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In footnotes or endnotes please cite AIP interviews like this:
Interview of Emilio Segrè by Charles Weiner and Barry Richman on 1967 February 13,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Founding of the school of physics, Università di Roma, role of Orso Mario Corbino and others in recruiting young physicists; the decision to work on nuclear physics; financial support for and public knowledge of work at the university; contacts with other laboratories in Europe and the U.S.; available technology in Rome, ca. 1930; journal literature; visitors to Rome; circumstances of move to Università di Palermo, 1936; work and facilities in Palermo; early failures of physicists to recognize fission; early uses of cyclotron; mathematics and nuclear physics in 1930s; models of the nucleus and experimental work; circumstances of move to University of California at Berkeley, 1938; experiment and theory in nuclear physics at Berkeley; work on radiochemistry; alteration of half-lives of beta-radioactive substances; detection equipment; effect of work at Los Alamos Scientific Laboratory on nuclear physics; significance of nucleon-nucleon scattering experiments; entry into nuclear physics of students trained in technology during World War II; beginnings of high-energy physics; experimental physics and particle accelerators; fashions in physics; discovery of the antiproton; work considered personally satisfying. Also prominently mentioned are: Edoardo Amaldi, Felix Bloch, Niels Henrik David Bohr, Paul Adrien Maurice Dirac, Michael Faraday, Otto Robert Frisch, Guglielmo, Georg von Hevesy, Ernest Orlando Lawrence, Tullio Levi-Cività, Lo Surdo, Ettore Majorana, Lise Meitner, Ida Noddack, J. Robert Oppenheimer, Carlo Perrier, Franco D. Rasetti, Ernest Rutherford, Glenn Seaborg, Elfriede Segrè, V. Volterra, Chien-Shiung Wu, Hideki Yukawa; Columbia University, and Purdue University.
I'd like to start off by recapitulating a bit. You dealt before, in published works and in the interview with Thomas Kuhn in connection with the Quantum Physics Project, on the conscious effort of the physics group in Rome to get into nuclear physics, and you dealt also with the attempts to build up a physics department.
In that it was apparent that Corbino had played an important role in building up the department and recruiting people. One thing though, eluded us, and that is what role Fermi played in the building of the department. Did he take the same active role?
Perhaps this is an oversimplification, but you could put it so: that Fermi was the scientific and technical leader, and Corbino took care of finding the money and of the administration and so on, which was very simple and very minimal at that time as far as money was concerned.
On the other hand, it implied much more politicking, than you would expect because Fermi had enemies in Rome, had a lot of people who were his enemies and since they couldn't hit Fermi, they were rather inclined to hit smaller fry— that is, me or Amaldi or somebody like that.
Enemies within the University?
For instance, Lo Surdo, who was another professor, who when Fermi was called to Rome said, is a personal front to me to call Fermi here because I am enough. Why should there be anyone else?"
Is he the famous Mr. North?
Yes, that's the famous Mr. North. This was one and then there were others in chemistry and in various other parts who were essentially jealous. And one of the important functions of Corbino was to neutralize all these people.
But he actually did make pleas, if you like, to the engineering school...
As far as I know, only one, at which I was not present and which recruited Amaldi, although Amaldi was already registered for physics as far as I know; he was not registered as an engineer. And the recruitment of, say, Majorana (after all, the number of people is small), was done directly by myself and Fermi. For myself, through direct dealings between myself, Fermi and Rasetti.
So your recruitment was essentially limited to your close friend Majorana. You didn't take an active part in bringing people in after that time.
No. Pontecorvo was brought in by Rasetti. You see, also, again, the recruitment of me was extremely simple because I was very anxious to study physics; and all that was missing was somebody who could teach it or would teach it.
At what point in the long negotiations between you and Fermi did you finally decide that yes, Fermi and Rasetti were people with whom you wanted to study?
What happened was this. I was interested in physics myself since when I was six, seven years old. I have, so to speak, documentary proof: I have books and things of that type. But then I went to the school of engineering, and then I met Fermi, as I have said many times. Now, during the last part of 1926 and '27, especially in '27, Rasetti and I climbed mountains together and talked about physics. He taught me a lot of physics. Then in '27 I went to the Como conference with Fermi and Rasetti. In fact, I came down from the Matterhorn where I had been with Rasetti and went down to this Como conference where (I still have the pictures) I saw all these people— Rutherford and Millikan and Bohr, who were all there. This was September.
Now, in October, I went to Rome, still a student of engineering. Then I said, "All right, I will start to come regularly to the physics department." Because also my family was not so enthusiastic about the idea that I would change over to physics because I had already made four years of engineering. I mean I was just at the end of the engineering course. And so I started to go there and this happened in the fall of '27, and then I got so involved that I saw that I couldn't do both things. I went to both engineering and physics, but I couldn't do both. It was just impossible.
A much beloved uncle of mine was a prominent engineer and didn't like the idea that I would go to physics, but he died in the winter of 1928. In those months the changeover happened.
How long was it after you actually transferred to the physics department that you went into the army? I know that was 1928.
I went into the army in '28. I think what happened was this, if I remember right: I went into the physics department informally at the end of '27 and then more and more. I took my doctorate degree in July of '28 and then immediately thereafter I went to Spoleto in the army.
Was that compulsory service?
Yes, I had to go. In fact, I had to attend officers' training school. And I went to Spoleto. It was quite interesting. I still have all the pictures. I was there with Courant and Hilbert I remember. In the army I was I think the only officer reading Courant and Hilbert in German in the Italian Army. I don't think there were many more.
I think you described some of that...
The famous incident of falling off the horse, in the Quantum Physics manuscript.
Oh, did I say that?
And Raman came to visit.
Yes, that was later. That was in '29.
Let's fill in a few of the details we wanted to know on that earlier period. The thing that is most dramatic is Corbino's declaration that we're now getting into a new field, and there are two new fields in the future. You described this in various places.
May I say that in this connection, in writing the life of Fermi I looked through the documents and I have found all the speeches of Corbino, which exist and one can quote. I don't have them just here, but I have them in the other room.
I'd like very much to get copies of those because this is the very early recognition not of an individual research, but, in fact, "Here's a whole new field for us to get into."
I can give you the references, and I have photo- copies of most of the speeches of Corbino of that time.
Now, one of the first steps was to dispatch various members of the group to different laboratories, and you've described how you went to Hamburg and someone else went to...
Rasetti went to Pasadena and Amaldi went to Debye at Leipzig. Then Rasetti went to Lise Weitner.
Oh, he went to both places. He went to her in Berlin?
Yes. He first went to Millikan in Pasadena. There were several expeditions. First, that was still in the spectroscopic time—Rasetti went to Pasadena; I went to Zeeman in Amsterdam, and Amaldi went to Debye to study x- rays. There we were still making spectroscopy, and, in fact, I was there to make an investigation in spectroscopy— really not to learn techniques. The learning of techniques happened about one year later.
Also in the summer.
Summer, winter, and so on.
So the expeditions actually were divided into two phases—those where spectroscopic techniques were being studied (and atomic and molecular physics) and then later. Was there a second phase where your specific assignment was to go out and bring techniques back for nuclear physics?
No. If you want to a little oversimplify things: they were divided into two types of expeditions—the ex- pedition in which we wanted to make experiments which we knew of; say, Rasetti wanted to make Raman effect; I wanted to make Zeeman effect of quadrupole radiation. These were experiments which had been tested on a small scale in Rome, tried, and we just wanted to take advantage of the bigger facilities of these places.
But this is all before the decision to get into nuclear physics.
It was all before. This is the first phase.
The second phase, which happened in '31, was merely to learn techniques. And that is where Rasetti had dropped spectroscopy and went to Lise Meitner to learn radioactive techniques, and I went to Stern to learn molecular beams and so on.
Can we perhaps trace the things that were learned in that second phase, the things that you learned about molecular beams, the kinds of things that Rasetti learned and the things that Amaldi learned from Debye in the later work in Rome?
It's not possible to trace it that way?
Wait a moment. I never made a molecular beam in my life after that. I never used those techniques which I learned. And I would say also that Amaldi used them very, very little. Instead, what Rasetti learned became very useful because Rasetti learned how to prepare a strong polonium source, which is something that he then transmitted to me. In fact, he told me how to make these sources because he remained in America and there was a polonium source in Rome and I had to prepare it because he couldn't come. He told me, "Do so, and so and so." He gave me extremely detailed instructions on how to do it.
From whom did he learn that?
From bacher, I think, Philipp and Erbacher. Anyway it was in Meitner's laboratory. And he also learned how to make a cloud chamber in Meitner's laboratory— always Rasetti—and then we made one in Rome.
So there was a direct transfer of techniques.
That's the only direct transfer of techniques. Otherwise we didn't...
Majorana did not participate in this expedition to learn techniques.
No, no, no. Majorana was a complete theoretician, number one. Number two, he couldn't learn from anybody, only from books.
How were these long trips financed?
The Rockefeller Foundation
Individual fellowships. Getting back to Rome, after the desire to get into nuclear physics, the develop- ment of a general capability—not necessarily exclusively nuclear physics but a general physics capability—we know that some work proceeded then and this work has been described. I'm curious to know, though, how it affected other aspects of the physics department there. Was there teaching of courses of nuclear physics?
That happened was this: First of all, Amaldi told me—and I had completely forgotten, but he put it in his Majorana biography—that in the fall of 1930, late fall of 1930, he started a seminar in which what one did was to read Rutherford's "Radiations from Radioactive Substance," which had just come out, reading and discussing this book. Now apparently this seminar lasted a very short time; was disbanded because people scattered. I went to Hamburg. I don't know what happened. We can find it there. The teaching was minimal in Rome. We taught a few hours a week but very elementary courses with very few students, no recitation, nothing.
Were these students who were majoring in physics?
Well, they were merely people training themselves to be high school teachers and girls were a good many of them. It was a very light load.
This implies that you were being supported by the University because of your function as a research group.
Yes, but we were supported with such meager salaries that we didn't cost anything.
What about the support for the research itself?
Also that didn't cost anything.
You describe one instance of Fermi picking up the telephone and getting a thousand dollars.
Well, that was the biggest grant of all, and it was 20,000 lire, which was the equivalent of a thousand dollars at that time, but this was already after the discovery of artificial radioactivity.
He couldn't get 20,000 lire every time he picked up the phone and called the National Research Council.
Oh,no, no, no. This was a very exceptional thing.
But did you feel that the lack of funds inhibited the research that was possible there?
To a certain extent, but not really terrifically. The real problem was thelack of a shop and of an adequate mechanic.
Were these the things that prevented you perhaps from building a cyclotron or some other kind of accelerator?
We couldn't have built a cyclotron.
There was a remark made I believe in the Reviews of dern Physics, that was the memorial issue to Fermi, that said you had considered building a cyclotron at one time.
Yes. Well, in fact, we tried even to get to build a cyclotron. It was the twin, I discovered later of the magnet of the Marconi Company, which was used by Lawrence to make the 37-inch cyclotron. But Rome at that time could never have built a cyclotron. We had no con- ception. You see, it was a different type of physics. It was done on a few tables with string and sealing w It was extremely simple. It cost very little. And if we had started building a cyclotron, I don't know what would have happened.
Was it a question of a difference in the level of technology—in other words, that the supporting technology just wasn't available at the University?
Not really because if you saw Rutherford's laboratory at that time, the apparatus of Rutherford were riot very different. It was that physics was done in that way.
Just a different style.
Yes. I mean the budgets of Rutherford's laboratory were also extremely small. You find them in the books on Rutherford. He had maybe ten times as much as we had, but still very little.
So, in fact, there wasn't really much discussion about it. It was pretty obvious that a cyclotron couldn't be built.
Well, first of all, the cyclotron in 1930 was barely being built. If you go and see the first Lawrence cyclotrons, they were toys—they were not serious things.
But what about in later years in Italy, some time before you left. Had some thought by that time started?
Well, this is true. In '37, '38, they built a Cockcroft-Walton. They built one.
At Rome, yes. It still exists: It's now out of use but they keep it there.
Who was left to do that by that time?
It was done in the institute of the Sanità Pubblica and it was done by Amaldi, Fermi, Rasetti, Ageno and various other people. And they brought in quite an appreciable amount of industrial help—Condensatori Ducati, the Italian electrical industry, which was not bad. I mean they could make insulators and transformers and rectifiers, these kinds of things. We always had some dealings with Philips.
That would have been primarily for medical purposes then.
No, no, it was for physics. It was used very little because there was the war, but it was meant to make neutrons by[d,d]reactions.
You said that was at the Sanità Pubblica.
Oh, yes. But the Sanità Pubblica was a strange outfit. You see, all the radium that we had, with which we made the neutron work, came from there. The Sanità Pubblica was an outfit which was in theory...Well, it was a big institute—large, much larger than the physics department—which had a part of chemistry, a part of bacteriology, a part of physics, a part of this and a part of that, with a Professor Marotta as director.
Now, Marotta was rather an expansionist. He was a man quite willing to help. He's now maybe 78 years old, and he has had tremendous trouble. I think they put him in jail or they want to put him in jail, because they say that he did not administer the institute according to the rules, which may be true. But he was always a man who wanted the greater glory of his institute. For instance, when the question came of making penicillin, he got in Professor Chain and started making penicillin at the end of the war. Emanation was used to cure cancer, so he got radium. He was one of the first in Italy who had radium. And then he saw that one could make important discoveries in physics. He said, "All right, we'll use the emanation for that. So what? I'll give you permission to use it."
Did this come from him—this suggestion? Or was he pressured...? Was this in response to a request?
Well, the thing was this: Trabacchi was the chief of the section of physics; he had been the assistant of Corbino, had his detached physics institute in the same building as our physics institute. We were very friendly with him. And he was in charge of pumping the emanation out of the radium of the Sanità So he started giving us some of it on his own. He said, "I'll not give it to the Sanità this week; I'll give it to you." Then he couldn't do this too much. He could do it once or twice, let's say, to make a test. And then he asked permission, and he got it. But the initiative of using that radium came from Fermi who asked Trabacchi who obtained the authori- zation so that he could give it to us. He had permission to do it.
Did you ever get any sources from other countries during this period?
No, in spite of what Mr. Pregel tells.
That's right,there was a story about making materials available.
Well, the sources that are one half of it— you had a job that would be called purchasing agent nowadays, and there are some interesting things that haven't been discussed. One is the reason for the cooperation of people at the chemical supply companies in Rome—there was one man in particular who gave you certain things free or on loan. What is the explanation for that? Why were they so generous?
All this was done completely informally. It isn't that there was a plan or anything. Fermi got the 20,000 lire. Now we needed the chemicals, and who is going to go and buy them? I said, "All right, I'll go." And I went to the guy, Mr. Troccoli, whom I knew. I don't know why I knew him, but I knew him, and I talked to him and I explained what we were doing and so on, and he got inter- ested. He said, "Well, sure." The present that he made to us probably had the monetary value of three, four dollars; and on the purchasing he may havè earned 20 or 30, I don't know. These were small things.
I was wondering whether there was any general knowledge before the start of the artificial radioactive work, general knowledge on the part of the public of the work that was being done at the University of Rome. Did they know that a physics department was doing this work?
Yes, it was known because...Well, one has to see in what year Fermi became Accademico—we can easily check it, but I'm pretty sure it was before the radioactivity. in fact, I know it was before the radioactivity [induced by neutrons was discovered]. And so people knew that there was this very young man, who was the youngest of all the Accademici, who were considered big shots and important persons, and he was in physics. People knew that much.
So it was on the basis of Fermi's name.
Well, the position. What you're implying is that it's not so much his name but the fact that he had this recognition.
Yes. But the number of people in the Academy was limited; there were, say, twenty. There was Marconi; there was Mascagni; they were all very important people—famous in Italy. And then there was Mr. Fermi. So if he had been chosen in that company, it must have been for some reason; and he was also the youngest of them all. So somehow, to Troccoli or whoever it was, that meant something. And then I went to Staccioli, who was a jeweler, and gave me the big brick of gold. I knew him quite well. In fact, occasionally when I have needed some jewelry, I always bought it from him afterwards. The ingot of gold was probably ten kilograms. It was very very heavy. He knew I would not file it. But otherwise, I couldn't have pocketed it and just run away. And then I was a known person. My family was known. You see, Rome, Italy, at that time was—it still is to a certain extent, but it was much more then—a small place. People were known. One knew more or less which family one was from.
That's true, because that's how you got into a large scientific circle right away through some of your friends as a boy, Enriques and so on.
During this period, what contact did the Rome group have with other groups? For example, I know that once the work was started, you did take a trip—you and Amaldi took a trip to the Cavendish.
That was alrèady '34.
The contacts were this: Before this work in radio- activity, our contacts were chiefly with Germany.
Fermi had been at the Solvay Conference in 1930, so that's before the radioactivity period; and he had met all the people there. Now, he knew well Heisenberg, Pauli, because they had been in Göttingen together. He knew quite well Ehrenfest. He knew well Sommerfeld. He knew, of course, very well Uhlenbeck and Goudsmit. He knew Otto Stern and had a high opinion of him. He knew Bohr; he had a very slight acquaintance with Bohr. He didn't know Einstein at all. He knew Millikan.
How did that come about?
Because Rasetti had been in '29 in Pasadena. In America I think that's the only man he knew.
Fermi's first year in America was 1930, wasn't it?
Yes, at Ann Arbor.
And at Ann Arbor he would come in contact with a large number of American physicists plus some other European physicists who might have been visiting.
Well, but the American physicists there were almost all students.
By that time Goudsmit and Uhlenbeck were already here.
Uhlenbeck and Goudsmit were already there. At Ann Arbor in those yèars there was Randall, who was head of the department. There was Colby, who was professor of theoretical physics. Then there was Williams, Dieke, Uhlenbeck and Goudsmit...
Laporte and Dennison, I guess.
Laporte and Dennison on the faculty, and then there were lots of young people—Bacher, Inglis and what-not.
And so it was through these trips that he took, these international trips, that the ties had been established.
Yes, but until Hitler, he gravitated much more toward Germany. He knew better Germany. But then once the neutron work was started, then what we did was this: We published everything in the Ricerca Scientifica because the Ricerca Scientifica was the official journal of the Consiglio Nazionale delle Ricerche, which subsidized us. It gave [Fermi] the 20,000 lire. And so they wanted to publish our stuff. And so we would send to them a manuscript, and they would print it as a leaflet and say, "This is the reprint of the article", and the article would come out, say, a week later or two weeks later; but they gave us the reprint immediately, which we would call now preprints, you see, but they were the reprints of the article which was coming. I think the bulletin came out every two weeks, and so they gave us a preprint immediately.
Now, we sent this around to about 40 people, to Rutherford at the Cavendish—the people there, Bothe, Hahn and Meitner, Joliot, and I don't remember now.
The various centers of research—Paris, the Cavendish, Berlin. In this country whère would you have sent it? Caltech?
Caltech certainly, and a little latèr to Columbia because there was Dunning and Pegram doing the same things. Probably we would send one to Berkeley—I don't know—and maybe to Chicago; to Ann Arbor because there were some personal friends. We spread them around. We sent them more or less to the people we knew. You see, people were not swamped with reprints like now, and so people read them.
Was there any refereeing system in this journal?
What journals did you read to keep up?
At that time we read a lot. We read the Proceedings of the Royal Society, the Zeitschrift fur Physik, the Physical Review, the Comptes Rendus, and something more if we were somehow told that there was something to be read.
Oh, yes. Nature.
Were there particular people who published in those journals that you read or were you reading them because those were the journals that had the particular categories of information you were interested in—or both?
Well, we would get the journal, you see, and we would look at the titles and the authors. But until the radioactivity work started, we read a tremendous amount of stuff. Well, we didn't read such a tremendous amount, but a large fraction of what was coming out, because the literature was quite small. So, for instance, if there was an important paper in solid state physics, we would read it; an important paper in spectroscopy, we would read it; in nuclear physics, whatever it was—cosmic rays, anything.
How did you know it was an important paper?
In part from the authors; in part that there was summary and we could see the content.
This was before the work with [artificial radioactivity].
Yes. Well, with that work, then we were much more hard put for time. You see, we were overwhelmed with things to do, so we didn't have so much time.
Were you corresponding with anyone, a scientist in another country at that time? Did you get any inform- ation that way?
Were any of the other people in the group carrying on a scientific correspondence?
Not scientific correspondence. Once in a while a ter would come.
How about visitors
Visitors, yes. We had visitors. But let me say first one thing. These leaflets that we sent around were read all over. In fact, Rutherford wrote us a letter. I don't know whether you've seen it. I had èven a picture of the letter that Rutherford wrote back saying, "Not bad for a beginner"—he wrote to Fermi—"and you'll be inter- ested that even Dirac wants to make experiments now."
This is right after the artificial radioactivity with neutrons.
Yes. There was once in a while a letter, yes, but not much. There was not much need, because what we did we published rather fast through this method of the Ricerca Scientifica.
Everybody read all the journals.
Yes, it was feasible. It was not like now. Things were easier. There was a smaller amount and also the stuff was written in a much more understandable way. I was this fall at the meeting of the Italian Physical Society, and I heard a succession of ten-minute papers. I was impressed at how much more intelligible they are there than here.
What is the difference? What makes them more intelligible?
I don't know. They speak much better.
But the same period of time is allotted...
Yes, but somehow they're better orators—I don't know. I was really rather surprised. I've been to New York meetings, and the things that were said were the same type of things, but they were said much better. I've thought sometimes that it has to do with this, but I don't know whether it's true or not—that the exams at the University in Italy are oral, so people are trained. The examinations in the universities for students are: "Prove such and such a theorem on the blackboard." So they are trained to do this.
But now coming back to what we were saying bèfore: You werè asking whether there were visitors. All the visitors had come in years before the nuclear work. We had had a tremendous number of visitors who had brought in a lot of life. We had had Bethe Bloch, Peierls, London, Feenberg from here...
Raman you mentioned.
No, Raman was just a day. By "visitor", I mean someone who spent some time really and participated in the life of the place. Bethe, Bloch, London, Pierls -who else? I can't remember now.
Did they circulate also on Rockefeller fellowships?
They had a tremendous impact.
Yes. And then when the neutron work started, I remember quite well that we had an application of somebody who wanted to come, and Fermi said "No", because we just didn't have the time. Nobody had the time anymore.
Was there really that sense of excitement and sort of a crash program feeling?
No, it was not a crash program or exciting. People there were not excitable. But there was a tremendous amount of work to do. You had to work from eight to noon and from three to eight.
Did you have anyone helping you other than the actual physics staff?
We had a student, Fea, for a little while, and then the little brother of the student, who was about 12, 13 years old, and he would make us little boxes of paper in which we put our samples and things like this, but there was no help to speak of.
It was full time on research with very little time taken out for teaching...
Very little time. Fermi would teach probably six hours a week—give six lectures. I had my three or four hours a week, and so had Amaldi, and Rasetti had also some, but that's all. We taught not tremendously difficult things. We didn't have to prepare very much.
Was any new group being raised, any successors being developed? You mentioned that the teaching was on an elementary level, so there were really no graduate students, I gather.
We were the graduate students. We were what you would call the graduate students. You see, the Ph.D. in Italy is sort of a master's. It's after four years with a very small thesis. So it's fair to say that the Ph.D. is somewhere between thè Italian doctorate and the libera docenza. I don't remembèr now which year I took the libera docenza, but it must have beèn certainly '34, '35. So you could say I was an advanced graduate student, and so was Amaldi.
With some teaching responsibilities.
With teaching responsibilities, yes—a teaching assistantship.
Just another point on the circulation of these reprints, the advance circulation of them. They were in Italian. Now, was it common for people to be able to handle this in other countries?
I don't know
They must have in some way.
They were short. They knew they had to read thèm; they were important; and so they had an Italian friend or some friend who knew Italian.
Or a dictionary...
I don't know. You see, at thè Cavendish, for instance, Blackett's wife is Italian; I don't know. Maybe she translated.
Goldhaber was there and he could read Italian.
Goldhaber can read Italian?
Yes, because he learned it from his parents who learned it in Egypt at one time.
Yes, and maybe Occhialini was at the Cavendish. Occhialini was at the Cavendish around that time. Frisch, Placzek and Bloch knew Italian.
Speaking of the Cavendish and the publications, both you and Amaldi visited Cambridge in '34. You mentioned that before. Was the purpose of the trip to get the early work with neutrons published?
No. You see, in Rome it's hot in the summer, so in the summer we always closed the Institute—even now. I mean everybody goes away. So where do we go? Amaldi's wife expected a baby. We didn't want to do terrific things. So we decided to go to Cambridge in part to see what we would learn from them. You see, we had lots of things to learn—how to make a linear amplifier, how to prepare sources and so on. Then to speak and to see Rutherford. And so we went there. I think we remained there for maybe a month, six weeks—I don't remember exactly, but not a tremendous amount of time. I remember there was one of these lanes in Cambridge with two poles, and we would always gauge Mrs. Amaldi whether she could pass between them. We said, "When you can't pass through these anymore, then we go back to Rome."
In time to have the baby.
She just made it.
The brother of Bhabha was in Cambridge at that time, I think. Oh, Placzek and Bhabha were also in Rome.
In the following year, 1935, both you and Rasetti came to Columbia. I know, Rasetti came to Columbia. Did you, too?
I see. Together?
Yours must have been just a short visit was it not?
Let me think a moment. Are we speaking of '35 or '36?
Well, there's some confusion. When did you start at Palermo?
We have that in 1936.
I started at Palermo in the late fall of '35 and I then I went from Columbia directly to Palermo. This I know.
Then it's the summer of '36 that you went to Columbia.
In '36, Amaldi and I were both in Columbia. And Amaldi then went to Tuve. Merle Tuve in Washington. Wait a moment. I'm mixed up.
In the Reviews of Modern Physics article you mention that in the spring of 1936...
I was both in '35 and '36 at Columbia.
Well you certainly mentioned that you were there in 1935.
This is the part that's confusing. You said that "When the fall of 1935 came and we should have gone back to Rome, Rasetti did not want to re-enter Italy, I had been appointed director..."
I went to Palermo in the fall of 35. That's right. Now, I got married then in February of '36, and I was in Palermo. And then we want back to Columbia— Elfriede and I, my wife and I—in the summer of '36 because we had no children. Then my son was born in '37.
Now that we've established that, the question is, Was this also on the Rockefeller fellowship?
No, this was on my own money.
I see. What was the purpose of going to Columbia? Why did you select that—the first time, in '35?
In 1935, you see, in those years we all already smelled...I don't know how you would say it in English, but in Italian we would sày, smelled a dead man in Europe." I mean it was clear that Europe was going to end in a catastrophe. So we were all trying to find places where to go if and when we had to run. Also, we had this theory, that a world war would start in the summer, and so it was bètter to be away. (Brief Pause in Interview)
The summer of '35 was the summer of the Ethiopian affair. So we went to Ann Arbor. Then from Ann Arbor we went to Columbia. Then Fermi had to go back for some reason. I stayed in Columbia more or less as long as possible to see how the competition for Palermo would end, because if I won the competition for Palermo, I'd have to go.
Was this the concorso?
Yes—concorso for Palermo. So I was at Columbia more or less just waiting to see. If the concorso had gone against me, maybe I wouldn't have gone back for a year— I don't know. But anyway I was dilly-dallying there. And then I got a telegram that I had to go back or renounce the job, that I'd been appointed and I had either to go or renounce it. And so I went. This I remember because I went practically at the same time when they started the sanctions against Italy in the League of Nations. There wasn't anybody on the ship. There were perhaps twenty persons on the Rex or Saturina, or whatever its name was.
So we went back. These were hot-headed fascists (on the ship) who, I still remember, when we arrived in Italy, kissed the land. I said, "Well, these people are crazy in the head." I remember that quite well.
Before you leave Columbia, how did you find things there? Who was there?
Dunning, Pegram, Mitchell, Goldsmith, Rabi, but Rabi was doing molecular beams. We're talking now of nuclear physics. These are the ones I can remember. Then there were various students—Powers...
What was characteristic of their work at Columbia? What were they doing and most interested in at the time?
That was one of the few places where they did pretty good neutron work. Dunning had this linear amplifier, which was quite interesting for us. We made a velocity selector to find out about the velocity of the neutrons. Pegram did a lot of it with his own hands, and we got that machine going. They had neutron sources. I don't know how they had these sources. They were not radon sources. They were radium plus beryllium sources. But the equipment at Columbia was comparable to that in Rome.
They didn't actually start using an accelerator to make sources until Fermi was there, did they?
Oh, no, that was much later.
So there wasn't that much difference in equipment and the types of problems, would you say then—I think you did say—that Columbia was the closest in style and research program to Rome?.
Yes, in many respects.
I'm not rankinc them on a scale, but the concern with these types of problems and the facilities.
Of course, for instance, at that time Lawrence had already the cyclotron, which did colossal things, but we didn't see the cyclotron. I didn't see it until one year later. And it wasn't used.
In other words, it didn't contribute new knowledge to nuclear physics?
Very little because the effort was entirely con- centrated in making the accelerators. They didn't even have good detectors.
What were they using as detectors?
Lauritsen electroscopes, but rather primitive ones, and counters which were not working well. I don't know whether they were not very interested, but they certainly were not able to use the cyclotron as a research tool.
This is 1935 that you're talking about.
'34, 35—those years. I remember they prepared a tremendous source—1 curie of sodium and sent it to Ann Arbor— which really stunned us.
You went back to Italy, directly to Palermo. Why this move? It seems that the group in Rome began to break apart. People went off in different directions just about this time. How do you account for this change?
Well, I mean the group was not very big. You see, the group was small. See, Fermi and Amaldi stayed then. I had to either fish or cut bait, because I had won this Palermo competition, and I had either to renounce it or to go there. There was nothing else.
Why did you apply for it in the first place?
Because at that time a professor of physics died every ten years; and when one died, you had to get that chair if it was available. Otherwise, you were stuck for the rest of your life. And it was very difficult to have one of these jobs.
Did Palermo have any reputation for work in physics?
No. But I built it up, and it was not a tremendously bad place. And anyway you had to start there. You see, the career of a professor in Italy at that time— to a certain extent even now—was so that you were in a big place, like, say, Rome or Bologna or some place like this until you could win a concorso. When you won a concorso, you went where they sent you. And then you went back to the big place when you were old and no good. So the real productive period, the best years, were after your doctorate when you were still in the big place and before you won the competition, you see.
But at Palermo you did work...
At Palermo I was very lucky, and I did very good work at Palermo.
You had the responsibility for actually creating the research program there, did you not?
You see, you speak of the "research program" and so on. Nobody would say the research program anything. You were the boss there. You were God, so to speak, in Palermo. Everything depended on you. I mean it was a very authoritarian organization, and you did whatever you wanted. You had to teach, you had to organize teaching, and you had to do the research, if you wanted to.
How many people did you have with you there?
You were the department.
Well, I was the department. I found there a man who's still there. He's still an assistant there. He was an idiot and still is. He could never make the grade, and they out him there, then by seniority he got a sort of entrenched position, and there was nothing you could do to remove him. As I say, he's still there. All right. Now,this was a liability. He was no help.
Then there were two or three empty places. I put in Santangelo, who's now professor at Modena, Cacciapuoti who's now professor in Pisa. And then I put in Mando, who's professor in Florence. Then the next thing I tried to do was to get another, chair of theoretical physics, and I got Wick there, who is now at Columbia.
Where had Wick been before then, Rome?
Wick was oscillating between Rome and Turin but essentially in Rome—sort of fellowships. Palermo was his first job.
This is all within a very brief period of time, within a three-year period.
And what type of facilities were available for research?
In Palermo there was a building and some cash and things were cheap, so it was quite easy within a matter of two months to make adequate—not rich but adequate— for those times chemical facilities. I bought an electro- scope, and I got radioactive substances from Berkeley, so I startèd work there.
Then there was one very lucky thing at Palermo that there was a professor of mineralogy who was on the upper floor of my institute with whom I became very good friends, and I liked him very much. He was a very nice gentleman, Perrier, and he was a good chemist. So we could do radiochemistry. I taught him radioactivity and how to make samples and so on, and he taught me chemistry. We worked together.
Then there was a physiologist, Artom, whom I taught the existence of radioactive tracers at that time. He's now in North Carolina.
You published three papers with Artom during that period.
Can you descibe that work, a little of what motivated it. This was perhaps what we would now call biophysics.
It's quite simple what we did. We're now in 1936. I had friends here in Berkeley and they sent me pieces of deflectors which had been irradiated in the cyclotron, and they had radioactivities of periods long enough so that you could put them in a letter without air mail, because there was no air mail, and they still would be active when they arrived in Palermo. All right. When they arrived in Palermo, I used to put the letters on the electroscope and say, "Well, this is a good letter" or "a bad letter".
Who would send you these?
In part, McMillan, in part Emo, an Italian friend of mine, Count Emo, who was working herel; in part Lawrence. It isn't that we stole them.
Well, you met them in '36 when you were here.
Yes, and I had brought some back myself. All right, when we got all these things, I started to make chemical analyses. Perrier and I started to separate the various elements. One thing that was apparent was that there was a lot of radioactive phosphorus in all the samples. There was radioactive phosphorus for the very good reason that in Berkeley they used to irradiate phosphorus without covering it, so that the whole place became covered with radioactive phosphorus. It was an unbelievable thing. The deflector and so on—they were covered with radioactive phosphorus. I had these tremendous samples of phosphorus, and I didn't know what to do with them. I knew Artom. Artom was the brother of a cousin of mine. He was a physiologist and I went to him and said, "Now look, I have radioactive phosphorus." He didn't know it existed—I don't know. Anyway I explained to him what radioactive phosphorus was, what one could do and so on. And then he said, "Oh, but I am just working on the metabolism of phosphorus in the liver. This is a Godsend. This is just exactly what I need."
So I told him how to use it and measured it for him. In fact, Elfriede measured it to a certain extent, and we started doing this work which is quite famous— just because it was the first of that type.
That was the initiation of the radio tracer technique?
Well, not the initiation. Hevesy had done it before. But it was [the first) of that type, radio-lipids and so on and there were important results.
This is all in the Palermo period. After your first year at Palermo, you went to the United States again.
Yes. But the important thing that happened then was that we found technetium, which was the first arti- ficial element. You see, in this famous deflector, when we started making chemical analysis, we said, "Well, maybe here is this element-43 that nobody has seen. Let's keep our eyes open and see whether we can identify it". Which we were able to do after a while. We got long-lived isotopes of this stuff.
Then the way I came to Berkeley in 38 was because I wanted to do the short-lived isotopes of technetium.
I was in America in '33 for the first time, then in '35, '36 and '38. In '38 I remained.
In '36, did you go directly to Berkeley and spend the entire summer there?
No, in '36 we started in Columbia, Elfriede and I. And then it was so hot—she was not feeling well and was expecting a baby, who was born later in '37—and so after a while, Columbia was too hot and humid and we said, "Let's go to Berkeley." This is '36 now, and we stopped in Ann Arbor, and then on the Challenger—I think it was—we arrived in Berkeley. In Berkeley we hired a car, we went around and saw the West and so on. And then we returned to Palermo.
What was your impression of Berkeley? By that time they were developing a school of physics here.
As far as I can remember, they had these tremendous machines, which were very impressive, but they didn't know much physics. There was a great difference between the excellence of the machines and the relative poverty of their use. This was my impression as far as I remember.
Did you come to know any of the people doing theoretical work? Oppenheimer was here at the time, and I guess there was probably a large group of students.
Well, in '36 I met Oppenheimer only. I met Phil Abelson; I met McMillan; quite a number of the people working with Lawrence, and Lawrence of course; oh, I think Kurie and Cooksey and maybe[R.L.]Thornton—I don't remember now.
What did you do here? I understand what you did at Columbia, but this was directly something...
In fact, I did here much more useful things than at Columbia because I looked at what they were doing, and I told Abelson, "Look, you bombard uranium and look what to do with this because there are mysteries in this object. Nobody understands what's going on. And try to bombard it with fast neutrons, with slow neutrons, and try to understand..." I had no inkling of fission of course (I don't want to say that I suspected it.) But I knew that there was a mystery, as everybody who was working in that field knew. So I tried to get him to work on that as much as possible.
And then I went to see the West. I went to see Grand Canyon, Utah, etc. Then I came back and I got a box full of samples which I took to Palermo—long-lived radioactivity.
This brings me back to an earlier question that I think you had, Barry, on Corbino's speech in 1934, on the reaction...
Oh, yes. The question was related, again, to the public knowledge of the work that was being done and also to the effect that Senator Corbino's speech had on the research group. There are several places where it says that Fermi was very upset about the announcement of the so-called element 93.
Well, this was because after the irradiation of uranium, we found these radioactivities and we worked and worked and worked on them for quite a while, and we wanted to discover the transuranic elements. But the thing was mixed up. The tests were tests of this type: we put in isotopes of everything we could to show that these were not isotopes of anything between lead and uranium. And then of course we couldn't put transuranic isotopes, obviously, and so we said, "Well, beyond uranium they will behave like rhenium, osmium, iridium", which was an error, but anyway we thought that they would behave like this. So we used more or less rhenium, osmium and iridium as carriers. And we got some activities. And then since we knew generally that the reactions were (n,r) followed by beta emission, we said, "Well, maybe this is 93", and we tried to work this into a scheme. But in time things always got more complicated, and Fermi was always very skeptical. Finally, there was a public occasion when Corbino announced...
You see, Fermi wrote articles in Nature saying that "these are not isotopes of anything between lead and uranium, and maybe thus they are transuranics. However, there are troubles". They were very cautious [comments]. The thing he didn't want to do at all, was to give them names. And Corbino in the Italian Academy on an occasion gave a speech, and he said "Well, although Professor Fermi is very cautious and so on, I am quite convinced that these are transuranic elements and they call them Ausonium and Hesperium". Then Fermi was very mad. But everybody believed that for quite some time, for years—until Hahn.
Was there much reaction from other countries? You mentioned that there was a New York Times article that disturbed him, too, but what about from scientists them- selves? Was there correspondence, or a challenge, or a- greement?
Well, there were only two more groups who had ever seen this. One were Hahn and Meitner. And the other were the Joliots. Now, the Joliots were not saying anything. Hahn and Meitner were finding all kinds of transuranic chains more or less in the same way as we did. There was no violent disagreement. When we made certain reactions on certain things, they always found about the same thing. We more or less agreed.
But the thing which is beyond understanding is the famous story that Ida Noddack said, "It's uranium splitting"
That's right. And we saw the reprint. I remember this reprint as if it were now. I asked Hahn, "Have you seen it?" (The Noddack paper). A few years ago, I mean. Hahn said, "Yes, I have seen it."
"Well, why didn't you pay any attention to it?"
"I don't know."
And I don't know why we didn't pay any attention to it in Rome. I really don't.
But in each case you had seen it; you had read it.
Oh, sure. We had read it. There's no doubt about it.
Have you ever gone back to that paper afterwards?
To Noddack's paper, to see if there wasn't anything...
Well, you see, there was a complicated story. Years after—In '37, '38 and '39—I became convinced, and quite properly, that the Noddacks were a mixed type of people. They had done excellent work on rhenium but they had been plain dishonest—there's no other way of saying it—on technetium 43, or what they called masurium. You see, at first they thought—and it could happen to anybody—they thought they had discovered it. But then I visited them, and I saw them and I talked to them, and after having seen them and talked with them, by '37, I was convinced that they were dishonest.
I even have a letter from Hevesy saying that he also has the same con- viction. Well, they were not really quite dishonest; they were in this situation: Their work on rhenium was good—there was no doubt about it. It was excellent, and they had discovered rhenium. The work on masurium just wasn't right. And now we know there is no stable masurium. But they had a hope. By that time (1937), they must have felt that it was not right, but they had the hope that maybe after all, element 43 might turn up. And then they said, "All right, if we say nothing re- tracting our earlier work, we can always say that we have discovered it." And so they never took it back. They died without ever taking it back, always saying that they had seen masurium.
Of course, this wasn't a factor—this knowledge came to you later—in making you suspicious?
Not in '34, but it was in later years—in '36, '37. And then in '38 fission was discovered. There was no doubt anymore.
Also, as soon as I left Rome, I had no access to radioactive sources anymore.
Nothing at Palermo.
Except things were mailed to you there.
Yes, but they were irradiated in Berkeley, and I couldn't irradiate what I wanted. I had to take what was available. Now, I even got uranium to be irradiated in Berkeley to get it back. But I found it in Berkeley when I came here in '38. It was still being irradiated because they didn't irradiate these samples very carefully. They would put them near the cyclotron when somebody remembered it, and then they had to unscrew a screw and they would take it all away.
There was no charge, by the way, for any of this? It was just a courtesy?
Sure, it was just a courtesy. But it was not done very scientifically or very carefully. At Berkeley at that time, all the effort was to make the cyclotron, to make bigger and better cyclotrons. It was so absorbing a task that all the efforts and money went into that, mental energy also—everything. (Pause In Recording)
Before we get into the whole period at Berkeley, I'd like to go back to the earlier period and ask you a question on the relationship of mathematics to the nuclear physics that all of you were doing in the period from 1932, say, to 1938. What kind of mathematics was necessary to do nuclear physics, at least the experimental part of it?
It depends what you wanted to do. In the experi- mental part, you need very very little. But if you wanted to understand neutron diffusion—"neutronology" —Or the theory of the reactions, then you had to be quite sophi- sticated. Remember that we had Fermi who was a very powerful theoretical physicist. So, for instance, if you see all the studies on the diffusion of neutrons done by Fermi, they are very sophisticated and we understood them. As students we were pretty well prepared for that time. We all knew quantum mechanics, which nobody in Berkeley knew, except Oppenheimer and a few of the theoreticians.
For example, Fermi used these Monte Carlo techniques. Were they true Monte Carlo techniques
He invented the techniques. I don't know what they were precisely. He never published them, and he only told me later they were Monte Carlo procedures.
There's a story that when Bethe came to visit Fermi, Fermi showed him some of his shortcuts in calculations. In other words, Fermi was innovating....
No, it was not that Fermi was inventing shortcuts. This is said very nicely by Bethe. I asked him in my biography of Fermi, and he put it down. Bethe came from Sommerfeld and said that he was taught that you put a problem in an equation and then you solved the equation and then you do the problem; whereas Fermi taught him essentially you don't put the problem in an equation. You make a simpler problem, which has a similarity with what you want to solve and which you can solve. This was the chief thing of Fermi. He always could do that.
I remember, for instance, at the time there was a complicated perturbation in the molecule of hydrogen which was needed by Stern in the magnetic moment of the proton. And Stern didn't know how to calculate it. And Fermi called Wick and told him, "Now, look, you make this model, this is not a hydrogen molecule, but you make a ring with something that does this and does that and what-not. Now you calculate that, and from this we'll see what the hydrogen molecule does." That was something calculable. Wick calculated it and he understood what was happening in Stern's experiment.
This was characteristic of Fermi's work even in later years, in high-energy physics before his death, his approach to problems.
Sure. For instance, you can see it in the diffusion of neutrons. He always makes the right approximation. He always makes a problem in one dimension instead of three. This is the working of a physicist.
In a similar vein, how did the current theoretical concepts of the nucleus, the model of the nucleus that existed at that time, affect the work that was done in the period?
Very little. At that time, (1934-35) the model of the nucleus was Gamow's, the barrier and something inside—nobody knew what. But this was the only thing that one knew. And one knew something about spin and statistics and so on but nothing say, about orbits, levels or the drop model, nothing. One knew that the nucleus was made out of neutrons and protons, but one didn't take anything else seriously at all. And Fermi operated with his nucleus as the potential well with a Gamow barrier, and that's all he used.
All the time? For how long a period did this dominate his thought?
Until the Bohr paper came out with the drop model. Fermi didn't like the Bohr paper very much. Essentially he thought that he was somewhat vague in his conceptions and not quantitative enough.
Wasn't it a difference between the two styles?
One was concrete and the other was more...
Well, that's a different story. I think it had to do also with other things. I think that it had to do with the fact that when Fermi was young, Bohr involuntarily snubbed him and harmed him.
There was a particular paper. You did discuss this in the Quantum Physics interview.
Of course, Bohr and Fermi were very polite and Bohr went out of his way in warning Fermi in 1938 of the impending Nobel Prize and in his hospitality at the end of that year. Fermi went to Copenhagen to a conference if it was necessary, but you will see that Fermi went very seldom to Copenhagen, if at all.
Also, the way Bohr used to write was not to Fermi's descriptive taste—at least the Bohr of that time. I don't mean the young Bohr. In fact, Fermi discovered the neutron resonances, experimentally, and he took a completely agnostic point of view. He said, "I'm going to measure the energy at which each resonance occurs, the width and everything I can." But for a long ong time, he even said, "I don't want to recognize that these are resonances. I recognize that there are strong absorptions. Whether these are due to selective velocity or different species of neutrons, what it is—"hypotheses non fingo". He would say [this] and smile ironically.
What did he believe?
Well, I have printed this in his biography in some detail. You don't know. Fermi was not very talkative. But he was very cautious. He always said, "We proceed according to the rules of Bacon", and he would say this smiling, not seriously. "The facts. We will make our experiments and then the experiments will tell what it is."
Other than Fermi, how did the compound nucleus model affect the interpretation of experimental work?
Not much because it was not something on which you really could put your hands and your teeth very clearly in '35 and '36. Later, with fission, it became helpful. But even there, it was always too vague and nebulous and semi—qualitative.
So what was the picture—you had some picture I assume, of the nucleus in your mind.
We didn't have much of a picture, no. There were resonances—we knew that. The Breit-Wigner formulae were believed and were very important from the beginning.
But it wasn't a question here of challenging one model or another or posing one against another?
You were doing experimental work. You were trying to get results, and you weren't necessarily relating those results to models.
To models, no.
This is a very interesting point because it's not often clear. It may be that we tend to pose a certain order...
No, in fact, we were rather diffident of models. We wouldn't take them too seriously.
This was in the 30's.
When would you say in experimental physics that this situation changed?
Well, at Los Alamos, with fission and so on, since one had to try to get numbers, and Bohr was there, one would try to have him make prophecies. But I don't know...I think Fermi at the bottom of his heart, would have liked to see from the beginning, much more the shell model than the com- pound nucleus. This is my interpretation. I may be wrong. He's not here. But if I have any knowledge, I think the shell model would have appealed to him because during that time there was D'Agostino, who was our chemist; he was rather ignorant and he would say, "Well, radioactive potassium is going to behave like radioactive sodium because of the periodic system."
And we would tell him, "But now, look, the periodic system is in the electrons and not in the nucleus."
And he would say, "Well, but there will be a periodic system also in the nucleus, and it will be the same."
And Fermi would smile and say, "Well, you see D'Agostino tells you."
So there was something.
There was talk of a shell model in the '30's, but not enough to become effective...
Well, after the war when Maria Mayer started to work on it in Chicago, she got the magic numbers. Fermi told her, "Look at the spin-orbit coupling." So that means that he had thought about it because he knew where the key was.
And you think that this may have been on his mind even in the '30's.
It may have been in a primitive, imperfect way. I don't know, but I wouldn't be surprised.
Elsasser had worked on some sort of a shell model.
And Bethe had some ideas along this line.
So there were rumblings certainly in that period, and he might have shared in that.
Sure. One was aware. But this is already a little later. You are speaking already of later years. Of course, the Bethe article with the optical model—I read it, and it impressed me tremendously when I read it. But I think by that time I was already here at Berkeley, and I don't think I was anymore in communication with the people in Rome or with Fermi.
What was the reaction to the beta-decay work at the time and in subsequent years in the '30's? Was there immediate recognition?
Fermi said immediately, "This is a thing for which I shall be famous."
He had that feeling?
Oh, yes. He said it immediately. "This is the biggest thing I have ever done."
Did he say that before he began to get the response of colleagues other than the Rome group? Had he already had their approval or did he just sense this at the time he was doing it?
He said this by himself. You see, Rome was very isolated from the rest of the world. Furthermore, who would be the colleagues to answer him at that time? There would have been Pauli. Pauli certainly wouldn't have said that anything was all right. And Heisenberg probably didn't pay attention to it. On nuclear models there was a lot to do in Rome, but before the beta ray theory. In '31 and '32 with Majorana and the exchange forces. The nuclear forces were studied very actively at that time.... But then it petered out when the experimental work started. You see, the experimental work was tremendously time consuming and absorbing.
Also, at the beginning after the discovery of the neutron, one hoped [for] very much out of Majorana exchange forces: that they would lead to a quantitative understanding of light nuclei and God knows what. But then one saw that this was not the case, and so the study of the nucleus from first principles was already petering out by '34, '35.
I'd like to return to these general questions a little later and to get back to your own career towards the end of the period at Palermo. What were the circumstances of your leaving Palermo and coming to Berkeley? When you made that trip was it with the idea of permanence?
No. No, I left Palermo with a return ticket, and I arrived in New York. I met Szilard. "Oh, what are you doing here?" He was a good friend of mine. I knew him quite well. "What are you doing here? What's going on?"
I said, "I'm going to Berkeley to look at the short- lived isotopes of element-43," which was my plan. "I'll work there the summer, and then I'll go back to Palermo."
He said, "You are not going to go back to Palermo. By this fall, God knows what will happen! You can't go back.
I said, "Well, I have a return ticket. Let's hope for the best."
But I had gotten the passport for my wife and my son before leaving, because I smelled that the situation was dangerous. So I took the train in New York, Grand Central, and I bought the newspaper in Chicago. I still remember it. I will remember it as long as I live. I opened the newspaper, and I found out that Mussolini had started the antisemitic campaign and had fired everybody. So there I was. So I had the ticket and went to Berkeley. I started to work on my short-lived isotopes of technetium, but at the same time tried to get some job. Then I got my wife here.
When did she come?
The days of Munich, so the fall of '38.
What kind of negotiations did you enter into at Berkeley in order to get situated?
Well, I arrived here. I didn't say anything. I started to work on technetium. I met Seaborg at that time. I was very well prepared; I knew what I wanted to do, so I was very rapidly quite successful in finding these new isotopes and doing what had to be done, so one day, Lawrence came and said, "Would you want to stay here a little more and not go back in October?"
I said, "Well, I'll seriously consider it."
Whereupon Lawrence went to Alaska. I said to myself, "Maybe I'm being too smart here. I have outsmarted myself. He may change his mind."
Well, anyway, he came back, and he gave me some money for some months. (Pause In Recording)
You came to Berkeley in the summer of 1938 to do research. You then were employed at the Radiation Laboratory through the rest of '38 and into '39 and you went for a short while and went to Purdue, then came back when you were offered a position by Raymond Birge in the physics department.
As a lecturer.
That was in January of1940.
That was January 1st of 1941. And the reason why I know this so precisely is that in the meantime...You see, in '38 there were all kinds of things happening. Fission has been discovered, and I had been doing all kinds of very interesting work. I had done a lot of things—isomerism, and what not. Now, from Purdue I went to New York and I saw Fermi. In New York in December, 1940.
Laura Fermi wrote something about your visiting them in Leonia, New Jersey.
It was the end of the year in 1940.
You apparently had already started teaching at Berkeley when you visited Fermi. Is that right?
No. I went from Purdue to Fermi. And then I returned to Berkeley. This was the end of '40. So it means that I had had in the Radiation Laboratory, say, from 38 to the spring of '40.
Then I went to Purdue.
Tell me one thing. When were the Netherlands invaded? This was the spring of '40, wasn't it? Yes, because the war started in September of '39. The invasion of the Netherlands was the spring of '40. In the spring of '40, I was already looking for jobs, and I had gone to Tulsa, Oklahoma, to speak with some oil companies and what-not.
You had considered working in private industry.
Well, I mean I had been given gentle hints by Lawrence that this was probably the best thing for me to do and I decided not if I could avoid it.
But then in the summer, I met Professor Lark-Horovitz (Karl) of Purdue and at his invitation in the fall, I went to Purdue, probably always looking for jobs. But I had a very vital interest to stay in Berkeley because the machine was so good. I could do these things that nowhere else I could do. So I went in the late fall of 1940 to Purdue. From Purdue I went to New York. In New York I met Fermi. And on December 15th—this I know because I have a paper—we decided to make plutonium. We had a conference with Pegram, Fermi, Lawrence, who was in New York at that date, myself, that's all, all four of us. And we decided on the irradiation of uranium to make element-94 because Fermi and I suspected that element-94 would be fissionable with slow neutrons; and hence, if you could make a chain reaction with natural uranium, then you could make element-94 and you could separate it out and make a bomb without separating the isotopes but by a chemical separation.
And then on January 1st—and that's why I know January lst—1941, I came back to Berkeley with the idea of making plutonium. I had worked with Seaborg at the time of technetium before. I saw that this was more than I could handle, and I asked Seaborg whether he wanted to join. Then he brought in Kennedy. Then both brought in Wahl, who was a graduate student, and then we started to do the plutonium work, January '41.
Was this in connection with the government at that time?
It was all before that.
All before—no government, nothing. It was all private. That's why we got the patent on it.
The patent which was subsequently issued. In '46, was it?
I do not know if and when the patent was issued, but the application was made in '41 as soon as we got the results.
Let's backtrack just a bit. Where were you when the announcement of fission was first made?
What was the reaction here generally?
Well, the reaction was: why didn't we do it? Of course, I think there were quite bitter feelings because Phil Abelson had been seeing x-rays of fission products and not understanding them. And when fission was announced, then he recognized that he had seen them all the time. But at that time, it was not so easy. You see, there was a lot of diffidence against foreigners, and to a certain extent also Lawrence—I don't know. But, say, or instance, Abelson would be told, "Don't speak to Segrè because you can't tell what he may do.", although I had told Abelson two or three years before to work on uranium because I knew there was something suspicious. I still have decay curves of irradiated uranium Abelson took for me in 1936. Now, I don't claim at all that I would have understood fission from Abelson's x-ray results, but I had never seen them before the discovery of fission.
There was a strange mixture of provincialism in Berkeley andnot much knowledge really.
Not much knowledge of reaction...
This is in general.
Well, Oppenheimer knew high-faluting theoretical physics.
Oh, yes. Oh, yes. Oppenheimer knew quantum mechanics.
Electrodynamics, quantum mechanics—he knew all these things. But he was very snooty. He knew the answers to everything even when he didn't know them, and was not a man with a very good experimental sense at that time. At Los Alamos he was quite a different person. At Los Alamos he was much better.
Was there much exchange between the theoretical people here and the experimental people?
Yes, but of a very strange kind. In other words, the experimentalist didn't learn the theory, didn't learn enough quantum mechanics really to understand. And the theorist did not go down and really try to understand what happened in the experiment; so that the experimentalist would say, "I have found this and it's a very strange thing." And the theorist would concoct a theory to explain this without looking at all at what was really going on.
There was a very typical case, which is an amusing story. It happened shortly after the war, but it gives you an idea of what was going on. With the new cyclotron, they made neutrons by stripping the deuterons on another element— I can't remember now what. The neutrons came out with a certain angular distribution which had a minimum in the center. And there was a seminar, a great meeting, on what had come about and so on. And Oppenheimer immediately made a tremendous theory—why it should be so, and so on.
Why there should be a minimum at that point?
Yes, and how one could explain it and what-not It was very interesting, it showed this and it showed that and so on. And I said, "But what if there is a lead brick in the center where the neutron should come out?"
And this of course was an insult. Well, they went to look and there was a brick—
Did you know this?
Well, common sense. I knew more or less how they did these experiments. I knew that they had bricks and so on, that they could put one there, that there was perhaps some reason to put a brick in that place. I mean this gives you some idea of the relation between theory and experiment.
I know there were joint colloquia between Stanford and Berkeley. Were these just theoretical?
And they involved Bloch and Oppenheimer, I was thinking of in this case.
Yes, but Bloch was much better. You see, I was used to discussing theory with Fermi, and this was something of a different class—just had nothing in common—especially when it came to relation between theory and experiment. Fermi knew what he was talking about. He didn't know only the mathematics.
This is what you describe in the Quantum Physics transcript as "experiments in theoretical physics." I presume what you mean by that is that there was always a very close tie between the amount of theory you allowed yourself and the experiment that you were working on.
Well, and anyway it was all in the same brain in the case of Fermi.
Another case that was very typical, around 1940 or something like this: I invented a chemical method of separating isomers, which is a very elegant thing, a very nice thing, which I like very much; and I reported on it in a seminar. Oppenheimer would say, "It can't be. It's against the conservation of energy."
I said, "Well, look, first of all, the thing happens Secondly, the explanation is this—and it isn't against the conservation of energy", and I told him the explanation.
"No, no, no. It can't be. It can't be."
"All right, but it is."
Then I wrote to Fermi, "Look, I've done this experi- ment and this and this happens", and so on.
And I got a letter, which I have saved, because Fermi wouldn't write this so easily. He said, "Oh, what a nice experiment. I wish I had done it myself." Which was not common for Fermi. Fermi was never a person to say so.
So the theory here was not really very fruitful for experimenters. This is what I want to say.
Did you have much contact with Fermi in the years before Los Alamos?
No, very little.
But you mentioned the one visit east after Purdue.
He came here for the Hitchcock lecture, and I went to Leonia, and these are the only two times I can remember. Fermi by that time had become very secretive. You couldn't talk to him anymore.
Because of the war work?
Because of the war work, yes.
Did you have contact with other groups of people in this country with similar interests or were you pretty much...?
I had contact with Bloch quite a bit. There were students of mine, like Miss Wu and postdoctoral fellows. I talked to Seaborg. I don't know whether he was a graduate student, but he was certainly younger than I am and was learning from me essentially and Joe Kennedy quite a bit.
Meanwhile, what had happened to physics in Italy in these years?
I spoke a little but not much to Alvarez and McMillan, more to McMillan than Alvarez. Alvarez was very temperamental and very difficult to talk to. Thornton I talked to a little, but mainly about machines. Martin Kamen. Those are more or less the people I talked to.
Did you maintain contact with people in Europe?
Yes. Amaldi came here.
When was that?
Amaldi was here when the war started in September of '39. He was in my house when the war started. I can still remember Amaldi as red as that book there, whether he should go back or not.
Oh, and Plazcek I saw quite a bit, George Plazcek.
There was a little correspondence, not too much. But of course on the uranium, there was voluntary censorship from the very beginning.
But how about the people at the Cavendish who had in the earlier period been doing work in which you were very much interested, the neutron work in the early period?
Well, Rutherford had died and the Cavendish was more or less in dissolution.
They certainly weren't working in nuclear physics.
Well, they were a little. I mean I knew very very well Otto Frisch because we had been together. He was the assistant of Stern when I was in Hamburg, so I knew him very well, but never corresponded with him.
By the way, he's coming in April to the American Physical Society meetings to give a talk on fission in historical retrospect.
Frisch applied to come at the time of the neutron work but Fermi said, no, just because he couldn't spare the time.
Oh, was he the student you mentioned before?
Yes, that was Otto Frisch.
How would you characterize the type of work that you were doing at Berkeley up until Los Alamos? In other words, if someone asked you to describe the general type of physics you were doing at an earlier period, you might have said neutron physics of a certain type...
Well, it was radiochemistry and physics, something between physics and radiochemistry.
Well, then this started in Palermo really.
Yes, it was a direct continuation of what I had done. You see, what I did was this: First I tried to discover new elements, and the first had been discovered in Palermo. Technetium was in Palermo, and in Berkeley astatine and plutonium—plutonium together with Seaborg, and astatine with Corson and MacKenzie, who were students at that time. But this was radiochemical work.
And then, always to try to find some peculiar phenomena which would throw light on some nuclear effects and could be understood. For instance, the big question of nuclear isomerism, which at that time was somewhat mysterious. Then there was an hypothesis of Weizsäcker which proved to be right. Now if the hypothesis of Weizsäcker was correct, then certain rather farfetched and remote things should happen. I tried to see whether these happened to see whether one could explain isomerism by the high spin of the nucleus.
Another thing that I tried at that time (I finished it after the war, but I started it at that time) was this: All right, if a beta-ray is emitted the way it was described by Fermi's theory, then it should be possible to change a half-life of a K-capturing substance by chemical means. And I tried this, and then after the war I did it. So it was something applying rather chemical techniques to physical problems in the field of nuclear physics.
The reason why I tried to do this was quite simple.
Chemistry was very cheap, and I knew something about it. The money in Berkeley was unbelievably tight, so as far as, for instance, detection methods, I was worse off in Berkeley than in Rome.
What did you use?
An electrometer which is now in the museum. But that was all that I could have. I could never have a Geiger counter, because all the money went to make the cyclotron. Now, you could have these tremendous sources, but the detection—you had to do absolutely everything by yourself, and I was not very skilled in electronics or in making these detectors. So I had to get away with the simplest possible things.
I remember the first time I put together an ionization chamber, which I built with my hands; an electro- meter amplifier, which Lee DuBridge built for me because he was spending the summer in Berkeley and was an expert in this. I said, "Can you do me this?" And he did. It's still there. Another little thing that I put together. And we had the most primitive methods.
What else was going on with the cyclotron, though, other than the attempt to...?
Medicine, medicine, radiation killing patients, killing patients, killing patients.
Did much of the research support for the cyclotron come from hope for medical progress?
In part. In part it had to do with the fact that Lawrence was a humanitarian and he thought he should help mankind with the cyclotron.
This was a trend. Of course at Caltech the Lauritsen tube was originally used for this purpose.
Even the radium of Madame Curie—all the money came because of Curie therapy.
There was plenty of detection equipment around the cyclotron itself, was there not? That is, Alvarez...
Alvarez was much more skilled and much better than I am in making things—much more able.
But he certainly had Geiger counters that were working well and so forth.
Not tremendously. But he knew much more electronics than I did.
We're going to talk with him and we're going to get the story of electronics, certainly after the war, which is a thing that he can fill in, I think.
Well, after the war it's another story. I'm speaking now of before the war. In fact, at that time I met Clyde Wiegand, who is still with me. The poor guy saw me trying to make a power supply, and he was a pretty good man—he had worked in a radio station before becoming a physicist. He saw me making this power supply, and he said, "Would you mind—Could I make you a power supply?" He just was suffering over what he saw. So he made me the power supply.
Of course, Miss Wu was there. But our instruments were very primitive.
What kind of teaching were you doing at the same time?
I taught practically, I would say, every single upper division physics course that there is in this University, and a good number of the graduate courses—whatever was needed. I was relatively well prepared at the time, and I could teach spectroscopy; I could teach optics. In fact, Chamberlain was a student of mine in an optics course— optics and spectroscopy. That is where I first met him. And then I taught elementary quantum mechanics. I taught atomic physics. I taught mechanics. I taught thermo- dynamics and so on
This was in the period of '40 to '43.
At that time everybody was going to the war, and Birge was very hard put to have somebody who could teach these things, and so that's why he put up with the foreign accent.
When did you become a citizen?
But you were able to go to Los Alamos in '43.
Oh, yes. I was one of the founding fathers of Los Alamos, you, see, because there was a strange situation in Los Alamos.
Maybe 20 or 30% of the leadership was foreign.
It was called "a city of foreigners".
There was Rossi and there was Staub and later Fermi came. There was Bethe, Teller, myself. There was quite a number, probably more.
Let me ask you at this point a general question about the effect of this upheaval, the war period, on physics, on nuclear physics. Of course this breaks down into your own work and your own career. But we're also interested in the role of fission itself. What did fission contribute to nuclear physics? Did it play a significant role or not? By this I mean the subsequent development of the field.
Yes, yes. First of all, it gave a pretty good proving ground for the drop model. It was quite amazing how Bohr could predict things. Some predictions were right and some were wrong, but on the whole there was quite a number which were right, how he could predict them in Los Alamos on his drop model. Not everything was right, but on the whole it was useful. This one thing.
Secondly, there were untold new isotopes that came about-sane new things that one could see.
Then the possibility of having colossal steady neutron sources through the reactors.
So it made a very important contribution.
When the period at Los Alamos was coming to an end, when it was apparent that people would be going back to civilian life, were they planning a new program for nuclear physics? What did people have in mind to do? What did they think was possible now? What did they want to do?
I think it was very clear what people wanted to do. At least I remember my own case fairly well. When I came back the first thing I wanted to do was to change the half- life of the substances, because I had interrupted that work before. That was my luck because when Miss Wu and I started to work on it in 1940, we did not know beryllium was poisonous. If we had not been interrupted by the war, we probably would have poisoned ourselves. When I resumed the work in '46, I knew the dangers. (Side Two of Tape)
So that was one of the things I wanted to do, and I had been interrupted in 1940.
Then there were things started in Los Alamos which we wanted to keep on doing. And then at that time there was the delusion that if one could measure proton- proton scattering at high energy, one would make very substantial progress in the understanding of nuclear forces. And so there was a great effort to make neutron proton and proton-proton scattering; and as soon as the machines were able to do it, we started doing that.
Then the mesons came.
You started producing them artificially.
In '48, the artificial mesons. At first there were the cosmic ray mesons in '47 and then the artificial mesons in '48.
Let's just use this point to backtrack a minute on the original Yukawa idea of nuclear forces in 1935 and the subsequent discovery of the mu meson, as it's known now, by Anderson I guess in '36-'37. What effect did this have? This is another question, I know, its nuclear forces and its higher energies through cosmic rays. But what effect, if any, did this have on your thinking prior to the war?
It wasn't your field, I know.
Not much, not much. But not many people....people were working a little on mesons. But of course the big thing there happened in '46 or '47 when it was found that there was a mu meson, that the mu meson was not the one of Yukawa; and this is something I would like you to find out I tried very hard, repeatedly, to find out from Yukawa what were his reactions when it was found that the cosmic- ray mesons were not what he predicted.
It seems there was some writing by Tomanaga and others in the war period in Japan, that had already been speculating, that the mesotron was not the predicted particle. This speculation had started in the early '40's.
But as speculation maybe—I don't know.
Suggestions. I don't know how serious it was.
But it was proved by Piccioni and Conversi. It was proved that the mu mesons of cosmic rays, the mu mesons are not the Yukawa mesotrons—whatever you want to call them—the particle. And the Yukawa particle was found a few months later. There must have been about half a year— something like this. Now, I would like to know what were the thoughts of Yukawa in that half a year, but I have not been able to find out. Put it in your May conference and see if somebody knows.
Yes. We might be able to find it out at this point.
I wrote Yukawa and he didn't answer, and I asked through Morita, "Please answer", and I never got an answer.
Why were you trying to find out?
Well, Yukawa first makes the prediction on 'the particle. Then the particle is found in cosmic rays. So he must have felt pretty fine—I mean that's all right. Then it is proved that the particle of the mass predicted by him, is not his meson. Now, what must he have thought?
Oh, before Powell's discovery. I see.
That's right. In the interim.
Yes, that's very interesting. I see your point. I'm sure that there's an answer. We'll follow it up. I interrupted you.
There are two mysteries in nuclear physics. This is one: what Yukawa thought at that time. The other is why people didn't discover fission earlier. This is another mystery.
There is something that people generally cite about the way they treated....
The mass-defect curves.
Well, develop that and then I'll tell you what I was thinking of—the way they treated their sources experimentally. They always seemed to be blocking off.
Yes, that's, true. They were blocking them off. But if somebody had thought that there was fission, he wouldn't have blocked them off. Now, why was Ida Noddack so totally rejected by everybody?
Yes, that's a good question because it may have been some sort of a matter of taste involved.
I'll tell you. It's a question for which there is no answer because I asked Fermi and he was very cagey. At least I couldn't elicit any clear answer from him. "Why didn't you think of fission? When you read Ida Noddack—what were you, asleep?" As far as I am concerned, personally, I would say I was too stupid, which is not an answer. It begs the question.
In some of our interviews we've come across other people who have asked the same questions. Why didn't they do it, because they were doing it and they didn't know they were doing it. They were close to it and it didn't occur to them at all. The answer may be just that. It just didn't occur to them.
Yes, but we had been told. We had read a paper and there's no denying of this. You see, these are not fools. Hahn and Meitner were no fools, and Fermi wasn't a fool, and Curie and Joliot were no fools—especially Curie-Joliot who were people who tried everything á la Faraday. They were willing to try anything.
It's a selective filtration of information. For some reason this was screened out.
You were saying, on the period after the war, that one of the important events was the artificial production of mesons in 1948, around that time. You were talking about the types of scattering that people had in mind; this was just at the end of the war, and that when the machines became available, a lot of people went into that. How much of this desire for new types of scattering was caused by the realization that it might be easier to get higher energies now because of more money for research, more organized teams...?
No, I think that the idea was this. At low energies up to so many MeV, you see only s-wave scattering. Now, out of s-wave scattering, one can prove that one can get only the information which is summarized by the scattering length and the effective range—two numbers. These two numbers were approximately known, fairly close. One knew that they were the same for neutron and proton, so one knew the charge—independence of nuclear forces. One knew a lot of things.
But what one really wanted was not these two numbers only, but a precise, functional description of the neutron-proton or the proton proton potential.
And one thought that if you can see not only the s-wave but also the p-wave, the d-wave, and so on, you might get this information.
I remember quite clearly, for instance, that people said, "Oh, as soon as we know the p-wave, we know everything. All the problems of nuclear physics are solved."
Of course, as soon as the p-wave was seen, well, one couldn't understand anything. The next thing was that one had also to see the d-wave. By now we still have to see the h-wave or thereabout, but the problem has changed. We know that we are not going to get a simple answer such as a potential. But there was this feeling at the end of the war.
Also, they would say, "If it is a Majorana force, or if it is a Wigner force, or if it is a Heisenberg force, it would do this" or "it would do that", and so on. There were all kinds of theories so there was great effort to get this information which was thought to be very funda- mental—and it proved not to be.
Well, this is then a whole shift of emphasis of people who previously were not interested in nuclear forces, now in this period became interested. Is this true, that people began to be more interested in nuclear forces...?
Well, people were interested before. But one thought that one now had the way of attacking the problem. You may be interested in something, but if you don't know how to do it, your interest is platonic. And they thought now: "We know how to do it." There were the bigger accelerators.
In fact, at that time at the end of the war, there were drawn up programs which I think I could still find—and they're written—in which the high-falutin' theoreticians, would tell what were the things of central interest to physics.
At Los Alamos?
Los Alamos, here and everywhere. There are reports of that type. They're a lot of nonsense. It showed that these people really don't know very much. When you ask these questions of the theoreticians, unless they are Einstein, which is another story, but the pretty good, run-of-the-mill good theoreticians, they are very parochial. They say, "Well, you have to know the triplet scattering in proton-proton and then you will know everything. Which is not true, of course.
But many of the somewhat ignorant experimentalists believed them. The more ignorant they are, the more they believe the theoretician. Then they go and do that kind of thing, which is useful of course, but then they find....
It's not the answer. Now, how can you characterize the change in the machine work and the work with detectors here after the war?
Oh, there were several very substantial changes. The first big change was the invention of the phase stability, which really permitted to make machines not by brute force but by a trick. This is the idea on machines which really turned the tide.
McMillan and Veksler. And on the other side, money became available so that you could do things... I remember that before the war, the facilities, except for the cyclotron, which is a big exception, and except for the machines and the sources which were extraordinary, the detection facilities in Berkeley were no better, not to say worse, than in Rome or in Palermo—or comparable. And after the war, of course, money was plentiful; so one could do and one could have help.
Well, what money went to solve the detection problem before the war? In detectors themselves. One needed electronics...
The electronics? The radar?
The scaling circuits and the integrating circuits and the amplifiers, and so on.
But these all came after the war.
Yes, so the problem before the war was not money. It was technology so far as detection goes.
No, it was a combination because, say, before the war, if I would have had, say, a couple of good technicians with some skill in the electronics, which existed at that time— it was the tail of the Depression—plus, say, $10,000 a year to spend, you would have seen—I don't know what, but something you would have seen.
Yes, I see the point there. It was a question of insufficient finances to take advantage of the existing technology before the war. There was a certain level of technology which was not being utilized. This is the point you're making.
That's right. I mean we were at the point then that when we wanted to bombard uranium to make plutonium — that was a pretty important thing — I had to write Fermi, "Send me the uranium because the Radiation Laboratory can't buy a bottle of uranium to irradiate". And every single penny that could be scrounged in any way, from salaries or anything else, went to make a bigger and better cyclotron in a way in which you have no idea. I mean we used to laugh and say, "Well, now, look, if we don't get any detector, we make one micron more of pole/piece. We add one micron to the diameter of the cyclotron.
Was this a widespread feeling here?
I had it, I don't know about the others.
But it was deeply felt.
For instance, to get a little detector, we had to go to chemistry.
I had another question on another change after the war. How did the style of research change? We've talked of the machines, the detectors, and the money, and the problems to be tackled. We discussed that. But was there any significant change in the style of research, the patterns of communication, the idea of working...?
Well, there was also this: quite a number of very good students coming with the G.I. Bill of Rights, who had had previous training in electronics or in technical things in the Army or Navy, so that they could help on research immediately...I can remember quite a number of them in Los Alamos, in Oak Ridge, and so on. So you got a number of students who were much more mature, technically, than before, much more proficient. They were older and they knew more technically and were very seriously motivated and so it was a pretty good time.
And so you had them as a cadre here.
Yes. Well, I mean, in other words, a student now— you have to teach him everything. They know theory but they don't know anything practical. And at the end of the war, they were pretty well prepared.
How did these people fit in? How were they used?
They were graduate students. They wrote their theses. Say, for instance, Herb York was my student. He had been working at Oak Ridge and was very proficient, and he came to me with a problem—proton-proton scattering. We worked together. And Clyde Wiegand had been with me at Los Alamos as an electronics engineer, technician, whatever you want, and he was quite an expert. He was as much of an expert as anybody else in my group.
So the war, either through Los Alamos, through the Radiation Laboratory, or through just the plain Army, provided a place for these people to serve an apprenticeship.
Yes. Even the plain Army.
This is a new thing. I don't think this has been pointed out before.
How about teaching after the war? Was there any change in that?
Not particularly. Except that because of the G.I. Bill of Rights there was some crowding in the classes and very seriously motivated students.
Would you characterize the research interests and the accomplishments in the period, let's say, before 1955- in that decade from the end of the war to before 1955—in the same way that you characterized it just before the war In terms of your own interests, what were the characteristics?
At that time I did high-energy nuclear physics essentially. At the end of the war, I did a sort of rounding up and finishing of nuclear physics, like the change of the half-life, the spontaneous fission and things of that type. Then we started systematically this neutron- proton, proton-proton scattering.
Which is high-energy physics already.
Which is high-energy physics. It's already high-energy physics.
When did you start that?
As soon as the cyclotron started to work.
I think the paper with Serber and others, the 184-inch—I think that paper was in 1947.
Yes, it was the end of '46 and '47.
Then everything is of a pattern from then on?
From then on, until the Bevatron starts to work, you see. This is a big project. This neutron-proton, proton-proton scattering was a colossal project which lasted from '48 to '54—six, seven years—and it's still going on. It's still going on all over the world now. We were the first to do it because we were the first to have the machine. But they keep on doing it at CERN, at Brookhaven, at Dubna and with more detail, more precision, polarized targets and so on. This is a problem that will go on for God knows how long.
And then we made the antiproton work. But then, after the antiproton, the Bevatron here was superseded by other accelerators, so we cannot do antiprotons now here. We are inferior as far as sources.
And so we went back to do a type of physics which to me has always appealed—namely, experiments which are important to decide some points of theory. For instance, the beta decay of the pi+, which was done. It was not done by me, but it was done by people in my group. I don't work with my hands anymore now, but I get Wiegand and these other people who do the work. So we had taken rather various subjects in particle physics, which have a purpose, not just to measure because we want to measure, but for which there is a reason to measure, and try to do it.
But the choices are limited by the capabilities of the machines.
By the techniques, the capabilities of the machine, the techniques we have, and also try to find something which is interesting, a combination of all these things.
Would you say in any sense that nuclear physics is a closed field, and if so, when for you did it become closed? When did the problems lose interest for you?
Well, let me put it so: At the end of the war, when the particles—mesons and so on—were obviously imminent, it was clear that those would present a greater field of interest than nuclear physics. This was clear.
Now, when nuclear physics closed (I don't think it is completely closed now)...but it has come to a point at which you know a tremendous amount of stuff. You have these models. You can predict pretty well with these models what's going to happen to a nucleus that you don't know—where the levels will be and so on. There are many elegant problems. But it is, I have the feeling, at the end—like spectroscopy somewhat.
Yet there's great excitement, is there not, over the theory of nuclear matter, the work that was started by Brueckner and carried on by Bethe and other people?
It depends who you are.
Well, this is one line of...
Who has the great excitement about it? I don't.
I anticipated that response. Let me ask this question, though...
I would say the last really very startling thing that happened in nuclear physics are the orbits—the Jensen and Mayer—and the collective model of Bohr, the last two. Of course by this I don't mean the non-conservation of parity in beta decay—that's another story. But that is mixed. You see, it's not all nuclear physics. It's in part particle physics; in part, nuclear physics. The interest there is not so much in the nuclear aspects as in the interaction, the beta interaction. And the fact that you do it in cobalt is almost an accident. I mean you would prefer very much, if you could, to do it with the neutron or to do it with the mu meson and not in cobalt It's an accident to do it in cobalt.
That's a question I was going to ask. That's one answer to the question. That is, on the interaction between particle physics and nuclear physics, are there any other evidences of ways in which particle physics has brought new insights to nuclear physics or vice versa?
This non-conservation of parity is a big thing because it is probably the major development of physics after the war, and there both nuclear and particle physics have interacted. Then there are of course innumerable techniques which come from both.
Do they generally start at the higher energies and then become adapted for use at lower energies or is it the other way around?
Both. For instance, the germanium solid-state detectors start at low energy and go up. And the rapid electronics is going from high energy down. It depends.
Are there any groups of people who are sort of brokers between the two fields, people who try to keep a foot in each?
They are developing now. It's a recent development, but of course it is very very difficult because the fields have become so intricate and so complicated. It's extremely difficult for a poor guy to keep up with one field, and to read in both is impossible.
When did this begin to change, where it was necessary to have a full time involvement in a field in order to do any work in it? In the earlier period you could work in several fields, and you could know all the physics. But this more recent period...
Well, I would say the last person who knew all of physics was Fermi, maybe Bethe. But no, because he doesn't know particle physics. So I would say the last person who knew all the physics of his day was Fermi.
Let's ask a hypothetical question. Could a Fermi still maintain his reputation today?
This is a question that has been asked many times, and I don't know. You see, you'd have to resus citate him. I would be very curious to see what would happen.
Let's just take the question of techniques. I know it's difficult to answer in general, but in techniques comparing the Fermi trolley, let's say, and other devices and other approaches to developing techniques to the techniques that are required now, the types of electronics. It seems to me that....
No, that is quite how you handle that. You just get people to handle those things. You don't do everything by yourself, that's all.
Do you feel that Fermi would have adapted to this style?
I don't know. But either he adapts or he stops doing experiments.
I think the question is meant not so much as an "if" question, but the historical contrast between the styles today—whether, in fact, physics...
Well, you see, already at the time of Fermi, Fermi didn't push the buttons on the accelerator.
No, he told someone.
He told somebody.
How much of the development of the new techniques, of the giant machines and the investment in them in terms of staff and finances, determined the types of questions that are asked in physics and the types of research? Is there less flexibility today or more?
Well, you see, there's this. First of all, any experiment lasts a year or two—something like that. So you can't do physics à la Faraday. So if he had to do them in high-energy physics at one year apiece, it would have been quite a problem. So there's no question about that. This is something terrible, but it is inescapable.
Somebody has clearly identified for us the idea that at one time experimental physics was done by building apparatus for one experiment only and then disassembling it after the experiment was over. Now you have a machine into which a great deal has gone. The machine exists. You don't disassemble it afterwards. And to some extent, because the machine exists, you tend to play the machine out.
You can't make this a general rule, because for instance, physics was made by building a spectroscope. You didn't disassemble a spectroscope once you had made it. Rowland [Henry A.] ruled his grating, and having ruled the grating, he increased the resolving power and kept on finding all kinds of things in the spectra that nobody has seen before him. Galileo made the telescope and found all kinds of things. He didn't disassemble it.
He just turned it to new applications. But the question is: are these instruments that are being developed today as flexible and as available for a wide variety of applications as these earlier instruments that you mentioned?
The problem is this: that when you have an instru- ment, like, say, a Rowland grating—Rowland rules his own grating and then he can play with it for 20 years and make discoveries. He can rule five, six and he gives them all over the world to a few friends, and they can keep on working with those. In fact, I remember quite well that when I was in Zeeman's laboratory, the instrument was a grating that was a gift of Rowland to Zeeman, and this was still the thing. But this grating, all you had to do was focus it and take a picture, and that was it. But this was the instrument.
The trouble is that now when you want to make an experiment, it takes a year instead of a day and it costs millions or hundreds of thousands. This makes all kinds of problems. First of all, there is a great temptation to make experiments which are sure. So you measure something, and of course when you are sure that you measure something, it's also improbable that you make a discovery because already you know what you want to measure. It's not quite sure that you don't make a discovery, but it makes it more difficult to make a discovery.
Secondly, it takes so long that a person can make in his scientific life maybe five, six, seven experiments; whereas Faraday made 14,000. Now, suppose you are as good as Faraday. Faraday made 14,000 and say, he probably made 14 big discoveries. So it was one in a thousand. If you go on a big machine and you are as good as Faraday, you make only 20 experiments, so, you see, no discovery.
We've been going a long time, so I'll ask a few more questions, if you have the patience, and then I think we'll take it to the end of this stage. What I'd like to review for a minute is the whole idea of when the machines really became effective as far as contributing to the knowledge of nuclear physics. The implication was that perhaps they were getting to be effective just before the war and then really came into their own after the war. Is this what you were saying before?
Which machine are you speaking of?
I mean in general.
No. Cockcroft-Walton and so on—they were effective much longer, much longer.
All machines of course in that sense were effective, but let's say the large accelerators—the cyclotron and then from that the whole generation of accelerators.
No, no, but, you see, the Cockcroft-Waltons were effective as soon as built because they were built in Rutherford's laboratory where the interest was physics. It was not machines. It's a peculiar development...Also, I think the Pasadena accelerator must have been useful earlier than the Berkeley ones.
Well, Lauritsen [Charles C.] was getting results. It was not used as an accelerator until after Cockcroft-Walton; in other words, about 1932. But then they used the tube as an accelerator, and they were getting a lot of results in '32, '33.
Yes. The Berkeley cyclotron...The first important things that I can remember of the Berkeley cyclotron that today are still of some significance is probably my work on technetium done in Palermo in '37, and then the measurement of the magnetic moment of the neutron by Alvarez and Bloch must have been '39, '40. The discovery of Carbon-14 must be later than that. It was also before the war, though.
These are the types of things—I see. Another question. You mentioned about the change of interest and the desire to study nuclear forces at the end of the war when it became apparent that one could do so effectively. And this led then, with the development of higher energies, to the whole breaking away from nuclear physics. Now, in this period, how can this change be reflected in the motivations of people going into physics? In other words, someone coming into physics after the war is coming into a new kind of physics with new kinds of problems. Did these people, though, generally have the same motivations and interest in the same general types of problems?
I don't know. If you speak to the graduate students, they are unbelievably snobbish nowadays. They're very strange, at least to me. You see, they say, "Well, fission is not fundamental. Poof! It's not worth my attention." My reaction would be: "If I could discover fission, I would be more than glad to do it." But if you ask any new graduate student, he will tell you that it's not fundamental enough.
What does that mean in this case? What is he interested in?
They are all interested in getting the Nobel Prize, and they have the idea that if they study something fundamental enough, they get it and otherwise not. This is rather a cynical view, but there is some truth in it.
And "fundamental" in their view would lie in the field of particle physics?
Fundamental means something that makes them famous.
That's a rather restricted meaning on it.
Fundamental in the sense of understanding the structure of matter? Fundamental in the sense of theory?
Frankly, I don't know. When you speak of fundamental… This may be too cynical. But I think by fundamental, they mean applause from the listeners.
That was the sense of your reply before. I think the point was that people feel that you're more apt to get applause in certain fields than in others.
There is a great deal of fashion, snobbism and so on until somebody who is really a good physicist makes a discovery and changes the fashion.
Let me ask you a personal question. On reflecting on your own work, what do you feel has been the most significant work that you've done?
The discovery of the new elements.
The discovery of the new elements. Is this in terms of its impact on physics or in terms of the satis faction which you got out of it?
Oh, the question of satisfaction is something quite different. Satisfaction, for instance, depends on very personal questions. For instance, I can remember with tremendous satisfaction when I separated the nuclear isomers by chemical means because I thought of this and I could do it in two days. Now when I say this, of course, I didn't even mention the slow neutrons, because I think probably the slow neutrons are not mine, but are Fermi's. Otherwise you should put the slow neutrons in it.
What about the antiproton?
The antiproton is a very interesting thing, but, you see, the new elements—this is now quite personal—is something done at the bottom of Sicily by myself and only myself with very small means. The antiproton I had behind myself a Bevatron, lots of people helping, a strong presumption that it would be there; so it's a technical achievement, a respectable technical achievement—I don't say no.
The antiproton work is sometimes cited as one of the reasons that the Bevatron was built.
Well, I think that's a very great exaggeration.
One of the reasons. That was one of the first experiments that people planned for the machine.
When the machine was built, one could calculate the threshold for forming antiprotons, and so since one had to decide on an energy, one said, "All right, let's go above the threshold." I think this is all that you can say for the Bevatron being built for the antiproton.
Historically, what was the significance of the discovery of the antiproton? Was it a psychological relief to know it was there? Did it validate Dirac's theories?
It went much beyond validating the Dirac theory. First of all, it was said that it was there. But, say, Maurice Goldhaber lost $500 on a bet. So I mean he was willing to bet $500 that it wasn't there.
Secondly, it goes much beyond because you can't say that the proton obeys the Dirac equation by any stretch of the imagination. It has an anamolous magnetic moment and so on.
Nowadays—we didn't know it ten years ago—we know a very complex structure. And so it really means, if you can make an antiproton, symmetry, not only in electro- magnetic interactions but also in the strong interactions in the weak interactions, in everything else, in all the other particles that you can make that are connected with the proton and so on.
I see. You don't have that with the positron.
No, the positron is strictly a Dirac particle. Nor with the muon. The proton is really a much more stringent and severe test of invariance under charge conjugation. And of course, when you have a sneaking suspicion that such an object may exist for 25 years and you haven't seen it in cosmic rays, having looked for 25 years, well, you better be sure it is there once you can see it, because it's a very very fundamental question. If the antiproton had not been there, if one could prove that there is no antiproton, then the whole theory of physics would completely change.
Is that an example, is your work on the antiproton an example, of what you said was your taste and the type of work you like to do—to choose an experiment that is crucial to a particular theory? Was that the motivation in that case?
You could say that, yes.
You characterized your present style of work and your present interests in recent years as that.
To a certain extent, yes. You can say, yes.
Will you say it, though? Was that the factor present? Did that factor play any role in it?
Well, it was obviously a very important thing to do. We thought we knew how to do it, so we tried.
And yet in terms of the personal satisfaction, you found the discovery of the new elements and the one...
Well, lots of things. I mean, say, I was tremendously delighted when I found the Zeeman effect of the quadropole lines, spectral lines, shortly after I had my doctorate. In other words, if you say, "Well, all right. I think now I really understand how this damn thing works. And if it does, it has to do something very strange." Then you try it, and, sure enough, it does it. This is essentially the idea.
It's neatly tied up.
Well, like, say, the change of a half-life of a radioactive substance. It's written in all the books—it was written—that you cannot change it—"It's impossible to change the half-life..." All right, now you really understand how beta-decay works. If it works according to the way they say it does, it should change. Let's try it. It changes.
Now, this is not the finest kind of physics. I mean certainly this is not Einstein. But I don't have Einstein's brain.
This is the real guts of physics, the feeling of confidence in knowing that...
No, you see, Einstein thinks of extra super things. So does Rutherford. But I am neither Einstein nor Rutherford.
This reminds me of a question I think we forgot to ask about two hours ago. Maybe it could be the last question. When Fermi was a very young man, he entered a concorso through, I believe, the University of Cagliari, and he was not accepted, and the story is told that it was because of all the professors, there were only Levi-Civita and Volterra who were "Einsteinian" or who were modern physicists in that sense. Is that an apocryphal story or is it true?
The story is this: The professors at that time were Levi-Civita, Volterra, Somigliana, Marcolongo and Guglielmo. Now, Levi-Civita and Volterra were famous mathematicians, first-class people who knew what they were saying and doing. Guglielmo was a poor man coming from Sardinia, had never come out of Cagliari all his life. The only thing he did was to hide thousand-lire bills in the books of the library so that when he died, the next professor started to find, once in a while, a thousand-lire bill.
Somigliana was a man who in his youth had done important things. He lived to be over 90; he was a descendant of Alessandro Volta. But by the age of 60 or 70, he had gone to a conservatism in physics which was completely pathologic. He hated anything done after 1880. He said science was finished in 1880 or 1890—I don't know, some- thing like this. He didn't know anything of the more modern things. And he had done important work. I mean the formulas of Somigliana are quite famous, but he had done them 40 years before. And the fifth man was Marcolongo, who was essentially a nonentity.
So they divided two against three. And also they did put Fermi in second place. They didn't leave him completely out, but they put him in second place, and this prevented him from getting the job. They took a much senior man. Fermi used to tell me this story, that what happened was this: Volterra and Levi-Civita said, "Well, Fermi is obviously the better man. There's no question."
The other guy said, "Oh no. This is all fashion, it will change next year. This is all nonsense and so on."
And so they split two and two, and the poor Guglielmo, from Sardinia, said, "Well, I don't understand anything, neither one side nor the other. I go by seniority. Giorgi is older. I vote for Giorgi." And this is what happened.
The institution of the concorso has certain resemblances to, say, the graduate record exam or something of this sort.
Well, like an entrance examination or like an examination for a position. I think there are some institutions in the United States that are similar. You take an exam...
The concorso is not an exam. You never see your judges. You send your papers in.
Right. You don't answer questions, but you apply and they judge your work.
Who were your competition when you applied for the University of Palermo?
First, I made another competition for Ferrara, I believe. The first winner was a man by the name of Specchia. I do not remember the second. Both were mediocrities. The third was very good—Bruno Rossi. And I was left out in the cold. Fermi was one of the judges, but Fermi was the most impartial man that there is in this world. If you were his friend, you were in danger, because he was so afraid of not being impartial that there was nothing to be done. Anyway, I had no quarrel with the choice of Rossi. The other two were just nincompoops, but the other had the votes, and they said, "There's no question. We want two, and then you can put one of your young people." And the judges were: Majorana, the uncle of Ettore Majorana, Puccianti, Fermi, Pochettino, and I can't remember the fifth. Corbino—I was told by the daughter of Corbino that she found in the archives a stinging letter that Corbino wrote to Majorana saying, "What kind of things were they up to choosing these people and not the people who knew some physics?" But I didn't know it at that time.
What archives was this?
The private archives of Corbino.
I wanted to ask about him. He seems like a fascinating man.
The two instances that you cited he speech in 1934 and the other one in 1931—these are amazing, showed great wisdom.
Corbino was a very great man.
Has anyone treated him biographically in any sense? By this I mean not a full-scale biography, but some articles?
Yes, in the life of Fermi, I put down two or three pages on Corbino. But I went to see, his brother. I didn't know Corbino very well. I knew him from far away because he was a very important man, and I was a very young guy. But I have now learned a little more from his brother and from the archives that his daughter has and so on. It's a very strange story. It reminds occasionally of the "Gattopardo" by Lampedusa. The father of Corbino was just about to become a priest when he ran away with Garibaldi in Sicily. And then he came back after seven or eight years on the continent, married a girl who was of a good family, moderately well-to-do, and then they had seven children. I think the third or fourth was Corbino, the physicist. The wife, the mother of Corbino, didn't know how to read and write because women didn't learn how to read and write in Sicily in 1870. But when she was about 50, she decided—by that time the son was a professor—that it was a scandal that the mother of a professor wouldn't know how to read and write, so she learned by herself out of newspapers.
And then there are all the stories about Corbino. Corbino was educated first in a seminary. A bishop wanted to make a priest out of him, but he got out of this when he was 11 or 12, very young. He went to his mother and said, "I don't want to stay in the seminary anymore."
The father, who had studied for the priesthood and had still an attachment, wanted...But the mother defended him. So he came out. And then he studied absolutely as a prodigy. He came out of school very very fast, very early, but always poor.
And then, through a relative of his—it's a complicated story—he landed in Palermo as a student. And there very young—he was probably 21, 22—he discovered the Macaluso Corbino effect, which was an important thing, the anomalous rotation of the plane of polarization of light, which made him fairly famous. He was still a high school teacher for several years, and then finally in 1904, he won not one but two concorsi—one for physics and one for electrical engineering. He was in Messina for four years until the earthquake came and destroyed everything. He escaped miraculously.
By that time, the professor in Rome, who was Blaserna, an old gentleman from northern Italy, rumored to be the lover of the queen mother of Italy and certainly the president of the Senate of Italy, decided he needed some young men there because he didn't know enough physics to be director of the institute and got him to Rome in 1908.
As soon as he arrived in Rome, he worked very fast. He was brought in as a consultant in some engineering things. And so very rapidly he had a dual interest in science and in affairs—in economics. Then he became a consultant of big industrial firms—of General Electric. If General Electric wanted to make an investment in Italy, they consulted him.
In 1920 he became Minister of Public Works, I think, or of National Economics in the Cabinet of Bonomi and became a Senator. He was appointed Senator by the King. And then Minister of Education. And then he wrote an article on the "Anti-Industrial Spirit of Italy", which is very interesting.
Then Mussolini was looking for a minister of industry in his first government. And somebody—I don't remember who—told Mussolini, "Well, you should read this article." And Mussolini read it and said, "This is my minister then." And he became a minister of Mussolini, but he never became a member of the Fascist party. Thus, Corbino was a minister of Mussolini without being a member of the Fascist party. Then he was fired by Mussolini, and then there were lots of things.
When did he die?
In '37. He died very young.
I didn't know you had all this information, but you have included it, I guess, in the Fermi biography.
Yes, I had put it in the biography. Corbino is really a very interesting man—in many ways one of the most interesting people. If I knew really how to do it, and I had the information and so on, I would be delighted to see a life of Corbino written.
It might be good to have a translation made of that 1930 or '31 article.
If you want, I'll give you all the references.
I'd like to borrow a copy and Xerox it and return it to you or ask you to do it some time. Perhaps it's safer that way.
Methods of mathematical Physics.
La Vita E L'Opera di Ettore Majorana 1906-1938 (Accademia dei Lincei, Rome, 1966).
Ernest Rutherford, James Chadwick & C.D. Ellis, op. cit. (Cambridge University Press, Cambridge, 1930).
Remark appears in Quantum Physics transcript, p.18; not Rev, Mod. Phys..
Otto Frisch. See pp. 37-38 this transcript.
The name was given by Perrier and myself after the war in 1946.
* Ida Noddack, Angewandte Chemie 47, 653 (1934).
Faraday made 14,000-odd experiments in his life.
Reprints in Segrè's File.
"Biographical Introduction", E. Segrè; The Collected Papers of Enrico Fermi, Vol. I, University of Chicago Press, 1962.