The Manhattan Project

Robert Thornton's Interview

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Robert Lyster Thornton was the assistant director of the Process Improvement Division of the Tennessee Eastman Corporation at Oak Ridge, Tennessee. In this interview, Thornton remembers Ernest Lawrence asking him to join the Manhattan Project just after Pearl Harbor. He explains the development and workings of the Beta plant at Oak Ridge. He also discusses the challenges he faced separating uranium isotopes, the uranium enrichment process, and the thousands of men and women who helped in the process.
Date of Interview: 
February 9, 1965
Location of the Interview: 
Berkeley
Collections: 
Transcript: 

Groueff: Hello? Hello? Recording, San Francisco, Berkeley, February 9, 1965.

Robert Thornton: Well my first connection with the radiation laboratory was in about 1933 when I came here on a post-doctoral fellowship because it was not long before then. And I then was working with Professor [Ernest] Lawrence and others on the development on the cyclotron metal accelerators. And so I was in Berkeley off and on in the period between 1933 and the war. I went to the University of Michigan for a while and then I came back here and then went to Washington University in St. Louis. And I was at Washington University when the war started.

Just after Pearl Harbor, Professor Lawrence called me up and asked me whether I could join the effort going on here in Berkeley on the – well I did not know what it was at that time. But whatever it was. And I agreed to come out here. So I joined them and started working on the electromagnetic process at that time. Actually, the initial work within the planning of it had been done before I came to Berkeley.

Groueff: So you came from St. Louis?

Thornton: Yes.

Groueff: And when you came, the project was just—

Thornton: In its very earliest stages.

Groueff: Early stage.

Thornton: But it had started.

Groueff: The idea was already—

Thornton: Correct, in existence.

Groueff: In existence, yes. And then you joined as a physicist.

Thornton: As a research physicist, yes, for the laboratory.

Groueff: And what was your particular work or field in the laboratory?

Thornton: Well I was working as a physicist or in some senses as a development engineer or a development scientist on the development of the actual separation of equipment. In its initial phases, I am in the laboratory here. Later on in the war, I have forgotten the exact date. It is a matter, which could be easily checked when Tennessee Eastman got into the project where they were going to build to operate the plants in Oak Ridge after they were constructed by Stone and Webster. And I joined the Tennessee Eastman staff shortly after they got into operation as assistant director for process improvement, which was mostly all their research or development section.

Groueff: So you moved there to Oak Ridge?

Thornton: To Oak Ridge.

Groueff: And you lived there.

Thornton: I lived there during the latter couple of years of the war. Prior to that time, I spent some time – I had visited Oak Ridge several times in the early stages of the construction of the plant and other facilities. And prior to that, I had spent some time in Boston working with the Stone and Webster engineers on the design of the equipment and so on as, if you like, a scientific representative of the laboratory who will try and answer the questions, which came up from day to day in the transformation of the laboratory drawings into commercial equipment.

Groueff: When this plant was being built and the factory refinished, the construction was practically finished. Before anybody knew exactly the size of equipment, the magnet, or everything that I find very interesting how everything was being developed simultaneously.

Thornton: That is true to a certain extent. The major outlines of the equipment were clear. But there was always possibility for a detailed improvement in the actual separating mechanisms or equipment, which was then a minor part of the total plant. But in view of the large multiplicity of units which are inherent with the electromagnetic process, a serious manufacturing problem when you wanted to change the design of some particular element to something that work better.

Then there would be a large number of these modified parts to manufacture, procure, and so forth. It is also characteristic of the electromagnetic process that the equipment runs for a limited period of time in a single run as we called it until the charge was fed into the equipment was exhausted having gone through the separation process. Then the equipment would have to be dismantled, completely torn apart, and reassembled.

Groueff: Without the stopping the whole—

Thornton: Without stopping the whole thing, there would be a single magnetic structure, which contained many of these separating units. And one or more of them could be removed without interfering with the operation of the rest of them.

Groueff: So that is from the gas diffusion or the—

Thornton: The small individual or separate units, which would work independently, one from the other.

Groueff: But when and by whom were the decisions for the design made about how many magnets or whatever you call it?

Thornton: That was a growing thing. The initial construction was on a much smaller scale than the final plant was. And to some extent, you might call it the pilot plant. The first construction to Oak Ridge involved the construction of a comparatively small magnet, which would involve a very small number of separating units, two or four. I have forgotten just now how many. And these were used for both the development work and for training operating people.

Groueff: But at Oak Ridge, not here?

Thornton: That was at Oak Ridge.

Groueff: Here, your first gig was at 184.

Thornton: Yes, and then also with some other magnets, which we built specially for the purpose.

Groueff: And when you started, it worked. When you started, it was a pilot plant and—

Thornton: Actually, this pilot plant in Oak Ridge, which was used for training purposes, was constructed simultaneously with the first of the major separating plants, buildings. There were many buildings, which were entirely separate one from the other. But since it was only much smaller, it was, of course, completed much earlier and hence could be used for the training and development purposes.

Almost all the time I was in Oak Ridge, I worked on what is called the Beta plant. The Oak Ridge plant worked in two stages. The Alpha plant would take the natural uranium and concentrate it up to a certain rather variable limit.

Groueff: Yes.

Thornton: I do not suppose it is classified now, but it was. That was of the order of ten to fifteen percent, something in that range, perhaps somewhat lower. And then the second stage or the Beta plant would take it from that stage up to quite a high, but somewhat variable concentration. And since this was the second stage in process, there was a great deal of difficulty in making the first stage work and getting it planned and so forth. The second stage was rather an orphan. And as the plant got into operation, it became of critical importance to get the necessary engineering and design work on the second stage in hand because without that, the design would be—

Groueff: Was that designed entirely in Oak Ridge later because—

Thornton: The initial designs were made here. But I think it would be fair to say that the bulk of the design work and many changes, changes which were necessary to make the plant operate, were made in Oak Ridge.

Groueff: By your group or a bigger group?

Thornton: It was a mixed up business. I, personally, and a few others were actually employees of Tennessee Eastman Corporation. But the laboratory also had a substantial number of scientific staff and technical staff and even a few engineers of the laboratory down in Oak Ridge. A composite group was made up out of Tennessee Eastman people and laboratory people in the case of the Beta plant under my direction. And I was the head of that phase of the work to develop the equipment, get it in operating conditions. And, in fact, initially, we operated the first stages of the plant.

The Beta plant, of course, had different problems from the Alpha plant in as much as the material that it was using as the feed material was already enriched. And hence, chemical losses in the lead processing when only a fraction of the material would be processed. And the other part of it would be scattered all over the equipment.

Now this had to be all quantitatively chemically recovered and fed back into the process. Otherwise, you would have had no output at all because the average number of times a atom, if you like, had to go through the plant was about five. Well if you lost twenty percent of it each time, you would be getting none coming out.

So there were entirely different problems at that time connected with the Beta plant. Many of the more difficult problems were connected to the chemical processing and the quantitative recovery of every fraction, or possible fraction, of the feed material.

Groueff: How would that solve a complete tightness?

Thornton: Complete tightness by fabricating everything out of stainless steel so that it could be cleaned with very strong solvents—acids, and so forth. And many of the parts of the machine as you perhaps know are made of graphite. And those, with the material embedded in those could be recovered by essentially burning the graphite and then processing the mineral residue to extract the uranium from it.

Groueff: It was in very, very small invisible—

Thornton: Small—well in some cases visible. [It was] literally scraped off. But you had to actually get the material that was deeply embedded into the equipment and so forth.

Groueff: And some special measures about cleanliness or by your personnel—

Thornton: Were all very important.

Groueff: And this part, the Beta—since the beginning the idea was to process the natural uranium from natural state to the complete concentration only in one, in Alpha.

Thornton: Perhaps that was initially the idea. But very early, that was recognized that that was not going to be possible.

Groueff: I see.

Thornton: As you probably also know, there was an interconnection between the diffusion plant and the thermal plant. The thermal plant was used to feed the Alpha plant this slightly enriched material.

Groueff: The gas diffusion—

Thornton: The gas diffusion plant product was delivered to the Beta plant and in concentrations. The first deliveries were essentially in concentration that the Beta plant would process. And this, of course, meant a continual design and change problem with the Beta plant because as the diffusion got more and more stages and the diffusion plant came into operation, the concentration of the material would be steadily increasing from twenty to twenty-five and so on percent. And these changes involved modifications in the Beta plant so as to ensure it was operating efficiently at the new concentration.

So a continuing program had to be carried out as the feed material concentration changed. It was, of course, mixed. The feed material was a mixture of the materials that came out of the Alpha plant and the material that was coming from the gaseous diffusion plant. As their concentrations became very disparate, the diffusion plant being much higher. As I recall, I do not suppose they were mixed anymore. This would be a waste of effort.

Groueff: Yeah.

But in the early stages, they were not.

Groueff: It is a very complicated also mathematical thing now to change every day practically?

Thornton: No, you did not have to change it every day. The concentrations were not changing that fast. But every month or so, you would have to be slightly modifying the equipment, particularly what we called the receivers, the pockets in which the enriched material was collected after the separation process.

Groueff: Again, the final product, the official materials for Los Alamos came from Beta.

Thornton: Yes. None of the material from the Alpha plant was of any use to the Los Alamos as far as I know except for measuring cross sections and things like that for enriched material. Not for any serious weapons development.

Groueff: Was there any particular day or moment that we can pin down, the moment when the first final concentrated enriched fissionable material was produced that you celebrated?

Thornton: I was too busy.

Groueff: So it happened gradually?

Thornton: The material—I do not know what the shipment schedule was that we sent it to Los Alamos. But it was certainly sent in very small quantities every few days.

Groueff: Every few days.

Thornton: I do not think it was ever held up.

Groueff: Very late then into a few weeks only before the actual bombing.

Thornton: Yes, yes, that would be so. And again, during the war years, things were highly compartmented. I was not supposed to know, for example, the things—

Groueff: Even you didn’t know?

Thornton: I was not supposed to know anything about the diffusion plant. I was not supposed to know much about Los Alamos. Of course, de facto, you actually know more about some of these things than you were perhaps supposed to know.

Groueff: Was your job finished when you delivered?

Thornton: That was my responsibility. And as I said, I was busy working on that. And I did not happen to have much time to think about anything else.

Groueff: What did it look like physically? Is it a powder? The enriched fissionable material—

Thornton: It looks identical with the unenriched material in the same chemical form. I do not know. I am not even sure whether—I doubt it was shipped to Los Alamos in the metallic form. I suspect it was shipped in some kind of a salt. I perhaps knew at one time. But I do not recall anymore.

Groueff: The way it comes out of your plant, what is that?

Thornton: Well it would come out of that as essentially a very impure metallic deposit. Impure in the sense that it would be mixed with—the collectors were made of graphite so there would be a lot of the mixture when it was scraped off and the things finally burned. There would be a lot of the mixture of graphite with it. And a lot of mixture of other spotted metals such as the constituents of stainless steel and things like that. So it would be very impure.

Groueff: What color would it be?

Thornton: Oh, blackish.

Groueff: Blackish and like a metallic powder or?

Thornton: Usually rather hard, something that would flake off and it was rather hard.

Groueff: Hard blackish metal, impure.

Thornton: In flakes and so forth.

Groueff: Physically, how would you bake it in a—?

Thornton: Well it would be scraped off. And then it would be immediately dissolved and go through a chemical purification process.

Groueff: I see. Is it highly dangerous for radiations?

Thornton: Part of the uranium isotopes, of course, emit Alpha particles, but they are rather simple to protect against from the personnel radiologic point of view. Of course, when you were working with the enriched material from the Beta plant, then particularly when it would be aqueous in solutions, which then would have a moderating aspect of a reactor. Then, of course, it was important to do the processing in small batches so as to keep the amount below radicality.

Groueff: But in your plant, you did not have to diffuse it like in a reactor?

Thornton: No, there was no intense radiation associated with the operational plant.

Groueff: I see. So you were presence and I mean in the same room.

Thornton: Oh, yes.

Groueff: With the material.

Thornton: Oh, yes.

Groueff: And the plants were not like the gaseous diffusion—completely automated?

Thornton: The nature of the electromagnetic process and one of its inefficiencies is that because it is working with these very numerous small units, which will concentrate only a few grams at a time, the number of units, number of people (employees) was very large.

Groueff: I see. And working inside and where the racetrack is or whatever you call it, not through these instruments like—

Thornton: Well that is not necessarily it at all. The hazard there – only hazards there would be in connection with the high voltages, which we used. But that is a standard industrial hazard.

Groueff: Not radiation.

Thornton: Not radiation, the only radiation problem was in connection with x-rays and then coming from the high voltage mechanisms. But there was no radiological problem associated with the electromagnetic plant. There would, of course, be some chemical poison hazards associated with the chemical separation process because all of these heavy, apart from the fact that they are radioactive if they get concentrated in the body, are also poisonous.

And so there would be toxic problems—lots of toxic problems associated with the chemical processing. But those are no more severe than any other with production of oxide or anything, for example.

Again, you do not want to meet by the ledge.

Groueff: Do you recall any particular difficulties that sounded at certain moments like impossible obstacles to solve?

Thornton: It certainly seems that there were many times when we seemed to—I think that was consistent with the whole process was a complete impossibility to solve. But certainly, one of the most discouraging problems was when the first of the Alpha racetracks was built. There was probably a lot of dirt brought into the magnet coils. And one of the magnet coils shorted in the plant and it became deeply inoperable in about a week.

Groueff: After everything was ready and built.

Thornton: Everything was assembled and just because we were going to try to make it work. And the whole thing had to be torn apart and the magnet coil sent back to Allis-Chalmers to be completely taken apart and re-fabricated.

Groueff: Well what was wrong then?

Thornton: Just dirt.

Groueff: You could not calculate in advance?

Thornton: Well in the part of assembly and perhaps also in the part of manufacturing. People were not as careful as they should have been is what it came down to. Some of the troubles I had was in Milwaukee. Some of the trouble in Oak Ridge. Well that is what part of it was a lot of dirt got into the auto circulating system and circulated all around and the tanks itself. It settled out in the tanks and caused electrical shorts.

Groueff: And the whole thing stopped.

Thornton: The whole thing stopped.

Groueff: And what happened then? Did people like Lawrence or General [Leslie] Groves come?

Thornton: They were mad as heck.

Groueff: Did they all come to Oak Ridge?

Thornton: Yeah, both Lawrence and Groves both visited Oak Ridge frequently.

Groueff: Frequently, yeah. And your immediate superior so to speak was? You were responsible to whom?

Thornton: Oh, gosh, who was it? It was so long ago that I even forgot the name of the person. I was the assistant director of the process improvement.

Groueff: And there was somebody who—?

Thornton: There was a director of process improvement.

Groueff: But he was from Kellex.

Thornton: He was born an industrial man rather than a—

Groueff: Scientist.

Thornton: Well he was paid as a scientist. But he was not an academic scientist such as I am perhaps. He was more an industrial scientist. His name slips me at the moment though. As matter of fact, it will come back to me.

Groueff: So you were detached from Lawrence’s group at that point.

Thornton: Yeah. And I worked extremely closely with them as I already indicated. And, in fact, my initial feeling was that I would be more effective working with the Radiation Laboratory group rather than the transfer into Tennessee Eastman. But General Groves personally asked me to do so and said that he thought it was the right thing to do when he was running the business and there was a war going on. So he said he wanted me to do it.

Groueff: Yeah, your group’s relations with General Groves were very good, no.

Thornton: Oh, yes.

Groueff: You did not have any of the frictions that he had with some of the Chicago scientists?

Thornton: Well, I think with many of the Chicago scientists and others suffered from the fact that General Groves had an enormously difficult problem on his hands getting all of this stuff built and tremendous responsibilities. He was the person who was really responsible for it all. And so yes, he had quite a lot of friction with them.

He always got along very well with Ernest  Lawrence. And I will not say I always agreed with him or enjoyed when he was very mad about something going wrong and he was inclined to ball you out. Can you not get this thing done faster than this? Not that I was always pleased with him, but I always respected him and, in fact, I was also surprised. I hand it to Groves. He did a very good job.

He deserves a a very tremendous amount of credit for his success with the Manhattan Project. There are many I know who do not think so. I think that they are just completely wrong.

Groueff: The project needed some driving leader.

Thornton: Without him or the equipment, there would have been no Manhattan Project—a successful Manhattan Project. There would have had to have been somebody like Groves to do it because the whole—I am not saying he is unique and nobody else could have done it, but somebody who acted in much the way he acted would be necessary to have gotten that project carried out in time.

Groueff: What was the manner—talking about leadership and drive—of Lawrence as compared to Groves, did he have the same dynamism?

Thornton: He had the same, but it was different because they were different people. Lawrence certainly understood the attitudes of the scientists very well.

Groves was trying to understand the attitudes of the scientists. He was a trained engineer. He was in the Corps of Engineers and an extremely able man. But he did not necessarily understand scientists and how they think. He was very shrewd in his judgment of them. And quite shrewd and quite well informed in his opinions as to what things were good and what things were not good. But he certainly would have to rely for technical detail on people whom he trusted. And certainly, Lawrence was one of those people he trusted very closely. And there were others too, of course.

Groueff: And Lawrence had a big respect for Groves also.

Thornton: Yes.

Groueff: How was Lawrence as a leader and a scientist in his manner? I want to put some personal sort of description of the man.

Thornton: Well he certainly has an extremely dynamic personality.

Groueff: But you were friends with Lawrence.

Thornton: Oh, yes. He was a very friendly, outgoing person.

Groueff: He was not a damn strict bossy type.

Thornton: He did not like people to make the same mistake twice.

Groueff: But in his approach, he was not a shouting—

Thornton: Oh, no, no, no.

Groueff: Understanding, friendly?

Thornton: And he would never ask you to do anything he would not be quite happy to do himself, which helps.

Groueff: Oh, yeah. And he was a great worker I will say.

Thornton: A very hard worker and he knew what was going on. He had a fabulous gift for keeping in touch for the important developments both in this Manhattan District Project, but also in the rest of his scientific career. He certainly was one of the people whose influence on American science was extremely great.

Groueff: In what respect?

Thornton: In the sense of his leadership, his visions to what could be accomplished, what would be accomplished, and in particular, in his conviction, which he put into practice that the way of physics as it was developing was going to involve the expenditure of large sums of money. And such things as these big cyclotrons, big accelerators and so forth that these would require large laboratories to use them, to develop them and use them that they would have to interdisciplinary. In other words, he was – right from the start, he was much interested in the medical applications of nuclear physics. Of course, his brother, Dr. John Lawrence, whom you probably will be talking to—

Groueff: Yeah, I will have that same—

Thornton: He would know Lawrence better than most people. He, of course, is a medical doctor. But he is now director of the Donner Laboratory, which is a biomedical section of the large radiation laboratory. But anyway, what it was with his connection with his brother and his natural interest in medicine from that angle, he always was very much interested in the applications of medicine to nuclear physics or nuclear physics to medicine and again, in relationships with chemistry and so forth.

So he was a believer in the large interdisciplinary laboratory, which of itself would be a large institute having rather substantial numbers of people with substantial amounts of money. And he had these ideas before the war. Nowadays they are commonplace. Before the war, they were comparatively rare except to maybe big industrial laboratories like the Bell Telephone Company or the General Electric Company.

Groueff: He understood the problems with the big industries.

Thornton: Yes, quite well. But his interest was not in industrial things. His interest was more in the application of these ideas to fundamental or academic type research.

Groueff: But unlikely to academic type standards, I have an impression that he also had a great talent for shall I say—salesmanship is not a good word, but to explain to the projects. He knew where to get funds or support, how to get it, public relations.

Thornton: And his enthusiasm, he had a very personable personality. He was very enthusiastic. He was very successful in this. And, of course, in those days, again, before the war, it was very important to have that personality if you were to get the large grants, which he did receive from the Research Corporation and the Rockefeller Foundation provided the money for the big cyclotron the year before the war. These things were very strange things for new foundations to be doing in that period.

Groueff: And without him, all this work during the Manhattan Project should have started much later.

Thornton: That, of course, is not so. He had not too much to do in some phases of it, such as the diffusion plant and so forth.

Groueff: No, but the electromagnetic.

Thornton: The electromagnetic process would certainly not have been developed without him. He believed in it and he was able to convince people that this lousy method would indeed work. As you know it is not a good method of separating isotopes now with the present technology.

Groueff: The Lewis Reviewing Committee, when they went back, I read their report was rather pessimistic—they were not very much convinced by the method. But they were all taken by his enthusiasm. But why do you say that? And you are not the only one. Everybody agrees with you. It is not a very good method. But it was good for this purpose to have it quickly done because—

Thornton: Because it was the only method. I think the argument would be something like this: it was the only method, which you could test out on a small scale. Well there is one other method, the centrifuge method, which was never used. Apart from that, take the diffusion practice. You build one set of diffusion and that has to be the whole plant.

Groueff: And then you see whether it works or not.

Thornton: Yes, whereas in the electromagnetic plant, you build one unit for now and you showed it worked. It produces so many grams a day and at such and such a concentration. Then if you build one hundred or one thousand of them, you get one hundred or one thousand times the output. It is so expensive.

Groueff: Expensive.

Thornton: Expensive both in man power power, and everything else.

Groueff: So in other words, you did not have illusions, even though it was your baby, that it was the best?

Thornton: If the other ones worked, they were going to do better.

Groueff: And you admit to that even now.

Thornton: Oh, yes. I could see it.

Groueff: But the problem was so let us have the material as soon as possible. No time to wait.

Thornton: It was a war.

Groueff: Yeah, but normally, you would not advocate that manner.

Thornton: No. It would make no sense. It is too expensive. If you want to make something, you do not try to make it in how many ways were tried? There’s the electromagnetic process—

Groueff: Five ways I think.

Thornton: The liquid thermal diffusion process, the straight [gas] diffusion process, there was the centrifuge process. That is four.

Groueff: And then the plutonium.

Thornton: And the plutonium—well that is not separating isotopes, that’s another thing.

Groueff: Four separating and one plutonium.

Thornton: Well, of course, in the plutonium business, there was two problems, which they came into, which were impossible to have known about or almost impossible to have known about until they got in a large scale. One was the matter of the Xenon poisoning of the reactor, which stopped it. Luckily, they had enough conservative power at the time so they were able to get around that. And then there was the problem of the spontaneous fission of plutonium 240, wasn’t it?

Anyway, there was that, which made certain types of detonation impossible. And so there were problems such as that that were not known when that started. As for the diffusion plant, there were questions as to whether the barriers could be manufactured, the pumps, how reliable they would be, whether they would all get plugged up with this integration product, separation of products from

corrosion and so forth. Whether the pumps could be built or the seals would leak and so on.

Groueff: Did you have some similar problems in the electromagnetic method?

Thornton: Yeah, there was I suppose similar problems. But they could be worked out on a single unit. You did not have to apply them to whole plant if you are not going to be working on the whole plant.

Groueff: What were the main problems that you [encountered]?

Thornton: Such things as mundane problems, as insulators that would crack under the high voltages and things like that.

Groueff: What problem?

Thornton: Insulators and so forth. There were many technological problems. But they were all, if you like, comparatively minor. They were extremely troublesome. But you could always make the part better.

Groueff: So even since the beginning, you knew even though it was not economical, the process would work?

Thornton: You knew you could make it work if you were willing to spend enough money into that.

Groueff: There was doubt like gas diffusion or the reactor?

Thornton: It is different in that sense.

Groueff: But technologically, still, it was an enormous performance, no?

Thornton: It was very difficult technology.

Groueff: Then all those firms like Eastern Kodak or Stone Webster or Allis Chalmers, etcetera, did they solve some of those problems themselves?

Thornton: Oh, yes, everybody would. Yes, the laboratory did many of them. But many of them were done by these other people. And, of course, one of the problems, which one had, was the operation of these units was quite ticklish. And the product and the types of employees whom one recruited, most of them were girls from the surrounding communities that knew absolutely nothing about science, technology, and so forth. And one rapidly learned that it was useless to try to explain how something worked. They had some of the most ridiculous ideas about how some of the equipment worked. But in terms of those ideas, by one means or another, they knew how to make the necessary adjustments. One did not worry much about it.

Groueff: They had to know just to turn something to the left or something to the right?

Thornton: Or tell it to maximize various meter readings and so on.

Groueff: But not having any clue what it meant?

Thornton: They did not really know what those knobs were doing.

Groueff: Weren’t you a little bit nervous at the beginning when you put all those uneducated girls to operate?

Thornton: Well one was but one rapidly found that like many of these problems, which require a certain amount of manual dexterity, concentration, and learning by experience that you do not have to understand how it happens. You can drive your car. I can drive in my car very happily; I do not know how it works.

Groueff: And of course you had supervisors if something went wrong.

Thornton: They would be more experienced. The top supervisors would have perhaps some technical training, engineering training, or what have you. And they would understand what was going on. But as the plant was expanding and more skillful operators became foremen and so on, they still did not know much more than they did. But they were able to make the equipment work.

Groueff: Did that require several say dozens or hundreds of girls?

Thornton: Hundreds.

Groueff: Hundreds.

Thornton: One girl could operate several of the units, two or three of the units.

Groueff: And you had hundreds and hundreds of units?

Thornton: I guess jointly it must be in the thousands.

Groueff: Thousands.

Thornton: Of course, in the chemical processing and so on that, of course, was done by technically trained people. You cannot do ticklish chemical separations with untrained people. But the actual operation of the units themselves was done with comparatively untrained people.

Groueff: Who were the few people who had designed this around Lawrence?

Thornton: [Ed] Lofgren was one of them, he is still here; [Burton] Moyer, he is also here; [John Reginald] Richardson from UCLA; Byron Wright, now at UCLA. William Brobeck, who was our chief engineer at that time, made very great contributions to all of this. I mentioned [Kenneth Ross] MacKenzie at UCLA. I do not think I did. And there were many others. Those were the names, which come quickly to mind.

Groueff: So those people were among the inventors of the magnet.

Thornton: I would say probably developers rather than inventors.

Groueff: Was Lawrence personally participating in that work?

Thornton: Very extremely actively. And there was, of course also a group of English scientists working both in the laboratory here and to a lesser extent in Oak Ridge in the electromagnetic process under the leadership of a Professor [Mark] Oliphant.

Groueff: I see.

Thornton: Who was an Australian and in fact, he now is the National University of Canberra in Australia. But he came from England. He had been educated in England. He was a professor at Birmingham, as I remember, at the beginning of the war. He and a group of English physicists worked very actively with us and made many contributions.

Groueff: But Oliphant was detached. He was in radar, I think.

Thornton: He was at the radar in the early stages of the war. And then later was one of the first people at Los Alamos.

Groueff: I see. But you yourself—aren’t you English?

Thornton: I was born in England and educated in Canada.

Groueff: I see. So the major part of your adult life was spent—

Thornton: Well I completed my education getting my doctors degree at McGill University in Montreal and first came to Berkeley on a post-doctoral fellowship.

Groueff: And you remained here ever since?

Thornton: Yes. I did not get into the radar business because I did not become a citizen until just after that got started.

Groueff: Otherwise, you would have gone there?

Thornton: Otherwise, I would be in the radar business. They started to talk to me about going into the radar business. But then they found I still was not a citizen here.

Groueff: But why did they ask the top people here for the radar? Was the electromagnetic very important or it was before?

Thornton: That was before.

Groueff: Oh, before. And so this team was under Lawrence’s sort of leadership. And neither one of the main—

Thornton: I was not his principal lieutenant, but certainly one of his—

Groueff: One of his principal assistants in this particular thing—in developing the process.

Thornton: Yes.

Groueff: Well what was Dr. [Donald] Cooksey?

Thornton: Well Dr. Cooksey’s position was always he was an assistant or associate director of the laboratory. I am not quite sure which at that time, but one or the other. And his principal role in this was he was Lawrence’s right hand man and confidant and so on. He was privy to all of Lawrence’s thoughts and so on in these matters. He did not actively technically entrust with the project. He was intimately connected with the project in terms of the negotiations with [James B.] Conant and [Leslie] Groves.

Groueff: Sort of high policy approach.

Thornton: He was, as I said, his right hand man, his close associate, very close friend.

Groueff: He did not work as a specialist?

Thornton: No, he did not work as a technical specialist. In fact, he was never as skilled. Lawrence always kept very much on top of the matter technically. Cooksey, I think he would not think I was unfair to him if I said that he was not as closely in touch with it. He was not so much concerned with administration. His role was different from that. He was, as I said, Lawrence’s right hand man and confidant. But the direct parts of the administration of the laboratory for which he were responsible were rather minor. He was a staff person to Lawrence doing whatever he wanted him to do.

Groueff: If people were having troubles with their understanding.

Thornton: And worry about the details of various trips he would have to make. He would usually go with him and be in on all of the discussions and conferences. So he would be another person who was hearing what was said.

Groueff: But who acted as the chief of the laboratory?

Thornton: Lawrence.

Groueff: Lawrence himself.

Thornton: Oh, yes.

Groueff: And the development of Alpha plant was the same thing, Lawrence and you.

Thornton: As soon as there became a clear separation between the two, I was almost entirely associated with the Beta plant because that was clearly a complete problem. The equipment was not going to work and it had to be completely rebuilt. The first thing to do was to make the Alpha plant work so everyone went to do that and what was done on the Beta plant was completely unsatisfactory.

Groueff: And what was the role of Brobeck?

Thornton: The role as you would expect for the chief engineer.

Groueff: I see. So he was not a laboratory scientist?

Thornton: No. Well Brobeck, when you meet him, you will find he is a rather unusual man. He has a very great technical knowledge of the kinds of things, which were going on. His main role was engineering but he understood that it wasn’t just doing well “You do it this way, Bill.”

He would say, “Why do you want me to do it that way. What is it trying to do?”

And he would understand what it was trying to do and say, “Well let’s do it this way then maybe.”

Groueff: But was he an engineer for Berkeley or for Oak Ridge also?

Thornton: No, only for Berkeley.

Groueff: And all of these jobs were done by Stone and Webster or Eastman?

Thornton: Headed by the Eastman Engineers. Though again, Westinghouse and General Electric. But the principal manufacturers were Westinghouse  and Westinghouse made the mechanical equipment. General Electric made most of the electrical equipment. And Allis Chalmers did all the magnets.

Now under the general direction of Stone and Webster were the technical collaboration with the laboratory and as Tennessee Eastman became competent to get into it with them.

Groueff: Was the building of this huge magnet by Allis Chalmers something extraordinary because of the size or because of the silver coils?

Thornton: Well I was going to say, the silver coils are what made it quite extraordinary.

Groueff: I am going deep into this story because it is very unusual. And it is a very good story. But who discovered that silver should be or could be used?

Thornton: Well, it is well known that silver is a better electrical conductor than copper.

Groueff: But it is quite a good idea; somebody thought that you had silver in the treasury.

Thornton: Well, I do not know who thought of it first but it was obviously—when copper was in very short supply, you would not want to use copper in an area where you would make brass shell cases out of silver, for example, instead of using copper.

Groueff: Was that unusual?

Thornton: Sure, the thing was going to be perfectly safe. There was no damage. It was going to be returned if it stays in the country and so on. This was no problem. And it released many hundreds or thousands of tons of copper for general use.

Groueff: But normally silver is so much more valuable than copper, no?

Thornton: But it is not valuable sitting in a vault.

Groueff: Yes. But otherwise, technologically, it was not anything that extraordinary, no?

Thornton: No, there is no technological problem with using it. In fact, it was slightly better than copper.

Groueff: Now I mean the size of a magnet though.

Thornton: Well if you build anything much bigger and it has not been done before, you run into problems.

Groueff: It was not any major breakthrough like for the barrier, for instance?

Thornton: Oh, no. There were not those kind of problems.

Groueff: Plutonium, I found problems like canning or the slugs that they put—

Thornton: That was an extraordinary problem.

Groueff: Yeah. Or the optical instruments, periscopes. You did not have any problems with this?

Thornton: No, we did not have that type of problem.

Groueff: How many people worked, more or less, on this project, the electromagnetic here? About 1000?

Thornton: That would sound about right. I think there would be able to be more than that at the peak. Again, somebody liked Mr. [W.B.] Reynolds would give you a better figure than that. The total number—and I do not even remember, I perhaps knew at one time—what the total number of employees of the Tennessee Eastman or the Oak Ridge but I certainly do not remember now. It was certainly many thousands.

Groueff: And when you started the barrier, you had special personnel for that.

Thornton: Yes.

Groueff: But mostly Eastman Kodak.

Thornton: The development team was probably two-thirds laboratory and one-third productivity. But this was just because they were perhaps available and they were experienced. And it was clear we had these very difficult problems. And well I would not want this to come out in any article. But when the initial operation of the Beta plants started like the Alpha plant, it was kind of in shambles. But it was worse being in shambles with this extremely expensive material even though it has been tried around and been made using ordinary material. Still, when it came to using this completely scarce, partially separated material, the operation had to be good.

And so after a while, this technical group of mine operated about one-half the first building. And this was largely a moral factor because people were becoming convinced nobody could make this thing work. And so the only thing to do in those situations was well damn it all. There is no sense in telling them you could make it work. The thing is to go in and make it work yourself. And then if you can make it work yourself, then maybe the other people could see what you are doing and they can make it to possibly work. And that worked out that way.

Groueff: Was it in a separate building, the barrier?

Thornton: Separate buildings and fairly separate in security lines in terms of fences and so on too.

Groueff: So two different organizations?

Thornton: Not two different organizations, but if you have a pass to go into the Alpha plant, it would not get you into the beta plant.

Groueff: How did the enriched material reach the Beta physically? And how would you describe it?

Thornton: Well, it would presumably come in bottles, or in cans, or what have you. I do not know whether it was transformed into the uranium hexafluoride in the Beta chemistry section or the Alpha chemistry section. It could be either. I do not know whether it came as the hexafluoride or in some other purified form. 

Groueff: So then you work with it as a gas, hexafluoride.

Thornton: No, wait a moment. I said hexafluoride. And, of course, I mentioned raw material. That is the gaseous compound. It was used in the diffusion plant. No, I am sorry. My memory is just off. The material, which we used in the Beta plant, was a tetrachloride. We did experiment with using the hexafluoride as the gaseous compound and it had no advantage over the more reasonably handled tetrachloride.

Groueff: Is that a gas?

Thornton: The tetrachloride is a green salt.

Groueff: A green salt.

Thornton: No, a yellowish-green salt, more yellow than green, which would vaporize at a couple hundred degrees centigrade.

Groueff: So it arrived to your plant at the Beta as this greenish-yellowish salt?

Thornton: Yes, which you then would put into the units. And then they would have electrical heaters, which would warm them up to the temperatures. It would evaporate directly. It did not go through it sublime. It did not go through a liquid. When you heated it and back in it would sublime from almost a gas directly from a salt to the gas.

Groueff: And what was the interior in Beta? Did it look like a big factory room or other small units?

Thornton: It looks like a big factory room.