The Manhattan Project

John Wheeler's Interview (1965)

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John Wheeler was a theoretical physicist who joined the Manhattan Project in 1942. During the early stages of the project, Wheeler worked under Arthur H. Compton at the Metallurgical Laboratory, where he helped examine potential problems that could arise during the startup of the world's first nuclear reactor. Wheeler later became the lead physicist at the Hanford Site, where he solved the riddle of the B Reactor going dead a few hours after it started, an event that threatened to delay seriously the first production of plutonium. In this interview, Wheeler discusses his early collaboration with Niels Bohr on the liquid drop model of nuclear fission. He also discusses his involvement in designing the B Reactor and solving the problem of xenon poisoning that occurred during startup.
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Stephane Groueff: So I think the best thing is just talk. So if you want to start from the beginning and tell me a little bit about yourself, Dr. Wheeler, and where you come from and a few words about your career, and how you happen to get involved with the atomic project.

John Wheeler: Well I would say that my most important decision I ever took was to go to work with Niels Bohr. I remember writing the fellowship application when I was twenty-one years old to go to work with him because—

Groueff: In Denmark?

Wheeler: Yes. Because of a feeling that he was the person of all people who could see ahead into the future better than anybody else, what the directions and the trends would be. Unhappily, when I got there his son had just died in a sailing tragedy, washed overboard by a wave in the sound between Denmark and Sweden. But then after a few months he got back into the swing of things. And those were the days the neutron physics of [Enrico] Fermi was just being discovered. But then it was a big issue.

Groueff: By ’34, ’35.

Wheeler: Thirty-four and ‘35, right. I had to finish my doctorate degree at John’s Hopkins University in Baltimore. 

Groueff: At twenty-one?

Wheeler: Yes, twenty-one.

Groueff: You had a doctorate degree at twenty-one?

Wheeler: Yes, yes, you start early these days. [Laughs]

Groueff: So it was up to him and he said okay?

Wheeler: Yes.

Groueff: Come and study with me?

Wheeler: Right. And it was, of course, a very exciting time to try to understand why neutrons were taken up in the nuclei and the way they were. He looked for a solution to this problem because everybody before that time had looked upon the nucleus, the way he looked at the atom, like a miniature solar system that had visualized the nucleus as a place where the particles could move freely through the interior. But if that were the case then a neutron coming in from outside would be very much like a comet coming from outside the solar system. It would coast right through and go out the other side and never get caught. And on that basis, no neutron should ever be caught with any significant probability. Then here are these experiments of Fermi that show that neutrons instead were caught with large probability, an absolute paradox and complete contradiction of all previous ideas of a miniature solar system. 

So Bohr got forced to conclude that it was really quite a different picture of the nucleus, that is was not at all like a solar system and not at all like an atom but instead much like a drop of liquid where all the particles are close together. And a new molecule coming in from outside far from being able to travel through the droplet freely instead gives up its energy almost immediately like a billiard ball colliding with a whole collection of billiard balls on a billiard table and all of them trading energy. In this picture, one could understand why the neutron was captured and this led him to this liquid drop model of a nucleus. 

Well, I must say that my own personal inclinations still were to work in the areas that were still more puzzling even than nuclear physics: the nature of particles, the nature of radiation, the nature of gravitation. So that was my main work when I was there with him, the scattering of radiation by atomic nuclei and the production of pairs of positive and negative electrons out of a vacuum. And when I got back to Princeton—

Groueff: How long did you stay with Bohr?

Wheeler: Let us see, I was there a year.

Groueff: A year. And you worked regularly under him?

Wheeler: Yes.

Groueff: Experiments?

Wheeler: No, I am a purely theoretical physicist. I had done some experiments when I was a student and I concluded that one can make much faster progress doing theoretical work and understanding the experiments of others than through some exciting experiment one wants done. Why, he can get it sold to somebody else to do. This was the days of the Depression so when I returned from Denmark I took a position at [University of] North Carolina for three years. And then I came to Princeton.

Groueff: Professor of?

Wheeler: Assistant professor of physics at North Carolina. Then I came to Princeton as assistant professor in 1938, fall 1938. Then in the spring of 1939, January 1939, Bohr came to Princeton on a visit so we had a chance to resume our collaboration. That was the middle of January when I went down to meet him here at the pier in New York. Of course, he had been told by [Otto] Frisch [about nuclear fission], you undoubtedly know.

Groueff: And Otto Hahn and by Lise Meitner?

Wheeler: Yes. And Frisch and Meitner had not wanted to tell Bohr until he got on the boat because they knew that he would be unable to keep the secret. [Laughter]

Groueff: Why? He was a talkative man?

Wheeler: Yes, yes, he was with something like this. He had to talk about a problem like this. He would have to talk with somebody. So here, all this pent up thought of his from the trip on the boat was discharged on me when I was there at the pier to meet him in New York. 

Groueff: You went alone or a group of scientists?

Wheeler: Mrs. Fermi was there at the pier also to meet him.

Groueff: He told you the whole thing?

Wheeler: Yes. And of course, I stopped doing anything else.

Groueff: You were very excited.

Wheeler: Right. We started immediately to work. I can remember just in those very first days of how we rushed up to the library in Fine Hall in Princeton, Fine Hall being the place where his and my offices were. We rushed up to the library to get the collected papers of Rayleigh because Lord Rayleigh had done so much work on liquid droplets in the old days and he had a formula for the vibration of a liquid droplet. 

And then we saw how to transform this formula for the use of describing the vibration of a nuclear drop and then we analyzed the instability of this liquid drop when it gets too much electric charge on it and finally gets to the point of actually blowing up. 

As a matter of fact, in these more recent years, about three years ago at [University of California] Berkeley, Bowman, Harry Bowman at the radiation laboratory at Berkeley actually set up some experiments with droplets of liquid electrically charged to the point that they finally broke up. It was most fascinating to see a droplet wiggling and wiggling and finally breaking up. And he has very beautiful moving pictures of this process.

Groueff: An image of the breaking of the atom.

Wheeler: So it is really a very nice image of the splitting of the uranium nucleus. Well, of course, there was one of the issues that I remember so well just at the beginning since we were having to begin to talk about this subject with other people. There was no thought of any secrecy, of course, at this time. There was this point of getting a name for the process so we again rushed up to the library, and I can remember Bohr going two steps at a time, to see in the dictionary what could be found as a better word than fission. Fission had been suggested by Frisch and Meitner and was our lead up to “scission” and we looked at “spylation” and so on. But we concluded that fission had to be accepted even though it is a very unhappy word, in the sense that the verb, there is no good verb associated with it. This nucleus “fisses”. Well, some people talk that way.

Groueff: Not very efficient. He lived in Princeton at that time, right?

Wheeler: He did, at the Nassau Club. He lived at the Nassau Club since his wife had not come with him. Naturally, everybody at these times was concerned with political issues and we would from time to time go and listen to the radio when some important news item was coming across. Bohr had come to Princeton for the period from the middle of January to about sometime in May to work with [Leon] Rosenfeld, his collaborator from Denmark. I am trying to remember whether Rosenfeld was on the same ship with Bohr coming over. He must have been but I do not explicitly remember that. 

At any rate, the subject of their interest was this problem of studying the creation of pairs out of the vacuum, the possibility of measuring electromagnetic field quantities, and all the deep questions of principle that concerned Bohr—very far away from nuclear fission or nuclear physics. It has more to do with the nature of quantum mechanics because his interest was always the deep philosophical foundation. In a certain sense, he was a man who was a philosopher who looked upon physics as a proving ground for philosophy more than as a physics just as a way of finding out about machinery of nature. 

Although Bohr had been scheduled to give some lectures on that subject and did give them, he actually spent very much less time on that than he had expected because of fission. We had various encounters during that time with people coming from New York to discuss the question and other places as well. But there would be from time to time [Leo] Szilard, or there would be, of course, Fermi, in our discussion. 

Groueff: [Eugene] Wigner?

Wheeler: Wigner did not take at that point so much interest as he did a little bit later when Szilard got going on the idea of a chain reaction. The production of secondary neutrons from the reaction was one of the truly decisive points of which one began to get some hope that a chain reaction could go. And that was really the experiments of Szilard. They questioned why some of these neutrons were delayed. This was one of the many things that we worked on. Of course, we had to go systematically through all the different aspects of this subject. Why the neutrons were produced, why secondary neutrons were produced, the two different mechanisms. 

One, as the two parts of the droplet separate, part of the liquid you can say in physical terms gets left behind. Naturally, when you look at a droplet of water breaking up off under a water faucet, if you look very carefully, you sometimes see very tiny little droplets that are separated. You can see with your own eye, which is a very dramatic way to get a feel for these secondary neutrons. But the experiments showed that in addition to the neutrons given out right at the moment of separation, there were other ones that came up some little time later. And one really had no right to expect such an effect but it was happy that it did occur because these delayed neutrons made all the difference in the feasibility of control of the chain reaction later on. Of course, at this time you did not have the least suspicion you would be thinking along these lines later.

What was the most puzzling feature of the fission process? Well, the most puzzling and the most exciting was the question why uranium underwent fission with slow neutrons and why uranium underwent fission with fast neutrons but neutrons of intermediate energy were very ineffective at producing fission. This was a fantastic puzzle.

Groueff: Either very fast or slow.

Wheeler: Yes, but not in between. And we talked about this a great deal but the solution did not come to me but came to Bohr when he was walking one winter day across the campus from the Nassau Club to Fine Hall. He was talking to Rosenfeld and all of the sudden this idea came of uranium 235 and uranium 238 being responsible. It was uranium 235 that was responsible for the slow neutron fission and U-238 for the fast neutron fission. I do not suppose that you want to go into the technical side of that but it was important in giving some understanding.

Groueff: John, I wanted to ask you is it true that at that time when the problem of uranium 235 being responsible or not came that Fermi did not believe that? He thought it was the opposite thing. I heard that Dr. [John] Dunning was one of the doctors insistent of 235 and he asked them after that year to send him a sample of the stuff. So, Dr. Bohr was also convinced that it was 235?

Wheeler: The idea came from him first, yes. Nobody had proposed this idea up until that time, but there was great skepticism about it on the part not only of Fermi and others but also particularly on the part of [George] Placzek. Placzek had worked in Copenhagen in the old days and he visited from time to time our discussions and he was a wonderful person. He died in the meantime but had kind of a conscience in physics not to accept any idea until it is really proven. So I can remember betting him eighteen dollars and thirty-six cents versus one penny that it was U-235. 

He was at Cornell at this time. He had been a refugee and had to take what position he could. And he used to tell me, “I have a wonderful position at Cornell,” he said to me. Actually, it paid very poorly about twenty five hundred dollars a year. “I have a wonderful position at Cornell. They pay me ten thousand dollars a year, but I pay back seven thousand five hundred dollars a year for the privilege of being in America.” But anyway, he sent me a telegram at a certain point later on. A telegraphic money order for one penny. 

Groueff: He lost! [laughter]

Wheeler: Yes, yes. It looks to me [background voices] as if our group was made because of this question of skepticism. I still have this telegram that came with a telegraphic money order for one penny when the experiments were actually done and it showed the U235 would work. 

Groueff: At that time, were people like Fermi or Szilard all the time in contact with you? 

Wheeler: Yes, yes we had been in touch once a week certainly, once every two weeks. 

Groueff: Not physically working with you at Princeton?

Wheeler: No, no. It would be a matter of one or another person visiting.

Groueff: I see. Bohr, you, and?

Wheeler: Yes, the two of us were in day-to-day contact on this paper. Writing this paper on the mechanism of nuclear fission, which was the whole picture, what went on, why it went on, and what one could expect for the future. There were people in the laboratory one of my colleagues—Malcolm Henderson—was concerned with measuring at the cyclotron the energy set free in fission. And of course there were people at Columbia doing the experiments and people at Berkeley. 

January 15 as I remarked, or January 16, the date of Bohr’s arrival, came not very long before the period between semesters when one had a little time off. And then there was a Conference organized in Washington that had all that discussion about the whole subject and Bohr urged me to go but I had examinations to give and so I let my conscience get the better of me and I did not go. That just illustrates how quickly the whole subject became taken up by everybody. The major part of our conclusions we described in a paper at the April 25 meeting of the American Physical Society in Washington. I can remember very well the enormous interest at that time, people asking questions at the end of the paper. 

Groueff: You wrote it?

Wheeler: Yes.

Groueff: And Bohr was there?

Wheeler: Right, but that was only very shortly before he had to go back. The single most important prediction in our paper looking back on it from hindsight I suppose was the way of predicting the fission properties of nuclei that had not yet been discovered. Among these, of course, plutonium-239 was destined to be very exciting. We showed on our curves that this would be a fissile nucleus. So that already at this point then as we began to talk about chain reaction up to the point where he could think of this process of adding a neutron onto uranium-238 and making plutonium. So as the months went on, this dream came into being of an idea of a plutonium factory even before anybody had made any plutonium to measure fission.

Groueff: Plutonium was discovered already by Seaborg and by—

Wheeler: Yes, and by [Edwin] McMillan.

Groueff: McMillan, yes, okay.

Wheeler: And the Berkeley group a little bit later made enough to make a direct determination of the fissile properties of the material. But of course, that was in the secret period. But this prediction that it would be a fissile material was made already before the secrecy came onto it.

I had been associated with Breit, Gregory Breit. I had worked with him in the period just between the time I got my degree at John’s Hopkins and the time I went to work with Bohr. Gregory Breit was a very unappreciated person in the American scene and he was really the primary leader in nuclear physics in America. He was a professor of theoretical physics at Yale. I think that probably his own personality difficulties are the reason he is not more appreciated. But Breit was active in the very first days of—

Groueff: Breit?

Wheeler: B-r-e-i-t.

Groueff: Okay.

Wheeler: B-r-e-i-t. He was active in the first days of the project that was set up under Lyman Briggs in the Bureau of Standards. He went around to one and another center to act as a vehicle for coordinating work as being a person who was willing to spend a lot of time on it. He demanded a pledge of secrecy of each person taking part and I refused at that time on the basis that I did not know who I was taking the pledge to nor for how long it would be taken. [Laughs] I stayed with the open discussions. 

Well, naturally, our meetings got more intense and then their came the period when we really did come. Bohr had by this time left, our paper had come out, I had returned more to my old loves of the nature of matter and energy and left for the most part the subject of nuclear fission and nuclear physics. Although from time to time, I did do something on it. But I personally—this shows how stupid one can be—I viewed the war that was about to come forth as something that would not be a major; that it would not affect the United States in a major way. And I have always viewed my own lifetime goal as trying to put—I hope it does not sound too pretentious—trying understand how the world is put together. And I did not see much prospect that nuclear physics was going to—

Groueff: You said that Bohr was on the philosophical aspect?

Wheeler: Yes, this is really primarily my interest. Space and time is a subject I am working in at the present moment.

Groueff: To understand where we come from, where we are at, and what it is all about, the world.

Wheeler: Yeah, and the nature of time and what the future history of the universe will be, the days long off happily from now when the universe stops expanding and starts contracting. And then what kind of dynamics will we go through. Will it be like a water bubble, which collapses to make a very high pressures and high temperatures. Or will it be more like a glove, which turns itself inside out one finger at a time so it will escapes any catastrophic conditions and can go on into a new cycle of re-expansion as some water bubbles do. 

Groueff: So that is why Bohr’s personality had an appeal to you because he was interested also in the deeper issues?

Wheeler: In the deeper issues, yes. And, of course, his great life work was understanding the nature of the quantum principle. This amazing distinction between the observer and the object he observes in which the observer has an effect on the object he observes so that it is impossible to observe a thing without affecting that thing, and of course, Einstein’s complete opposition to this point of view. 

I remember Einstein’s last seminar, at least the last I ever knew of his giving. I had invited him to give at our lab at Palmer Laboratory in which Einstein spoke on this subject. He said, “Can one really imagine that God plays dice with the universe that it is a probabilistic description? If a mouse stands there on the floor and observes the universe, does this affect the state of the universe? Preposterous!” he said. Well you have probably followed the discussions between the two of them. It is very exciting.

Groueff: Not very much as a laymen. 

Wheeler: One time when Einstein was lying in a hot summer day naked on his bed and then Bohr came to call and they pursued the discussion.

Groueff: Where, Princeton?

Wheeler: In Princeton, yes, in Princeton. They carried on the discussion under these conditions. 

Well of course, to jump over things, Bohr went back. We kept in touch. We published a second discussion on some of the factors in fission. But then we, of course, lost touch after the invasion of Denmark. But then there came, naturally, the much-increased activity of people interested in fission. And in Princeton, we had our regular meetings also with the people from Columbia coming down and we ourselves in turn going to Columbia. 

Groueff: But secret or not?

Wheeler: No, this by then was secret. This was by then secret. The topic that interested me at that time was the theory of Wigner and Szilard of the nuclear chain reaction and about the mechanism to prevent nuetrons from undergoing unfavorable capture by concentrating the fissile material in lumps instead of spreading it uniformly in the moderator. 

Groueff: Who was your contact when all this, Breit?

Wheeler: Wigner, Wigner was the person at Princeton who was most active in this. And by this time, there were a number of others at Princeton—Ed Cruetz—working on experiments on small spheres of material. [Richard] Feynman at Princeton was a student of mine at that time but had got interested in the electromagnetic separation process. But then he joined the group at Los Alamos. But then there were these discussions where we would all go, and finally Chicago was decided upon. Then in January of 1942, my own going to Chicago to take part in the enterprise.

Groueff: Who contacted you first? Who made the offer?

Wheeler: Arthur Compton is the person. He made a visit to Princeton and said, “Will you come to Chicago to take part in the enterprise?” He was also of course talking to others, Ed Creutz he got. Wigner, he had more difficulty with. Wigner was concerned with making conditions about how the thing should be done. But, happily, Wigner also came.

Groueff: And you accepted immediately?

Wheeler: Yes, it took some doing because the chairman of our department, Henry Smyth—I do not know if you have talked to him at all yet—who wrote the Smyth Report, right.

Groueff: I have heard of the report.

Wheeler: He is a United States member now of the International Atomic Energy Agency in Vienna but he spends part of the year in Vienna and part of the year in Princeton. So it took a little doing to convince Smyth to release me.

Groueff: But you wanted to go?

Wheeler: Oh, yes indeed, because it seemed to me that this was—of course by now, Pearl Harbor had come and everybody was—it was clear that it would bring about the end of the war. It was a lot, absolutely. Well, of course, it was ’42. This was the end of January ’42. So then, I first went alone and then my family came later. 

Groueff: Where did you work in Chicago?

Wheeler: Well then, the place in Chicago was the Metallurgical Laboratory Building at Eckert Hall. And here was a very exciting time and I was put in charge of the information part of this service that is to try to circulate the story about how things stood in the reports. I produced a summary.

Groueff: To inform the other scientists, not the public?

Wheeler: No, just the others in the group. But that was a sideline activity. I mean that only took a half a day a week to keep that organized with secretaries and so on. And my own work was on the looking at what you might call “the bugs under the table”—all the things that might go wrong with the process. So I was already at that point starting to write reports on the temperature coefficient of the chain reaction and how this could affect the reaction. The question of control rods and how to keep the reaction from running away, and the question of poisons that might affect the reaction and slow it down. There was naturally this great division of opinion between the people acting there on the best method to make the process go—whether to make a pile built out of graphite and cooled by helium, or whether to make a heavy water reactor or to use light water as a coolant. 

And the idea of using light water was really not active at these first months, January, February, March; that only came onto the scene later. That was Wigner’s imagination. It is very interesting how people’s attitudes were colored by that one single simple number: the reactivity, K. Could one make K greater than one so that it would go over the top. We were concentrated almost exclusively on that one factor, every single thing that could be done. Purification, I remember going with Creutz to a metal fabricator in Ohio to talk about the process of purification of metal as one of the possible ways to get more metal quicker.

Groueff: Did Westinghouse do that out of their land division?

Wheeler: Yes, they in the end proved to have a very good process. Then of course, there was the question of getting pure graphite. But this concentration on this one factor, the multiplication factor really kept us I think from having an adequate perspective on the engineering side of life. And not deliberately saying, “Well, we’ve just have to pay the price it takes to do this in a good engineering way even if it does cause some multiplication factor.” So when in the end Wigner came forward with this idea of cooling by light water, this was rejected by most members of the laboratory and I myself thought it was a bad idea too, simply because it would eat up multiplication factor. 

I have forgotten whether it was July of ’42 or before or after, but about July when the engineering group was brought in. The Standard Oil people had suggested this. [Eger] Murphree was one of the advisors. And Tom Moore and his associates [Bill] Leverett and other people were then started work on building this reactor. I mean not building the reactor but making a design for a full-scale plutonium factory based on the helium process. And this is when one could see the sociological fissure in the laboratory. 

There were people there, particularly Fermi who were accustomed to doing things themselves as physicists and were not very eager with the idea of engineers coming in and taking over such a responsibility as this. On the other hand, I had no particular attachment myself to fission as a subject for life work. I mean, it was a distraction from my life work, and not something that I intended to stay in. So it made no particular difference to me that the army engineers and the advisory group had come out with the idea of an engineering group to work with. Fine, let’s get the job done. So I found myself one of the people spending more time than most other people working with the engineers as a physicist.

Groueff: You did not object. You did not object to it.

Wheeler: No, I was very happy to.

Groueff: Compton also accepted that.

Wheeler: Yes, of course he had accepted since he had been part of the decision. 

Groueff: But Fermi did not. And Szilard and Wigner?

Wheeler: Szilard and Wigner were not at all. So we had this group of ostracized people you might say [laughs], the engineers. And it would seem to me a shame because, after all, they were the people that had been told to get the job done and it seemed to me one ought to get in there and help them to get it done. Well the whole enterprise was soon seen to be at such a scope that this engineering group was not going to have the size to do it. I did not have the perspective at my young age to realize this but I think there were enough wise people to in looking at the whole process to say that we were going to have to get into a much larger industrial organization. And that is where DuPont was brought in.

Groueff: The first group before DuPont they came from where?

Wheeler: Standard Oil.

Groueff: Just individuals?

Wheeler: They had been picked out. They had been a group that had worked together previously. How many people were there? If I were to guess, I would say maybe ten people.

Groueff: Only? So you realize someone huge had to come in like DuPont.

Wheeler: Right. So I can remember our going to Wilmington for a meeting with the DuPont people. And this particular meeting came at Thanksgiving time so I was away on Thanksgiving Day from Chicago and from my family who by then had come there. And then we went back to Wilmington again and we were in Wilmington, well I was at Wilmington at the time of the December 2nd startup for the reactor. 

Groueff: So you were not there?

Wheeler: I was not present there and as a matter of fact, strange to say, did not feel any particular excitement about it because I somehow took it for granted that it was going to operate. And it did not—

Groueff: There was no suspense for you, I mean that it may blow up Chicago?

Wheeler: No, I mean it just seemed to me so straightforward in extrapolation from what one had already been doing that maybe I am too much animated by the theoretical point of view but frankly it did not mean that much to me. But I was fascinated with this whole new group of people I had met in Chicago. Of course, I had to stay at a hotel. And there were other DuPont people who had come in to help discuss this whole issue. They had come from out of town plants. And one of them in particular was Montgomery Evans. He was destined to be the plant manager in Hanford enterprise. And here night after night we would have these long discussions of industrial processes. He would be inquiring about the fission process and all the bugs in this and where one could go wrong. And I would be asking about the nylon and other things he had been in. 

Groueff: Where was that, in the hotel?

Wheeler: In the hotel in Wilmington. And there would be others drawn into our discussion. Sometimes there would be Herb Anderson there from Chicago. Sometimes there would be somebody else from Chicago. But it soon ended up that I was assigned full time there from Chicago to Wilmington to help in this design process. And having been through it once before with this other group of engineers, I knew very much more what to tell them about the nature of the process and what the issues were. And they, on the other hand, had to instruct me in many things, which were very hard for me to get accustomed to. 

The idea that you could not have one man who followed the process all the way through, that there were five different groups of people. A process engineer who would get the general idea of a reactor vessel. And then a design engineer who would have to consider the process of how you built this vessel to be strong enough. And then a construction engineer who would say to you, “Oh, no that design is no good because this requires welding and it is very difficult to get welding done in the field. We better design it in a different way so it can be built together because it is hard to get welders.” And then another group of people who would look at this and say, “No this design is not worthy,” this group is the operating group. This is going to be too complicated to keep going. It is going to cause us all sorts of difficulties on keeping a watch on the process. You have to redesign it.

Groueff: You have to modify it all the time.

Wheeler: All the time. And this specialization on different points of view was something that I could see that my physicist friends and I myself had never considered as the idea that Fermi had had of going all the way through and building the thing himself.

Groueff: You could not have done it.

Wheeler: It would not have worked. [laughs] 

Groueff: So you represented the Chicago group in Wilmington.

Wheeler: Right.

Groueff: And your contacts were mostly with whom at Wilmington?

Wheeler: Well, of course, there was [Crawford] Greenewalt who was the head of this whole group there and Roger Williams working close with him, then [Slim] Reed in the engineering department. 

Of course, it was very interesting. Talk about secrecy. One had, even in the DuPont organization, somehow to keep a kind of secrecy in the sense of making some of these decisions about how one was going to operate the process. In this group on the fourth floor where I was, and then only when one had talked this over, would one feel free to go upstairs and talk to the engineers on the tenth floor. One had to keep the engineers from knowing what some of the alternatives were so that when one finally decided on an alternative, he could tell the engineers, “Okay, you go ahead and do this.” And not let them be filled up with uncertainties. If one let them in on all these uncertainties they would not have the drive to go ahead and do things right.

But then we would go up after we had our party line set on what we wanted on the reactor vessels, for example, and talk to them on how, for example, we wanted the concrete shielding to be set up around the reactor. There were some topics where the engineers got into the act, they took stands, and this led to arguments going on back and forth. How should the graphite blocks be stacked up? Should they be laid out crosswise or parallel to each other? Your normal differences of opinion.

Groueff: This started even before December 2, before your experiment?

Wheeler: Well, the discussions were already beginning in Thanksgiving time, November 25 or there about. The biggest single decision that was going to have to be made was as between the helium-cooling that Tom Moore and the Standard Oil engineers and I had been working on with them in Chicago and the water-cooling process that Wigner that was by now quite enthusiastic about. Roger Williams was the person who had the biggest part in this decision. He had been through the process of making the ammonia plants for DuPont. Here they operated at unprecedented temperatures and pressures to make synthetic ammonia. No industrial process had ever been run under these conditions so he knew the difficulties of a thing of this kind. And he talked already; frankly, at this time about the difficulty of helium blowers and keeping them operating when they would be filled with radioactivity. 

He was much more concerned about that operating phase than he was about the point that Wigner was concerned about, getting the heat out most efficiently. That was Wigner’s point of wanting to put in water-cooling. But Roger Williams, in these first weeks he mentioned and discussed the point of choice between these two processes. A very wise man he made everybody feel that we were going ahead on the helium process in order that we should get going and figure out the things that had to be figured out in any case while he kept off on a side this decision in question until he could get more factors brought in on it.

Groueff: It was theoretically better. Helium would be better?

Wheeler: Helium, of course, would cause no loss to the reactivity; this was the great advantage. 

Groueff: But water would be more practical, I mean from a construction point of view?

Wheeler: Right, these huge blowers to blow the helium around. Well, they are enormous pieces of machinery. And these fans that blew helium around were to accumulate radioactivity. In the days while I was still in Chicago, the people who were opponents of the graphite cooled by helium had said that there would develop a new kind of chain reaction, a very bad kind of chain reaction, a chain reaction in which the helium blowing around through the graphite would pick up graphite dust. And although in the beginning it would be a very small amount of dust, it would be recirculated. And it would erode the graphite and release more graphite dust and then this would make more erosion and pretty soon the graphite would be worn away and you could never hope to take the pile apart and fix it because of the radioactivity. So the whole process would be ground to a halt. 

I actually got two other people together, we set up the equipment, we blew air through graphite, and we measured this as a direct way of testing it—negligible. But it just shows how intense people felt about these issues. So Roger Williams was really decisive in taking the decision. Wigner was, of course, making his voice felt very strongly on these problems and he urged, of course, the water-cooling very strongly. 

Groueff: Was there another suggestion by Szilard about some other cooling?

Wheeler: Yes, there was this liquid metal cooling, liquid metal. I do not remember at any time that our industrial friends ever took to this as being a good idea. It had too many unknowns. Air-cooling was regarded as giving too large a loss in reactivity. 

Groueff: But you did it in Oak Ridge, no?

Wheeler: Right.

Groueff: The pilot plant.

Wheeler: Yes, right.

Groueff: And for the Chicago plant, you did not need any cooling?

Wheeler: We just simply heated it up and left to cool by itself by ordinary external means. 

Well, of course, during this period in Wilmington, as the Hanford plant construction started, there was a question of being aware of what was going on. And during this time, I worked closely with [Dale] Babcock and Wendy as people who had been in this sort of thing before and all of us were reporting to George Graves who in turn reported to Greenewalt and Roger Williams. 

George Graves is a remarkable person. He had been through the Nylon process. It was he who took, I think, more than any other person the responsibility for putting in these extra tubes in the plant to take care of the poison. Everyday I would be working on these “bugs under the table” you might say, what would be the consequences of poisoning? What would be consequences of a bad temperature coefficient? What would be the consequences of a failure in the control rod system? And these memoranda that I would produce would then go to other people who would then go on with the engineering steps in the process. 

But Graves was a most blunt personality. He would say he knew nothing about radioactivity, never heard about it in his life. He would say, “Who in the hell told people to worry about this radioactivity?” So little by little he would, by questions, get into the subject in the most active and penetrating way by asking questions like this. 

Groueff: He was a strong personality?

Wheeler: Yes. And then he kept a book in which all these possible crises situations were catalogued and week by week he would follow what was being done on them and keep prodding people to prod the Chicago people to do experiments and checking on each of these points so nothing was left uncovered. I would make these trips sometimes with Babcock, sometimes with Wendy, sometimes with Graves to the Pacific Northwest to see the plant under construction, about once a month.

Groueff: You did not live there?

Wheeler: I did not go there until, let me see, this was end of November ’42 when I went to Wilmington and it was not until ’43.

Groueff: But you were in Wilmington?

Wheeler: [I was] between Chicago and Wilmington. I was living in Wilmington in’43 and then in July of ’44 I moved permanently to Hanford.

Groueff: To Hanford?

Wheeler: To Hanford.

Groueff: Oh, so you lived there with your family?

Wheeler: In Hanford, yes. Of course, it is a fantastic place. All the trains come in at midnight and there would be 300 people dumped off of each train at midnight that had been rounded up by what were almost cattle herders in the states of Oklahoma, Arkansas, Tennessee, and whatnot to get labor for the plant there. And these were people who were unfit for military service and the men who rounded them up just took ragtags and bobtails for this construction plant. As the men got off the train there were all these fleecers there ready to try to fleece them of whatever money they had. But then the sheep herders where there to try to make sure that they all got on their busses so that they were taken to the construction site before they could be fleeced of their money. There was one murder a week at the place.

Groueff: It was timing.

Wheeler: Yes, from thirty to forty thousand people there. The beer joint had windows that could be thrown up quickly so you could squirt tear gas in to knock people on their ass. That was at the construction plant; of course Richland was about forty miles away, Hanford and Richland. 

Groueff: And you lived in?

Wheeler: In Richland, which was  a much quieter place. But at any rate, of course, the most exciting single time was this time of startup and this catastrophic stoppage of the plant and trying to find out what was going on. But Babcock has written that up in history.

Groueff: Could you describe the day and a little of where you went and how it happened, who told you?

Wheeler: Well, of course, that day as every day I got up in the darkness of dawn, got on the bus, and went out to the plant to the 300 area so called, which is the area where all the experimental work was about ten or fifteen miles north of Richland, which is still twenty-five miles short of the plant construction area, a bit short of the place where the startup had actually taken place. And, of course, I had already followed the previous evening these difficulties that had been occurring.

So in the morning, happily, I had been able to get hold of the—I forget who it was who brought in the readings on the control rod position, but I think it was probably John Marshall or Leona Marshall who worked with Fermi on that. And so it was possible to see this time factor involved in the control rod going out and the time factor involved in the difficulty clearing itself up again. I had had enough previous experience with this, thinking about this poison question. I do not know how many memoranda I had written on the problem telling them to be aware that one could have a radioactive poison. So it was the most natural thing in the world to go across the hall and borrow a chart.

Groueff: That was in the 300 Area?

Wheeler: In the 300 area. And as I was speaking to Dale Babcock about this, [I said] bring back this chart and look over the chart of the radioactive materials to look for something that had the right period. Well there were a couple of candidates but then from the fact that the radioactivity, I mean that the difficulty was clearing itself up, it was clear that the parent of the radioactive material also had to have a lifetime of a number of hours. 

In other words, let me put it this way, when the pile was running it produced a precursor, this iodine parent or mother which had a life of a number of hours and then only after this number of hours decay, did the iodine form into xenon. And so only after a number of hours did the poison actually coming into being and start killing the reaction. On the other hand the Xenon had a lifetime of a number of hours. This one could say from the fact that the difficulty cleared itself up after one turned off the reactor the poison disappeared after a sufficient number of hours. So this told me immediately that the poison was not a permanent poison but a radioactive poison. At least this was the argument I formed.

Groueff: And in the meantime, the whole thing was stopped?

Wheeler: The whole thing was stopped, right. So from these periods it was possible then for me to conclude that this iodine Xenon thing was the reasonable thing. Well, Fermi arrived at about this time—

Groueff: They called him especially for that?

Wheeler: Well, he had been out at the startup area. He had been there already a couple of days before. So I cannot remember whether Fermi was called especially because of this difficulty or whether he was called anyway for the startup. But I do recall that he was most interested in this and that he immediately set to work calculating the curve of the control rod position from these two lifetimes to check for the readings and to see how much the total amount of poison was. Well, from this he drew the conclusion that that one did in fact have enough capacity there in the holes so he could load in enough additional tubes to clean up the poison.

Groueff: It was clear to you and to him that it was Xenon that was causing the trouble?

Wheeler: From this picture, yes. The minute that this picture was proposed, he accepted it, after he had gone through the calculations. The calculation, in fact, proved that it reproduced the control rod positions. The theories that had been proposed before that time by people on the spot as to what was going on, you’ve probably heard about how fantastic they were. There was one theory that there was a leak in the pipes and that water was going into the graphite and poisoning it, which was one idea. And then the reason it cleared itself up was that the water drained out of the graphite. 

And then another proposal, before one realized that it was clearing itself up, was that the river water had some kind of Boron or other poison in it, which under normal conditions, before the reaction had been going, flowed right through without any difficulty. But through some magic when the neutrons radiated the water this poison substance, boron in the water or what have you, was caused to deposit out on the tubes like a scale. 

Groueff: So nobody knew exactly what it was in the beginning?

Wheeler: Right, and there was also the proposal that [it could be] the nitrogen in the air. One already knew that nitrogen was a slight absorber of neutrons and the thought was that perhaps that the small amount of air which filled the pores of the graphite absorbed neutrons. And this caused the nitrogen preferentially to deposit in the reactor and so this brought in more nitrogen and so the effect of the nitrogen was somehow increased. Well, people in desperation are willing to try anything of course but the real credit for being able to make the reaction go goes to Graves because it really would have been—Yes, 25 percent extra space. If it had not been for him, I really do not see how we would have made out because it would have taken months—

Groueff: To build a new reactor.

Wheeler: Right. And then it would have been too late to be in good time for the warfare use.

Groueff: Were you present the day of the startup?

Wheeler: At the reactor?

Groueff: At the reactor.

Wheeler: No, I did not go to the reactor.

Groueff: Who were the main people on the Chicago team? 

Wheeler: Of course it was Compton as the policy director there and who spent a great deal of his time in contact with people outside with the committees direction. And then Fermi right there on the spot in day to day getting things built. And [Samuel K.] Allison really in effect between Fermi and Compton in the sense of acting as a director while seeing that people—

Groueff: Sort of general administrator. 

Wheeler: Administration and looking after salaries and he was very much helped by [Norman] Hilberry who had worked with Compton over the years as.

Groueff: They were the coordinators, Compton, Hilberry and Allison sort of the setup administrational process?

Wheeler: Right, right. 

Groueff: And Fermi was working mostly in what field?

Wheeler: Well, of course, Fermi was wanting to get this first reactor, or rather the first divergent chain reaction built. There were other people there—Wigner, the most effective of the theoretical people.

Groueff: So the type of reactor that was built in Hanford, was that designed originally by Wigner and his group? The water-cooled [reactor]?

Wheeler: The conceptual design was Wigner’s idea.

Groueff: And then it went to Wilmington.

Wheeler: Yes.

Groueff: For the design department. I talked some people there, Tom Gary was there.

Wheeler: Yes, yes. 

Groueff: And what was the role of Szilard?

Wheeler: Szilard was never one to act on a day-to-day job. Szilard was more a person moving around talking with one or another person. He did not like to tie himself down.

Groueff: He was the idea man.

Wheeler: Yes.

Groueff: Idea man, but he was not connected with any of the precise problems day-by-day?

Wheeler: No, he was not.

Groueff: But then why—I found a lot of resentment and sort of criticism about Szilard. Everybody said he was the most difficult man there and he was creating a lot of trouble. On the other hand, I have heard so much praise and admiration for him as an idea man, especially in the beginning of the war. 

Wheeler: Well it is a wonderful thing when you have so many different kinds of people in the world. But Szilard really was a gadfly to go around and keep people stirred up. Sometimes he made people discontented. But I should not talk about the semi-revolutions that he promoted from time to time of younger workers. 

There was a terrific impatience on part of younger men wanting to get the job done in a hurry and sometimes they got the feeling well, we could be going faster than we are. I do not think that everybody realized all the time how hard it was to get everything done. Ed Creutz was a real driver. He was one of those who was susceptible to the words of Szilard.

Groueff: Szilard was like their leader or something of the impatient group.

Wheeler: Yes.

Groueff: And I understand also from the Army people that he was resentful to them, to the Army people like Groves and the others, and also, to DuPont people.

Wheeler: Yes.

Groueff: And having a kind of probably superiority complex as an academic scientists.

Wheeler: Well, Szilard has always been that way. He used to find a certain amount of enjoyment in sticking the needle into people by using the superiority complex on them as a way to stir up discussion, to make people as effective as they can be in arguing with him. His idea of a discussion is not a nice friendly tête-à-tête but a real set-to where you wrestle with the other person like [Nikita] Khrushchev inviting [Josip] Tito out of the car to wrestle on the ground. That is Szilard idea.

Groueff: But very brilliant at the same time.

Wheeler: Yes.

Groueff: Very brilliant. I understand Fermi was much easier to work with and a simpler man.

Wheeler: Very straightforward, concrete, and business-like.

Groueff: He did not create any trouble?

Wheeler: No, not at all.

Groueff: And Wigner?

Wheeler: Well, Wigner is a person who can make a stand for a principle and do so very effectively. You know right now he is working on shelters and he has had to have another set to of the same kind he had in wartime days. The wartime days to this big problem of persuading people to put in the water-cooling, now he is working hard to persuade people about shelters that shelters should not be merely fallout shelters, they should be blast shelters. 

Groueff: He is a man with strong convictions?

Wheeler: Right and he objected against the engineers’ way of doing business because it is contrary to his way of doing business. His way of doing business is one person takes a stand on a position and he investigates all sides of the matter and then he takes the responsibility upon himself for saying, “This is right, because I have understood it all myself.” And not because somebody else has told you this, somebody else has told you that, because you have understood it. Whereas the engineer is by force constrained to work with other people.

Groueff: To take the word of other people.

Wheeler: on other phases of the process. So it is just a constitutionally different outlook.

Groueff: But generally the whole team works quite well together, the scientists and the DuPont people? Compton was keeping everybody—

Wheeler: Yes, I remember at this time that Szilard came the closest to staging a revolution with the young people that he got stirred up, myself included on occasion. I remember that Compton decided that something ought to be done for the moral of the laboratory. So what he did was, since it was the time of the construction of the reactor, to get everybody to take a turn in machining the graphite or helping to pile the graphite so that everybody would feel he had a part in it. Well, Szilard had thought this was a kind of a cheap trick and he would have nothing to do with it. [laughter]

Groueff: But everybody.

Wheeler: Everybody else did take some pride in it. 

Groueff: Where are you originally from Dr. Wheeler?

Wheeler: That is a very difficult question to answer because my father was a librarian. I have lived in so many places in the United States, born in Florida, lived there six months, lived in California for three years, stayed in Ohio for seven years, then a farm in Vermont for two years, the city of Baltimore for eight years. 

Groueff: Wow, but your father was a librarian in the universities or what?

Wheeler: In the public library, he is the person who has designed more public libraries in the United States than any other person.

Groueff: So you have been connected with books since childhood?

Wheeler: Since childhood, yes. My father is now eighty-one and he is continuing active. He just recommended a plan for the reorganization of the public libraries of San Diego. And he has just flown to Atlanta, Georgia to help reorganize their library system.

Groueff: Where were you educated, your high school?

Wheeler: My high school in Ohio, Youngstown--Ohio and Baltimore.

Groueff: And what college?

Wheeler: I went to college in Baltimore, at John’s Hopkins University. 

Groueff: When did you decide to go into physics, in high school?

Wheeler: In college, I started to be an engineer and then I decided that one has much more—he can build a bridge and it is torn down in one hundred years, but if he makes a discovery that is something that people can use forever. After my freshman year in college, I worked for a summer in  a silver mine in Mexico rewinding electric motors that pumped. I found that pure science is much more fascinating. But, of course, I had no idea one could keep himself alive working in pure science. 

Groueff: So you were attracted to science since—?

Wheeler: Yes, I can remember one of the very first things when I was three years old asking my mother about the world: “If you go there, what comes? Then you go on, but if you keep on then what? 

Groueff: All these questions.

Wheeler: This mystery, if you keep on, is there an end of the world?

Groueff: Did you read a lot as a child?

Wheeler: Yes. Yes, I can remember reading at the age of ten about liquid explosives and being fascinated with explosives. And so going out and we had explosives—I was then living on a farm and my father was ill and we had gone there for him to get well—we got some dynamite to experiment with and I blew off the end of my fingers. So first it was dynamite then atomic bombs, then hydrogen bombs.