isotope was responsible for the radioactivity of potassium. That'd been argued about for years. The potassium-39 and potassium-41 were well known, and many papers appeared in Nature magazine in which people were speculating, is there another isotope? Is there a potassium-40? Is there a potassium-42, or potassium-43, or some other isotope? This was right in 1933 or so, when nuclear physics was just coming in. 01:02:00I said, "Well, this is just made to order, because if I'm going to get attention around here, I need to be in nuclear physics, and here it fits in." [laughter]

So, what I did then, was to start working with potassium. And the way you did that was you got some potassium chloride, and you heated it with calcium filings, and you could make metallic potassium that way. We sealed off the potassium in little tubes with break-offs on them. I did the same thing with rubidium, for instance. That was kind of the standard thing that one did. Of course, at room temperature, potassium doesn't have much vapor pressure. So you had to run the spectrometer tube hot. But you couldn't run all of it hot--not 01:03:00the collector end--because the glass became, conductive. So, we had to separate the ion gun and the acceleration part from the analyzer part. You only heated that part of the tube, and some potassium would leak through the slit into the analyzer, but not enough to make any difference, and it would fall dead since it was cold there. It didn't bother you. It never got around to the collector itself, and that worked.

GRAYSON: So, basically, the problem of a hot-ion source is what you had to deal with.

NIER: Yes, that's right.

GRAYSON: The fundamental technological problem that we all have with samples even today. You had to devise a way of heating it, keeping it warm.

NIER: Devise a way of heating, correct

GRAYSON: Did you just wrap a heating tape around it?

NIER: Yes, just a heating tape around it. Well, we put a layer of asbestos on 01:04:00it. I should be dead! [laughter] I think the asbestos problem is badly overblown. But anyhow, be that as it may, you got a roll of asbestos, got a piece off the roll, wet it, let it dry on the glass tube, wound a nichrome heater on it, put another layer of asbestos on, and waited until the next morning and it would be dry. Or if you were not patient, you'd start putting electric current in gingerly, and it would dry out more rapidly; sometimes we put some water-glass on as a final coat to hold the asbestos in place.

GRAYSON: So, you didn't even wrap it with heating tape. You made your own heater?

NIER: I don't think heating tape was available in the United States. So we made our own heaters. Besides, it was cheaper!

GRAYSON: You made your own heaters, on the spot.

NIER: That was standard. And sometimes, if you wanted to take them off, you made a piece of aluminum tubing out of this aluminum sheeting, and wrapped it around and put rivets in it. That made a slip-on furnace, a tube-furnace that could be slipped on things.

GRAYSON: Okay, that's the end of this side.

01:05:00[END OF AUDIO, FILE 1.2]

01:06:00GRAYSON: [ . . . ] That was the primary way of volatilizing a sample?

NIER: Yes. Also, you could put a little oven into the source itself. A little locally-heated oven; that's what I did later, but not here at Minnesota. I did that at Harvard [University] when I worked with elements like calcium, and strontium, uranium, things of this kind. I had a little box that I could heat with a little heater right in the source.

GRAYSON: Kind of like a predecessor to today's solids probes that are heatable, but they were a very, very fundamental kind of thing.

NIER: Yes.

GRAYSON: Well then, what about that mass analyzer? Well we've, kind of, covered that. At this point, the early mass analyzer you worked with was essentially the solenoid design. Was this a derivative of your predecessor's instrument?

NIER: Well, there's P. T. Smith, Bleakney first, then Smith, who had come out with the idea where the analyzer was an arm on the side of the tube.

01:07:00GRAYSON: And that was essentially the technology at the time?

NIER: Yes. I have a picture of that, my first glass tube.

GRAYSON: He's going to give us a picture or a copy of that picture, right? Make a note of that, Tom. Now, you've got to detect this ion current at the other end of the tube.

NIER: Yes, and I was fortunate. In the midst of all this, the electrometer tube became available and we happened to have one. One of the other graduate students at the time had built this amplifier and so I had the use of it.

GRAYSON: We're starting from a faraday cup?

NIER: Yes, a faraday cup. I think we still used the graphite on a little fiber board for the resistors. But, about that time, you could also get S.S. White resistors. S.S. White was a dental supply place and I've never understood why 01:08:00they made resistors, but you bought a little black thing that was about the size of a fuse, like an automobile fuse. A little object about a quarter of an inch in diameter and an inch and a half long. It had leads molded in. Well, the way resistors have always been made. But this was solid, some black stuff, and I have a feeling . . . I don't know, it'd be interesting to hunt that down sometime . . . this was some of the stuff they made dental plates out of. They probably put graphite or some other electrically conducting material in it to make it dark. Somebody discovered that it had resistive properties. See, this was some kind of plastic . . . and so then, they made these things deliberately by just simply molding some wires in and you bought these things 109 ohm, 1010 ohm, 1011 ohm and so on. And if the resistance was a little lower than you wanted, you would file off or grind off some of it to make it smaller in diameter.

GRAYSON: This was to get the feedback resistance for the electrometer?

01:09:00NIER: Yes, but there wasn't any feedback in those days. I mean, it was the resistor.

GRAYSON: Okay.

NIER: You had the current go through it to get a voltage drop across it and the electrometer, just like any vacuum tube, measures voltage.

GRAYSON: Because you were working with small currents you needed a large resistance.

NIER: Yes, because the bigger the resistance for a given current, the bigger the voltage. Of course, the virtue of the electrometer tube, was that it used very low voltages. They're very well made. I still have some here by the way. Some of the original ones, and . . .

GRAYSON: Is it possible to swipe one?

NIER: Well . . . you can look at it.

GRAYSON: Or look at it or take some pictures of it.

NIER: I don't think there are many of those around. And that was the standard that everybody used for measuring small currents. The voltages on the tube . . . instead of the standard vacuum tube in those days which had like 90 volts or 135 01:10:00volts or 200 volts on the plate--were 4 volts or 6 volts. So you never ionized any of the gas that was left inside. They were carefully made, under a very good vacuum. They used oxide-coated films, so it didn't get very hot, so you didn't have X-rays or much ionizing ultraviolet. The result was the internal impedance looking into it was very, very high, like 1013 ohms or 1014 ohms or more; so when you put a resistor across the input, it wasn't shorted by the tube. They used balancing schemes by making a bridge out of the tube. It was a pentode, so it had several electrodes in it and you had a galvanometer between the screen grid and the plate. The galvanometer measured, then, the unbalance of the circuit when current flowed in the resistor between the cathode and input grid.

01:11:00GRAYSON: So, then, the output of the tube was measured by the galvanometer deflection? Is that the way it was hooked up?

NIER: Yes.

GRAYSON: How did the signal information get from the galvanometer to the recorder.

NIER: Well, the light reflected from the mirror on the galvanometer to a scale. And you read the deflection.

GRAYSON: So, you read the scale off as you went along? And adjusted the put-and-take-box.

NIER: Yes. That's right. And then you took the reading. You waited till the galvanometer got to equilibrium, five seconds or so. You had to have the right damping resistor in the galvanometer so it didn't oscillate. It took time.

GRAYSON: Yes. [laughter]

NIER: Except for the long time it took, you could still make very good measurements. You could also get by without a resistor and just measure the charge build-up in the capacity of the system. You then got a rate-of-drift 01:12:00measurement, and you'd measure the rate. In all of my work at Harvard, where I'd worked on very rare isotopes, I did just that. (Figure 7) I took the resistor off and watched the rate of drift. You could measure currents about 10-16, 10-17 amperes. You waited, like, 30 seconds for the spot to cover the scale, and you worked backwards for calibration.

GRAYSON: So, the drift measurement would be kind of like an integrative . . .

NIER: That's right, an integrative measurement.

GRAYSON: . . . integrative measurement, compared to the electrical detection scheme.

NIER: That's right. And that was used by people long before my time; there were people doing ionization measurements with radioactivity. They had been working with that kind of technique for years. I mean, that was nothing new. That was the technology of the times.

GRAYSON: That was standard practice.

NIER: Right. We sometimes forget that individuals were doing some pretty exacting experiments in the 1920s.

GRAYSON: They didn't have the technology we have today, but they were still 01:13:00using what they had to make very good determinations.

NIER: They were doing some very good measurements. Slow . . .

GRAYSON: That's interesting. As an aside, I talked to a friend of mine once, and we were going to do a little discussion of . . . [beeper beeping]

NIER: Pill time. I'm sorry. Go ahead.

GRAYSON: Okay, we were going to do a little local course on mass spectrometry for some of the people in St. Louis, and I told them, "I'll bring a spectrum from a magnetic machine, you can bring a spectrum from your quadrapole machine, we can show them the difference." And he said, "I can't get a voltage versus mass signal out of my quadropole mass spectrometer." The computer takes everything. How can you do that? You have to be able to look at the mass spectrum in reality somewhere along the line but, in modern instrumentation, in a lot of modern instrumentation, it's not available, you cannot look at it.

NIER: Black box.

01:14:00GRAYSON: So, I think the point that you mentioned about this early work is that people certainly knew how their machines were performing every step of the way.

NIER: That's correct.

GRAYSON: Because if they weren't working correctly, you certainly were aware of it.

NIER: You knew it right away.

GRAYSON: What about some of those problems, incorrect performance? Obviously, we're talking about experiments that worked. There were some that didn't work, right? You had problems or difficulties.

NIER: I was very naive when I was here doing this work. One of the interesting things that I ran into was mass discrimination. We didn't worry much about discrimination in the instruments; I guess I didn't know enough. You sensed from things that you knew, that it must be working. You'd put nitrogen in and people had measured the nitrogen-14, nitrogen-15 ratio roughly. So, you knew it worked.

One of the things I encountered, but not really seriously until I went to Harvard after I left here, was how to make sure that the ion source doesn't 01:15:00discriminate. I became pretty good at judging the performance of the source by changing various parameters and seeing how an isotope ratio varied. For instance, what I used as a standard when I was at Harvard, was mercury, because there was always mercury present, because of the mercury vapor pumps. I would compare the ratio of the mercury-204 isotope to the mercury-198. I think if you look at a modern isotope table, the mercury-198 is very close to 50 percent higher than the mercury-204. So I would look at the mercury, and I would diddle with the ion repeller voltage that you used to push the ions out of this ionizing region and fool around with other things. If you used extreme values, 01:16:00you might get funny ratios; instead of 1.5, you'd get 1.6 or 1.7 or 1.3 or something of that sort. So, I got to be pretty good in estimating when it was working right. Keep in mind, we had no standard isotope mixtures that you could go against. It was just your intuition and experience.

GRAYSON: Well, at the very least, though, you were tuning the instrument to a point where the ion source operation would be standard.

NIER: Standard, yes, and not critical. For instance, you could change some of these parameters so that the values you got didn't change much over a big range, and then it would drop off the end. You worked in the middle of the range. It was always a system of compromising. And this was . . . experience, I mean you had to learn and it took a lot of feel, you couldn't have a technician come in and take data tomorrow morning. You had to do it yourself.

GRAYSON: Right. So all this data that was acquired with regard to the isotopes . 01:17:00. . there were a lot of little techniquey things that were done . . .

NIER: It was just full of it!

GRAYSON: . . . in order to make sure that when you got to the end, and there was an answer, that it was indeed an answer which represented a measure of reality as opposed to just measuring something that came out.

NIER: That's right, that's right . . .

GRAYSON: You've got a source discrimation problem that you had to deal with. Tuning it so that it wouldn't discriminate between the various isotopes. What other kinds of problems did you have to deal with to ensure that you had an answer that you could put in the literature and not have someone come after you with a . . . [laughter]..blunderbuss.

NIER: Well, you worried about impurities, of course. If you were talking about rare isotopes, you were always worried about interference. You did tricks like change the electron accelerating voltage. In potassium . . . see, I found potassium-40 when I was here. [3] That's what really set me up in business because it was only abundant one part in 8,600 I think, something like that. And that was really very difficult, but I remember we did 01:18:00tricks. When you ionize potassium, it takes . . . I don't know what the ionization potential is--about 3.8 volts or some number below 5 . . . way, way down. And so, if you ran the electrons slow enough, you'd eliminate most other impurities and interference. You'd do tricks like this. Or if you're dealing with vapors, such as potassium, I'd change the vapor pressure by heating the source or cooling it and seeing if the potassium-40 tracked to 39-41. You did various tricks of that kind, you worried about doubly charged ions interfering or whether you got doubly charged when you wanted them. You did all these kinds of tests. And again, as I say, this represents experience. You got a feel of when things were right.

GRAYSON: Well, you're keeping a very critical eye on what you're doing, every step of the way, to ensure that you're not making assumptions which will get you 01:19:00in trouble later on.

NIER: That's right, that's right.

GRAYSON: And, purity would be a problem. Did you rely on, for sources of these materials say . . . for instance, potassium, did you rely on a chemical house or did you have special samples made?

NIER: Well, both. But most of the stuff came out of bottles from chemical houses. It wasn't till later that I had lead samples made for me when we were doing the geological work, but that was because you had to make those. But most of these things just came out of bottles. You could do a pretty good job making potassium and rubidium, for instance. When you made it yourself out of the chlorides, with calcium, you automatically got a pretty pure assay on it.

GRAYSON: Because?

NIER: The process itself did it. And then the vapor pressure; other things were not that volatile, so you'd distill the stuff over, and get pretty good stuff.

GRAYSON: There were a number of different things that helped you to get it. And 01:20:00it was, again, another aspect of the whole measurement problem that you took into account as you proceeded to do this work, and to determine these isotopes.

NIER: That's correct, right.

GRAYSON: So, now your recorder in these days was really, the person individually. He wrote down the results.

NIER: With a pencil . . . and a notebook.

GRAYSON: [laughter] Then you did what--did you plot the data?

NIER: Plot it on graph paper, on 8-1/2 x 11 graph paper, 1/2 inch standard paper. [laughter]

GRAYSON: And took into account all of the multiplication factors?

NIER: You had a shunt on the galvanometer to cut the sensitivity so you could change scales. So, we'd have steps like factors of two and a box that you switched. And generally you made the shunts yourself. You could also buy these, 01:21:00but I think we made our own. We had precision resistors and you bought multiple point switches--and you wired resistors between the points; and that was it.

GRAYSON: So, basically the technology of the vacuum system was there, pretty much to the same level as we have it today. Some of the detection was getting there with the advent of the electrometer tube. In terms of recorders and sample inlets and actually mass analyzers, the technology was kind of not where it is in modern-age, yet. I mean, there was a lot of evolution that had to be done. But fundamentally, the vacuum system and some of the electrical detection was pretty far along.

NIER: Yes, was really quite far along. As I say, I came in just at the right time on that. The interesting thing is that, nobody used inverse feedback 01:22:00amplifiers yet. And the first ones we used were during the war or just at the beginning of the war. They ended up in all of the Manhattan Project instruments which we developed. There had been very few publications on inverse feedback amplifiers.

GRAYSON: What we know today as the operational amplifier.

NIER: The operational amplifier . . . that's right. Of course it was all vacuum tube stuff in those days so it was sort of tricky the way you wired stuff together. But we started using them in about 1940 for our work. They were never as stable as the plain electrometer, so at first we used them only for measuring large currents; for example, we used them when we did a multiple collection with the instruments used for analyzing uranium in the Oak Ridge [Tennessee] plants used for isotopic separation.

01:23:00Actually, we started using feedback amplifiers here in 1940, well more like 1941, when we separated carbon isotopes for biological experiments. [4] We had to do a lot of analyses, so we built the first system where we could measure the 44 peak, CO2 with the inverse feedback amplifier and then balance a fraction of the current against the current from the 45 peak. You would have a low impedence output on the feedback amplifier; put a decade box across it and then take a fraction of that and balance it against the 45 peak. Then you used the galvanometer as a null reading device. And that's when we started measuring ratios directly.

GRAYSON: So, that really represented, for the isotopic abundance work, a technological step forward.

NIER: That's right, a real step forward.

GRAYSON: A step of real significance. Because the answer was almost there and 01:24:00basically, it was just a matter of getting some stability.

NIER: There were a few publications on inverse feedback amplifiers at the time when I was at Harvard, from 1936 to 1938. The people there in electrical engineering were very good, and they knew all about inverse feedback systems and I learned a lot about how you build inverse feedback amplifiers. There were two guys by the name of [F. V.] Hunt and [R. W.] Hickman who were faculty members there, who had worked on inverse feedback circuits for high voltage supplies. [5] They had a publication on it and I learned from them how to build inverse feedback devices.

GRAYSON: Do you feel that your background in double-E [electrical engineering] helped you here again?

NIER: Immensely.

GRAYSON: Because you were able to pick up where they were right away and you could see exactly what it was they were doing.

NIER: I understood right away what they were doing. And there were tricks, like especially in the power supplies because you had high voltages and you had 01:25:00problems isolating things and getting it down to a low voltage. There were all kinds of tricks, so unless you understood circuit theory you couldn't get very far.

GRAYSON: I would gather, then, the dynamic range of these instruments--even the earliest ones you worked with--was really quite good.

NIER: Yes, it was quite good. You see, at Harvard, I had a standard glass galvanometer scale 50 cm long and you could read this to a fraction of a millimeter. The light spot was focused and it had a hairline that projected an image on the scale. You could read that to say 2/10 of a mm. Then your shunt on the galvanometer changed the range a number of times. And if you used drift methods for very small currents, you picked up another factor of 100 or 1,000. So I suppose, we were playing with million to one dynamic ranges. It was cumbersome, but it worked.

01:26:00GRAYSON: Yes, but essentially, mass spectrometry has inherent in it the need for that type of dynamic range capability.

NIER: That's right. Yes.

GRAYSON: And even though at the time, the technologies were not as advanced as they are today, you were actually making use of the full dynamic range then.

NIER: Yes, that's right.

GRAYSON: You mentioned Harvard a number of times. Maybe we should move on to Harvard for a minute. But first, you were encouraged by Tate to get into a different area. Were you, kind of, kicked into a different area? [laughter] Did he recognize that what you had gotten into was valuable?

NIER: Well, indeed. When I was able to do the argon in one afternoon, and then 01:27:00moved on to potassium and found K-40 [potassium-40], then I was really high on his list.

GRAYSON: So, you moved up from the bottom to the top? [laughter]

NIER: Yes, and there was another fortuitous thing that happened in connection with that, which is most interesting. Tate was editor of the Physical Review and we published in the Physical Review. I'd made the K-40 discovery in spring of 1935, just about the time he was ready to leave for the summer to go to Columbia where he taught a course in summer school. My paper on K-40--it was a letter and I have copies of this by the way--went into him as editor. So, here he was, my advisor, and also the editor. [laughter]

GRAYSON: That's an interesting situation. [laughter]

NIER: And I was his student. He was very cautious and did not like students making mistakes.

GRAYSON: He had your whole life in his hands. [laughter]

01:28:00NIER: Well, he accepted the paper as editor, and it was in press. You couldn't stop the presses. As I say, this was an interesting field at the time. There was a guy at the Department of Agriculture, his name was [A.] Keith Brewer, who was really a pretty good physicist. He was working on isotope abundances in the alkali metals and used thermal ionization in his work. You heated up a salt of the element you were interested in and got ions out. Brewer also was working on potassium, which I didn't know at the time. He had a nice instrument, and with thermal ionization you didn't have the impurity problems; at least of the kind 01:29:00we might have. While my letter to the editor was in press, Brewer sent in a manuscript to the Physical Review in which he stated that potassium-40 could not exist with an abundance [of] even a tenth as much as I said was there. So, here was my advisor and the editor of the Physical Review. [laughter] I don't think he called me, but I think he wrote to me. I may even have the correspondence.

GRAYSON: That would be worth looking for.

NIER: It would be worth looking for, because this was most interesting. But anyhow, I know I was quizzed, "Did I do this, did I do that, am I sure on that?" And I convinced Tate that what I had done was all right. So, he wrote back to Brewer and told him of my work and that this was being published and wouldn't he, Brewer, like to do his work over again to check. Whereupon Brewer did it 01:30:00over again and he got 1 in 8,300 instead of 1 in 8,600. [6] Well, I only claimed an accuracy of 1 percent. So, we agreed. What had Brewer done wrong? He had nice flat-topped peaks. His resolution wasn't as good as mine. He had nice flat-topped peaks, so if you're looking for a little bitty thing in a valley between two big things, between potassium-39, potassium-41 if you have a nice flat-topped peak, all it does is raise the level in the valley. And he didn't see as sharp a bump in there as I saw. So, when receiving Tate's letter, he did something; probably narrowed his slits, and of course, he found K-40. Then, he published a value confirming the value I had turned out. His letter to the editor is in the literature, a few months after mine.

GRAYSON: So, basically, Tate was kind of in a tight spot. Because, he had work 01:31:00from his student, who was very young, that said X . . .

NIER: Who was very young. [laughter]

GRAYSON: Yes, who was very young, that said X, and here was a fellow . . .

NIER: Who was experienced, he was an older man. And he had a very good reputation. He had done good work . . .

GRAYSON: And who had published before in this area . . .

NIER: He was an authority . . .

GRAYSON: Was recognized, and so, he must have asked some pretty incisive questions before he sent this back to Brewer and said, "Do it over again."

NIER: Well, this didn't hurt when it was all over with, as you can imagine.

GRAYSON: Yes, definitely. [laughter]

NIER: So that's what really was a decisive factor, I'm sure, in my getting a National Research Council Fellowship. After all, here I was, twenty-four or twenty-three years old and had found a new isotope and it was an important one because of the radioactivity business and so on. I'd demonstrated that an authority in the field had done it wrong, so what more do you want? [laughter] 01:32:00So, that was very helpful.

GRAYSON: I assume Tate had the connections inside the system that would have set your . . .

NIER: Yes, he was a wheel. He was the editor, and he was on the council of the American Physical Society, and everything else, and on the board of the National Research Council. So, he could write letters and say this is a guy you ought to support, and soon, and so on.

GRAYSON: So, you were going from the low man on the pole, so to speak, to the top of the pole. It was almost fortuitous wasn't it?

NIER: That's right. Well look, I've been retelling you these things that happened. You had to be there to take advantage oft he opportunity. It's always true, but, you know, the opportunities were there, that's just the point. That was a very fortunate break because there were only two fellowships in physics, two in chemistry, two in biology. That wasn't very many--in the whole United 01:33:00States. I got offers, then. I had the fellowship, and of course the schools said they'd like to have these people come as post-doc's, it didn't cost them anything except for their lab expenses.

GRAYSON: At this time you were a post-doc?

NIER: Well, I had just gotten my degree in 1936 here. So in the spring of March or thereabouts I got word that I'd been awarded a National Research Council Fellowship, 1,600 dollars the first year and if you were appointed a second year, it would be 1,800 dollars. That was a lot of bucks. So, where to go? That was the next step.

GRAYSON: Okay, then you had, to choose . . .

NIER: Yes. Bleakney got in touch with Tate or with me and said "Why don't you come here, [to Princeton] and carry on the tradition?" See, two other guys had already gone there and why not me? Meantime, [Kenneth T.] Bainbridge, at Harvard, who was in mass spectrography in the business of measuring precise 01:34:00masses, had built this beautiful double focusing machine, together with a guy by the name of Ed Jordan who had gone to Harvard as a post-doc to work with him. Bainbridge was one of these wonderful people that you wish you could meet all the time because he was very generous and very interested in helping people. He assured me money from their private funds. After all, Harvard had endowments. There was a fund called the [William F.] Milton Fund--named after somebody, some benefactor. I think they offered me, for my lab 5,000 dollars. Which was a lot of bucks in those days. That'd be like 100,000 dollars or something like that today.

GRAYSON: And it was prestigious institution.

01:35:00NIER: Right, and free shop-work and the like. They had machinists. So, he offered me that opportunity. And told me about all the wonderful things: I could come there, I could supplement their mass work, I could be the abundance guy. He had a good reputation, he was real first-class scientist. Bleakney on the other hand was also very good. Well, Bleakney said if I came Princeton, I could build a super-duper spectrometer using their cyclotron part time. They were just building a cyclotron. And, I could build a bigger 180 degree spectrometer than anybody. Everybody was thinking in terms of 180 degree deflection in those days. I could have had a radius of curvature of 2 feet or more. Cyclotrons magnets had a diameter of 6 feet or more. The idea was that I could have the magnet part-time.

01:36:00Well, I thought about the matter a little bit and decided, for a variety of reasons, that I should go to Harvard rather than Princeton. One of them being that to be realistic, to think that I could have the magnet for much time . . . to have them take all of the guts out of the cyclotron and replace it by the spectrometer at a time when nuclear physics was really hot just didn't seem very realistic. Not that they wouldn't have treated me well, in other ways. But the whole scenario didn't seem very realistic. Also, I thought, maybe instead of everybody from Minnesota going to Princeton, somebody ought to go to Harvard for a change. Tate didn't discourage me. He agreed that was a good idea. This was a very happy thing for me. I think it would have been a more friendly atmosphere at Princeton. I would have felt much more at home there, because Harvard, at the time, had a reputation of being . . . I wouldn't say "unfriendly . . . but it was, kind of, New England cold, and they were pretty formal.

01:37:00[END OF AUDIO, FILE 1.3]

GRAYSON: Okay, we're recording Side B of Tape Two, and Harvard was a cool place. [laughter]

NIER: Cool weather-wise and cool otherwise. [laughter] Well, I found Bainbridge extremely friendly. The people I met were extremely pleasant. The people were 01:38:00not all New Englanders. True, the atmosphere was a bit formal, but friendly. And I found everybody to be extremely cordial.

GRAYSON: Even then, the Midwest and the Northeast Coast have this difference of . . .

NIER: Oh yes, there's a different culture.

GRAYSON: Yes.

NIER: But, it turned out a lot of the Harvard people were Midwesterners and Westerners. True, you had a lot of hangers-on from the East that stayed there. One of my very good friends I shared a lab with was working on high-pressure stuff there. It was a big lab, and I had one side of it and he had the other side of it. He was from California, for instance. So, there were people from all over. It was really quite cosmopolitan. And Bainbridge was very helpful.

At the same time, I also got an offer to work at General Electric. They were 01:39:00interested in hiring people who had just gotten degrees for summer jobs and also graduate students. So, I was offered a job at GE, working for the summer before my fellowship started in Fall. I went to Schenectady [New York] for the summer months, and my boss was [Chauncey] Guy Suits, who later became the director of research for General Electric. But he wasn't at that time. He was a promising young man in the lab. I worked on arcs or something like that. He was interested in vacuum arcs, and the techniques I had, of course, fit right in. It wasn't the most productive summer. I don't know if I did him any good, but I certainly learned a lot.

GRAYSON: And, you probably made some connections there that helped you later on, perhaps.

NIER: Some. I got to know him, I got to know [Saul] Dushman.

GRAYSON: Okay, that's a nice guy to know. [laughter]

NIER: A nice guy to know. We became good friends later on. I met everybody else: 01:40:00Albert Hall, who was the associate director, I met [Irving] Langmuir, even [Willis R.] Whitney, who was the pioneer in the lab. So, I met all these people . . . I'm sure they didn't remember me. But, Dushman did. I met other young people like myself, I got to know people. I knew Fred [Frederick] Seitz, he was one of those working there in the summer also, and stayed on. There were quite a few. John [P.] Blewett, one of Bleakney's students in mass spectrometry, also had a job there, working on something else. So, I got to know other people.

GRAYSON: GE had a number of summer appointments.

NIER: Yes, working in basic science.

GRAYSON: Okay, do you know if they had an ulterior motive.

01:41:00NIER: This was a recruiting scheme, if that's what you mean. You know, get a line on young people . . .

GRAYSON: Okay.

NIER: The standard thing that goes on at many places.

GRAYSON: But they had to commit to the concept that these people had valuable talents and assets for the future of General Electric and its products.

NIER: That's right. They wanted to look at the young people, and see, they didn't have to make any commitment.

GRAYSON: Sure.

NIER: It was a neat way to do it. Very good.

GRAYSON: Well, the same thing is done today.

NIER: Oh, it's done everywhere. The government has a lot of post-doc positions at the Bureau of Standards, and at the Naval Research Lab, and places like that, with the same kind of idea where it's a one or two-year thing, except that in my case, it was three months.

NIER: So, that was a good experience.

GRAYSON: And then you went on to Harvard?

NIER: I went to Harvard in the Fall. But, more important than that, before I settled at General Electric, which was around 1 July that summer, the summer of 01:42:001936, I went to Harvard to meet Bainbridge. I had never met him. I had an old car then that just barely got along. He and another family from the electrical engineering department at Harvard shared a big house in New Hampshire. This was the standard thing, you rented houses on an abandoned farm or something like that. So, they had me as guest over there for a weekend. I met him very briefly at Harvard, and then he went up to New Hampshire, and invited me to come up there later on in the summer. We sat around for about a half a day, and talked about what I ought to be doing. This was the beginning of July, and I wasn't going to be coming until September. We came up with the design of an electromagnet--this 2-ton electromagnet--which became the basic magnet for the 01:43:00instrument. The decision was, we should make something bigger, get away from the solenoid, and then you'd get a stronger magnetic field by having an electromagnet with a smallish air gap. So, we came up with a magnet that had a two-inch air gap, and I think it was 12- inch diameter poles. Something like that. (Figure 7)

GRAYSON: This was still 180 degree deflection.

NIER: Still 180 degrees, yes. And so we built it, and it had a five-inch radius. That was the original 180 degree tube that fit between the poles of the magnet. This whole thing was sort of designed there, between us. I don't know how much my contribution was and how much Bainbridge's was. He certainly contributed a lot on the magnet design. He knew about how you built magnets.

GRAYSON: The basic idea of a 180 degree deflection instrument, was that in the literature?

NIER: That's what everybody had used. [laughter]

01:44:00GRAYSON: The idea of putting the ion entrance right at the edge of the magnetic field was already used?

NIER: No, you had the whole thing immersed. And what I had to do was to build an ion source that would squeeze into a tube that would fit into a two-inch air gap. And this is where the modern ion sources came from really. From that everybody else has pretty much copied. You see, the ion sources that I was acquainted with, which Bleakney had used, which P.T. Smith had used, which Wally Lozier had used. You had a long electron accelerating system because it was in a solenoid. The ion sources were five or six inches long. You accelerated the electrons in stages, and you had diaphragms to screen the sections. You did a very careful job of defining the electron beam without having stray fields. That 01:45:00was important if you were going to do electron-impact work quantitatively. But if you were just going to play with isotopes, it didn't matter. It was a matter of compressing the source enough so that it would fit into the tube. So, we used a 45 or a 48 millimeter tube--48 millimeter, I think it was--which would fit in a two inch air gap, along with an oven around the tube. I still have one of the tubes.

GRAYSON: Well, I'll need to get a look at it.

NIER: You can look at it. I have some old tubes up here.

GRAYSON: I need to get a picture of all these wondrous old things.

NIER: It was a matter of designing the source to fit that gap, which I did.

GRAYSON: What you're saying is that there was a point of departure here, and, you were trying to take all the stuff your predecessors had done and squeeze it into a smaller space?

NIER: Squeeze it into a smaller space.

GRAYSON: Or were you trying to actually redesign the whole concept of the ionization region?

01:46:00NIER: No, I think the idea which they had was sound. It was a matter of squeezing it, so it would fit in there.

GRAYSON: Okay.

NIER: Without losing too much.

GRAYSON: Okay. So you were still trying to get some of the capability of their design.

NIER: Oh yes, very definitely. And so, you didn't do as good a job of separating the fields which accelerated the electrons and the ions. It didn't work that well. But it was good enough for the isotope work. And that was what I was going to work on, was isotopes, see?

GRAYSON: Now, when was that design was worked out? Over the summer, or when you started working at Harvard? In the summer you had decided on the . . .

NIER: The magnet, that's right.

GRAYSON: Having established that, then you had to deal with fitting the ion source in the air gap.

NIER: That determined how much space we had.

GRAYSON: Yeah.

NIER: I suppose I thought about it during the summer. And when I came back in September, I started working on it. Because I got there right after Labor Day, 01:47:00or Labor Day weekend, in September, and I had spectra before Christmas.

GRAYSON: Okay, that was 193 . . . ?

NIER: 1936.

GRAYSON: 1936.

NIER: So, in three months, I had an instrument running. Now, Bainbridge, in the meantime, once we'd decided on the magnet, had gone back to Cambridge [Massachusetts]--I think he commuted--and had got the magnet started.

GRAYSON: Sure. Because that would be a pretty substantial piece of work.

NIER: Yes and they had a good shop. First-class guy at the head of it. And industry was interested in jobs. Of course, Bainbridge's idea was: you had only the best, you had to have special materials. So, he got hold of Armco iron with low carbon . . . good magnetic properties; and he contacted whoever it was in Ohio on how these things were made. They cast a big yoke, a big C-shaped yoke, 01:48:00and prepared coils on it. Remember, this was using about five kilowatts. They had water-cooling tubes; they drew square copper tubing for cooling tubes. Square copper tubing!

GRAYSON: Sounds like a first-class operation. [laughter]

NIER: First class. But, industry was interested in jobs. Boy, I'm telling you there was a Depression, it was in the middle of the Depression.

GRAYSON: So, if you had money, and . . .

NIER: If you had money, boy, you were king . . .

GRAYSON: And if you wanted square copper tubing . . . [laughter]

NIER: You got square copper tubing. [laughter] They didn't mind drawing square copper tubing on special order. So, by the time I got back, in September, the magnet yoke may have even been delivered. It was being machined--they probably 01:49:00machined it at the factory. Certainly, that magnet was running by November.

GRAYSON: Now, the pole faces for that . . . were they 180 degree?

NIER: Full circular. Everything was symmetrical. Full circular.

GRAYSON: But the ion path was 180 degrees.

NIER: 180 degrees.

GRAYSON: So you had that tube in there.

NIER: And I have a good picture of that instrument, by the way.

GRAYSON: Yes, yes. [laughter] We've got to add that to the list of things to collect. Did you put a glass tube in this machine?

NIER: Glass. It was sort of horseshoe-shaped. The ion source was in a cylindrical part, and attached to that was the 180 degree analyzer, and you brought out an arm at right angles to that; I have a reprint on that.

GRAYSON: The glass-blowers must have loved you guys.

NIER: It was wonderful! And they would do these beautiful ring seals so you could separate the source part from the analyzer part. Now, I did all the glass-blowing on the little stuff. Like, you see, if you wanted to change the 01:50:00source, you cracked the tube off. As I think back, I think it was 45-millimeter tubing. See, it took a little skill to heat 45 millimeter tubing and not have strains in it.

GRAYSON: Yes.

NIER: And you weren't always successful, so you sometimes had problems. But we had a very good glass-blower at Harvard, as we had here.

GRAYSON: Was it pumped by a mercury diffusion pump?

NIER: Yes, all mercury. I had two systems. One for the inlet system and one for the mass spectrometer.

GRAYSON: Did they use liquid nitrogen there or were you still using that carbon dioxide bath?

NIER: Both. But, I think we used liquid nitrogen more frequently.

GRAYSON: It was easier to get there . . .

NIER: It was easier to get there than here.

GRAYSON: And so, by December, you were actually getting spectra.

NIER: Yes, I got my first spectrum of mercury.

GRAYSON: Did the detection scheme use the faraday cup-electrometer tube?

NIER: Very much like I'd used here. I built the thing up, and they knew about 01:51:00this technique. But I built my own amplifier; I had some help from the shop. But I did all the wiring myself.

GRAYSON: Okay. Could you also do the integrating type of measurement?

NIER: That's right, that's right.

GRAYSON: Charge drift, was that you called it?

NIER: Yes.

GRAYSON: Was there anything in the literature about how that was done, this charge-drift measurement?

NIER: I suppose, if you look back to 1915, or sometime like that . . . but it was understood. You simply charged up the capacity of the system. And the voltage was equal to the charge divided by the capacity. So, you just built it up.

GRAYSON: When did the first publishable data come off the machine?

NIER: Pretty quick. In the Spring. [7]

GRAYSON: And that was done on?

NIER: Well, I played with krypton and xenon, and mercury, about the first thing . . . so, my first paper involved a number of elements.

01:52:00GRAYSON: Mercury . . . you mentioned it before. People looked at it because it was in the vacuum system.

NIER: Yes.

GRAYSON: I guess there was information in the literature on the isotopes of mercury then?

NIER: Not as good as I was able to get.

GRAYSON: That's around 200, and the performance of this machine at Harvard was absolutely better than anything you had before.

NIER: Oh yes, 200 was a lead-pipe cinch. [laughter] No, I worked up in 300, when I was working with uranium and such.

GRAYSON: Okay.

NIER: So, there was no problem. I got another break at Harvard. It was a marvelous place. In addition to the people, they had marvelous facilities. They had a 100,000 volt storage battery, which had been used by a guy by the name of Duane, for precision X-ray measurements. The battery was used to get the voltage 01:53:00accurate for X-ray studies. It consisted of 50,000 little glass cells, each having one or two watt-hours capacity. When Duane completed his research the cells were emptied and dried out. If people needed a low capacity storage battery for research, there was a technician who reactivated the cells by filling them with sulphuric acid. So, I had 2400 volts of battery. It was a little dangerous. [laughter] I got a nice burn on it one time. Got across it . . .

GRAYSON: Yeah. There was no current limit.

NIER: No current limit . . . this is how you get electrocuted. So, aside from that hazard . . . everything went well. [laughter] Most of the time I accelerated ions by at least 1200 volts, and I guess at times, I used up to 2400, but I don't remember . . .

GRAYSON: So, let's see, for the higher masses, you'd go to the lower accelerating potentials anyway.

NIER: Well, you had to use as high an accelerating potential as possible, because that's what helped your resolution.

01:54:00GRAYSON: Sure. This was a fixed-field . . . the magnetic field was fixed?

NIER: Oh, no . . . electromagnet.

GRAYSON: Okay.

NIER: Then I had a problem with my magnetron scheme; it wouldn't work. I thought it would be a lead-pipe cinch but the stray field outside of the magnet would not track the field in the gap, because of the hysteresis in the iron. So this was when I had to build an amplifier to control the field of the generator itself. It was a DC generator, and they employ a fixed magnetic field, which the armature turns in. One adjusts the output voltage by changing the DC current through the field coils of the generator. So I had to build an amplifier that would control that, using the output voltage of the generator with a feedback system, and that's when I made use of these wonderful people there in the 01:55:00Electrical Engineering Department, Hickman and Hunt, who knew all about feedback amplifiers. I got a lot of good tips from them about how to build it, but I had to build it myself.

GRAYSON: Well, you had the technological know-how.

NIER: That's right; it wasn't easy by the way, because of the hunting of in high gain feedback systems. There's a lot of time-lag in a loop involving a generator. So, feedback is all good and well, but you get into oscillations if you don't do it right. A lot of effort went into perfecting the circuitry. But, it was possible to stabilize the generator well enough, that we got the stability we needed.

GRAYSON: So, what you really were using here was a stabilized power supply.

NIER: DC. That's right.

GRAYSON: As opposed to the method with the solenoid.

NIER: That's right. So, I had to stabilize the output of the generator. The thing that worked to help you, was that the magnet itself had a high inductance, so it didn't respond rapidly. All you needed to do was to make sure that the average of the voltage you pressed on it stayed pretty good. There was still 01:56:00ripple, because you never get rid of that in a DC generator. But we got it down, so it was pretty damn good.

GRAYSON: The whole concept of that magnet and its size and the power required to drive it, obviously, you wanted a magnet with a fairly high magnetic field.

NIER: Yes.

GRAYSON: You just looked at the technology at the time, and decided the parameters you needed to make this particular thing.

NIER: Well, I think once we made the decision to have a five-inch radius of curvature for the instrument; then, it told you what the relationship between the magnetic field and the accelerating voltage had to be. We wanted to use, a couple thousand volts accelerating potential so you knew what the magnetic field had to be. We pushed this up, I don't know, 8,000-10,000 gauss, something like that. It was very good magnet material.

GRAYSON: It was very high for that time.

NIER: Oh yes, very high for that time, that is correct. But that's what pushed the whole thing up to something that was different.

01:57:00GRAYSON: So, basically, there was a decision to get a certain performance, and then, given that; you had a certain accelerating potential required, and so on, and that's what drove the design.

NIER: That's what did it.

GRAYSON: The earliest work that was published was on xenon and mercury. In the case of mercury, you were measuring the isotopic abundances?

NIER: Well, there were values in the literature--I've forgotten exactly--but I think the only values in the literature were produced by Aston. This was accomplished with a photographic plate as a detector, measuring the density. How this guy ever got anything out of that, I don't know. It was amazing how well he did, you know. But, on rare isotopes, he usually was off. Because, remember, his apparatus had lots of grease and wax joints and water was present. Ions were produced in an electrical discharge. So, Aston missed the boat on rare isotopes 01:58:00generally. He either found things that weren't there, or didn't find them or had other problems. There was some question about his mercury results. The mercury-196 isotope, for instance, is a very rare one, and he was off by a factor of five or thereabouts in the amount--I don't remember exactly, but he was off. I could show there were no other isotopes such as mercury-197, mercury-195, mercury-203, and so on. I was able to establish that beyond any doubt.

GRAYSON: So as late as 1937, even though mercury had been in mass spectrometers probably from the first year, that was probably the first time it was really accurately known what the isotopic abundances were.

NIER: And the amount, that is correct. And those values we got then are still pretty good, you know. The people since then have done it with separated isotopes and precision calibrations, and so on, but if you look at the original values, they're not bad.

GRAYSON: Now, you spent several years at Harvard?

NIER: I was there two years.

01:59:00GRAYSON: Did this collaboration with Bainbridge work to his satisfaction?

NIER: Oh, he was very happy.

GRAYSON: So, he was pursuing the mass measurement problem?

NIER: Mass measurement, yeah. That's right.

GRAYSON: And you were pursuing the abundance measurements.

NIER: And he'd gotten into other things, also. They were going to build a cyclotron at Harvard, and he'd gotten involved in that. He was very happy. As long as I was getting along, he felt his role was to see to it I could do what I wanted to do. It was an assistant's utopia.

GRAYSON: It was an ideal situation. [laughter]

NIER: [laughter] Really, an ideal situation. A most wonderful person . . .

GRAYSON: Much better than having your advisor tell you that, "Gee, you did it," and publish it . . .

NIER: No, and he, he was just wonderful.

GRAYSON: So, what do you feel were the most important things that came out of your stay at Harvard?

NIER: Well, to be sure, determining the isotope abundances was interesting and important, because it was the first time people had done reasonably precise 02:00:00measurements of abundance. Now, I might say, at the very same time, by coincidence, Bleakney, and several students at Princeton were doing similar things, but hadn't moved in the direction that I had. They did some other nice things on isotopes at the same time I was at Harvard. They were working on different elements. There was never any overlap.

GRAYSON: Okay.

NIER: So, I continued with that work. But then the significant thing that happened in that period was the introduction to geochronology. It happens that this was a heck of a good place to be for this. First of all, T. W. [Theodore W.] Richards, who was the atomic-weight chemist of the early part of the century and got the Nobel Prize [Chemistry, 1914] for his work on atomic weights, had a 02:01:00marvelous collection of stuff that he left behind when he retired, or died, or whatever happened to him. And his successor was a guy by the name of Gregory Baxter, who had all of this material. You have to remember that after the discovery of radioactivity in 1897 or 1898, or whenever this was, people became interested in geochronology when it was realized that uranium and thorium decayed to form lead. So, measuring the atomic weight of lead was important. That became a hot field in 1910 or so. That's when Richards did his work. Chemists showed, that if you had common lead, you got an atomic weight of 02:02:00207.21. And then, if you had uranium-lead you got a weight near 206, because 206 and 207 came from the decay of uranium. From thorium, you get close to 208. So the chemists were measuring the atomic weight of lead to tell how much common lead impurity was present in these different specimens.

Then there was a guy by the name of Alfred Lane, a geologist, who was retired and lived near Harvard. He had been at Tufts College--it's now called Tufts University--which was in Sommerville [Massachusetts]--a suburb next to Cambridge. He was one of the very few persons in this country interested in quantitative geological age measurements. Not just stratigraphy, but numbers.

GRAYSON: This would be in 19 . . . ?

02:03:00NIER: 1936. I was introduced to him, when word got around that I had a mass spectrometer that could work on lead and uranium, and other heavy elements. I'd suddenly made a lot of new friends, you see. Lane was a wonderful guy. He was a funny guy, but wonderful.

GRAYSON: In what way?

NIER: Well, sort of, peculiar. He bustled around, and really had interesting mannerisms. First-class scientist, and a very well-known geologist of his day. He used to come around with a little bag, and he was getting a little absent- minded, and his mind would wander, and he had a little notebook he wrote in. He had very interesting mannerisms. Wonderful guy. And, so, he was very interested in my work, and tried to promote it, getting samples and things for me to work on. So I spent most of my time, or a very large part of it, working on things related to geochronology.

GRAYSON: And Bainbridge felt this was fine?

02:04:00NIER: Oh, he encouraged this, he thought this was terrific. That was one of the attractions, why he said I should come there; because I had opportunities to enter the field of cosmology.

GRAYSON: Okay. In some cases, a guy like that would try to commandeer your abilities for his own pursuits.

NIER: Oh, no, no. He wanted good science to be done, and he saw that this was good science. Through him, I met Baxter who provided me with very pure samples of lead, and made it into lead iodide for me, which was volatile. You could put it in our instrument, and heat the part which contained the sample. Baxter made wonderfully pure lead iodide for me.

GRAYSON: So, these samples at Harvard had been collected by a fellow who was more interested in the decay scheme between the radiogenic elements.

NIER: Well, in the geochronology thing, in using atomic weights for telling how 02:05:00much impurity was present in common lead.

GRAYSON: Okay, it was the whole business of using isotopes from radiogenic sources for dating. Was that concept pretty well fleshed out at the time?

NIER: Oh, yes. It had been done for years. You measured the amount of uranium and the amount of lead. From the atomic weight of the lead, you tried to decide how pure it was. From alpha-particle counting measurements of uranium and thorium, one knew the rate at which these elements decayed to form isotopes of lead. From the amounts of lead and uranium isotopes in a uranium mineral and a knowledge of the decay rate of the uranium, one can compute the age of the mineral.

GRAYSON: So, your ability, to look at the isotopes of these elements was really opening up the door.

NIER: It was a new dimension.

GRAYSON: It was a tremendous experience.

NIER: Yes. I could do one sample in a day. Actually, the measurements took me an hour, but I had to clean the instrument up because you filled it with lead iodide vapor that had to baked out of the system between samples. So, I could only do a sample every other day, but the actual analysis took me about an hour. 02:06:00I could do in an hour for which the chemists, in making atomic weight measurements, needed weeks. Everybody was very much interested and supportive. And Baxter--and this was quite a break for me, again this business of being in the right place at the right time--Baxter became intrigued with mass spectrometry. He was an analytical chemist of the very highest-order in wet chemical methods. But he became interested in the mass spectrometry business that could do the determinations in so short a time. So, he fed me common lead samples that they had accumulated way back even before his time. From T. W. Richards' time. I ran a dozen or more of common lead samples and I found that 02:07:00the isotope abundances varied, although the atomic weights were the same. [8] Well, his first reaction was, "The mass spectrometer has to be wrong, because after all, we chemists have done this so carefully for so long, with so many people. What could be wrong?" The reasoning didn't take into account that you could have a coincidence: that the variations with isotopic abundances were such that the average weight remained the same. Just a crazy coincidence. I mentioned this in my story in the reprint I sent you.

GRAYSON: Yes.

NIER: On my reminiscences of . . . I don't know if you have that or not, if you know about it, Tom.

GRAYSON: Yes, I think I sent Tom a copy.

NIER: Okay. At the same time, there was a guy by the name of Arthur Holmes, a very famous geologist, a very good geologist, at the University of Edinburgh. He 02:08:00was interested in quantitative geological measurements. Are we coming to the end [of the tape] here?

GRAYSON: Yes, I think we better stop on this tape, we're about to run out.

[END OF AUDIO, FILE 1.4]

[Nier and Grayson are looking at cartoons taped to the doors of a cabinet in Dr. Nier's office.]

NIER: This one was given to me by a friend who sat in front of me at the 02:09:00football game after Minnesota had lost. [laughter] He thought it was appropriate for me because in the cartoon one character says to another "Anyway, we have a better physics department than they do!"

GRAYSON: Speaking of football and mass spectrometry, I was up at the University of Nebraska once, and the person [Michael L. Gross] who runs the mass spec center there takes out an ad in the football program.

NIER: They take out an ad?

GRAYSON: Yes, they have an ad in the football program. How's that for getting PR?

NIER: That's interesting, isn't it . . . yeah.

GRAYSON: You have to do everything you can.

NIER: Right. There's some wonderful ones. There's some German ones [cartoons] 02:10:00that are wonderful. See, she says to this dog with the sad look. "What is more important--that you should not catch a cold, or that the people shouldn't laugh at you." [laughter] Then, I think this one's wonderful. "This is reality, children. We simply can't switch on another program." The man said as he changed a flat tire on the car. [laughter]

GRAYSON: [laughter] Yes, life is not a TV. When would be a good time for a photo opportunity? Would you want to take a couple of pictures?

NIER: Anytime, whatever you say. You can take some in the lab if you want.

GRAYSON: Well, I wouldn't mind getting some in here. I was just kind of looking at your organization of books and papers.

NIER: Well, it's not very good.

GRAYSON: "Not very good"?! I think it's excellent. It's a lot better than mine! [laughter] Mine is simply a file, and . . .

NIER: Yes, the things I haven't sorted are over there.

GRAYSON: Yes. Oh, I see some old ASMS [American Society for Mass Spectrometry] bound volumes over there. That's encouraging.

02:11:00I like that arrangement with some general order to the shelves.

NIER: Yes, that's right.

KRICK: What's great is that they can be archived later on.

GRAYSON: Now, are those your own personal copies of the journals? So, you get to take off all of this on your income tax, right? [laughter] You subscribe to all of these journals. I guess you can't deduct much anymore unless you have a substantial fraction in journal subscriptions.

NIER: I don't even try. I'm trying to stay off the list of people that should be investigated regularly. [phone ringing]

Excuse me.

[recording paused]

GRAYSON: Let's continue with, Tape 3, Side A. Does anybody recall where we stopped? [laughter]

NIER: Oh, yes. We were talking about Holmes.

KRICK: Holmes.

GRAYSON: Okay, Tape 3, Side A and we were talking about Holmes. So we'll pick up with Holmes. In the meantime, I'll be taking some pictures. Do you suppose it'd be okay to close the door. The typewriter is making a lot of noise.

NIER: Yes, I think we should . . . of course.

02:12:00GRAYSON: Holmes. And I may just move around and take an odd picture or two while we're chatting, in kind of an informal situation. So, Holmes . . .

NIER: Yeah. Well, um, let me think for a minute. Holmes had just come out with a paper, and this is mentioned in the article that I wrote for the Annual Reviews. [9] He had just come out with a paper in which he said that the lead ores could not have a magmatic origin. [10] I believe the argument went that they always had the same atomic weight, and therefore, the same isotopic composition. In the magma, the lead would be in contact with thorium and uranium, and you ought to be generating uranium-lead and thorium-lead at the same time. Therefore, the 02:13:00atomic weight of the lead ought to be varying. What he didn't take into account, which nobody took into account, was that you had the crazy coincidence I mentioned earlier.

What happens is that the half-life of thorium is about four times that of U-238 the principal isotope of uranium, and the abundance of thorium, in the earth, is about four times that of uranium. So, you generate about equal amounts of Pb-206 and Pb-208 when the two decay together. You see, if you think of a couple of hour-glasses, the sand gets piled up at the same rate. Okay. The atomic weight of common lead, 207.21, is about halfway between. There's a little bit of 207 also from the decay of U-238. So, you generate not only U-206, but a little bit 02:14:00of U-207, and the U-206 and U-207 balance off the U-208. You can have various amounts of radiogenic lead but you always get about equal amounts or uranium and thorium lead, so the average atomic weight doesn't change. Now, if you made real precise measurements of the atomic weight, you'd find it changed, but within the precision of the chemists atomic weight determinations, it was not measurable.

GRAYSON: So, this is another case where your data is flying in the face of some expertise that's out there. This is the second time now, right?

NIER: That's right.

GRAYSON: So, what happened then?

NIER: Well, when this first happened, Baxter didn't believe me. He gave me unknowns--as I told in this article--as if I were a freshman in analytical chemistry. And after doing three or four of them and coming out with consistent answers he said, "Well, it has to be so." Then he made the interesting comment, he said, he was glad that he was nearing retirement. [laughter] He was a 02:15:00wonderful guy. He was quite formal, very stiff in a way, but very friendly, and very nice, and had a real sense of humor.

GRAYSON: The competition was getting too tough, huh? [laughter]

NIER: Getting kind of tough, so he was glad he was getting near retirement.

GRAYSON: So, what about Holmes?

NIER: Well, I wrote to Holmes and I described this in the article a little bit. There was a professor at Harvard by the name of Gratton. He was in economic geology, and they'd been teaching their students about the origin or lead ore all this time. And here Holmes, also an authority, comes out with a contradictory idea on the origin of lead ores, and Gratton was just fit to be tied. And there were others the same way. So, Gratton was just delighted that I'd come up with the data which refuted Holmes theory. I wrote to Holmes, and he was delighted, too . . . or other reasons. And I met him later, as I've mentioned in the article, and we talked about it a little bit, and he said, 02:16:00"Gee, how was he to know that there was this coincidence, that it would be this sort of thing," and so on. He was very friendly to me. We exchanged Christmas cards for years. I visited him in 1954, had a nice afternoon with him and his wife, also a geologist. Very friendly, and we even did analyses of lead samples for him afterwards, so we kept in contact with him for years. He died in the 1960s, so that was the end of that. But it was one of these cases, I wish I'd got to know him before. You know there's so many people like this, that you wish you'd gotten to know, but it was too late.

GRAYSON: But, at least, he was enough of a scientist to realize . . .

NIER: Oh, yes. Well, he told me . . .

GRAYSON: . . . that even though his work was correct, that there could possibly be another explanation.

NIER: Yes, well, he jumped on the bandwagon then and was very much a fan of the isotope work. As a matter of fact, he was the first one who pointed out, what I should have done a long time ago . . . Although I'm trying to figure out why I 02:17:00didn't . . . that you ought to make use of these variations, somehow, to tell you something about the age of the common lead minerals. I did do things like this, starting with the older, the most primordial minerals and so on, but I never took the real step of tying everything together. I don't know why, but I have a feeling that somebody restrained me. Because it had occurred to me, but they said "Well, you better not stick your neck out that far," [or] something like that; so I never did. But, Holmes jumped on the bandwagon.

At the time the earth was believed to be two billion years old. And he said, on the basis of these measurements, it ought to be at least three billion years old. Others came up with 3.3 billion years. And later on, when Clare [C.] Patterson did this precision work on meteorites, that's where the 4.6 billion figure we now use comes from. But it's making use of the variations in common lead, and working backwards. I was starting to say that, if you take a primordial sample and add to it various amounts of other lead of known age you can work back and figure out how long the addition must've been going on. So, that was really the start of the lead isotope field. I was very happy to be 02:18:00involved in it.

The other interesting thing which occurred at that time, of course, was the measurement of the uranium isotopes. [11] I had lead samples, both common lead and uranium-lead and thorium lead, which I'd gotten from Baxter and also through Holmes. Not through Holmes . . . I mean, through Lane. There are actually two uranium series. There's the U-238, that decays to U-206, and the U-235 that decays to U-207, each at a different rate. So, you have like two hourglasses, running at the same time, see? So, if you measured the isotopes of lead accurately, and you knew the isotopic composition of uranium accurately, you could then determine and compare the ages by the two 02:19:00methods. But one didn't know the relative abundances of the isotopes of uranium accurately. Aston had observed the isotopes on his photographic plates, and showed that for U-235 there was a little smudge on the plate. But that's as far as he got. So, people had guessed at the relative abundances of the uranium isotopes, but I think they were off by a factor of three or some amount like that. It was realized then that we could now accurately measure the uranium isotopes. Bainbridge was certainly in on this thing. We'd all talked about it. And Lane, of course, was just delighted at the prospect that I might measure uranium isotopes. So the question is, how do you do it? So I'd looked back and seen what Aston had done, and he had used uranium hexafluoride; so I said "Well, gee, that's the thing to use." Well, UF6 was a rare commodity in 1937.

GRAYSON: You didn't just go buy that, did you? [laughter]

NIER: You didn't just buy it by the kiloton as one can now. So, Lane said "We'll find somebody to make some." He got a grant from the Geological Society of 02:20:00America, to have somebody make it, but he couldn't find anybody who was willing to take on the project. He had 500 dollars, but he didn't find anybody who was either willing or able. Probably not willing. Because there were people who could do it. But it wasn't easy. So, the money reverted. And the question is "What else should I do?" And then I looked, and I went over to . . . what is it? "Mellor," is that the chemistry book, the one that tells you how to make stuff? [12] Used to be kind of a bible, in two volumes. It showed you how to make all kinds of compounds. I went into the chemistry library at Harvard and looked up how to make other compounds of uranium. And what you did was, you took uranium oxide and mixed it with carbon, and pass chlorine over it, doing it at 1000 degrees, or some awful temperature. I was hoping to make some uranium tetraflouride or bromide, which was volatile at my oven 02:21:00temperatures. See, I'd already had the "oven technique" of putting little ovens in the source, so I could introduce the uranium that way.

Well, I told Baxter about that, and the story I like to tell, which is a bit of an exaggeration, but probably not much, was that he was so offended by the technology that I was describing that, as a good chemist, he decided that he'd better take charge. [laughter] Baxter taught class at Radcliffe College and he often dropped by my lab on his way there. One morning I came in and there on my 02:22:00desk were several sealed quartz tubes containing uranium tetrabromide and uranium tetrachloride. It was very hygroscopic, so you had to rush to get a little bit into the oven and then into the vacuum system. I worked with both compounds and made the first measurements of the uranium isotopic abundances, and that's where the 139-to-1 came from.

GRAYSON: That is, in 19 . . . ?

NIER: 1937.

GRAYSON: And so, the relative abundances of the various isotopes of uranium became known.

NIER: In addition to U-235 I was able to measure U-234, which is in equilibrium with the U-238. Its abundance is only one part in about 17,000.

GRAYSON: Okay. This was done on either the bromide or the chloride or both?

NIER: Both.

GRAYSON: And so, that would've required working up around, what? Mass 340, 350?

02:23:00NIER: Not in this case, It turned out we got an abundant number of metal ions so we worked with these.

GRAYSON: It probably was simpler to work with the metal, because of the many isotopic peaks from chlorine and bromine.

NIER: The isotopes are both lousy.

GRAYSON: You would have all kinds of other information.

NIER: The spectrum at the uranium position was very clean and I have a reprint of it here for you.

GRAYSON: Oh. Excellent.

NIER: Knowing the U-235/U-238 ratio [was] important, because that added a whole new dimension to age determinations. Also, I could come up with a number that was not known at the time: the ratio of the activities of the uranium and the actinium series. The uranium-series referred to the decay of U-238 going to U-206. The actinium series came from the U-235 going through actinium to U-207. 02:24:00And the number I came up with was 4.6 percent, which is still a good number, fifty years later. The uranium isotope ratio I gave was 139 to 1. I said it was good to 1 percent. The latest accepted value is 137.8. So the early value is still within 1 percent. I was lucky; the uranium measurements were pretty ragged, but I took a lot of readings and averaged them. I think I was a little lucky, in that I came out within 1 percent of the presently accepted value, which is really pretty good when you stop to think of the difficulties with the measurements.

GRAYSON: So, a lot of these little experimental details were particularly 02:25:00critical in doing these measurements, making sure the ion source was not discriminating, and making sure that the samples didn't have impurities that you were getting confused by, and so on. So, you always had a healthy skepticism about what you saw and were willing to look for all other possible explanations and eliminate them: variation of ionization potential, etc . . .

NIER: As many of those things as you could perform. Of course, with the little oven in there, you see, it was easy to heat or cool it, and you could run different pressures, and see if things tracked.

GRAYSON: So, a common experiment was, then, just to change the amount of sample entering the ion source.

NIER: All the parameters you could lay your hands on, yes.

GRAYSON: And make sure that you got several determinations and do the statistics.

NIER: Yes. It worked out quite well, but again, experience was terribly important in this, because you got a feeling of what flew and what didn't fly. You'd get this feeling.

02:26:00GRAYSON: Then, would you say that that represents the major thrust of the work that occurred when you were on the NRC Fellowship at Harvard?

NIER: Yes, it turned out to be, in retrospect, to be the main thing that I did at that time. I was pretty busy doing that, by the way. [laughter]

GRAYSON: What other things were you doing at the time?

NIER: Well, the other thing that was interesting. One of my friends was a guy by the name of Earl [A.] Gulbranson, who was an instructor in chemistry up at Tufts. And he was interested in carbon isotope variations in nature, and we collaborated on an experiment. And I always felt I let him down, because I didn't follow up on the work as I should have.

GRAYSON: Because?

NIER: I didn't follow up on the variations we discovered in carbon isotopes. This probably took place in 1938. Things overlapped into 1938, from 1937. We found that natural carbon isotope abundance ratios vary by about 5 percent. In 02:27:00limestones, the C-13/C-12 ratio was 1 in 88 or so. For a piece of wood or other organic compounds it was more like 1 in 93. Gulbranson was a very good chemist. He made the samples, and I analyzed them as CO2. We even looked at the CO2 in air. I remember driving down a side road, outside of Cambridge one dark night, with a funnel sticking out to bubble the air through a tube dipped into a solution containing calcium hydroxide. We precipitated the CO2 to form calcium carbonate. And later Gulbranson would change it to CO2. This is how we obtained air samples. We studied, about a dozen different sources of carbon. That was the beginning of looking for variations in carbon isotopes. That was done so long ago, most people today don't realize the first measurements were made over fifty years ago.

GRAYSON: Now, did that work get into the literature then?

NIER: Yes, it was published. [13]

GRAYSON: And this was with, I'm sorry, what was the guy's name?

02:28:00NIER: Gulbranson, Earl Gulbranson. The paper is in my list of publications.

GRAYSON: Okay. So, that was kind of a seminal work, but you really didn't do any more along that line of study--the C-13 type work.

NIER: Yes. We followed up and did some more of it here, later on, with a graduate student, a chap by the name of Byron Murphey. [14]

GRAYSON: Do you have a feeling for the number of publications that came out of your NRC Fellowship time at Harvard? Were there three, four, six, eight?

NIER: Six or eight would be more like it. They're all kind of interesting, in that they all had something that was related to isotopes. It's in the list, you can pick them out easily.

GRAYSON: I guess that was a two-year appointment?

NIER: Yes.

GRAYSON: Bainbridge, I guess, had an opportunity to ask you to stay there if you wanted?

NIER: Yes.

02:29:00GRAYSON: Did you have that opportunity to stay at Harvard?

NIER: Yes, yes.

GRAYSON: But you elected to come back to Minnesota?

NIER: Yes.

GRAYSON: Okay, could you kind of explain that one? [laughter]

NIER: [laughter] Well, it was a difficult decision, and it was not based primiarily on scientific reasons. My wife was an only child, whose mother had been a widow for many years. My parents were getting quite old. They were almost old enough to be my grandparents. I had a sister who died very young, I was the only one. Neither family had very much money. And the problem of staying there, when I could come back here and help, played a very important part in the decision.

I had an offer of three jobs in 1938. Condon wanted me to come to Westinghouse to the research lab. Harvard said I could stay on as an instructor, but there 02:30:00was a problem. This was when Conant became president, and the tenure situation was very uncertain. So, the young people had a real serious morale problem. There were two retirements here in the department. And, Tate had become Dean of the Liberal Arts College and was anxious that there be some continuity in the work he had started. Also, the people here knew me, and I had done well at Harvard, so, they were anxious for me to come back. I had to choose between these three jobs. I decided against Westinghouse, fond as I was of Condon, whom I liked very much. He was director of research at Westinghouse. Harvard made it attractive, and you never know: Should I have stayed or shouldn't I? It certainly would've been a happy situation. There was no question of that, but I 02:31:00didn't see how we'd ever cope with the problem of the family, with both of us having the problem of parents who needed us. So, I decided that I'd come back here. Financially, the offer was about the same as Harvard. I knew my way around, felt more comfortable, and I felt living here in the Midwest was preferable to living in New England. Anyway, I felt more at home. So, all these things added up, and I made the decision to come here. While my initial appointment was as an untenured assistant professor, the chance for promotion seemed a lot better, because Harvard had been dropping people right and left.

GRAYSON: Really? What was the reason for that?

NIER: Well, there'd been a lot of hangers-on who were on as instructors at 02:32:00Harvard, for whom there was no future. And they just hung around, hoping lightning would strike. In fact, the young people there whom I knew thought I was out of my mind turning down a chance to stay at Harvard. They may have been right, I don't know. But it's just one of those things, and how do you judge? Certainly, professionally, I'd have done very well there, because they had all the support for me. Better than here, as a matter of fact. However, Tate was awfully good about helping when I came back. Bainbridge was always good to me, no matter what. When I left he felt badly, but he let me take my spectrometer tubes with me. Tate, out of his research budget, got money for me to build a magnet like the Harvard one, and so on. So, I had, you know, six in one hand, and half-a-dozen in the other. Teaching loads here were awful, so I had to do a lot more work, whereas at Harvard it would've been much lighter.

GRAYSON: So, tell me a little more about the teaching loads.

02:33:00NIER: Well, you had two full courses that you had to teach, plus some extra things, and so on, and that took a lot of time. Especially starting out from scratch. The first year was very rugged, very rugged.

GRAYSON: Would these be like introductory physics courses?

NIER: Yes, I taught an intermediate course and an introductory course, but a large class: a couple hundred kids. You give a speech every morning. Four times a week plus a quiz. Plus all the kids bellyaching about the quiz grades and working with the graders.

GRAYSON: And then they want partial credit. [laughter]

NIER: They want partial credit of course, exactly. [laughter]

GRAYSON: We'll have to get a copy of that cartoon, so that those people who hear this tape and look at this transcription will be able to understand "partial credit." [laughter]

NIER: I think that's a marvelous cartoon. (Figure 8)

GRAYSON: So, basically non-scientific or non-professional things drove your choice to come to Minnesota at the time. So you made that decision, and did come 02:34:00here, and essentially, by that time, I guess your reputation was pretty well-established.

NIER: Yes, yes.

GRAYSON: And you didn't have any trouble with Tate coming around giving you left-handed hints about where you were going.

NIER: Oh, no. Everything was wonderful. They did everything they could. I was very happy.

GRAYSON: Okay. So, did you just, kind of, continue along the lines of your work at Harvard?

NIER: Well, I had to set up a new apparatus again. Tate had arranged for the magnet, so we copied the Harvard magnet. In the meantime, they had improved techniques in casting metal, and so on. I had to wind the coils myself. It was "Number 8" wire or some size like that.

GRAYSON: So, how does one do that?

NIER: Well, you learn how. You go to a lathe, and have spools made, great big brass spools. I can show you the magnet. We still have it . . . it's used in another instrument.

GRAYSON: Yes, we need to take . . .

NIER: . . . and you can get a picture of that, too. And, so with the help of the guy in the shop we wound this magnet.

GRAYSON: This was an enamelled wire?

NIER: No, this was cotton-covered stuff that we had.

GRAYSON: Oh, wow!

02:35:00NIER: And then we had to paint it with black caulk for making it thermally conducting, sort of like tar. It was a mess! But you did this on the lathe to get a better space factor because the heat conductivity was important. As in the Harvard magnet, we used water cooling tubes to keep the coils from getting too hot.

GRAYSON: Did you say you used square tubing too, or? [laughter]

NIER: No, we didn't use square tube. We had round tube. [laughter] I became an expert in winding coils, which I didn't have to do at Harvard, because they'd had it all done for me. There was a lot of brute work I had to do here just getting started again. But I had an instrument running by Christmas.

GRAYSON: So, you came here, when? At the beginning of the summer? End of the summer?

NIER: In the middle of the summer.

GRAYSON: Middle of the summer.

NIER: I left there about August.

GRAYSON: And brought?

NIER: I had the spectrometer tubes that Bainbridge gave me, and the magnet was 02:36:00being built during the summer. I'd sent the details to Tate, and he had arranged it for me. So, the magnet was delivered in Fall, but the coils had to be made yet, and I had to participate in that, so I spent a lot of time with the machinists in the shop winding coils. Well, it wasn't that bad, but you know, it took time.

GRAYSON: Yes. Well, definitely. It's a time-consuming job. How many miles of copper wire do you suppose you had?

NIER: Well, it was pretty heavy stuff, so it wasn't that many miles, but it was a lot. When you see the coils you'll understand; they weighed 500 pounds apiece or so.

GRAYSON: So, even though you were rebuilding your whole apparatus and instrumentation, you were able to do things in a very short period of time.

NIER: Yes, well I had help, and I got some money for it. Then I had to build a regulator for the generator. The generator here wasn't as good as the one at Harvard. It wasn't as steady. So I had to build this thing all over again, the regulator for the generator. But then, I had some help. I had a grant from our 02:37:00graduate school so I could hire undergraduate students, who were good. They were kids who knew how to build electronics devices. So, I had people building these things for me. By that time, we also could get away from using batteries. We built, I think it was a 1200-volt power supply for accelerating the ions, which was electronically controlled. I had a very good student working on that.

GRAYSON: That kind of electronics technology . . . were people building high-voltage power supplies at that time, or, was that a common thing to buy those?

NIER: In some limited cases. People had Geiger counters and instruments like that. To be in physics, you had to build devices of that kind. This was different than high current supplies and things like that. By that time, I'd learned how to do it, thanks to my connections with the Harvard electrical engineers.

GRAYSON: So, all that business about feedback was put to good use again.

NIER: Oh, yes. Good use, that's right. See, there's a real advantage to having an engineering background.

02:38:00GRAYSON: Well, it's one of the things that's becoming obvious to me. If you'd had a straight, classical physics background, a lot of this instrumentation would've never come to pass.

NIER: Never done. Never come to pass.

GRAYSON: Because you would have hit a brick wall. You knew that you needed an XYZ, but you didn't know how you were going to get one, and you didn't know anybody who was going to be able to do it.

NIER: That's right. You didn't even know who to talk to.

GRAYSON: Yes, but with the double-E background, you immediately knew what to do.

NIER: That's right, that's right. It's just terribly important. You can't over-estimate this at all. [laughter]

GRAYSON: So, a nice combination of fate.

NIER: Yes, yes.

GRAYSON: I think we're about to the end of this tape, so why don't we stop before we go any further.

02:39:00[END OF AUDIO, FILE 1.5]

[END OF INTERVIEW]

GRAYSON: We're starting Side B of Tape 3, and Dr. Nier is talking about an article published in the Physical Review, 1935, in which the potassium isotope--potassium-40--was discovered. [15] Now, he's telling us about the lettering on the figure.

NIER: Well, Professor Tate, who was the editor of the Physical Review, was accustomed to doctoring up documents that came in that fell short, in one way or another. Often this was the case in the lettering. And especially, when he got 02:40:00foreign things--the Germans especially, I think, were not accustomed to doing their own drawings. They would send in just a rough draft of the drawings, and expect the editor of the journal to do the finished draft. So, he was accustomed to fixing up figures. But he didn't like the lettering I had on my drawings. So, the result was, he did it over. If you look at random at the Physical Review of that era--the 1930s when he was active as editor--you'll find many papers in which the lettering will look like that in my article, which appeared in the 1 August 1935 journal. This is all hand-lettering, you understand. We recognize his very distinctive lettering. You saw a lot of that in the journals of that time.

GRAYSON: This was a free-hand lettering that he did?

NIER: Freehand, yes.

GRAYSON: Okay.

NIER: He was very good at it.

GRAYSON: It is very good, and it is clear and legible.

NIER: [laughter]

02:41:00GRAYSON: Okay. Let's see. Where had we ended?

NIER: We were back in Minnesota . . . just a minute.

GRAYSON: Oh yes, you'd decided to move back to Minnesota.

NIER: Well, I was just getting going, wasn't that it?

GRAYSON: Yes, you'd finally gotten your equipment together again, and were working on it. You had it ready to produce results again. So, at this point, what exactly did you get involved in initially, when you first started again in Minnesota.

NIER: Well, when I came back, I wanted to pursue the work on isotopes, which I'd been working on originally here, but more so at Harvard. And, I had, as I said, two mass spectrometer tubes which I'd built at Harvard, which Bainbridge allowed me to take back with me. And I had additional lead samples which I'd gotten at 02:42:00Harvard also and then some that I got from our geology department. I wanted to look further at variations in common lead. And then I also had samples of uranium lead that had come from somewhere or another, I suspect through Alfred Lane or maybe through Harvard, I don't remember. One of the things we continued was the work on the variations of the lead isotopes. Also at the time, I gave a paper at the American Physical Society Meeting in Washington in April 1939, which would be fifty years ago on the iron and nickel isotopic abundances. [16] I'd gotten my instrument going in time, around 02:43:00Christmas or shortly after, and the abstracts were due in late winter. [laughter] So, I made it.

GRAYSON: The game then, was the same as it is now. When the abstract deadline comes around, that's when the work really gets done.

NIER: Really gets pegged, you see. [laughter] So, I had a paper on that. And that's what I reported on there. Now, there was an interesting story about that paper. The secretary of the American Physical Society at the time was quite an elderly man, who was a little bit out of touch, and was getting a bit senile. So, he didn't know exactly what these different fields were, where the papers fit. And, my paper on the isotopes of iron and nickel didn't seem to fit anywhere. But there was a solid-state section on the kind of things solid state people worried about--phase diagrams, and so on, in metals. This was on Saturday afternoon, the last afternoon of the meeting, you understand.

02:44:00And my paper, which didn't seem to fit in with phase diagrams and stuff like this, was the last paper of the afternoon. So, it turned out that that session had a small group. As things were, there were a few dozen people there when things started. But when my paper came on, everybody walked out, except the chairman, my wife, and somebody else. And I remember the chairman of the session was Ed Condon, who I knew already, as I said, the man who was later going to be the Director of the Bureau of Standards. So, I had this small courtesy group who listened to me tell about the isotopes of iron and nickel at the American Physical Society meeting. So, that was the crazy thing that happened there. However, that was the meeting right after nuclear fission was discovered and 02:45:00where I met [Enrico] Fermi. I knew John Dunning already, who was the man in charge of the Columbia cyclotron, and was interested in nuclear physics, and through him, I met Fermi at that meeting.

GRAYSON: At that meeting?

NIER: At that meeting. That was April of 1939, and fission had just been discovered a few months before. It was one of the things that was talked about a lot at the meeting. And that's when I got acquainted with Fermi. So, that was a positive thing that came out of the meeting.

GRAYSON: Well, my feeling of meetings is that more than half of the meeting may actually be in the contacts you make. The papers That you attend are a small portion of the meeting. [laughter]

NIER: I think more than half. It goes on at lunchtime or in the corridors. Dunning had figured out that, if I just souped up the spectrometer a little bit, I could collect enough separated isotopes of uranium to make possible a determination of the fissionable isotope. He knew how much uranium it would take 02:46:00to detect fission if they bombarded my samples with neutrons. I don't remember the exact conversation, but he pointed out that if I could collect some fraction of a microgram of uranium-235, they ought to be able to verify it was the fissionable nuclide.

Now, it had been predicted by [Niels] Bohr and [John A.] Wheeler, that uranium-235 ought to be the one responsible for the slow neutron fission. But it had never been demonstrated experimentally. That was the whole point of it. So, we went through this calculation. Then, in the meantime . . . a lot of things were happening. I had gotten interested in isotope separation. In particular, C-13 which seemed to be useful as a tracer for biological purposes.

GRAYSON: When did that start?

NIER: Well, you see, there were several papers published in about 1937 or 1938 02:47:00in Germany. [Klaus] Clusius and [Gerhard] Dickel, C-L-U-S-I-U-S and D-I-C-K-E-L, published something about the thermal diffusion column. [17] You have a hot wire in a vertical tube and a cold wall around it. If you want to do it in quantity, you'd have to water-cool it to get enough power in. Then, you put a gas in, anything you want to. And what you have between the hot wire and the cold walls is a gradient--a concentration gradient of the isotopes, of the isotopic molecules. It's a phenomenon that you can't explain by elementary kinetic theory. It takes a more sophisticated theory, because it depends upon the law of force between the 02:48:00molecules. The molecules coming in one direction encounter others from the opposite direction with different temperatures and speeds. It's a subtle sort of effect. It'd been discovered many years ago by [Sydney] Chapman and somebody by the name of [David] Enskog, I believe it was, in 1910 or thereabouts. But it had never been put to use, as best as I can determine. And these guys, Clusius and Dickel, pointed out you might use a column like this as a fractionating system. It would repeat itself, and because you'd get a convection flow up and down with the gas moving like a roller-towel and you'd keep concentrating heavier molecules at the bottom of the column in this way. I don't think they enriched isotopes initially, but they separated some gases this way. It seemed natural to use methane gas for separating carbon-12 and carbon-13. It was light, and involved carbon.

So, I built a column, and as a matter of fact, if I remember correctly, it was 02:49:00started before I left, and Jay Buchta, B-U-C-H-T-A, who was head of our department, was awfully good about taking care of everybody. He could never turn down anybody who asked a favor, and he would try to help, and he saw to it that the shop continued working on this in my absence when I went down to the meeting. So, when I came back, a lot of the column was completed. I proceeded, and showed immediately that we could separate carbon isotopes in small--very small--amounts. And then, of course, the column was made longer and longer. We had an empty elevator shaft downstairs. So, my original column was 24 feet long, and we enlarged it to 36 feet, got another floor in, and we had another column in parallel finally, where you circulated between the top and the bottom of one, but that came later. Anyhow, I was producing enriched carbon, and thinking it could be used for nuclear experiments, separate targets for bombardment, and so on. But also, I knew a lot of people in the biological field who were just 02:50:00anxious to get their hands on separated carbon isotopes for tracers. So, I began producing enriched carbon.

GRAYSON: Now, what was the whole concept of doing this? Why did you want to do this enrichment?

NIER: Well, it sounded like fun. [laughter] And it seemed like a useful thing to do, I don't know. And, as I say, I knew people in the medical school, I knew people in the biology departments who were interested in the possibility of this, doing tracer work. See, carbon-14 was not yet then available.

GRAYSON: So, you had a kind of inkling in the back of your mind what you would like to do with this if you could get it, if you could enrich it.

NIER: That's right, there'd be uses for it. I might not use it, but somehow or another, I always had these friends who could use it. I belonged to the faculty club, where people from one department used to sit with people from other departments. It was very interdisciplinary. Nowadays, the organic chemists sit at one table, the historians at another, and my physics friends are all sitting 02:51:00at a certain table. They never sit with anybody else. I usually try to sit with other people, but that isn't done much any more. So, I got to know a lot of people in other fields, which is one of the important things about a faculty club, I suppose.

GRAYSON: So, you're saying that, maybe, over a lunch, at one time or another, a problem was posed to you, "Could you do this?" And you thought, well, maybe not, and maybe you thought about it some more, and . . .

NIER: That's right, there were a lot of connections like that, and I did get a lot of people started on work of this kind, through this sort of informal contact, which is one of the wonderful things you can do in the right environment. So, we were producing C-13 and I had very good friends in chemistry, who were friendly competitors in this, they got into it also. Ivan Taylor, who used to be active, was a very good analytical chemist. He died too young, of cancer some years ago. And another fellow by the name of George 02:52:00Glockler, was interested in this, too, because the physical chemistry of the whole process was an interesting one. So, they built a column in the chemistry building around an open stairwell. They used to have open stairwells.

So, we were friendly competitors in this business. They didn't have as good of machine-shop facilities as I had, so my column worked better. You had to have precision between the center wire and the tube. We didn't use a wire, because we wanted to get more throughput, so we had a tube, a heated stainless-steel tube, with a heater inside of it, about an inch or an inch and a half in diameter. And then, there was a water-cooled brass tube outside, with the spacing about a quarter-inch between the hot and cold walls. But it had to be very precise, because if it wasn't symmetrical, then the thing wouldn't work right; the fractionation wouldn't continue on. If I remember correctly, my colleagues used pipe instead of tubing. I used tubing, which was precision stuff, and had fancy spacers to center the hot tube. A lot of the parts I had to make myself. But the 02:53:00shop gave me wonderful help. So, we built the columns, and were producing carbon. When the plant was expanded in a year or two after that, we were producing routinely 10 percent C-13 from 1 percent. So, you could do some pretty decent tracer experiments.

GRAYSON: Now, did this thing start out evacuated, or did you charge it with gas?

NIER: Well, you started with it evacuated, of course, and then you filled it with methane. We got pure methane, natural gas, from some particular well in California, and they gave it to us free, because it was cheap. We'd get cylinders, and we'd just have to pay the shipping costs.

GRAYSON: And then, once the system's charged, then you'd turn on the heat?

NIER: You'd turn on the heat. At first we did it batchwise, but then later we fed fresh methane continuously into the top of the column, and then took out 02:54:00enriched stuff at the bottom. Actually, you shouldn't feed in at the end in a fractionating column, you feed in someplace in between. So, one end takes out one kind of component and the other takes the other. That's the way you'd run a fractionating system, but I don't think we ever got that efficient. I think we just had fresh methane going past the top, and took out the heavy at the bottom.

GRAYSON: When you were doing this in a step-function charge type thing, how long did it take for the separation?

NIER: Pretty slow. [laughter] The output, I don't remember what it was now, but the output was about a liter of gas a week. This ran at, I think, just about atmospheric pressure,

GRAYSON: That was about 10 times concentrated?

NIER: That was about 10 percent concentration. That's the order of magnitude. 02:55:00And, friends of mine in physiology used it for tracer experiments in metabolism studies, I think, with mice, something like that. And then, I had other friends in botany, who grew radish plants in a bell jar with this, and then they could make sugars, that were labeled, because they let the plants do things for them, you see.

GRAYSON: Were they trying to get to the labeled sugars, or were they trying to . . . ?

NIER: Yes, labels.

GRAYSON: So, there were actually taking your product and reducing it further?

NIER: Making other things out of it, making further things out of it.

GRAYSON: Okay.

NIER: But this was what led to the 60 degree instrument, rather than the 180. It became apparent that not everybody could have a 180 degree instrument that weighed two tons, and took a five kilowatt, stabilized generator to run it. And of course, we had expanded needs. I had graduate students working on different projects and we were pursuing several programs at the same time, and the 02:56:00capacity of the spectrometer wasn't enough to do what we wanted.

GRAYSON: Okay, so now, we're talking about the late 1930s, early 1940s?

NIER: That's correct.

GRAYSON: You had gone to the APS [American Physical Society] meeting, and met Fermi, and shown this iron-nickel work that had been misplaced, and at the same time you were also doing this work with the carbon, both producing it and analyzing it.

NIER: And analyzing things for people. And I had students to help me on the analysis, of course.

GRAYSON: Okay. But all of this work was all being done on one machine?

NIER: One machine. The 180 degree machine, with a two-ton magnet . . .

GRAYSON: Which was a biggie, okay.

NIER: That's right. Yes, sir.

GRAYSON: So, we're, kind of, poised here in a period where there's a lot happening all at once.

NIER: That's correct. And I was teaching eight hours a week. [laughter]

GRAYSON: [laughter] Of course, by this time, you had the course material down pretty well. [laughter]

NIER: Better. [laughter]

GRAYSON: [laughter] And still giving partial credit. [laughter] So, I did see a 02:57:00copy of the letter from Fermi that he had sent to you. The impression that I got from the letter is that he was kind of gigging you, like "Hey, kid, get to work on my project!" [laughter]

NIER: Well, it's interesting. I never met him again, which was too bad, because I never got to Los Alamos [National Laboratory] until after his death [in 1954]. So, I never saw him. I may have seen him in Chicago [Illinois] after that, but never had a chance to visit with him again, because it would have been interesting to our earlier contact review at that point. But certainly, he was interested in it. And see, they had a very good group there at Columbia. First of all, there was Dunning, and there was Herb [Herbert L.] Anderson, who made a name for himself, as an assistant to Fermi, and the other people around there, so they were very interested in all aspects of the fission problem. And Fermi was never that convinced, you see, about the uranium-235 business. I raised the question with Wheeler a few years ago, and he acted as if they always knew that U-235 was responsible for the fission of uranium. But nobody had ever demonstrated it. So, I don't know. Well, I'm sure they were quite sure of what they were doing, but still it needed demonstration. And that, of course, was the 02:58:00interesting thing. And to demonstrate that you could separate enough that way that you could actually do something with it. That was an important point, you see?

GRAYSON: Okay, I'd like to take a little bit of time then, and just explore that whole experiment. I understand that initially, you finally did get some UF6, which you hadn't been able to get before. Is that correct?

NIER: That's correct.

GRAYSON: But then, when you did actually try and do the experiment with UF6, it didn't work.

NIER: It didn't work.

GRAYSON: And what was the problem there?

NIER: Well, I met Fermi in April of 1939. During that summer, I was working away on the diffusion studies. Actually studying the thermal diffusion of gases by having two bulbs at different temperatures, and studying how much the isotopic concentrations varied. This was basic stuff. And that's when I got started on the wedge instrument, the sector instrument, at the same time. And, we were carrying on the lead work at the same time as well as running analyses for 02:59:00people who were using our carbon. So, you see, we had a full situation here. Well, I had been in touch with Dunning, on and off. I don't know if I still have the correspondence. I lost a lot of that after the war, because it got mixed up with classified things which went to Oak Ridge [National Laboratory], so I may have even lost it. Or it may be buried somewhere, or have been thrown away by this time. But anyhow, I certainly was in touch with Dunning. There was a guy by the name of [Aristid von] Grosse--von Grosse, actually--who was a very, very good inorganic chemist, who'd been with Universal Oil Products in Chicago, and gave up his job there, and went to Columbia to work with Dunning on fission after it was discovered. He knew all of the chemists who knew something. And so, they arranged for me to get some UF6. Where it came from, I don't know. Maybe 03:00:00the Naval Research Lab was manufacturing it then, because they were going to [use] liquid thermal diffusion as a possible separation method.

Anyhow, I got some UF6. And this would have been in the Fall of 1939. I don't know exactly when, now. And just put it in my instrument like any other gas. We tried to see what we could get on targets, placed at the end of the magnetic analyzer. In place of the faraday cup, we just put some little strips next to one another at the location of the normal outlet slit of the instrument. We found that you couldn't tell the difference between the targets I called uranium-235 and uranium-238 because the UF6 is, sort of, a sticky substance, and it went on everything. And the amount that just diffused around the whole spectrometer tube was just too much. It was a gas at room temperature. And so, 03:01:00you couldn't tell anything.

It was at that point then, and I think this final decision was made over the Christmas holidays, that we decided that we would have to approach it someway differently. Get rid of the UF6 and use a relatively non-volatile substance like uranium tetrachloride or bromide, with an oven in the source, and then when the vapor hits a cold surface, it falls dead. It will never get around to the collector in a 180 degree instrument without ionization and separation. So, that was the decision.

GRAYSON: So, basically, you're going back to use the same type of materials . . . ?

NIER: At Harvard. In fact, I could have done the separation at Harvard years before. [laughter] For the final experiment, I built an instrument with a 03:02:00seven-inch radius glass tube. We covered the inside with Aquadag, the colloidal stuff which you baked on. It made a nice black surface and was a good conductor. The whole source, the electron bombardment system, the little box with the oven, etc were on the end of a stem that went in through a ground joint. And I have pictures of this, by the way. This was the first time I departed from using all-glass systems. We actually used a grease joint to put this in. And the collector, the same way, had a ground taper with the collectors in it, coming in from the other side. Well, we got it going, and were able to soup up the heater in the source and get a higher pressure. Actually, I don't think we had a real arc. But we probably had a glow discharge in the source. I had much bigger ion currents than I'd ever gotten before. Within about a day's running or 03:03:00thereabouts we managed to get enough uranium-238 so you could actually see it on the target. A little smudge.

GRAYSON: So, you could actually see the sample build up as the experiment was running.

NIER: You monitored it on the uranium-238 collector. I had a meter connected to it and measured it with an electrometer.

GRAYSON: Yes.

NIER: So, then you do a calculation. It's so many amperes for so many hours, how many atoms in Avogadro's number and all of this stuff. You can figure out, predict how much uranium-235 should be there. You just add a fifth.

GRAYSON: So, the collection arrangement was essentially two independent collectors?

NIER: Two independent collectors. They were little strips of nichrome or platinum. And the resolution wasn't all that great, but it was good enough. Uranium-235 and uranium-238 are, you know, three mass units apart.

03:04:00GRAYSON: Yes. So, basically, the machine essentially just ran.

NIER: You had to babysit it, because it would drift off of the peaks. You couldn't just leave it overnight or anything; and you had to keep watching the current because the material would be depleted, so you'd have to soup it up. Or if it got too warm or something . . . because it wasn't just a straight electron-impact ionization, there was some kind of a discharge there, the pressure was high enough. So, it was, kind of, erratic.

GRAYSON: In order to actually get this thing to go in a length of time that was reasonable, you were really pushing the whole instrument.

NIER: You were pushing everything. When it was run as an analytical instrument an ion current of 10-10 amperes would have been a pretty hefty current. This was more like 10-9 or 10-8.

GRAYSON: Significant . . . yes.

NIER: And you began to get a space-charge problem, though, because, the ions weren't all that fast. I remember now, the voltage supply on this machine was 1200 volts. It was the power supply that accelerated the ions. You do the 03:05:00calculation in that range, and you find that the space charge . . . the repulsion between ions begins to be a problem.

GRAYSON: So, basically, you were right at the edge of where you could work.

NIER: Just about. Oh, and the vacuum really was bad. You see, the decomposition of the compounds gave you icky chlorine and bromine in the machine. The vacuum wasn't as good as it could have been. That's one of the things that limited you, too.

GRAYSON: Then, at the end of the experiment you removed the collector and sent it away?

NIER: That's right. And the stories that were told are really so. On a Friday afternoon, which if I remember correctly, was 1 March 1940, I wrote a letter, and pasted the little targets on the margin of the letter. I went down to the Minneapolis Post Office--in those days it was open twenty-four hours a day, you 03:06:00could mail letters--and sent it "Airmail/Special Delivery" to my friend John Dunning. This was before the days of Scotch tape, and I don't know how I fastened it on, but I think it probably with a piece of a Dennison label. Dennison labels go back, way, way back. The letter still exists, but I don't know its whereabouts. I should have asked, since I kept no copy.

GRAYSON: You didn't take it to the Xerox machine?

NIER: [laughter] I didn't take it to the Xerox machine, that is correct. And since it was a long-hand letter, I wanted to get it off in the afternoon, because there was a plane that night. And, so I mailed it. And Dunning called me, woke me up on Sunday morning. I was still in bed, it was very early Sunday morning, and they had worked all Saturday night, and had demonstrated that, 03:07:00indeed, the one that I called uranium-235 gave fissions with slow neutrons, and the other one didn't. It was very definite. And that's the story.

Well, then, the letter. I saw Dunning hundreds of time, literally, afterwards. And I never asked him for the letter or a copy of it. There were copying machines existing later on . . . I can see why he might not have wanted to give up the original letter, but after all, it was my letter. But be that as it may, I never got a copy of it. And, it turned out, he died some years ago, and his wife guards all his stuff jealously. And I've put it up to one of the historians at Columbia to see if they couldn't get their hands on it and get a Xerox for me, at least, but there's no hope. He tried, as he was interested. So, as long 03:08:00as she's living, this is not possible. She was very devoted to John and had some strange notions about the value of something like this. You know how people get.

GRAYSON: Sure.

NIER: So, you just don't know.

GRAYSON: But for the sake of anyone who might want to follow it up at a later time, there's a good chance that . . .

NIER: It's in his papers, because he saved everything, and I know he had it, because he had that and many other things. [18]

GRAYSON: Because that would be a quite an interesting document to try to locate some day for posterity.

NIER: Indeed it would, indeed it would.

GRAYSON: Mailed . . . hand-carried and mailed, probably for less than three cents . . . well, air, special-delivery, it might have been ten cents.

NIER: With special delivery it was ten or twenty-five [cents] or something, which I paid myself.

03:09:00[END OF AUDIO, FILE 2.1]

GRAYSON: . . . talking about John Dunning's relationship to the Manhattan Project.

NIER: Well, that was the beginning, you see. John was very interested in this all the time. He was the one that started the ball rolling. He was always interested in the electric power aspects of the problem, and of course, recognized, with the war coming on, that a bomb was a real possibility. But I 03:10:00know he always stressed the power situation and felt that in the long run, you had to have some way of separating U-235--that you would do it in large quantities--to make it practical. He had a very, very good group of young people and some not so young with him there at Columbia. In particular Gene Booth, Eugene [T.] Booth. John was a very imaginative, flamboyant type, a real entrepreneur who might wander off into the wild blue yonder. Although he was very sound in every respect, he was always on the optimistic side of things, whereas Gene Booth was a young, very conservative-type person. This was a wonderful team because Booth would hold Dunning down to practical things, because he could sometimes find flaws in John's extrapolations, and so on. So, 03:11:00they worked together, it was just a marvelous team, wonderful people to work with and I just loved those guys. Gene and I are still very good friends. I haven't seen him for a long time.

Later they pursued the diffusion separation process. I got into the Manhattan Project through them, as I mentioned in this historical article I wrote for the Chemical Society. But I don't know if you want to include that now or if you want to talk about the sector instrument.

GRAYSON: Well, I suppose, probably, while we're started into the nuclear fission-type thing, perhaps we can continue to explore some of the details of that, as it . . . basically, you're saying, in the 1940s, in early 1940 period, Dunning had a vision of what was coming?

NIER: Yes. Well, I think we've got to talk about the sector instrument first, because that plays an such important part in the Manhattan Project, later on. 03:12:00Coming back to our previous discussion about all the activities we had that required mass spectrometers . . . it became obvious we couldn't do it all with a single 180 degree machine, so we needed more capacity. I remembered so well that Bainbridge's mass spectrograph had a combination of 127 degree sector electrostatic analyzer followed by a 60 degree magnetic one. That's the way they did their mass analyses. I also remember reading papers of a guy by the name of Bill [William] Stevens, who was I think at the University of Pennsylvania at the time, and somebody by the name of [Michael] Barber in England. They had 03:13:00published papers in the early 1930s about focusing charged particle beams with sector magnets. They pointed out a general theorem if you have a source of charged particles emanating from a point and send it through a sector magnetic field, if the apex of the sector and the source of the ions and collector are in the same line, then the diverging beam will focus at the collector. The 180 degree case is just a special case where you open up the apex angle to 180 degrees and the straight line is the diameter of the circle. Theoretically, any angle would do. If it wasn't for the fringing fields, you could have a 1 degree sector. It seems like the question is if you're going to do this, what angle should you choose? And I thought about this a little bit, and choose 60 degrees (Figures 9, 10, 11, 12) because the 60 degree deflection worked so well in the 03:14:00Harvard machine of Bainbridge's; and in part because of other considerations. When I thought about other angles, it turns out that it would have taken quite a bit more magnet for 90 degrees. If you stop to think of it, going from 60 to 90 is quite a bit more. Also, if you were going to have a flattened tube that you fit between the poles, it was a lot easier to bend something through 60 degrees, rather than 90. Flattening tubes isn't the easiest thing in the world. Later, we perfected the technique of bending and flattening tubes to any angle but at that point, we didn't know how to do it well.

GRAYSON: So, now you're thinking about making metal flight tubes, at this point?

NIER: Yes, metal flight tubes.

03:15:00GRAYSON: Even though glass was primarily what had been used up until then?

NIER: Yes, but now, you see, if you wanted to use an electromagnet, you had to have a narrow air gap to exploit it. So, there wasn't room for a glass tube. I never built a sector glass one.

GRAYSON: Okay, so the technology forced you into this.

NIER: But then you had to have glass to metal seals at the source and collector ends. In the original tube, of which I have a photograph, we had a copper tube which went through the analyzer. Five inch lengths of Kovar tubing were silver-soldered to the copper tubing. The source sat on one end, the collector on the other. Glass tubes which encased the source and collector were sealed to 03:16:00the Kovar. Now the presence of the Kovar really buggered things because the Kovar is very magnetic and you had a big piece of Kovar right next to the source. You wanted to use a magnet for collimating the electron beam but the magnet magnetized the Kovar and affected the ion trajectories. This didn't work too well. Subsequently, we changed that and all the tubes we built afterwards we continued the copper tubing all of the way to the source and collector and made the glass to metal seals through Kovar cups which fit over the copper tubing; well away from the source and collector.

GRAYSON: So, you moved the glass-to-metal sealing arrangement as far away from the magnet as possible?

03:17:00NIER: Yes, it was quite far away; anyhow, you no longer had a problem. The only difficulty you had was working with the Kovar. You had to be careful because it cracked if you didn't anneal it properly. So, there was a lot of little technology we had to learn.

GRAYSON: Yes, It sounds like a mess, to be quite honest with you. [laughter]

NIER: It was. [laughter] But it worked.

GRAYSON: I've done enough of that kind of stuff to not like it at all.

NIER: But that's the way the thing went. We standardized on a 6-inch radius for the magnetic analyzer.

03:18:00GRAYSON: And so now we've got 6-inch radius, 60 degree sector instruments.

NIER: That is correct.

GRAYSON: And for the magnet for these, you still used an electromagnet.

NIER: Electromagnet. But you could run it off of a couple of automobile storage batteries instead of a motor generator.

GRAYSON: Okay, that's a big change in power requirements.

NIER: That's right.

GRAYSON: Was this because of physical size?

NIER: Yes.

GRAYSON: The magnetic fields weren't as high?

NIER: We didn't go quite as high with the batteries. In the case of higher fields, we had to still use a generator but I had the stabilized generator by then. But for light molecules, such as carbon dioxide we could use batteries. Those were the days of 6 volt automobile storage batteries and I think we had two or four of them.

GRAYSON: What would high mass be for this type of machine?

NIER: Well, at first, we were just shooting to do carbon dioxide, but then we extended the studies to heavier molecules.

03:19:00GRAYSON: That was still with the battery . . .

NIER: No, when we went to the heavy elements we had to use a generator.

GRAYSON: Okay, so, somewhere the battery power supply was not adequate, I mean, you had to use something else to get to higher masses.