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Oral History Transcript — Dr. Victor Weisskopf

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Interview with Dr. Victor Weisskopf
By Charles Weiner and Gloria Lubkin
At Dr. Weisskopf’s office at M.I.T.
September 22, 1966

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Victor Weisskopf; September 22, 1966

ABSTRACT: Origin of interest in nuclear physics, discussions of compound nucleus, Copenhagen, 1936; work on interaction of evaporation and nuclear temperature, 1936; Breit-Wigner formula; application of evaporation model to nuclear reactions; postwar work in electrodynamics and nuclear reactions; relative merits of compound nucleus and shell models, 1950-51; explanation of independent particle motion by Pauli principle, 1951; estimates of shell model radiative transition probabilities; optical model and relation to compound nucleus models, 1953-55; emigration to U.S., 1937; initial impressions of American physics community; teaching and research at University of Rochester, 1937-43; visits to Cornell University; elaboration of evaporation model; effect of Bethe-Bacher-Livingston REV. MOD. PHYS. review articles, 1936-37; contact with physicists at American institutions; summer schools in U.S. and Europe; role of conferences; centers of nuclear physics research, 1930s; the atmosphere and social aspects of life at Los Alamos and subsequent effect on physics, 1943-47; effect of war work at MIT on electrodynamics and nuclear models, 1947-55; visits to Brookhaven; collective model; role of nuclear spectroscopy; origins of high-energy physics; relations among nuclear structure, meson physics, and field theory; current (1966) work in nuclear physics in Europe; the future of nuclear physics.

Transcript

Session I | Session II

Weiner:

We’d like to pick up where Professor Kuhn’s interview left off. Now that you’ve had a chance to briefly go through the transcript of the interview that was done in 1963 with Tom Kuhn in regard to the quantum physics project, I’d like to take a few points that occurred at the end of that and lead into a new period. You mentioned that you first became interested in nuclear physics in the early ‘30’s, and that at least one of the factors was that you wanted to go to the United States, and that you knew it was a field of important interest here, Now how serious a remark was this?

Weisskopf:

Yes, in fact, I was struck by this myself when I reread it. It was not a decisive factor. It was not at all, in fact. Maybe it’s even misunderstood the way you quoted it. Because I think, but I may [go] too quickly now, that I only said that was one of the factors why I had chosen the publication, Physical Review, and not a European journal. This is true. When I did this work, up to this moment, all my publications were in the Zeitschrift fur Physik or in the Danish Academy proceedings. And this thing I sent to America. That action was certainly dictated by the fact that I wanted a job in America.

Weiner:

Yes, you said that you wanted to advertise your existence.

Weisskopf:

But not the choice of subject — no, no, I think this is a misrepresentation. I’m not sure that I said it, but if I said it…

Lubkin:

You feel that you became interested in nuclear physics before you had decided to come. Can you pinpoint what started it?

Weisskopf:

Look, this is a very difficult problem to answer, even in general, because everybody has a very different mechanism in which he finds the topic he wants to work in. Now I can tell you my mechanism, which might be different from others, but it is almost a regular event at any time. It is the following: that I am not a specialist, I like to be interested in many things. And I’m a very, so to speak, extroverted social animal; and when people around me talk about something, I would like to understand what they are talking about. Also, I have a very strong pedagogical vein in me, I like to explain things and I like to explain things simply. Therefore, whenever I hear people discuss, I tell myself, “This is not well explained. I must get into it because I think those people do a bad job in explaining,” And I want to explain it better. Just to give you an example, I spent months and months working, not successfully, to understand superconductivity because I was totally disgusted by the way people explain superconductivity. They may think that you can understand it now, but I haven’t yet read an explanation which I consider an explanation, which means that something is really clear enough to explain [it] to a senior. So I always have had this tendency when I hear something which excites other people, to listen to it and to find out about it. And then when I hear those people explain it, I find they do a terribly bad job and I feel I ought to get in not because I want to work in this field but just in order to explain it better. This is the way I went into many fields, and this is the way I went into this field of nuclear physics. At that time I was in Copenhagen and I was in fact busy with other things, with electrodynamics, because that was the way I started out. But then there were so many people talking about nuclear theory in a rather confused way that I said, “I have to understand this.” Then also Bohr talked a lot about it, the compound nucleus. And so I tried to formulate it. I did not in fact want to contribute anything original. I just wanted to formulate it clearly. And that is the way I got to the temperature concept and the application of thermodynamics to nuclei which was my first contribution to nuclear physics — the interaction of evaporation and of nuclear temperature, which happens to have been done, as you know, by Landau in a similar way; but that was independent.

Lubkin:

Was he around in Copenhagen at that time?

Weisskopf:

No. This kind of work he did I knew [of] only through the papers.

Weiner:

Were there discussions in Copenhagen about nuclear physics? Were there colloquia?

Weisskopf:

You know, life in Copenhagen was extremely informal. One did nothing but talk.

Weiner:

In this case, who were the people there that seemed to be most caught up in nuclear physics?

Weisskopf:

Kalckar. He died. Placzek was another, who at that time was there with me. A fellow who also died, by the name of Williams, a Britisher — the Weizsacker-Williams method, Weizsacker wasn’t there, but he came off and on. I’ve probably forgotten a lot of important people.

Weiner:

These were the ones that come to your mind, the ones that were especially concerned.

Weisskopf:

Yes. There was Frisch, Halban, Kupferman. He is dead. Bethe and Peierls, although they were not there, but they came.

Lubkin:

You say that Landau and you worked independently on this statistical model. And I notice that in this paper you footnoted that Landau had begun it.

Weisskopf:

Yes.

Lubkin:

Were you in correspondence with him? How did it come about that you even knew about it?

Weisskopf:

Well, I saw his paper after I had started working. Probably somebody told me about it because I am not a good literature reader. Somebody told me, “Look, what you are talking about reminds me very much of something I saw somewhere.” This is usually how I would have found out about it. And then I read the paper, and wrote Landau a letter. I knew Landau very well from before, personally.

Lubkin:

You were in the Soviet Union...

Weisskopf:

Yes, I was in the Soviet Union several times before I wrote this paper.

Lubkin:

You say that this was your first nuclear physics paper, but by publication date there’s one on exchange forces between elementary particles.

Weisskopf:

You know, I saw it today, and I don’t know what this paper is.

Lubkin:

I have a copy.

Weisskopf:

Please give it to me.

Lubkin:

I alluded to this before. It sounded to me like you were thinking about a theory of nuclear forces there, in ’36.

Weisskopf:

Yes, to use the weak interaction forces. Essentially, in very modern language, it means using the W particle (intermediate boson) instead of the pion as the generator of nuclear forces, and then assumes some crazy properties which really would give a strong bind. Yes, but this is not really nuclear physics. It is a hit at the fundamental problem, and it is my experience in field theory from electrodynamics [that] made such an idea possible. This was a hit at the fundamental problem coursing through the structure of nuclei. What is the nuclear force? I said it before. This is not nuclear physics. It sounds like nuclear physics, but it is fundamental field theory. That belongs in my field theory period.

Lubkin:

In what sense does this duplicate Yukawa’s theory, if at all?

Weisskopf:

It just happens to be wrong and Yukawa was right. When was it, in ‘36? At that time I knew Yukawa’s theory, but the pion was either undiscovered or barely discovered and not believed, whereas the beta decay, the weak interactions, were well-known. So it is quite tempting, quite reasonable, to go back to that and say, “This at least we know.”

Lubkin:

Did you immediately feel after the pion was found that this was no good?

Weisskopf:

I would think so, yes. I didn’t stick to this very long. The fact that I forgot it shows it to you. Now things come back to me, but I did not really believe this.

Weiner:

You were talking about how you started in 1936 and you mentioned the excitement about nuclear physics. Was this not true earlier?

Weisskopf:

It was true earlier, but it was especially true here, because these were the first years of the compound nucleus. In fact, my paper...I’ll tell you a story. I’m not sure whether I told it here [in Kuhn’s interview]: about my difficulty with Niels Bohr over this paper? I think that will be an answer to this: There was tremendous excitement in Copenhagen because that was the time of gestation of my nuclear physics paper, of this paper on temperature. This was before publication of course. It was just the time when Bohr came around with the idea of the compound nucleus. And therefore there was tremendous excitement. Everybody talked day and night about nothing but the compound nucleus. And Bohr and Kalckar were just about writing their famous paper. And you know how Bohr writes papers. I mean he works by writing papers. He says he’s going to write a paper and then begins to think about the problem. The paper is printed 15 times and changed and so on. Now, during this time I produced my paper on the evaporation, which of course [to] some extent is based (in fact, it says at the beginning) on Bohr and Kalckar’s paper and goes further than that. Now, comes again this business about America into it.

I was, of course, very interested because I liked the paper, and also because of my American future I wanted this paper published as soon as possible. And I was in a rather difficult situation because I couldn’t publish it before Bohr and Kalckar published their paper because it was definitely based on it and it would be looked on rather badly. Then I came into one of the baddest situations of my life. Consciously or unconsciously, I don’t know — I sent it off at a time which I think was too early. And Bohr and Kalckar had again decided to wait because they always say, “Tomorrow the paper is going to be sent.” The trouble was that Bohr and Kalckar were in America and I was in Copenhagen, and somehow I got mixed up, and the fact is that this paper appeared at the desk of The Physical Review before the Kalckar paper was ready for publication. I, of course, sent the manuscript to Bohr, who was at that time somewhere in America, with a letter that I’d just sent this manuscript to Physical Review. And then I got a very sad and sort of reproachful letter from Bohr — actually from Kalckar because Bohr does it always that way. Let’s say (I’m putting it now stronger than it was) but how ungrateful I am, all Bohr did for me, and in fact he tried to get me a job in America and I am sort of jumping the gun with this paper. Then he reproached me for sending it in too early and also for certain formulations in the introduction which did not enough emphasize the priority of Bohr’s and Kalckar’s idea.

Now, that was a very disagreeable letter to get. I felt extremely unhappy because I also felt that I was to some extent innocent. I was accused correctly, but I didn’t do it willingly; it was a series of misunderstandings. I didn’t do it consciously. I thought that their paper was out. I was extremely unhappy. And in particular I was unhappy about the accusation that the introduction didn’t emphasize Bohr’s work. De facto, it did to some extent. I changed very little after having a long correspondence with Kalckar. One word or two were changed. I think it says now quite explicitly that it’s based on Bohr’s and Kalckar’s work, but that was also contained to some extent in the first edition. Perhaps I should say this was the only time when there was any conflict between Bohr and me, and that is why I suffered very much from it. And this is perhaps an illustration which also describes the spirit at that time in Copenhagen; it was all in the air. It was in the air.

Lubkin:

Did Breit and Wigner come at that time?

Weisskopf:

Yes, it was about the same time. Was the Breit-Wigner paper before mine or after? It must be almost the same. Yes, it must be very close, and I think Breit-Wigner must be before.

Lubkin:

I think the publication date for Breit-Wigner is earlier.

Weisskopf:

But not much. It must be half a year or so.

Lubkin:

I don’t have the month.

Weisskopf:

It is very much the same. But, of course, it’s a very different approach. You see, Breit-Wigner are looking at the structure of the resonances, and I was looking at the thermodynamics of it, of the average properties. It’s almost the opposite approach to the compound nucleus. It’s the same theory, but it’s the opposite end of the theory.

Lubkin:

Were you talking things over in those days?

Weisskopf:

Not with Breit and Wigner. But Breit-Wigner was extremely well-known. It was a trade term. I mean everybody spoke of this.

Lubkin:

They were talking about it before you had really finished your work.

Weisskopf:

Oh, sure, sure. But I would never consider that the paper I did was in any way impinging on this. It’s a different aspect. And, as I said I think in my interview, one of the interesting things in my paper is the fact that it was the first time in literature — at least Stern told me so — that the thermodynamics of very small objects had been considered.

Lubkin:

What were the repercussions of this in later years?

Weisskopf:

I think that paper is probably my best-known paper because of the whole idea of evaporation. Although I must admit it is not me who said it the first time — it was Frenkel and Landau — but I think it is the paper in which evaporation is treated in the greatest detail. And as an American paper, it is more available than the others, which is why it is most important. I mean the way the evaporation was treated in this paper was then taken over in the literature. As I said, I think it is the most popular paper I’ve ever written.

Lubkin:

Can you trace some sort of subsequent development of this idea?

Weisskopf:

Oh, yes. The whole development of reaction, of the theory of nuclear reaction on the basis of the compound nucleus picture was based on this theory (Professor Jensen does not agree). There is of course a series of papers by myself later but not only by myself — there were other people in this period — particularly by the experimenters on the idea of inelastic scattering, particularly of heavy nuclei, because this theory, being a statistical theory applies more to heavier nuclei than to light nuclei. So the reaction theory of heavy nuclei — this idea that a fast neutron comes in and slow neutrons come out; the fast neutron tears up the nucleus and the evaporation then is slow — has led to the development of the theory of Feshbach and many others.

Lubkin:

Which Feshbach? Are you referring to the first one with Hauser?

Weisskopf:

Yes. Feshbach and Hauser. All this development, in fact, is an outgrowth of that temperature idea.

Lubkin:

And then you’re saying that the optical model is...

Weisskopf:

Now that’s a new step.

Lubkin:

You don’t feel there’s a derivative in it.

Weisskopf:

In a way, yes. Sure, everything is derivative. That is a new step forward. You can say that the exploitation of Feshbach and Hauser is an exploitation of the evaporation idea. And many experimental papers — papers by Barschall in Los Alamos…Let me come to this because that is perhaps the most interesting thing which yesterday I thought I have to tell you. A whole reaction theory was developed, not only by me but also by other people. There was a paper which I wrote with Ewing. You know I have a really bad conscience about this paper. I’ll tell you why. Now this is an aside. You have noticed that my first paper was with Wigner because alphabetically I was lucky with my first collaborator. It’s great if your name starts with “W” that your first collaborator should be Wigner. This paper, on the line width as you know, was an important paper, and to be the first author of an important paper together with Wigner is a stroke of luck. At that time I made a vow: “This is a stroke of luck and I have to thank God by making a vow that I will always stick to the alphabetical order, never mind what comes.” And Ewing tricked me. Ewing is the only paper which is Weisskopf and Ewing, but it was his fault. He changed it without my knowledge. And I had big fights with Wiley when the book on nuclear physics came out (Blatt and Weisskopf) because he wanted to make [it] by Weisskopf and Blatt. And I said, “Under no conditions.” The Ewing paper is the only blot and I’m very unhappy about it.

Weiner:

What was the general procedure as far as the order of names?

Weisskopf:

The general procedure was always that the so-called senior author comes first.

Weiner:

This changes when you get a large group, though.

Weisskopf:

Yes. And nowadays when it is so hard to get a senior author, it’s the alphabetical order that is followed.

Lubkin:

Then your philosophy with a graduate student, for example, would be that his name would come first.

Weisskopf:

Absolutely, except if he’s called Zacharias or something.

Lubkin:

But this is not always true. I don’t think this is anywhere near standard practice, is it?

Weisskopf:

No.

Weiner:

You were talking about that Ewing paper.

Weisskopf:

Yes, there is an interesting point here. On the basis of the thermodynamic paper, which I wrote, you could develop a theory of reaction, which was made by Kalckar, and by Bethe, and by myself, and many other people. The theory of nuclear reaction is the basis of the compound nucleus model, the famous thing that you split the reaction in two parts — the formation of the compound nucleus and the decay of the compound nucleus. Now, on this basis you could predict cross-sections. In Los Alamos the following thing happened, and this is unfortunately not public. You could predict, for example, the fission cross-section. For the first two years when the experiments were made, the fission cross-section of uranium 235 turned out to be one-third of that prediction. And I said, “It cannot be true.” This time I stuck to it. I’m very proud of this because I said, “The measurement cannot be true…There must be a fluctuation because, after all, this theory gives only average values.” I said, “You were measuring at very low energy. You must have just hit by accident a low hole in the uranium nucleus. The average cross-section must be the value which is given by that theory. It’s a heavy nucleus, and all the other indications (which I don’t want to quote now) in that respect and so on point to the fact that uranium is a wonderful example of a good compound nucleus. The fluctuation is a fluke. It cannot be the average cross-section.” And I stuck to it until the last year in Los Alamos when the whole measurements were labeled, and, true enough, the cross-section goes up to the predicted value where it sticks.

This I think was a very nice triumph of that compound nucleus theory, which I wouldn’t say is only my theory — it was worked [on] by many people — but it is based on this fundamental idea of Bohr and Kalckar and the temperature. It was a nice idea — and this theory really showed this powerful force. And nowadays it’s very much used in general to get the first idea of the order of magnitude of the cross-section. Well, this was the story of the compound nucleus. Now, this is very interesting. As time went on, I would say that the great years of the compound nucleus idea were the war years, and very important was the paper by Bohr and Wheeler on fission that predicted the 235 and that little episode I told you about and many others. Most of the estimates of slowing down neutrons, which are very important in nuclear engineering, [are] all based on it and it works pretty well. In fact, when I wrote the book…Perhaps I should tell you a little more. When I came back from Los Alamos to this place, I had essentially two research plans. One was to go ahead and work out all these ideas in nuclear physics, essentially working out the details of the compound nucleus reaction theory which I started in Los Alamos but hadn’t had time to do. And right away afterwards, maybe still in Los Alamos I had another idea that I would like to write a textbook on nuclear physics. In fact, there is a Los Alamos report, which was even translated into Russian, about nuclear reactions. It’s probably not on that list. But that essentially would be the first version of one chapter.

So I decided that I’d write a book on nuclear physics. When I came back, however, I was again interested in my old field of electrodynamics; and, as you probably know from this [Kuhn] interview, I was always worried about the infinities and I considered this unfinished business. I heard discussions about the difficulties of the Lamb shift, although the Lamb shift was not yet done. It was at that time called Pasternack shift because Pasternack, as you know, had some very vague indications of the Lamb shift.

Weiner:

You covered some of this [in the Kuhn interview].

Weisskopf:

I’ll leave it out. I should only talk about nuclear physics.

Weiner:

No, we were talking about you.

Weisskopf:

My nuclear physics.

Weiner:

Your career in general and we’ll get into the electrodynamics when it comes up.

Weisskopf:

Most of it is already in there, especially the story about the calculation with French. On that I spent let us say 50% of my time, and the other 50% I went on with straightening out the theory of nuclear reactions, particularly, the nuclear reactions with boundary conditions, to define the boundary condition of the incoming waves of the nucleus on the basis of statistical motion. Again, I would say this was very much pedagogical because it all grew out of the fact that I had to give lectures in nuclear physics at Los Alamos and at M.I.T. And then Herman Feshbach and I developed together this method of boundary conditions, which is again a mathematical refinement of the compound nucleus idea (an outgrowth of Bohr-Kalckar, my paper on temperatures, the experiences of Los Alamos). And this is the paper (Feshbach and Weisskopf) about the boundary condition model.

Lubkin:

Do you mean Feshbach-Peaslee?

Weisskopf:

Yes. And I think there was also Feshbach-Weisskopf before but there were a whole bunch of papers. At that time it seemed to us that the compound nucleus was a very good picture. And this lasted until about 1950 when several things occurred. First of all, the magic numbers came slowly into the center of interest, which of course somehow are contradictory to the idea of compound nucleus. And it is certainly true to say that the strength of Bohr’s personality — all the bunch of Bohrists like myself — probably had a dampening effect afterward on the discovery of the shell model. Then around ‘50 the magic numbers came up and also refinements in the measurements of nuclear reactions showed that not all predictions of the compound nucleus are necessarily true. That means that the compound nucleus theory just gives you the right values, but there are phenomena that you cannot describe with the compound nucleus. For example, there are what one now calls direct reactions — that means reactions in which the particles are not amalgamated with the nucleus, but have a more direct effect throughout every nucleus. These phenomena became more and more known because the measurements were more accurate.

Lubkin:

Were these the Barschall measurements?

Weisskopf:

No. The Barschall measurements come a little later. No, these were scattered measurements by many people. The Barschall measurements have an importance for the crystal ball, later. But anyhow if you read the book, strangely enough, you would never believe that this book (that is still the textbook of nuclear physics) was finished at such an impossible time. It was actually conceived and written completely under the compound nucleus atmosphere and only contains chapters that are sort of hung on about the difficulties of the compound nucleus picture, and there is one chapter on the shell model which was just written after the completion of the book.

Weiner:

But you say that you were feeling pretty satisfied with the compound nucleus idea even at the time of the shell model.

Weisskopf:

Now, wait a minute — I’m coming to that. At the time when the book came out, I definitely had the impression that it was probably a very bad moment to finish a book, that the compound nucleus model was probably only part of the truth, and I didn’t know what the truth was. The shell model was there and nobody knew why. And there were seemingly some independent particles there…[some strong interference which obliterates several sentences]…Of course when we wrote the book, many times we tried to isolate the problems, the main points. And there was a lot of very good formalism that can be used in different fields. But the actual nuclear physics period when this book came out, in ‘52, was a very critical period. Now, after the book was finished, it was clear that my main interest and the interest of our people here (and everybody’s for that matter) was: “What is all this business with the independent particle?” And then came a serious paper by myself trying to elucidate this. I do not mention here, by the way, the papers that are not nuclear physics. At the same time the whole meson discussion went on, and I wrote a paper with Fermi and Teller on the two mesons, the trouble with the two mesons.

Weiner:

I think you might take this particular story to its logical conclusion and then go back and put in what you left out.

Weisskopf:

So it was necessary to explain why is it that the independent particle model can be applied at least in order to get the spectrum of the nuclei. Maybe this was the paper that I published in Science.

Lubkin:

This one on nuclear models in ‘51?

Weisskopf:

That’s right. In ‘51, on nuclear models, I consider this an important paper so far as I’m concerned. The nuclear model paper — I’m not sure whether it was the first time, but maybe for me it was the first time — this idea was used that you might be able to explain the independent particle motion by the Pauli principle. Namely, that it is true what Bohr says that the particles collide a lot, but you cannot make use of their collisions because the Pauli principle forbids them. All states are occupied and therefore it is as if they did not collide. This is a kind of qualitative explanation why the independent particle model is true, in spite of the fact the interactions are strong. I am quite sure that as usual I wasn’t the first to say that, but if I may say so, I think I was the first to say it clearly. Therefore, I think that this paper had a lot of influence and people got more accustomed to this idea. It appeared, in fact, before the book was out, but just in the last period, because the book was finished in ‘51. But the idea is not in the book.

Here is another paper, which is in the book, where I think I contributed something original — that is, to get more information about radiative transition. It turns out that the transition probability for gamma ray emission of nuclei depends very much on the difference in angular momentum by very large factors. Just because it depends by some very large factors, raw estimates are very useful. At that time I published estimates of what one should expect on the shell models for radiative transition probabilities in nuclei for different types of radiations — quadrupole, octopole, magnetic or electric. I must say I, at that time, found this a little thing I could do just as a by-product of a book I wrote. But it has turned out that these formulas have been used very, very much by experimental physicists to classify transitions, to recognize transitions. In fact, this is, I think, the only thing that my name is connected with. They’re called the Weisskopf units, these units in which one measures. So it has been a very popular thing. It wasn’t intended to be that. It came from this idea of the explanation of the shell model. Then since we were always extremely interested in nuclear reactions, the next task was: how would the new ideas of the relative independent motion of particles in the nucleus change our old compound nucleus picture for nuclear reactions? In a way this was a very critical thing because it had been so successful, and now seemingly the foundations were taken away. So how can we do it? There must be a way of understanding it. There now came a whole series of papers which I think laid the foundations for unifying these two views in respect to reaction. And these were the papers by Feshbach, Porter, and myself in 1953. There were several papers. And then in l954 “Model for Nuclear Reactions with Neutrons.” These are essentially what we call the cloudy crystal ball, and are not necessarily new ideas. Serber and Fernbach had the same idea.

We didn’t quote them, for which I have a very bad conscience, but we didn’t know about them. And there were some other people you mentioned who had the same idea. But, again, I think we mostly did the application for nuclear reactions, which means we tried to describe nuclear reaction of particles to come in and come out on the basis of this. And mainly we tried to understand how this goes over into the compound nucleus theory under certain conditions, and how one can therefore understand the phenomena at both ends — the direct reaction and the compound nucleus reaction and how this in fact can be explained by the same mechanisms. The experimental basis of this cloudy crystal ball model for reactions was given by the measurements of Barschall. And in order to understand these measurements — the energy dependence of neutron measurements — (and this is the whole joke here) one had to distinguish between fine structure and coarse structure of resonances, because it turns out that the behavior of fine structures is given by the compound nucleus model and the coarse structure by the crystal ball model. And these things fit together. Now, about this fitting together of these two concepts, a lot of thinking was done — first in a rather muddled way and then clearer and clearer. And I think the really final formulation is the one with Friedman. This paper I think also had a great influence.

Weiner:

That was in ’55.

Weisskopf:

I think this paper with Friedman was the first time it was clearly demonstrated how the two pictures fit together.

Lubkin:

Excuse me. Did you know about the Barschall results before?

Weisskopf:

Yes.

Lubkin:

And so your attempts were motivated by…

Weisskopf:

But sometimes, you know, we’d be working very closely together. Sometimes, for example, we’d make our theory and we told Barschall, “You’d better look at that and see whether it works.” And that turned out to be correct: particularly these broad resonances were partially predicted by us. This was described in one of these…

Lubkin:

I have your Friedman paper here.

Weisskopf:

(going through papers) There were these curves here, you know — the average value of Γn/D, the neutron width. These were two resonances. They were predicted and later found. This is Barschall measurements and Brookhaven.

Weiner:

And this was in Reviews of Modern Physics, paper 57.

Weisskopf:

This is a review article.

Weiner:

Let me ask at this point, how far in the future you intend to take this thought, or do you wish now to get back to the earlier period? We’ve covered too much ground in too short a period of time. But you showed the sequence of certain papers and that was good. Now I’d like to get back to more specific things and environmental things, too. One of them relates to coming here to this country — how this came about. In your interview in connection with the quantum physics project you mentioned you had been having regular correspondence with Bloch and with others who had been describing conditions here. How was the job obtained? Earlier you mentioned that Bohr was involved. Did he contact people at Rochester?

Weisskopf:

Yes I suppose. I’m not quite sure, but I think the situation was this: at that time Seitz left the University of Rochester and took a job in Philadelphia at Penn. And Lee DuBridge, who was the head of the department at Rochester, said to Niels Bohr: “We are badly in need of a theorist. Can you recommend somebody?” And he recommended me. Whereupon I got a letter from DuBridge in ‘36 asking whether I would like to take an instructorship for $200 a year. It would be good especially for the young boys nowadays to realize that I was offered a job for $2400 a year in 1937 though I had written this kind of regular paper, and I had this job as instructor for three years. And in ‘43, six years later, when I came from Los Alamos my salary went to $2700 and I had an assistant professorship. I’d like the boys to know this. And I had a very happy life — I don’t complain — but when you see how people react today to jobs…

Weiner:

During this period did you have a heavy teaching load?

Weisskopf:

No. That much I must give to Lee DuBridge — never more than two courses, and sometimes less than two courses.

Lubkin:

You say you had an assistant professorship at Los Alamos?

Weiner:

No, when he went.

Lubkin:

You had just been promoted before you went.

Weisskopf:

Yes, a year or so before I went.

Weiner:

These two courses — were they offered to graduates or undergraduates?

Weisskopf:

It’s usually one undergraduate and one graduate, and later on only one course. So it was never a big teaching load.

Weiner:

Did you consider going to England?

Weisskopf:

Yes.

Weiner:

What would have been the relative advantages or disadvantages in your own mind at that time?

Weisskopf:

Intellectually, none. If I had gotten an offer of the same kind of permanence, I would have gone to England, simply because it was nearer and it was a big transition to go to America. But, you see, there were several reasons. First, I think the English had a very short-sighted policy towards refugees. Gosh, what they could have gotten at that time for nothing! And they didn’t even try. There was only one man who attempted it and that was Lindemann, Lord? what’s his name?, at Oxford. He got a few people. But he had to fight very hard against the authorities. You had difficulties with citizenship and, last not least, we all saw it coming on the horizon — the war, Hitler, and the unpreparedness of England. And that was also a reason not to go there.

Weiner:

What about, as well as the social factors, as I’ll call them, the state of Physics?

Weisskopf:

The state of physics at that time was not particularly attractive. It was not the opposite of attractive.

Weiner:

Where is this?

Weisskopf:

In America. But it was not particularly more attractive in England. Look, at the same time — I think I said this — when I had the instructorship at Rochester, I had a professorship in Kiev in Russia. Did I say this?

Weiner:

No.

Weisskopf:

Well, I got at the same time an offer from the Soviet Union under materially much better conditions than here, but of course it was obvious…It was ‘36, the purge was already starting; it was clear to anybody it was an impossible situation.

Weiner:

What was the origin of that offer? Was Landau involved in it?

Weisskopf:

Yes. I was in the Soviet Union several times and they knew me very well there. Also a number of refugees were there, but clearly that wasn’t acceptable. America was quite attractive scientifically, as after all, in 1936, a few cyclotrons were already working and obviously nuclear physics was blooming here. A lot of refugees were already here. After all, I was a latecomer, I was much later than most of the names one knows. And so the attraction was quite big. But if the political angle had not been there, I think the attraction of England would have been equal because nuclear physics at that time in England was also blooming.

Lubkin:

Was there any key man who made it worth going to the USSR other than Landau?

Weisskopf:

Oh, yes. There was Tamm and Labutsky (?). It was quite lively, but not comparable to the United States.

Weiner:

This decision-making is all taking place in 1936 — right? And then I gather that when you received the offer from Rochester you accepted it on those terms.

Weisskopf:

Yes.

Weiner:

Did you proceed directly to Rochester or did you have any free time?

Weisskopf:

No, I proceeded directly to Rochester, but I spent a lot of time at Cornell because I knew Bethe very well and it’s not very far.

Lubkin:

Do you feel that he influenced your work…?

Weisskopf:

Yes.

Lubkin:

For how long a period would you say that you relied upon each other, or was it only one-sided?

Weisskopf:

Well, I think only after I came here. No, also before, though before I hadn’t had so much contact. Let us say after I came here, during the pre-war and the war years, I was very close to Bethe, and he influenced me a lot, and I didn’t publish anything without very extensive discussion with him. And I would say I was sort of independent of Bethe in the ‘50’s when I worked less with him.

Weiner:

What sort of a group was assembled at Rochester and what was your reaction as a European coming to an American university for the first time? Did you plunge right into teaching?

Weisskopf:

Actually it was very delightful there. It was still sort of a small university of a relatively high intellectual level. I think it was much better than I expected. It was really pleasant, a pleasant life. In spite of financial difficulties, it was very pleasant.

Lubkin:

Did you realize that the offer was a poor one when you accepted it?

Weisskopf:

Yes, I was told so by my friends. This was a period when Jewish refugees hadn’t much to choose from — a period when you were asked were you expecting children, and you said, “No, we at first expect parents.” It was literally so. With the little money we had, we had to pay the way of my mother, my brother, my sister corning over. They were facing death and they had to come over. It was a difficult time.

Weiner:

Where were they at the time — in Vienna?

Weisskopf:

Yes.

Weiner:

And when did you bring them over?

Weisskopf:

Just shortly before Hitler — ‘38, ‘39.

Weiner:

Did they settle in Rochester?

Weisskopf:

My mother lived with us. My brother went to Omaha. He’s now in Chicago, and my sister taught at Bryn Mawr at first. But, I must say, it was a very romantic time with tremendous help and sympathy from the social environment. It was really a good time, I will not complain. It was a successful time, a time of human relations. We had an enormous amount of friends, and warm and helpful.

Weiner:

Were you accepted at Rochester?

Weisskopf:

Completely. There was not the slightest…It was one of the most wonderful times just because it was hard. Some of the affidavits for my family were written by people we happened to know, wealthy people. There was help from all sides, intellectually interesting, exciting. It was wonderful. The same also at Los Alamos. I must say the Rochester and Los Alamos times were really the most humanly rewarding times…

Weiner:

It was really a very rich period for you in a personal sense.

Weisskopf:

Tremendous. All our friends with whom we are close now come from then.

Weiner:

How soon after you got settled at Rochester did you begin visiting other physicists at other universities?

Weisskopf:

Oh, right away. Of course I started out by visiting the Europeans like Bethe or Teller. I was very close to Teller. He was in Washington at that time, and I went very often to Washington to talk with him.

Weiner:

In connection with a meeting of some kind or just personally?

Weisskopf:

Oh, meetings made it cheaper but mostly because I wanted to discuss ideas with him and with Wigner. But of course very soon I had contact with the American physicists. The first summers we went to California, spent some in Stanford. This was due to Felix Bloch, whom I knew well from Copenhagen. But there we met a lot of American physicists — Rabi, Oppenheimer. In fact, on the way to California we always spent several weeks on Oppenheimer’s ranch, and there I met all the theorists — you know, Furry, Serber, Phil Morrison, and the Oppenheimer crowd — and in New York, too. So this was perhaps one of the really impressive things for both me and my wife, that within the shortest time one was in the midst of a society that was extremely appealing and interesting and active, and in fact we felt much more like refugees in Europe than here.

Weiner:

In Copenhagen, you mean?

Weisskopf:

Yes, we felt not at home in Copenhagen more than we felt here or in Zurich, although I liked Zurich very much, and I liked Copenhagen. Copenhagen is the city of my wife so there we had family. But I mean it was really astonishing to us how accepted we were. It really gives you something to think about. Take Los Alamos. Of course, Los Alamos in a way was a city of foreigners. True enough, still it impressed me very much. I was in fact the mayor for two years. I was elected mayor of Los Alamos.

Weiner:

They were scientists…

Weisskopf:

Well, there were also lots of mechanics there. It was a city of 6ooo. And that was after five years of being in the country. It was in ‘43 and ‘44 that I was mayor of Los Alamos, and I came to the country in ’37.

Weiner:

You became a citizen in ‘43, too.

Weisskopf:

Yes. I know myself that this is not average United States, this community — I wish it were. I’m singing here not a patriotic song about the U.S. I’m singing a patriotic song about the society of physicists, and I do it with my full heart.

Weiner:

It is very interesting to know your reaction to that period. I know that Laura Fermi is intending to write a book or is doing some research on this whole question of the reaction of…

Weisskopf:

I’d like you to tell her that I’d like to talk with her.

Weiner:

I haven’t discussed any of this with her, but if I do, I will refer her to your experiences. It may be a personal view that she’s taking — I don’t know. I don’t know if she’s attempting to survey the field.

Weisskopf:

Certainly this is a very positive...

Weiner:

Let’s not wait too long before we get on to the next session, in which I think we will first talk a little more about this period and then proceed on with a lot of things that have been left out.

Session I | Session II