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Interview of Eugene Feenberg by Charles Weiner on 1973 April 14,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Early career through 1939. Midwestern background; education at University of Texas, graduate work at Harvard University in theoretical physics under Edwin C. Kemble and John Van Vleck, 1929-1933; traveling fellowship (chiefly in Germany, 1932); positions at Harvard, University of Wisconsin, Princeton University, and New York University. The nature of theoretical nuclear physics work in the 1930s including nuclear models and Feenberg's work with Eugene P. Wigner on nuclear forces. Also prominently mentioned are: John Bardeen, Niels Henrik David Bohr, C. P. Boner, Gregory Breit, Walter M. Elsasser, Wendell Furry, George Gamow, Julian Knipp, Ettore Majorana, R. L. Moore, Otto Oldenburg, Melba Newell Phillips, Roberts, Simon Share, C. G. Smith, Arnold Johannes Wilhelm Sommerfeld, Carl Friedrich Weizsäcker, (Freiherr von); Institute for Theoretical Physics (Copenhagen), Niels Bohr Institutet, and Raytheon Corporation.
Today is the 14th of April, 1973, and we're now in a different location, at the university instead of the motel. We were talking about various courses you had. You said you didn't have any from Van Vleck. You mentioned that George Washington Peirce and others. You mentioned you had a quantum mechanics course from Kemble. Would this be at the time he was writing his book?
He started writing his book around that time, I guess.
It was a relatively new subject at the time. This is 1929 we're talking about.
That's when I started. I had the quantum mechanics course the following year, 1930. So I suppose Kemble had been thinking about writing his book for a number of years, but I don't know exactly how he began it or exactly when.
It's still relatively new for quantum mechanics and I just wondered how the lectures were tackled. Was there any work assigned as to reading, or strictly lectures he gave that you took notes on?
I think that's right, just lectures basically. I don't remember that there was any reading assigned in the literature.
Were there many people taking that particular quantum mechanics course?
Well, how many? I really am not sure. There might have been a dozen. Probably not more than that. I don't know. There was just a small number of graduate students at Harvard at that time. I think perhaps the group that entered with me was ten or twelve, I never had a figure in my mind but there weren't very many.
This would have been one of the first strictly theoretical courses that you had up to that point.
Well, it was one of the first courses in theoretical physics that I took.
How soon did you decide that you would be working with Kemble? How did that come about? Or did someone decide it for you?
No, I think it was left up to me. I really didn't know Van Vleck, and the rapidity with which Slater disappeared from the scene after his lectures was a bit discouraging. I guess I liked Kemble. He seemed to be a pleasant and relaxed sort of person. I spoke to him. I must have spoken to him about the theoretical work, and I guess that's how it happened.
Was the decision taken first to work with him, then a problem chosen?
Actually, I think he asked me to do a few things. There were a few questions in his mind in connection with his book, and I did a few small things for him. Then I think I got interested in the scattering problem, the quantum scattering problem, and I talked to him about it. And he felt it was all right for a thesis problem. He encouraged me.
You got interested in it, by this time, in starting to read the journals.
I had read some of the papers.
Prior to the thesis research, were you involved with other students in colloquia or such activities?
No. No, I don't recall anything of that sort.
Your background for this problem came from course work.
Of all the possible problems that one could turn to, why did you choose this one?
Well, it was simple — at least it could be stated simply. Scattering of slow electrons by neutral atoms, scattering with hydrogen, is a problem that is simple to state, and just possibly it could be done without too much labor. So it seemed suitable.
What was the nature of your relationship with Kemble once you started to work on the problem?
Well, he didn't bother me. I mean he left me alone. And I guess that's the best thing to do. As I discovered myself as a faculty member advising students — I remember 12 years ago, I assigned two problems to two students at the beginning of May and then in June I went away with my family for a month to Wood's Hole, and when I came back, they had done a major part of solving some very difficult problems which I didn't know how to solve when I left them. So it's a good thing to do with students, leave them alone. Unless they need help, unless they ask for help.
Were you aware of anyone else working on a related problem, someone you could communicate with?
Well, nothing very similar. I know Hubert James — have you ever met him?
No, I've never met him.
Now, let's see, I guess Kemble was the official advisor for his work, but he also was involved with a man in chemistry by the name of Coolidge, doing the — it must have been the hydrogen molecule, which was an extremely difficult problem with a tremendous amount of numerical work, and at that time of course, no electronic computers. They had hand computers — pushing buttons and turning the crank. But they worked out very cleverly systematic procedures to help make things possible, and they finally got an answer that was comparable, in accuracy, with earlier work of a similar character on the helium atom. You know, six figure accuracy. So it was a demonstration of the power and accuracy of quantum theory.
This was going on while you were doing your work, you were discussing with them.
Yes. I must have had some conversations with James. But. I got some equations and solved them after a fashion. It was the basic part of the thesis. There was nothing of any consequence. What survived of some consequence was a theorem that I discovered, which is called the cross-section theorem. I don't know if you've come across it. It seemed pretty useless and I never realized that it had any value, but it relates the total cross-section in a collision, taking all inelastic processes and all break-up processes that might occur, and elastic scattering as well, it relates that quantity to the magnitude of the imaginary part of the forward scattering amplitude, that is, the elastic scattering amplitude in the forward direction. Well, of course, the forward direction is right in the incident beam, so it's not something you can measure directly, so it didn't seem very practical. I think that was the reaction of most people who saw it. But it was discovered also by Bohr and Kalckar, and they published it in a paper some time after I published it. But they did something with it. They did something useful with it. It must have been one of their papers on the statistical model of capture processes.
What year was this paper?
I must have published in '33 and '34 and they must have published in '36, I guess. It was just a few years. But they didn't know of my calculation. And I suspect that the idea of the theorem was really known. I've never seen any earlier work on it, but I have an idea that it had been developed somewhere, maybe in acoustics or in radio. So there's a good chance that it was already a known result but without anybody ever having published it, or maybe it had been published and was known, but the author and the original paper forgotten. Anyway there was no connection between these two papers.
That came out of the thesis work itself.
That was part of the thesis, yes. The only part that really was of any significance.
But it was not recognized as such at the moment.
That's right, yes.
And you think the significance was recognized when Bohr and Kalckar —?
They pointed out how to use it. They used it. Then other people have since found it very useful in what's called dispersion theory, dispersion techniques for analyzing scattering and resonance problems. So it's a basic useful result. But again, this merged into what you might call the public domain. Everybody knows about it so nobody knows of its having a history.
When you submitted the thesis what kind of time period was involved? You started in '29, you got the degree in '33, yet in '31 you had this traveling fellowship.
Yes, then I was abroad for a year and a half. I wandered around in Europe without much point or purpose. I really wasn't mature enough to be sent over that way. I was in Munich for a while, Sommerfeld's place, and in Zurich at Pauli's institution, and In Rome with Fermi. I met Majorana there. He was a very poor linguist. So am I still. And so we had a little conversation with the aid of a phrase book. He seemed like a pleasant young fellow.
Did you discuss — by that time, he'd —
Well, yes, we talked, he actually gave a seminar on his forces, nuclear forces. I remember Uhlenbeck and Inglis were there at that time and they thought it was a very big thing. David Inglis was there, yes.
Were you interested in the particular problem?
I must confess, I didn't know what was going on — I missed that lecture. Well, anyway, it would have been in Italian. I could have understood some of the formulae but I guess I wouldn't have understood much of it. Anyway, I wasn't deeply involved. Then I went back to Germany to Leipzig, where at the time Hitler was taking over, and the storm troopers were parading in front of the Jewish stores and that sort of thing. There was an American physicist in Leipzig at that time, Charles Zahn, have you ever met him?
No, I've heard of him.
I don't know where he is now. I presume he's still living.
I came across his name recently. He was studying there?
He wasn't studying. He had some kind of fellowship. I don't know exactly what. He was a bit older than I. Well, anyway, as I say, I didn't do anything serious in this period.
When you went to Leipzig, how long did you stay?
I was there in Leipzig maybe a month, and I got a letter from Harvard suggesting that I should come back. I guess because of the political developments.
Hitler took power the end of January, '33.
Yes. This was after that, a couple of months later, in the spring.
It wasn't until around April that the dismissals started occurring, do you recall that?
Yes, a lot of people had left already, and there were graduate students who didn't know what to do. Let me see. Debye was still in Leipzig. There were a lot of people still there. Majorana came to Leipzig at that time, he had some kind of Italian fellowship. Apparently Fermi sent him to Leipzig to be with Heisenberg for a while. And I recall a seminar, no a colloquium at which Heisenberg spoke, something on nuclear forces. Majorana was in the audience, and Heisenberg asked him to come down and tell about his version of the exchange forces. I recall, Majorana was perhaps too shy or too conscious of his lack of, knowledge of German — I'm pretty sure that he didn't accept that invitation, didn't say anything — he couldn't do it. Anyway, it's a long time ago.
Did you have any. conversations with Heisenberg about his own work or about your work?
No, I guess not. I guess not. I was very much the graduate student. Well, like these kids out here. I didn't approach the great man.
Did a lot of listening though.
Yes, certain Y.
This was true in the other places as well?
You mentioned Munich, Zurich, Rome, Leipzig. What about England or Copenhagen?
No, I didn't go to England or Copenhagen. I was in Berlin a few days. I saw Wigner and Schroedinger and other people, but I didn't have any conversations with anybody.
Had you ever met Wigner?
No. I didn't meet him then. I saw him at a lecture, yes.
Now, this is an awfully long time, a year and a half. Let's try to break it down. How long were you in Rome?
Possibly three or four months, I suppose, and maybe I was in Leipzig a few months, and maybe six months in Munich.
And Zurich about how long?
Oh, several months. I think I was not supposed to wander around like that. But, well, I guess I didn't bother too much to find out what the rules were. But anyway, I got back intact.
They paid for this on a traveling fellowship that enabled you to do this, you had all the introductions that you needed and so forth.
Well, I started off with a letter saying that I could come to Munich, and after that, I made my own arrangements. I found nobody objected, when I asked if I could come.
Were you there all of '32?
Yes, I guess I was, the year of it was '32, yes.
You went to Munich when?
Let's see, when had I gone? I left in September of '31. I was working at Raytheon during the summer. My father was ill at that time, and he died during the summer. I don't know the exact time. Maybe it was in June, and so I went home, and well, there was a little money, insurance and savings, I guess, so I advised my brother to go to college. He had recently graduated from high school. So he was working, I don't remember what kind of job, but anyway he did go to college, to SMU, and had part time jobs also, and made some connections which finally led him after he graduated to go to Milwaukee; he's located there now. Although he's also located in Florida, he's semi-retired now. And then my younger sister, a couple of years later, also went to SMU. But then I went to Europe —
— in September. That means you would have been there at the time of these events that I was talking about, the neutron — were you in Munich when the neutron came?
I don't remember. I have no recollection of learning about that event. I just don't remember.
By the end of your trip obviously you'd been reading about it, Heisenberg was talking about it.
'34 and '35 I was deeply interested, yes.
How would you characterize the effect of that year and a half? Were there things that you learned? You were exposed to new people with a different approach. Was it strikingly different than what you'd been doing before?
Oh yes, yes, of course. Well, I didn't take any courses. I listened to some lectures. I listened to Sommerfeld lecturing to his students. I could understand his German. I learned a lot of German by listening and by reading the newspapers in the restaurants — you know they had a custom at that time of keeping files of newspapers in the restaurants on some kind of stick.
Yes, a rack, they still do in libraries.
So I read many German papers. And so, I can still read fairly well, but I didn't acquire any Italian to speak of. And my French was never any good.
Did you go to France at all?
No, not at all.
I thought since you were in Europe, — in Europe you went mostly to German-speaking places?
That's right, yes.
Would you say by attending Sommerfeld's lectures, listening as you did, hopping around, you developed new interests or enriched your own training, or it gave you a different approach in any way?
Well, yes, I suppose so. It made me enormously aware of how ignorant I was. But on the positive side, I guess I learned a little by reading.
Were you working on any problem?
I was trying to do these papers on scattering theory, and I guess I must have published them while I was abroad.
Your dissertation work was done essentially on your own in Europe.
Kemble left you alone — he had to, you weren't there.
Did you communicate with him during that period?
I suppose I did. I don't recall.
I can check that, many of Kemble's letters are on film, I'll take a look at that. It would be interesting. One other question about the social and political environment. In '33 you were reading the German papers. What was the response to the emergence of Nazism in physics in the countries where you were? You say you were in Leipzig and you actually saw the storm troopers walking in front of the Jewish —
— yes, I did, yes.
I want to talk first about your reaction to this, then the kinds of discussions you were in or overheard.
Well, at first I found it very hateful and frightening. I know Zahn was incensed by it and so he said, "Let's go into the stores and show the Nazis that we're not scared of them." I thought it was a foolish thing to do, but anyway he persuaded me and we did and we were not molested. But that was a childish reaction — about the extent of our reaction. What about the Germans themselves — their discussions?
Nobody talked about it with me. I didn't know anybody well enough, I guess.
Did you see any manifestations of it within the physics institutes?
No, that I didn't see.
People showing up in uniforms —
No. It probably happened later, but this was the early days still.
When the Harvard people suggested you come back —
I must have sent a letter or two that sounded a bit inflamatory.
In what way?
I mean, there was the possibility that I might get into trouble — I don't know — anyway, they told me to come back.
To protect yourself.
I guess so. They were trying to protect me.
Uhlenbeck by that time was in America, at least for a while he was. '27 to about '35. I guess then he went back to Holland for a while. But anyone else you met on this traveling circuit? Did you meet Bethe?
Yes. lie was at Munich when I was there.
He was working I guess in the fall — two years maybe — but he was working in Frankfort or Tübingen for a couple of years preceding his dismissal. You may have seen him, you saw him in Munich, it may have been that summer?
Well, he was in Munich when I was there.
Not a student?
He was not a student, no. He was, I don't know, what do you call it, he was on the teaching staff, do they call them extraordinarius or something of that sort? Something of that sort.
He was still there, or it may have been a little earlier. Did you come into personal contact, if not with the top well known people, did you come in more personal conversational contact with some of the younger ones?
Well, a little, yes, especially in Munich. But there wasn't much talk about politics, I guess. There was a very sharp division into people on the left and people on the far right. I guess people in the middle were afraid to talk. I didn't really know anybody on the right, which is natural. I met a few people who seemed quite radical, or at least vocally anti-Hitler. But there wasn't much talking when I was around.
Was there any overriding impression you can recall, on the nature and focus on physics questions? You mentioned Majorana, and Heisenberg was working on the same —
that was in the beginning, see. That was something new. The big things I guess were theory of metals, or problems in the solid state. In Zurich, there were three young men who became big names. One of them was already well known, that was Pauli. He was at the Eidgenossische Technische Hochschule. Then there were two young men, Racah and Delbrück — I guess they were associated with Pauli or working under his influence. Let's see, Wentzel was at the other institution in Zurich, which I'd forgotten — But nuclear physics was a new thing. It just happened here and there.
Do you date the beginning of your interest in nuclear problems from this?
Well, I guess I must have got a bit of the fever then. After I got back and got the PhD, I was getting some teaching work at Harvard, while they were trying to find a job for me — it didn't occur to me that I could go out and try to find a job for myself. I mean, now young people write 100 letters or write 200 letters hoping to turn up something, but nobody had advertised that as the method of getting a job in those days. I didn't know how one would go about getting a job. I left it in other hands. I guess I wasn't very practical. But anyway, I was teaching, and the problem of the nuclear forces seemed interesting, and one could do simple and almost trivial calculations, and so I did a few, and stuck them in a desk drawer. So one day Van Vleck came into the office which I shared with Wendell Furry, whom you may have had some contact with?
Yes, he was in Copenhagen when I was there.
Very interesting fellow, a non-stop talker. I was on quite friendly terms with him and his wife at the time. And somewhat extreme political views, which I guess he hasn't changed to the present day, as far as I know. Anyway, he was never afraid to state them in public. But anyway, Van Vleck came in one day and said he thought maybe I ought to try my hand at making some calculations on nuclear forces. So I pulled out the calculations which I'd been doing in a somewhat relaxed way, for some time, and showed them to him, and he thought one might make something out of it, encouraged me to go on with them.
Interesting that this came from Van Vleck who himself wasn't working on it.
Oh, he was interested in nuclear forces then, and he actually wrote a paper on the neutron capture. And a student from Texas whom I'd known in Texas, Charles Fay, did a thesis with him on neutrons on the kind of Hartree-Fock type calculation of the capture problem. The results were mainly that you couldn't account for Fermi's discoveries very well that way. I think that was the main result. But there were some things of a positive character came out of it. But then pretty soon the Breit-Wigner formula came along, and Bohr's statistical picture of what happened... (off tape)
Yes, the picture rapidly changed, '36, you're jumping a bit now —
'37, '38 —
Just getting back for a moment to the calculations that Van Vleck had you do or suggested, that you did — what were you doing at the time in your own work, after your thesis? You published, first of all.
I published some papers. Well, I didn't like it very much. I mean, I wasn't very pleased with what I had done, so I was looking to something else.
The paper was on neutron-neutron interaction, mass of neutron and so forth, that was something you published in '34. Was that an outgrowth of something you'd —
I think I started that at Cambridge.
That was April, 1934. I guess you'd have been back almost a year then. Now, during this time you were teaching — at what level? I guess you were an instructor.
Yes. Well, I had a laboratory section in elementary physics at one time, I recall. And I taught the quantum mechanics for one semester. I'm pretty sure I did. In fact, I think some of the boys from Texas who came up a year or two later than I did took the course, as I recall.
So you became their teacher. By this time were you using any texts for the course?
This must have been before Kemble's book came out. No, I just used notes which I'd accumulated from reading and from Kemble's lectures.
And of course you were learning more from your own work too. Any of your work at this time that you could discuss in your lectures?
Anything related to your dissertation?
No, I don't think I had occasion to.
About your dissertation for a minute, I assume you had a committee, went before a committee?
A. standard committee? There were variations in your case Kemble —
I think they made up a special committee for every candidate. This was Kemble and Slater and Morse from MIT was on the committee, and there must have been two others but I'm sorry, I'm not sure who, perhaps Van Vleck and Oldenburg.
This was not only a defense of the thesis, but covering all the fields you were to be responsible for?
Well, maybe in the history of science, the student is exposed to difficult questions, expected to answer difficult questions, but in physics — and it's true then too I guess — if the student can give a reasonable presentation of what he's done, that's almost everything. Then the committee, the examiners, ask a few simple questions especially designed to be easy to answer, in most cases, and that's that. I think in this country it's generally taken for granted that if a candidate gets that far, I mean if his advisor has accepted his thesis and he's presenting his results, that 's essentially a formality. It's a step in the formal dance, it's what's expected and one goes through it, a ceremony.
A ritual, that's right.
Not a trauma, the problem was just to get the work done —
During this period at Harvard from '32 to '35 was when work on nuclear forces was getting started. You mentioned today your collaboration with Knipp. Feengerg: Knipp, yes. His father was at the time, or had been, professor of physics at Urbana, or maybe he'd been the chairman of the department there, I'm not sure at this time.
Loomis was for so long — the late twenties —
All right, anyway, he had been a faculty member there, and Knipp was following in his footsteps. So we worked together on these problems. I suppose it was presented as part of his thesis.
I see, you were sort of his thesis advisor.
In some sense, I suppose. At least for a while.
What came out of the work? The other paper on the alpha particles was that done at Harvard? It was in December.
I don't remember.
Received in December of '35. When did you go to Wisconsin, fall?
In the fall, yes. That is, during summer.
And this paper was also '35. Prior to this period, you mentioned that you went to Wisconsin. You mentioned the circumstances. Maybe we should go into that again, because this imilies prior contact with some of the people. When did you meet Wigner?
Well, I met him for the first time in Wisconsin. I mean, I'd seen him in Berlin but hadn't met him.
I see, so he had nothing, to do with your going there.
I don't know that you recorded how you happened to go there?
Oh well, there was a vacancy there because Breit went to Princeton for a year as a visiting professor, and Breit had gone to Wisconsin from NYU. Van Vleck had been at Wisconsin, and he came to Harvard, so Breit then went to Wisconsin.
Breit was also at Hopkins, I guess.
Maybe that's right. But you're right, he was at NYU, of course, at the Heights, yes.
How did it come about? Who got you into that?
Well, I suppose Kemble, and Van Vleck knew there was a vacancy there. I suppose the people at Wisconsin had written to Van Vleck, so I guess he talked to Kemble, and it was a convenient way to get me going. Give me a little shove off the parental bough, make me use my own wings.
Nothing that you saw though — it was just put to you.
Prior to that, your paper on the neutron-proton interaction, helium isotopes and so forth — this is something that you published from Harvard?
From Harvard, yes.
When you Worked on that, was there a group, any discussions with other people? Not necessarily at Harvard or in the Cambridge area — anyone you communicated with when you were developing the paper? Who would you bring it to for comment?
Well, I really don't remember very clearly, I guess I showed it to Furry and Kemble and Van Vleck. There was some kind of conference in Washington, and — well, they sent me to that conference, and I reported. I gave a brief report. I guess it was a conference of Gamow and Teller.
The one at George Washington University, the Washington Conference on Theoretical Physics, '35 would have been the first one.
Yes. Maybe it was that one. So I met Gamow and Teller.
This widened your circle. And were you writing to anyone in this period about your work or their work?
No, I don't think so.. I have no recollection.
The liaison with Wigner was after you got to Wisconsin.
And the collaboration with Bardeen, this was later, but I was wondering whether you had met him prior to that time? He was in the department, wait a minute —
— no, that was much later. Well, he might have served in it, but it was about three years later, I think. I was at the Institute, (Institute for Advanced Studies, Princeton) and I don't remember where he was. Maybe he was still a fellow at Harvard.
He finished at Princeton, and I think went up as a junior fellow at Harvard — that might have been in '35, '36.
Yes. Well, I heard him give a seminar at Harvard. I think it was before lie came up as a fellow. Perhaps they were looking him over.
I don't know what else I want to find out about your years at Harvard, unless there's something that you know that I haven't asked you about the period, which was characterized by —
'm trying to remember the name of a man on the faculty of Harvard who came over — he came there from Germany, but several years before Hitler took over.
Oh, of course. I had a course with him, as a student. He's a very good teacher. I know one of the boys from Texas did his thesis with him. He was very concerned about his English and about his lectures, so he asked me to listen to him, to be an audience of one while he rehearsed his lectures. So I did that for a few hours.
And got them in repeat form on the actual occasion?
I guess pretty nearly.
You were truly auditing.
Well, he spoke very well, his English was excellent, so actually the rehearsals were not necessary. But I guess he felt better about it.
As your work developed in the Harvard period, up to getting into Wisconsin, did you have in mind a particular nuclear model? Were you concerned with its development?
No. Not really. The big unknown at that time was the like particle interactions. They were basically looking for ways to get information about them, and if you worked on the two, three and four particle problems, the deuteron and tritium and helium 3 and helium 4, you really didn't need any model. Well, you needed a model of the forces. I mean, you had to write down the Hamiltonian, which contained what you thought was a reasonable description of the forces. Then you had to find a wave function which was a reasonable approximation to a solution of the Schroedinger equation, and you had the variational properties, the extreme properties of the expectation value of the Hamiltonian, to help you there. You could put in a very crude wave function into this formalism and get a fairly good value for the energy. So that was the standard way of attacking such a problem. And so we worked a bit at finding wave functions. We could write down simple functions with some parameters in them and vary the parameters to minimize the computed expectation values, and thus find the best parameters. It was an objective procedure that would definitely give you an energy that was too high, higher than the true eigen-value. It had that one-sided bound on it, so one had some confidence in what the results meant. Or alternatively, if you adjusted the forces so that they gave you the right energy, then you'd, know that the forces were too strong. So it had a valuable property in it. It's an extremely widely used formalism, I mean that property. But it was the sense of the kind of calculations which you do. Of course we were guessing at the. Hamiltonian, guessing at the forces, and so the assumed central potential was — I think the simplest thing to calculate with was Gaussian functions, bell-shaped things. And since no great mind had suggested that you had to have an inner core, a hard, repulsive section in the center, why, we didn't put them in. Somewhat accidentally, the numbers we got were about right. Nowadays, of course, people always have a hard core, the strong repulsive central section, and that makes a good deal of difference. It makes the calculations much more difficult. So actually new methods had to be invented to handle such problems. But at that time, without the hard core, everything was basically very simple.
What was your response to the models that were being developed by '35, '36, including for example, ideas that were going around — shell model, or Bohr's that came along about '35, '36. Elsasser.
Well, Bohr was a little later, I think, '36. But I was interested in the suggestions of the early shell model. For example, Elsasser discussed the experimental evidence, and he didn't seem to leave anything out, and there wasn't much evidence from beta decay or from knowledge of excited states to fit into the theory. That is, he used most of the experimental information in his papers, and there didn't seem to be much more to do with it, that one could do, at that time. You see, the later shell model, what made it interesting was that there was an enormous mass of experimental information which one could fit into the shell picture very simply. A lot of beta decay data, an enormous mass of such data, and gamma transitions, and the location of isomers, that was a big thing too in later information. Then there was a lot more information on moments, magnetic moments and spins, later. But all that was missing. So Elsasser's paper didn't break a dam. They used up all the water that was back of the dam and there wasn't anything to break it, any pressure to break it. But now, the still earlier suggestions of shell models, Bartlett and those in France, there was Guggenheimer, and I think Gamow had something about the windings in the-valley of stability, but this was perhaps rather impressionistic. Gamow was not strong on exact calculations. He was an idea man. Let's see — there was Goldschmidt in Norway who also said something about the magic numbers. But as I say, it didn't break a dam. The situation was quite different in 1948. You had all this tremendous mass of experimental material, just crying out for an explanation. And that's what happened. So there was a big difference.
Now, talking about '36 when you became aware of the Bohr model, did you see it as competing with any existing picture?
Oh well, the general impression at that time was that that demolished and completely eliminated any possibility of talking about the shell structure.
It was seen as a clear contrast to it.
Oh yes. After that, it was not respectable to talk about shells in the nucleus.
How did you learn about Bohr's model?
I guess I read about it. I didn't have any prior information.
I thought it might have been discussed at Wisconsin.
No, I didn't hear anything about it.
Let's talk about how you got involved in Wisconsin when you went there. In the Harvard period, you came back from your fellowship, became an instructor, finished up your dissertation, began new work, talked it over with your colleagues there. One thing I do want to ask, this meeting in Washington — it was the first sort of high level meeting that you attended, I gather?
Do you have any particular recollections of that occasion?
No, I don't, except I met Gamow and Teller. I met both their wives. Let's see, what was the situation? I may have stayed with the Tellers. I think I did. What happened? ... I think they were driving up to Ithaca, and they must have started to drive up to Ithaca that night and I went with them, on the way back to New York. When we got to Philadelphia, we stopped at Philadelphia, and then the following day I went on to New York. No, I don't really remember anything that happened, except that the people were friendly and congenial. Teller asked the hotel clerk if he had any rooms free, and the clerk replied, "No, we don't have any free rooms, they all cost money." That's all I remember. I don't have a good memory.
When you got through with the Harvard period, you went to Wisconsin with the expectation that it was only temporary?
Well, I knew it was for one year. Oh yes.
Was your teaching responsibility there pretty much similar to what you'd been doing at Harvard?
Well, I taught quantum mechanics to second year graduate students.
And how did you get involved with Wigner? How did you develop a relationship with him?
Well, in the first semester, a graduate student, Simon Share, asked me for suggestions about some problem, and so I suggested that he might try to do some theory of nuclear structure in the p-shell, that is from mass 5 to 16. So we were trying to write out some of the wave functions in that shell, and I found it very difficult because in the atom you had a fixed center of force and that greatly simplifies the treatment of the atomic problem, the description of the electrons, but in the nucleus there's no fixed center of force. You might say it's a democratic situation. Everybody's equal. This bothered me. So we didn't get very far. And Wigner came on the second semester, and he was in the office — we shared the same office — and after a couple of days, he turned to me one day and suggested that we should look at the shell structure, at the nuclear states in the p-shell. So he showed me how to calculate the wave functions, and it was very simple once it was explained. So I went ahead and I guess I worked several months on it, and got a lot of matrix elements, and worked out some of the energies. So using the kind of forces that it had seemed were indicated by the calculations that I did with Knipp — that was essentially how that came about.
It was just toward the end of your time there, but you then continued —
No, that was the end of my collaboration with him, basically.
And this is the one that resulted in this paper on the structure of nuclei between helium and oxygen, in '37.
The Share paper would show —
Well, Share and I did something else. We tried to get better approximations for the wave functions in describing the 2, 3 and 4 particle functions. And he also did a little paper on the Coulomb energy in helium-3, which is the only way it differed from hydrogen-3. He published that.
The one that you were on, nuclear forces, the approximate solution of the nuclear 2, 3 and 4 particle —
That's only one paper you published with Share?
That's all. I believe there was only the one paper.
And one with Wigner?
Was there anything else, since I don't have the full bibliography, any other papers you published from Wisconsin?, Maybe the one I mentioned before.
Oh, on the excited state? Yes, that's right. I guess I did that, must have done that the first semester.
Here's the paper with Share, and I think there was something I wanted to ask you about. In the paper with Share which was received in May '36, published in August, you refer to Bethe and Livingston, unpublished communications, and then there was also the Cornell symposium in July of '36 which somehow you squeezed into the paper, I guess it was sent in in May yet you're citing the July symposium. Do you remember that now?
I didn't go there.
It must have come through.
That's right, I must have heard about it, maybe, through Wigner maybe, or I don't know.
Well, you do acknowledge Bethe, communicating results. But you weren't at that Cornell meeting?
No. No, I didn't go.
Symposium on nuclear physics. Well. we haven't too much time, so I just want to cover in outline this very rich period — how would you characterize your work at Wisconsin, your year there? There are two pieces of work we talked about that are probably the main things. You had teaching responsibility. Did you have any contact with Breit or was he gone?
No, he was gone — no, I didn't.
You still hadn't met Breit?
Maybe I'd met him somewhere, probably at a meeting, but I don't remember. At least I had no intellectual contact with him.
How would you characterize this year in terms of your own, career?
Well, I guess it was solid achievement. I'm sure. It was a good year. I got very deeply committed to the strong interactions between the like particles, which was still up in the air at that time. he had heard from the Carnegie people that there really were strong proton-proton interactions. In other words, they basically checked what Milton White had found, and so I was very pleased by that. I should mention that Richard Present published a theoretical analysis of White's proton-proton scattering data and concluded that allowing for statistical fluctuations it called for a strong interaction between like particles. Present was a graduate student at Harvard when I returned from abroad.
Had you enough contact with Herb during the year, was he in a construction stage?
They were busy putting things together. I guess there wasn't really much conversation about what they were going to do with it. I just heard that when it was hot on his mind.
Were there any colloquium discussions, departmental discussions or journal club on problems of nuclear physics?
There must have been some of that, but I don't remember.
There was no separate theoretical group. The theoretical group in this case would have been you and Wigner anyway.
Wigner must have given some talks. But I don't remember.
During this period, you mentioned that you went to Michigan summer school from Wisconsin?
Yes, I think I was there the preceding summer and I went there the following summer. That following summer was when the proton-proton data — the papers had been written on the experimental work and on the theoretical analysis, and that's when the charge independence came out.
You mean after Michigan — it came out —
No. I mean when everybody thought about it.
Yes, right. Well, when did the isotopic spin work develop?
Well, that was Wigner's next paper. You see, when Wigner and I wrote that paper on the p-shell, we used the formulation that Knipp and I had worked on, where there were proton-neutron forces which depended on spin, and then there were some like particle interactions. And they were all about the same magnitude, but there was no suggestion that there was any formal identity. I mean, the connections were numerical connections, were sort of accidental, and they were interpreted as surprising but one didn't see any significance in the numbers being nearly the same. Then, as soon as one formulated the idea of charge independence, then you had a logical system, and so this made a big difference in the way one would present the shell model calculations. And this was where Wigner's quantum numbers, the new quantum numbers he invented, the principal one being the isospin — unfortunately he called it isotopic spin, which was a misnomer, you see. Where it was relevant, it described a set of levels in a system of isobars. It had nothing to do with isotopes. So ultimately I started calling it "isospin" and I think other people use the same notation. Anyway, Wigner was the inventor of the isospin. It's a natural consequence of charge independence.
That became something for you to work with.
Well, then at the Institute I met Melba Phillips. We did the p-shell calculations, using the kind of wave functions that the charge symmetry supplied as a good first approximation. This automatically brought in the isospin. The charge multiplets and the isospin. So that calculation was much simpler than what we did at Wisconsin. The results were pretty nearly the same.
Let's get you to Princeton, by the way, while we're talking about it. You said you applied by yourself — does that mean you got yourself to Princeton or did someone intervene on your behalf?
No. Wigner asked me if I would care to go to the Institute for a while, if I didn't have any other place to go, and I said I was quite agreeable. So he wrote to von Neumann and it was arranged. He stayed on at Wisconsin, for I guess another year.
Melba Phillips was on some fellowship there, Association of University Women.
That's right. Oh yes, that was the fellowship, yes.
While you were a temporary member of the Institute.
Yes, that's right.
That lasted two years?
Well, I stayed on a year and a half.
I see. Let's do a couple of things about how you got from there to NYU. Was this through Breit?
I really don't know. I was approached by van de Merwe, who was head of the physics department at the. Square, and T don't know, don't remember what happened.
That's another chapter, you remained there a while. But that year and a half at the Institute for Advanced Studies, we do have a record of some of the things you were thinking about, letters you were writing to Wigner at Wisconsin. I'm curious about the work itself with Melba Phillips, you were telling me how that got started. Did you just converge on the same problem, or did you invite her to work on it?
I guess I suggested it. She was agreeable.
These letters to Wigner that we looked at before — you were concerned about the packing fraction curve of tungsten, March of '37, for example. One of the points. Would you consider this a working out of a program of research that you'd started?
That's right. It was sort of a cleanup operation, I guess.
It was a relatively productive period for you. For example, the note on the Thomas-Fermi statistical method, how did that develop? That was something initiated at the Institute.
Is that right? Well, I don't really remember it.
Let me get to another thing. All of this that we're talking abcut took place in the Depression. You said when you went to Harvard, your father had planned to give you assistance but couldn't — how did you fare financially throughout this period?
Well, I think I mentioned Raytheon.
Right. I was thinking about after that.
Well, there was the salary as an instructor at Harvard, and the salary at Wisconsin. Let's see, I guess the salaries were somewhere in the range of $2400 or $2500, something of that sort, I think. And at the Institute — well, I don't remember really, probably $1500. I'm really not sure.
And you had no responsibilities.
That's right. And at New York University, I think again it was around $2500. This was a reasonable pre-war salary.
What were your responsibilities on that?
At New York University?
No, I meant your own, family responsibilities.
Oh. I wasn't married. I sent a little money home every month to my mother. But I had plenty. There was no hardship.
That was no factor then in any of your choices.
Did you return to Europe, after the traveling fellowship?
No, I didn't go back until, when was it? I guess some time in the 'fifties. My wife insisted that we go to Europe.
I just noted something that was on my mind when I mentioned Breit earlier — that you did do a paper with him in '36. A paper that had to do with the possibility of the same forms of specific interaction for all of the —
— oh yes, that was the charge independence.
How did this collaboration with Breit come about?
Well, my recollections here are a bit vague. He was not at Michigan during the summer, and for some reason or other I received a letter from him in which he expounded his formulation of this principle of charge independence. I think I made some suggestions about how it could be generalized. And we had a little correspondence, and he did some calculations, maybe I did some too, anyway we put it together as a letter and sent it off to the PHYSICAL REVIEW.
It was more than a letter, it was a paper.
A paper? That's right, it was a paper. It was a paper, yes.
That was the only thing you really did with him.
Yes, that's right.
You did one with Wigner, one with him, one with Melba Phillips, and then the next collaborative thing was with Bardeen in '38. I started to ask you about that the other day, but I'd like to review that — how came. Bardeen by this time was at Harvard as a fellow, I know —
Well, I really don't recall how that happened. He must have visited Princeton.
No, by that time you were at NYU, '38.
Oh, I was? It must have started when I was at the Institute, sure. I recall now. I recall now that we were working on it. We did meet to compare notes on this in Princeton while I was at the Institute. But it may have taken quite a while before we published it.
Anyway, it did not seem to meet anybody's needs. I don't think it was referred to in the literature. It was off the main track.
I guess one of you reported on it at the Washington meeting of The American Physical Society. The article was published in June, the paper was in April of '38, published in November of '38. It had been started back at Princeton earlier.
Yes. I don't remember who gave the paper at Washington. I mean, you present a paper and usually nothing happens. There's no occasion — nothing happens to make you remember the occasion.
Unless you get it criticized.
That would make it memorable.
During this period were you clearly identified in your own mind with a certain school of thought in the field or a certain group focussing on the same problems? Would you identify yourself with a group?
Well — no, I don't suppose I did, really. Not very strongly.
Well, you know, if you write in the period, you become associated with the people who publish at the same time, the ones you collaborate with. There weren't very many people working on these problems at the time.
Yes, well, that's true. I was interested in what other people did but I guess I didn't think in terms of any kind of grouping. Except I had a fealing, a strong feeling before the proton-proton interaction was definitely established that the German workers were determined not to consider it unless it was shoved down their throats. and that there was no interest in it in this country.
How can you account for that?
Well, their point of view was very reasonable. They said, "There's no direct evidence for like particle interactions, and all these arguments for it are qualitative and not logical, there's no logical necessity in the argument. There could be indications of something, but how much, one doesn't really know." Weizsäcker even gave an argument which is perfectly correct, that even if there's no interaction between like particles, that you would expect that two neutrons would be more strongly bound than one neutron. I mean, you can see it in the theory of how the wave functions are modified by the presence of additional particles. So that point of view was perfectly reasonable. But as I said this morning, it turned out to be wrong. You can give a reasonable argument — it may be correct, it may be wrong.
Well, there are all sorts of resistances to evidence that might prove it was wrong too, in the argument.
Was there a clear division of approach, let's say, compare Wigner's work and the work of Breit, compare that with the Copenhagen thinking, Bohr — was there any identification? Did you get the feeling Wigner himself was not close to any of the Copenhagen thinking, he was not a participant —
— no. I guess he was willing to look at it from any point of view that had a reasonable logical structure. No, he wasn't looking for accidents. But if there was some logical basis that could be developed, then he was interested. And so he was able to look at a problem from the point of view of a description in terms of single particles in particular orbits, the shell model description, because that had a certain logical structure and some connection with experiment. And he could also shift gears and discuss a more complicated, more general type of description, to which he was able to give some logical structure. But a lot of people took Bohr's point of view very seriously. They went overboard. I suppose Bohr himself went overboard. And so to them, this first type of consideration, with particles in definite orbits, in definite orbital states, was sort of silly. Not serious, not a serious approach to physical problems. So there was some division. And this persisted a bit after the war, but was quickly knocked out — there was just too much evidence.
Obviously during this period you were identifying more with Wigner's approach.
Yes. Oh, yes
— even though you were doing your work independently.
I guess that's right, yes. Bohr came to Princeton in '38. While I was still there. But he didn't stay long and he seemed to be in a hurry to rush off somewhere. Re gave one lecture, about his statistical interpretation of the nuclear reactions, and he wasn't available for any conversation. So that was the extent of my contact with Bohr.
Let me jump to the fission element. How did you first hear of fission?
Oh, I read it in the NEW YORK TIMES. Yes. I was somewhat isolated in New York. It's a long ways from Washington Square to Columbia, or to the Heights, so I didn't get around very much — there was a lot of talk going on but I didn't know about it. I read about it in the NEW YORK TIMES. I thought about it for a few days, till I thought I understood it. So I came up with the standard description. But it took me a few days to work it out mathematically. I remember, I asked I think Melba Phillips, she was at Brooklyn Polytech, and there was another, Jenny Rosenthal. Anyway, they were at some seminar or other at Washington Square, and I asked them how to do the mathematics. I wasn't quite clear on how one would calculate the change in the Coulomb energy, because the nucleus was distorted — and there was a decrease in Coulomb energy which would offset the increase in the surface energy, because of an increase in the surface area, the two compensating effects. And I was puzzled at first on how to compute the change in the Coulomb energy when the thing was distorted a little. So that became clear quickly, just by introducing the notion of a small distortion into an ellipsoidal shape, then it's easy to calculate that. So I got the standard result that Lise Meitner had gotten.
Which had not yet been published.
I hadn't seen it. I hadn't heard about it. So I don't know just what the dates were. Somebody, one of the editors of PHYSICAL REVIEW should have returned it to me and said, "Sorry, but you're late." But I guess maybe they didn't know about it either.
Someone else had already given the —
— yes, my understanding is, it was already well known in this country. A lot of people knew about it.
Then was the next thing you did on fission your experiment?
Yes. That was just an episode. Sort of a humorous episode, a kind of joke, you know. I knew there was talk about a fission bomb. So it occurred to me that one could make a little bomb, with just a few chemicals, and set it off, with fission. It was sort of silly, but anyway, I did it.
No chain reaction.
Oh, there wasn't any thought of that.
Like a chemistry experiment.
That's right. I went back to my high school chemistry. As a kid I'd played with nitrogen iodide.
The paper has a natural title, "Detonation of Hydrogen Iodide by Nuclear Fission." This must have attracted some attention, because I remember someone commencing to me, what an impact this made, the explosion.
Yes. Well, maybe it served the purpose of distracting the Germans.
In the same issue of PHYSICAL REVIEW, in the Letters to the Editor section, your paper is followed by one of Booth, Dunning and Slack on the energy distribution of uranium fission.
Yes, well, that was important.
That was a cyclotron paper. Well, I think what we should do is bring this pretty much to a close. Just to summarize a few things, by 1942 you got involved in the war work.
Yes, that's right. That was application of electromagnetic theory to Klystrons and micro-waves.
Oh, part of the radar work.
That's right. The big names are Bill Hansen, W. W. Hansen, and the Varian brothers and let's see, who else? Ginzton, and there are several others there.
That's another story, right. That was connected with the MIT Radiation Laboratory.
Well, I can give you a lead that you might someday want to trace down. At the end of the war, a man by the name of J. R. Woodyard, anyway, he was a close associate of Hansen's. And he suggested a design for an accelerator, particle accelerator involving a succession of Klystrons, putting potentials across gaps, and he had some details worked out.
That wasn't Terman?
No. It was John Woodyard. I think he went to Berkeley after the war, but I've never really come across anything that he's written or seen his name in the literature, since.
Let me check. There's a history of the Stanford linear accelerator, where some of the early things were done. I've met Ginzton. I could ask him.
Yes. Well, he probably knows about it.
He took up that work and introduced it at Stanford.
Yes, and Hansen was there and Ginzton and the Varians. The Varians they didn't go back to Stanford but they went back to start this Varian Associates.
The point of the story is that he did have that idea.
I think what we should do is stop at this point. There will be loads of things, when I reflect on it, that I see I should have asked you.