The Manhattan Project

Alfred Nier's Interview - Part 1

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Dr. Alfred Nier was an American physicist well-known for his work on spectrometry. Nier designed the mass spectrometers used for Manhattan Project experiments and his instruments were sent to all of the major Project sites. With his mass spectrometer, Nier helped prove that that U-235 was fissile, not the more abundant isotope U-238. Nier worked for the Kellex Corporation to design and construct the apparatuses used to monitor the separation of Uranium-235 and Uranium-238, as well as leak detectors for the K-25 gaseous diffusion plant. In this interview, Nier describes in detail his instrumentation at the University of Minnesota and his work leading up to the Manhattan Project.
Manhattan Project Location(s): 
Date of Interview: 
November 30, 1964
Location of the Interview: 
Unknown
Collections: 
Transcript: 

Stephane Groueff: Now, we could start with a letter of [Enrico] Fermi and a letter of [John] Dunning, because the way Dunning explained the thing that he had the idea that uranium-235 was—

Alfred Nier: The one that was responsible, yes.

Groueff: And that Fermi on the contrary, that’s the opposite. And [Niels] Bohr was like Dunning. He felt that 235 was responsible. But somebody had to give the proof. So Dunning wrote to you and asked you to underline the importance of the work, asking to do that and you let him.

Nier: Yes. Well, I don’t remember exactly when all this started. But I remember very distinctly meeting with Dunning and Fermi at the Washington meeting in April of 1939. And this is referred to in this copy of this letter, which I’ve written for our own archives. I remember we talked at some length there, standing in the corridors, as one usually does. The most important things in meetings usually goes on in corridors, not in the meeting rooms.

Groueff: Between the meetings.

Nier: Between the meetings. And I remember talking with them at that time. I suspect that Dunning wrote to me after that. Now I don’t think—

Groueff: I think it was April. I have—

Nier: Oh, you do? I see.

Groueff: Yeah. I think it was April.

Nier: Well, this may have been even before the meeting then. Maybe it was about that time. It must’ve been just about the time of that meeting. And then we exchanged correspondence, I know, during that entire period. And then in Fall, I seriously began looking into the question of making the separation. It happened that I had worked with uranium before. I was rather unusual in that sense; not many people had worked with uranium before.

Groueff: You were very young at that time.

Nier: Yes, I was. Well, I was born in 1911, so you can figure it out, so I was twenty-eight.

Groueff: Twenty-eight.

Nier: Yes.

Groueff: But you already had some reputation in this field.

Nier: Yes, because I’d been working in the geological age field—that’s measuring age minerals where uranium decays to lead from this hourglass effect. You measure the amount of uranium there is and the amount of lead there is. And then knowing at what rate this goes on, you can then compute the age.

Groueff: I thought that was a very new thing after the war, actually.

Nier: No, this had been proposed even – oh, I suppose right after, shortly after the discovery of radioactivity in the early 1900s. After radioactivity had been discovered and been worked with, it was appreciated then that this might be used as a way of measuring the ages of minerals. But the techniques were not available in those days. And even until the 1930s, the techniques were not very good. 

For example, the reason I had been working on uranium was that there was the question of how much uranium-235 there was relative to 238. There was a question even in 1937.

Groueff: Much before the fission of it.

Nier: Yes. It wasn’t known. And I made the first accurate measurement of the amount of uranium-235 there was. This is while I was a postdoctoral fellow at Harvard. And I determined then the number, which has become quite famous – 1 in 139. This abundance was my measurement. 

Groueff: Your measurement?

Nier: That was my measurement made at Harvard at that time. As a matter of fact, I’ll give you reprints of some of things if you’d like to have them, again, as background information, because that was in there.

And so I had had this experience of making these measurements. To know the amount of this was important from the geological age measurements point of view. That’s how I happened to get into it.

Well, I came back here. I joined the faculty here as an assistant professor in 1938 and set up a mass spectrometer, these atom-weighing instruments that we used, for continuing the work on lead and uranium, and other isotopes as well. And of course, this was 1938 and 1939. It was only the next year, so that I had barely gotten going on the normal work when this very exciting problem came up.

Groueff: Yeah, how did you learn about the [Otto] Hahn’s experiment?

Nier: Well, think it – I don’t know. This spread like wildfire, you know.

Groueff: It wasn’t only known to a few people?

Nier: No.

Groueff: Everybody knew, circles?

Nier: Immediately, it spread.

Groueff: That was the big excitement.

Nier: Yes, that was the first big excitement. And so everyone knew about it and there was all kind of speculation, of course: “Could you get practical atomic energy? Could you make a bomb?” All these things people were talking about then already. But I think what everyone felt was that any practical use would be very far off because it was realized, I think, even then, that it would take tremendous effort to separate enough uranium-235, after it was known that that was responsible, or to do any of these things. No one dreamt that there would be enough money spent to actually have a working model of anything.

Groueff: At that time, nobody knew whether the 235 was responsible or the 238?

Nier: No, this was not—although as you said before, there were some people who strongly suspected, like Dunning, who has unusual intuitive sense, he felt this—

Groueff: And Niels Bohr?

Nier: Niels Bohr, of course, would have. But there were others, equally famous people, who were not sure and felt it might be the 238.

Groueff: Like Fermi?

Nier: Like Fermi, for example. Although you can see the letter is quite open-minded. He doesn’t—

Groueff: Yes, he said either.

Nier: Either, or.

Groueff: Or.

Nier: Yes.

Groueff: Did you know Fermi before that?

Nier: No, I met him for the first time at that meeting in April, 1939, was the first time. Of course, everyone knew who he was, but I had never met him personally.

Groueff: He was very famous at that time – Nobel Prize.

Nier: Oh, yes. Even then, he was very famous.

Groueff: And you as a young man were very impressed by him?

Nier: Oh, yes.

Groueff: Like going to see the Pope?

Nier: That's right. Yes, but a very modest person and to be with him was a real experience. I met him subsequently a number of occasions and after the war when he was in Chicago, for instance, I got to know him a little better. But a person who you felt very much at ease with because he was basically a very simple person and his fame didn’t go to his head, and so it was very easy to be with him.

Groueff: And Dunning was a very young man, also?

Nier: A relatively young man, yes, there in the Physics Department at Columbia. Yes, he’s just a few years older than I am.

Groueff: So they asked you to try to—

Nier: To look into this problem because I had then, really, the best instruments in existence for this kind of work and probably would have the best chance of making the separation. And they thought I was the logical one to undertake this.

Groueff: Did you make the instruments yourself?

Nier: Yes, yes. Well, the shop there, of course, built some of it. Some of this was built by hand. As a matter of fact, I’ll show you the spectrometer. It’s sitting on the floor here and I’ll show it to you in a few moments.

Groueff: But did you design this spectrometer?

Nier: Yes, this is my own design. But of course, like all these things, it’s based on everything that’s gone before. But there are some unique features you put in. One of the interesting sidelights on this is that at that time, everybody was talking about using uranium hexafluoride, which of course, was ultimately used in the diffusion plant. And that was the substance people were talking about and therefore, I felt it was the thing that would be—it was completely volatile; therefore, it was easy to handle in that sense. It was like a gas. And so that’s what I started to use in my attempts at the separation. I’d obtained some through Dunning and [A.V.] Grosse. Have you met Grosse, by the way?

Groueff: No. Dunning talked about Grosse. He was the gas man, yes? I mean, with the hexafluoride.

Nier: Yes, a really excellent chemist and knew that field well. But I’d obtained this uranium hexafluoride through them for attempting the separation. And this would have been sometime in the fall of 1939.

Groueff: How did they send it to you?

Nier: I think, in a glass in a container sealed off, in a sealed-off glass bulb.

Groueff: Through the mail?

Nier: Through the mail, yes [laugh]. Or Express, I don’t know which.

Groueff:  It’s highly corrosive, no?

Nier: Yeah, but not if it’s dry. If it’s dry, it’s not corrosive at all.

Groueff: And it’s in gaseous form at certain temperature.

Nier: Yes, that's right. Above a certain temperature, it’ll be gaseous. Otherwise, it’s a solid and you see little crystals of it just like a little grain of salt, rock salt, or something like that. But it has a very high vapor pressure so when you have it in a container, there’s a lot of gas associated with the solid that you see.

Well, this is what I started on and I don’t remember the exact time but over Christmas vacation, I certainly worked on this.

Groueff: Where were you working [on the] material? I mean, what kind of laboratory?

Nier: In a laboratory just a few doors down the hall here.

Groueff: In the basement?

Nier: In the basement here at the Physics building, yes.

Groueff: Big laboratory, very elaborate?

Nier: No, no. Quite modest.

Groueff: Homemade?

Nier: Yes, all homemade, yes. The magnet – you would be interested to know – the magnet that I had, I still have. I’ll show you the magnet that was used as part of the spectrometer. But this was used after the war by the same French student, [R.] Bernasse, in some experiments he did. So it has a little tie here [laugh]. 

Groueff: Did you work alone, or you had some students?

Nier: At that time, I had a few students but this particular thing I did alone. It was one of these quick programs where you couldn’t wait for students to get around to it. So I did this all myself. 

Groueff: Did you do it during the day or after working hours?

Nier: Well, teaching loads in universities are not so high. I think at that time, I had seven or eight hours of classes per week. So when you figure that plus some preparation, that gave me about half time free. So I worked during the half time and Saturdays and Sundays and evenings and things of that sort. This was quite exciting, so one put in quite a bit of time on it.

Groueff: You knew that it was going to be something very important?

Nier: Oh, yes, yes, of course. And therefore, it was one of those things that was really worth putting effort in on it.

Groueff: But it hadn’t been done before?

Nier: No.

Groueff: Nobody had seen 235 separated?

Nier: Not separated. Well, that isn’t quite correct. Professor [Arthur] Dempster at the University of Chicago had, a few years before, had measured the amount – had seen, you might say, on a photographic plate, a blackening caused by the 238 and by the 235. But there was so little that it did nothing more than to develop a few grains, just like light would develop the grains on a photographic plate, and has shown that there was indeed an isotope of 235.

Then, shortly after that, I measured – with my instrument, measured – the amount and determined this number 139 to 1, as I had mentioned. But to get a large enough amount that you could make nuclear measurements, that had not been done at all until—

Groueff: Was large enough, meaning what?

Nier: Several micrograms.

Groueff: Is it visible?

Nier: Just barely. A small patch of it would be just barely visible. These targets, which I sent to Dunning and [Eugene] Booth and Grosse in New York, had a small discoloration. These were, I believe, little strips of platinum, which had slight discoloration where the uranium had deposited. It was just about enough for that.

Groueff: So you don’t see the uranium in the form of a powder?

Nier: No, no, no, no. There was a just a little discoloration of the metal.

Groueff: Of the metal?

Nier: Just a thin deposit. You could see that there was something really there, but it was just like a little discolored spot on there.

Groueff: It was unmistakable that it was caused by 235 and by 238.

Nier: Yes, yes. We had several targets in there spaced so that you would know where these things could impinge. And from knowing the geometry of the instrument and the measurements of the electric currents during the measurement, you could tell. There wasn’t any question about which target was which.

But let me go back on one more thing that’s interesting about this. After trying this uranium hexafluoride, I had all kinds of difficulty because it was a gas. Then more of the gas would get around to where the collector was of this instrument, would go directly around just as gas, then would go around as ions to be separated. And so these targets were always contaminated by this huge – relatively huge – amount of gas that just got around and sat down on the surface. Whereas the ion currents, which gave the separation, were much smaller and so no effect could be observed in these first targets.

Well then, finally, I gave up using the uranium hexafluoride and went back to using some other uranium compounds – the same ones I had used for my age determination work a few years before. Because when I left Harvard in 1938, Professor [Gregory] Baxter, who was the chemist there who had given me the chemical while he was there, had let me keep this – I had some uranium tetrachloride and uranium tetrabromide, which are not volatile compounds unless you heat them up to a high temperature. And these are the ones that I then used in this instrument. I had a little furnace, which heated them up just in the region where I would produce the currents. And then nothing got around to where the collectors were and therefore, I got the separation.

Groueff: The separation was not made from hexafluoride.

Nier: No, the original separation was made with tetrachloride and tetrabromide. I used both. And an interesting thing is that the electromagnetic plant – the Y-12 plant – used the same compound then. You see, [Ernest] Lawrence and his people in California had picked up this technique from me.

Groueff: And tried to apply it on a big scale.

Nier: On a big scale. They applied it on a big scale and they ended up – they tried all kinds of compounds and ended up using the tetrachloride. 

Groueff: Besides the hexafluoride.

Nier: Not the hexafluoride, no. This is an interesting little sidelight. But another thing that’s interesting is that I finally worked until February with the hexafluoride and then realized that this was a hopeless task, to try to do this kind of a separation with the hexafluoride. And then, hit on the idea of simply going back and using the same techniques I’d used several years before when I was measuring the uranium isotopes for the age determination, and built an instrument especially for that. And that entire matter took just ten days.

Groueff: And that’s for the whole experiment?

Nier: For the whole experiment. So I made my final – the separation was made on February 29 of 1940, and I started on that just about ten days before. Our glassblower blew this glass tube, which we call the mass spectrometer tube, for me just about ten days before. And I worked very hard and made the metal parts that went into it myself, and you will see them in this sample that I have here. And assembled all that and turned it on. And by the end of the week, I believe that February 29 was a Friday, if I’m not mistaken, because I mailed – yes, I believe it was.

Anyway, Friday was the day I mailed the samples to Dunning, and I had started the separation on about Wednesday and worked about two days. I have a notebook. We must look at that because there will be some dates and you can see that. And mailed this to him Friday afternoon and took the – the samples were fastened with a little piece of tape to a card or on the margin of the letter, which I wrote longhand that afternoon. I remember taking it down to the post office – the Minneapolis post office – which is just a few blocks from where you’re staying in the hotel – and sending it by air mail special delivery Friday afternoon. He received it on Saturday afternoon, I believe is when it was, and they worked all Saturday evening and all night and called me on Sunday morning. You may have heard that part of the story already. Have you heard this?

Groueff: Not the details, no.

Nier: No. But I was aroused by a telephone call about 9:00. I usually wake up early but I didn’t that day because the telephone – well, it was a long distance call from Dunning, 9:00 on—

Groueff: On Sunday.

Nier: Sunday morning, the Sunday immediately after February 29, 1940 it was.

Groueff: Right, and he said what was happening?

Nier: Yes, John [Dunning] pointed out that the samples had very clearly shown the difference, that they had bombarded these targets with the neutrons from their cyclotron and shown that the [00:18:00] fission fragments came off from the one which I had called 235.

Groueff: So your part was to separate them and their part was—

Nier: Was to measure.

Groueff: To see which one is fissionable?

Nier: Which one was fissionable, that is correct. And they did this by bombarding the targets – both of them, which I sent them – with the neutrons from their cyclotron.

Groueff: And one worked and the other didn’t?

Nier: That's correct. Now, this wasn’t a completely clean cut because there was a certain amount of background and the separation wasn’t quite complete. But the results were overwhelmingly in favor of the one. There wasn’t any question about it.

And they then suggest that we repeat the experiment, as one really should always repeat something of this kind, especially when it’s this important. And so that same week, I prepared some more samples using the identical technique, and this showed the same results. And then, we did some more later on, to go into this in more detail—other aspects in more detail.

But that is the history of the thing. And all of this is they started really from the middle of February, when the apparatus really worked, from the middle of February to, I don’t know, all of March. It was about a six-week period when all this happened.

Groueff: Did you announce it immediately to the scientific community?

Nier: Yes, we published this. We got out a note very soon on this. And again, I have a print of that I’d like to give you if you haven’t received it already.

Groueff: Yeah, I have it.

Nier: And I believe it was in the April 15 issue of the Physical Review, about that time.

Groueff: But when you succeeded and Dunning called you, probably you personally told some of your friends.

Nier: I don’t remember, I don’t remember. Probably.

Groueff: Did you then contact Fermi?

Nier: No, I think not. Of course, he was at Columbia then and so Dunning and he were in close contact, yes. At that time, he was still at Columbia.

Groueff: But after this, then you returned to your normal work.

Nier: More or less. 

Groueff: Or you continued—

Nier: No, I collected a few samples and then, of course, when it was definitely established that the 235 was responsible for the fission, then one of the important problems was, “How could you concentrate this?” This is the important thing: “How do you concentrate it?” So many people thought of different methods that might be used.

I’ve forgotten the exact date on this, but I undertook the responsibility to see if we could separate the uranium-235 by thermal diffusion, which is something different again than the ordinary gaseous diffusion, which was used. And this would have been probably later in 1940, would be the time on this. This became one of the government projects, and all the records were sent off after the war on this so I don’t really have anything to go on. I supposed that could be checked if it were important. But it was later on that year that we then undertook the project here to see if we could separate the uranium-235 by the thermal diffusion method. And I set up a column in a vertical shaft we had out here, which is now an elevator shaft, to try to do this, but we did not succeed. Which was not surprising, as was shown later on, that the conditions – well, it wouldn’t separate easily by that method, let’s put it that way.

Groueff: At that time, did you know that you were working, in a way, for building a bomb?

Nier: Yes. Well, by the time the government – see, up until then, this was all financed by universities. You see, there was no government money, although Columbia had had a little bit, I think, the uranium—

Groueff: They had the first contract, the Uranium Committee.

Nier: Yes. And it wasn’t until later that some of us got into it. I had done this contract, also, to look into this method of the thermal diffusion. 

Groueff: So you knew that it was—

Nier: It was of interest. It certainly had to do with the military application, yes, of course. Because the war was on then, although the United States wasn’t in it, of course. 

Groueff: You got more deeply involved with this atomic energy project, the Manhattan Project, later with the Kellex Corporation.

Nier: Yes, but even long before the Kellex days. Because as I remember it, the next thing I did was, as I say, after this separation of the number of samples for Dunning and his colleagues, then I undertook this one project to try to separate the uranium by the thermal diffusion method. This did not work out.

In the meantime, people became interested in trying other methods – the centrifuge, for instance. And we had the only instruments in the world, as a matter of fact, for measuring what other people were accomplishing. This mass spectrometer was really an analytical instrument, and these measurements on these isotopes, that’s what it was intended for. The separation was just an incidental use of it, you see. So my real field was the measurement of what we were doing.

And so I served – let me think for a minute – in – well, in the summer, yes, I had begun. I guess it would’ve been in about the spring of 1941. In the spring of 1941, I began to make measurements for other laboratories who were trying to separate the uranium by other means, or trying isotope separation. Not only uranium, but they might try it out on a compound that was easier to work with.

And so we rebuilt our apparatus. I had only this one apparatus, and so we made some changes in it and put it back again as an analytical instrument. Then we made measurements on these various methods that people were trying.

Groueff: But Dr. Lawrence with electromagnetic?

Nier: No, not that at all. That’s another – that comes a little later in the—

Groueff: What about the centrifugal?

Nier: They were working on this already in 1941. We got samples from Professor Beams, Jesse Beams, at the University of Virginia, who was one of the centrifuge experts in the world. Was then and is now. And he was trying experiments to try to separate with the centrifuge. And we got samples from them to try to tell them how they were succeeding or not succeeding in their measurements.

Groueff: And they were not succeeding, no?

Nier: They were not succeeding very well at that time. They had, I’ve forgotten exactly how much, but they had small amounts but not very much.

Groueff: So the centrifuge and the thermal diffusion were discarded a little bit.

Nier: Yes.

Groueff: Because of practical possibilities.

Nier: Yes, at that stage. Although a little later on, another liquid thermal diffusion entered the picture. Perhaps since you would like to know about this instrument, maybe I should tell about this first. So in the spring of 1941, [Harold] Urey and several others have been to England and had talked to the English. And I know not who else because this was all classified.

Groueff: It was Urey and [George Braxton] Pegram.

Nier: Pegram, that's right. And I had talked to them about this whole matter and apparently, the English scientists had thought more about this and knew more about some aspects of this than the Americans had suspected. Because Urey came back very much excited that more had to be done about separating uranium samples to work with.

And so in the summer of 1941, I took on a bigger program to separate a larger amount. I think it was 5 micrograms of uranium-235 I was to try to get. And we worked all summer long on that very hard and succeeded by Fall in separating perhaps not five, but several, micrograms. The purity wasn’t very good but these samples did lend themselves to some—were of some use. But it obviously was not enough to do really the crucial experiments that were needed to tell what the parameters of a bomb would be, for instance.

And it was at this time that Lawrence then, in the fall of ’41, became very much interested in seeing if much more couldn’t be provided. And he, of course, had the facilities, which we didn’t have here at all, to do this on a bigger scale. He had his cyclotron magnet, which could be turned over to this. And then, there were very few—

Groueff: At Berkeley?

Nier: At Berkeley. The old cyclotron, the 37-inch cyclotron. And of course, there were no – well, this had been discarded, essentially, for cyclotron work then, because they had the 60-inch cyclotron. Still, it was a bigger magnet than anybody else had in any university, I think, at that time.

And so in the fall of 1941, they began this work. I was invited to come out and spend some time to help them get going, as we had earlier communicated by telephone on some of the details on this. They essentially built an instrument as I had used for this original separation, only larger, and put it in the 37-inch cyclotron.

Groueff: So you were in contact personally with them?

Nier: Oh, yes, yes. And this was in the Fall.

Groueff: And then you went to Berkeley?

Nier: I went to Berkeley for about ten days and came home on December 4. I remember because the 7th was on Sunday and the 4th would be then on Thursday. I came home on Thursday evening, December 4, 1941, after having spent about ten days. Well, I had gone out the Sunday – well, whatever Sunday would’ve been. So I was there from Sunday for a whole week and plus four or five more days, and had helped them get going on the original separation that they did. And then they, of course, continued.

Groueff: They were successful?

Nier: Oh they were very successful in making larger amounts. And of course, they had a very large crew of people. Lawrence then, you see, was one of the few persons who had this kind of an operation going where he could—

Groueff: And he was very important.

Nier: Very important, very important, very influential and could put a lot of manpower and money into programs on a scale which none of the rest of us—

Groueff: And Washington listened to him?

Nier: Listened to him because he was so influential, yes, and was an optimist and an operator, as we would say. So he was successful in convincing people. And of course, the proof of the pudding is in the eating, and things of this sort. So it was very important that someone should take this kind of initiative because it was such a discouraging situation. Someone who, like he, who was so optimistic and so effervescent and whatnot, played a very important part in this whole program.

Groueff: He was always optimistic?

Nier: Oh, yeah, always optimistic.

Groueff: Contrary to Urey, who was—

Nier: Yes, yes, I would say yes.

Groueff: —who was curious.

Nier: Yes, yes, yes, that's right. Well, that was the end of my contact with the uranium separation, where I had anything to do with the separation as such. And it became apparent, after Lawrence took this separation over, on the scale that he could take it over, that I could do more important things, namely to help others on the measurement technique. Because there, we were the experts and it didn’t require the large facilities and so on to do this. So this is something we could do here. And so I devoted the rest of my time to helping on the analytical problems that needed solving.

So in the Fall of – well, in December, to be exact, December immediately after Pearl Harbor – there was a meeting called in Washington to discuss this whole program. See, then it was decided to go ahead on this on all fronts. And I was asked then to go into the problem of seeing if I couldn’t develop instruments for just uranium measurements, isotope measurements, so that there would be more instruments available than just the one I had for telling people how successful they were in their separation program.

Groueff: What were the channels you would receive your assignments? Before [General Leslie] Groves?

Nier: Mainly from [Harold] Urey. You see, Urey had charge of that.

Groueff: The separation problem?

Nier: The separation problem. And since he was the man who was the expert on isotopes – he was, after, won a Nobel Prize for separating deuterium, and so on. So I worked largely through him, but the contract then came from the Office of Scientific Research and Development.

Groueff: Dr. [Vannevar] Bush.

Nier: Yes, Dr. Bush’s office. And Urey had taken me at one time in to meet Bush to talk about the need for this. This probably was in the summer or fall of ’41 already. Urey had been pointing out how – he had always felt that much more had to be done in mass spectroscopy because this was the way you determine whether you were succeeding in all these projects. Yet they had allocated very little in the way of resources toward this part of it, which was essential if you’re going to tell whether you—

Groueff: And how come after your success they didn’t do the same installations, same facilities in different universities?

Nier: Well, I don’t know. Everybody was busy on different things.

Groueff: Your laboratory was the only one—

Nier: The only one from—

Groueff: With a spectrograph.

Nier: Yes, for making measurements for a time. But I know that after the meeting in December at the Bureau of Standards – this was on, as I say, after perhaps a week after Pearl Harbor, two weeks after Pearl Harbor, something like that, just before Christmas. I then received authorization to develop an instrument specifically for uranium isotope determinations and was asked to build four such instruments. And that project then got going immediately after the first of the year. That was in 1942. And we worked all Spring on developing this instrument, which became the prototype for the instruments, which were later built by the General Electric Company for the use in the whole project.

And at the same time that we were developing this instrument, we also had to do all the analytical work for all the laboratories.

Groueff: For the others?

Nier: For the others. So in the Spring of ’41, I had working with me a number of my students. One of them is now a professor here in our own department, Edward Ney, N-E-Y, who is now a professor on the faculty. And there was Mark Ingraham, who was the Chairman of the Physics Department at the University of Chicago, had been loaned to me by Chicago at that time to help in this. And so I had these two boys—

Groueff: Assistants.

Nier: —assistants, as well as several others who were a little younger. These were all young men in their early twenties.

Groueff: In their twenties.

Nier: Twenty or twenty-one or twenty-two, or something like this. Yeah, these are all young – you see, I myself was, this was 1942 – well, I was 31, something like that, so I was relatively old, you see. And there’s one other thing I should mention here, that I was also asked about that time if I would go through the University of Chicago. The Metallurgical Lab was just being established. 

Groueff: [Arthur] Compton.

Nier: Compton had me down and whether I wouldn’t join a group there to do some work. But it seemed at the time that with our unique facilities here, we had an excellent machine shop – small but nevertheless, this was important if you’re going to build instruments. And I had the facilities here, which were not being used otherwise. Whereas in Chicago, everybody was falling over one another as this project was being set up and they didn’t have the facilities to do the work as quickly as I had them here. So we could make use of facilities which already existed, so I thought that I’d better stay with this part of it.

Do you want to go on with this now?

Groueff: Yes, oh, yeah.

Nier: Then so we had this one program of building these four instruments ,and these were completed. Then—let me think for a minute. We completed not only four but three more by the summer of 1942. And I sent one of my boys – well, Ney went to the University of Virginia with an instrument. And perhaps, I guess it was two instruments, as a matter of fact, to help Beams and the centrifuge people there. Because Ney was the expert. He had just graduated from the university that spring at the age of 21 or 22 or whatever it was, and was the man who was to help the centrifuge people, telling them what they were doing. 

Ingraham took two instruments with him to Columbia to take care of the work there. Urey and his colleagues were working on separation methods. And then, of course, Dunning had already started the diffusion study with the small samples of barrier. There was Dunning, Booth, and [Francis] Slack and these other people there. And so Ingraham then took care of the analytical work for those groups.

But even before that, we were asked to take on several more instruments developments. The leak detector, the Helium Leak Detector, was started in the Spring of ’42.

Groueff: Was that something which existed before?

Nier: No, no. The idea that you might use a mass spectrometer tuned to a particular substance such as helium and then you could test for leaks using this as a sensing device, that idea had been really used by people who had mass spectrometers. But that you would put a mass spectrometer on wheels and have it in a foundry such as where they made valves or down in Oak Ridge, finally, in the construction plant, there was no one who had dreamt of doing anything quite like that or having it be portable.

Groueff: It was actually on wheels and you were pushing it?

Nier: You could bring it up to whatever you wanted to test, yes. Along the pipes or wherever you wanted to put it.

Groueff: But how did it work? If you wanted to test the pipe, you let the helium flow and then—?

Nier: Yes, the general procedure on this testing would be that you would pump on the thing that you wanted to test. For instance, if it were a tank or a pipe, you would have a large vacuum pump on this to evacuate it. Then, you would sample the gas steam pumped by that with a mass spectrometer. You simply attach the mass spectrometer onto the vacuum line and you sample the gas coming out of there. Well then, if there were an air leak, for instance, you probably would get – and the mass spectrometer was tuned permanently to helium. Now the helium content in the atmosphere is only about one part in 200,000, so you would see very little helium in the instruments. And these instruments were sensitive enough to see the little bit there was in the air.

Now, however, if you flooded the region – supposing you had a welded joint in the pipe or a tank. If you now sprayed helium on this from a helium tank – you’d have a helium tank with a hose connected to it and you could spray helium on the place that leaked. Then the concentration of helium in the immediate vicinity went from one part in 200,000 up to maybe almost pure helium, you see. So the response of the instrument, of course, went up terrifically.

Groueff: Who invented these gadgets? You?

Nier: Well, yes and no. I have a patent on it. But a patent that never turned out to be worth anything because other people proved they used similar methods in their laboratories earlier.

Groueff: The new thing about that, you did, was to apply—

Nier: Well, to develop a practical unit, really, a practical unit. 

Groueff: A practical unit you could adapt to these problems.

Nier: Yes, see, my role in all this really was much more of an engineer. I’m really, in many senses, much more of an engineer than I am a physicist.

Groueff: You built it yourself?

Nier: Yes, here in our laboratory.

Groueff: How big was it?

Nier: Oh, the whole instrument was maybe two feet wide and three feet long and then stood about three feet high, something like that.

Groueff: On wheels?

Nier: On wheels.

Groueff:  And who would push it? You or some—?

Nier: Well, whoever happened to—

Groueff: Each important joint or pipe or pump was—

Nier: Well, they could test this – generally, one didn’t just push these around. You’d set them up at certain stations, and then you might run a long post to this and so you could check like the pipes down at Oak Ridge. There, you see, they would have certain stations where they would have these instruments set up, but you had to wheel them to that. You might wheel them to another location, of course. 

Groueff: Is there a special name for this gadget?

Nier: No, just the “Helium Leak Detector” is the name by which it went.

Groueff: And you call it that?

Nier: Yes.

Groueff: And later in Oak Ridge, “Helium Leak Detector?”

Nier: Helium Leak Detector was the name for it. Or they call it the Mass Spectrometer Leak Detector, was another name that would be used for this.

This was, as I said, in the Spring of 1942. And we built, let’s see, four of those. Then deuterium became important in all this. And this is, of course, all the talk of the heavy water being smuggled out and so on. So there was the question of producing deuterium and Urey, of course, was very much the man on this, and then Hugh Taylor and others were in on this, too. And they needed instruments for measuring the deuterium. Also, how well they were succeeding in these plants where they were going to produce the enriched deuterium.

So we undertook the development of an instrument for that, also. And I built either ten or twelve of those and they went to various places. Several of them went up to Trail, British Columbia, where they had a plant for—

Groueff: Heavy water.

Nier: Heavy water plant. Several of them went to, I believe, to Columbia, where Urey was working then. There were three other plants. There was one in Morgantown. The DuPont Plant in Morgantown [West Virginia] had a heavy water plant there. Then there were several others. I’ve forgotten where they were, where these instruments went. A number of instruments went to each one of these.

Groueff: So you became more and more the specialist in instruments for measurement?

Nier: For measurement, that is correct. That is correct.

Groueff: And you were building them physically?

Nier: We were actually building them. We were manufacturing them, as well as developing them, you see. 

Groueff: The same team?

Nier: The same team, yes, they would—

Groueff: Two young boys?

Nier: Well, there were more boys than that in it. I must’ve had four or five then, or maybe six. And then, of course, the shop. We had these real good shop facilities here – small, but good – for doing this kind of work. We had a very good glassblower, and this was important because of lot of this apparatus was glass. And since there wasn’t much other war work going on here at the time, I had the use of these facilities, and everybody wanted to do something. So it was very easy to get cooperation.

Groueff: A glassblower, is that very specialized?

Nier: Very specialized, yes.

Groueff: Who was your glassblower?

Nier: His name was Greinke – Edward Greinke, G-R-E-I-N-K-E. He had been here as the University glassblower. He had some assistants, but he was the top man. Had been with the university a good many years and had built all of our scientific glassware for many years.

Groueff: He wasn’t a scientist, he was just a—

Nier: A technician, yes. He had received his training, I think, at Corning or someplace in the East. He came from the New York area.

Groueff: And he would execute everything that you would tell him?

Nier: Yes, he made the glass tube I will show you in a moment, which will go to the Smithsonian [laugh].

Groueff: So, even a man like that, he is very important.

Nier: Terribly important. As a matter of fact, at one time during the war when I worked for Kellex, our glassblower was having difficulty making some particular seals – glass to metal seals. And we sent someone out here, and Mr. Greinke made pieces for us while a man sat in a hotel downtown waiting for these to come and be annealed in the ovens. Then he carried them in the suitcase to us in New York so we didn’t lose any time.

Groueff: And he’d blow it with the mouth?

Nier: Yes, they blow this by hand.

Groueff: Like in the old days?

Nier: Like in the old days. And a lot of glasswork is done just that way. Of course, large production jobs you do by machine now. But these special things where they had only a few of a kind, there’s really no substitute for just sitting down and doing it.

But this kind of tells the story of our activities here from this period, from 1940 until I left finally in 1943. By the Spring of 1943, I don’t believe we were making many measurements anymore. But we were just working on the developments of the instruments, these various kinds of instruments.

Groueff: Yes.

Nier: A man whose name should also be mentioned in this connection, whose name maybe you have heard already, was Robert Jacobs who, with Kellex, then had charge of the leak testing there. He and I actually got into the Kellex organization through Manson Benedict. The three of us had been very close friends at Harvard.

Groueff: Benedict was your friend at—

Nier: At Harvard.

Groueff: Harvard.

Nier: Yes, well, we were all postdoctoral fellows. And I was there at Harvard from the years ’36 to ’38. I was a postdoctoral fellow. Jacobs had been before and was an instructor at Harvard. And Benedict was kind of a research assistant to someone at Harvard. He also had his PhD degree. So the three of us were personal friends.We used to go out to Harvard Square to have lunch together, you know, and things like this. So when Benedict got into this through [M.W.] Kellogg – you see, he was an employee of the Kellogg company – and he knew I was in this sort of thing, also. And he needed someone – he knew what a very good scientist Jacobs was, and Jacobs had actually gotten out of laboratory work then.

Groueff: What specialty was Jacobs?

Nier: He actually had been a high-pressure man working with high pressures. He’d been working with [Percy Williams] Bridgman, who was a very famous high-pressure man at Harvard. But Jacobs was just an awfully good all-around scientist and had a real engineering sense, which was the kind of thing you needed, this combination for these programs.

So Jacobs then went to work for Kellex in charge of their leak testing program to see that the proper procedures were adopted for applying these instruments to all the leak—

Groueff: With your spectrometers?

Nier: With our spectrometers. They used, also, other methods, which were not as sensitive as the spectrometers. You could just put a vessel underwater, for instance, and see it bubble, just like you look for leaks in an inner tube.

Groueff: Like a raft, huh?

Nier: Yes, you can use techniques like this, but they’re not nearly as sensitive. So he worked on this whole procedure of leak testing for the Kellex people. Our instruments then fitted into this picture, you see, as the techniques advanced.