Interview with Edoardo Amaldi by Charles Weiner in Florence, Italy April 9, 10, 1969

Transcript

Weiner:

This is an interview with Professor Edoardo Amaldi, and this is Charles Weiner asking some questions. We are sitting in a hotel room in Florence, and the date is April 9th, 1969. started in our conversation this morning, when the machine wasn't working, to talk about the sorts of questions that we thought might be of interest. The idea is not to duplicate what Professor Kuhn discussed but to supplement and then to extend it to a later period. But I would like to go back to the beginning in this case, because we know very little--about your early family background. I know that your father was a mathematician. He was professor of mathematics at Padua from 1918 to 1924.

Amaldi:

Yes and later in Rome.

Weiner:

I want to know a little bit about your early family life and how you got interested in scientific things--where you went to school prior to your study of engineering at Rome.

Amaldi:

Well, I was very much interested in physics when I was a high school student, and I was always interested, as you say, in mathematics and physics; and I wanted to study physics. And when I finished my high school, my family went for a summer to a village in the Dolomites; and I was with my family for vacation. This village was San Vito d'Catlore, and in this village Fermi was also on vacation. This was the summer of 1924, I believe. Fermi was very young; he was 23 or 24 years old. A friend of his had come to the same place. That was R. De L. Kronig who is now professor in Groningen. Kronig was a great friend of Fermi. They met when Fermi had been in the Netherlands to work with Ehrenfest. You know that he had been in Leyden with Ehrenfest for some time. He had met Kronig there, and so Kronig went to San Vito d'Catlore to spend his summer. They were quite young, but they were both quite good physicists already. I knew almost nothing. But in that summer I was extremely impressed by these two yo - people, and when they were hiking in the mountains, I started to follow them trying to learn something about what they were saying. I did not learn very much, because the type of conversation was too difficult for me. But certainly I was very much impressed by the personalities of Fermi and Kronig and the type of conversation they were doing.

Weiner:

You had no contact with them before. This was just coincidence that they were there?

Amaldi:

Well, it was partly coincidence, because my father went there because there were other mathematicians going to the same place. There was Guido Castelnuovo, who was later one of my professors, a well-known mathematician; and there was Enrico Bombiani, another mathematician; and, if I remember correctly, there was also Levi-Civita. My father was a great friend of Levi-Civita and they had written together a treatise on mechanics. Fermi also came there for completely different reasons, but in a certain sense there was also some connection. I had never seen Fermi before, and one could also say that it was an accident. It could have been that I did not come with my family, since usually I went for vacation by myself. I was very much interested in climbing mountains and at that time I created troubles for my family by climbing too difficult mountains. Usually I wanted to go by myself in order to be able to do what I wanted. But that summer I went with my family to San Vito.

Weiner:

Was it then that you made the decision to study physics?

Amaldi:

I was already interested, but that certainly made a tremendous impression to me--I should say that I met Segrè because I was very interested in climbing mountains. Segrè was already a student of engineering; he was a few years older than me. With him and with Ciaranti, who is now a well-known professor of medicine, we went to Grakasso d'Italia in Central Italy to climb the Corno Piccolo We were living for a few days in a mountain hut and there we were talking and discussing a lot because both Segrè and I were interested in physics. He had decided to start engineering, because it was not clear if it was possible to do a career in physics in Italy at that time. For similar reasons I also enrolled in engineering. I remember quite clearly that I said to myself, "Well, it does not make any harm," because in Italy at that time the first two years were exactly the same. There were only very minor differences. There was one extra laboratory for physicists, and there was a design course for engineers. So I had to do this engineering drawing course, and I followed the laboratory that was made for physicists since it was allowed to choose also this course. But I was not happy to be an engineer. Later it was very simple for me to change from engineering to physics.

Weiner:

You mentioned that you met Segrè. Under what circumstances did you meet him?

Amaldi:

Oh, he was a friend of Giovanni Enriques, who was the son of a mathematician and was a great friend of mine. So we had a common friend.

Weiner:

So it had to do again with your father's connections in a sense.

Amaldi:

In a certain sense. Giovanni Enriques and I had also been climbing mountains together.

Weiner:

I see. Now getting back to what you were saying, you didn't lose any time because of studying engineering.

Amaldi:

Yes. Well, Segrè lost some time because he went on studying engineering up to the fourth year. And the third and the fourth years in engineering are completely different from physics. So he had actually lost some time. I had not.

Weiner:

When did you make the switch? Was it after the second year?

Amaldi:

At the end of the second year. I used to go to the lectures of Corbino. The course which I give now at the University of Rome was given at that time by Corbino Corbino was extremely brilliant. He gave beautiful lectures--very brilliant, very attractive, and making nice little jokes to explain things in a very clever way. One day towards the end of the second year, he gave a rather famous little speech saying, "Well, I think that if there are people that are ready to do a sufficient effort, this is the right moment to change from engineering to physics. We've arranged now to have Fermi come to Rome. Maybe you don't know who Fermi is, but I'm absolutely sure we have never had in Italy for many, many years a physicist of this class. He's very young and he knows what is modern physics. We old people don't know, but he knows what it is; and if you switch over, there'll be a lot of opportunity for very interesting work." This was a very simple invitation. I had been for two years so interested, but in a certain sense had not had the courage to do it. This was the occasion for deciding to make the change. So the next fall I enrolled in physics. It was very simple. had to go to the Secretariat of the university and simply say that I wanted to change from engineering to physics. At the same time Segrè made the same change. The only difference was that he had lost at least one year. How he changed is explained very well in the biography of Fermi that he has written. This biography I think is a very good one. All old friends read it before publication and gave suggestions for improvements.

Weiner:

The manuscript?

Amaldi:

We read it in manuscript a few times.

Weiner:

talking about a new one that Segrè is doing.

Amaldi:

I read also that. I've written a number of comments contained in many pages that I sent to him.

Weiner:

He's pretty near the end, I think. It's done, but...

Amaldi:

He told me that after I had written these comments he has practically written again almost everything. I've not seen the final version, but I received it in manuscript some time ago. I read it very carefully, and I commented. It was rather well done. I added some details that he did not know, and he told me he has incorporated this into the final ver- sion. I've done the same for this Majorana biography. I've written the biography in a preliminary form. I've sent it to all people who knew Majorana, including the members of his family, and I have collected information from all of them and comments and have added all that they knew, what they could recollect. So I've tried to do the best that can be done.

Weiner:

We were talking this morning about Corbino, and it might be a good time now to interrupt the continuity of your story and talk about him. You were telling me some interesting things about his family background in Sicily at...

Amaldi:

Augusta. He was born in Augusta. That is a little town not very far from Syracuse. His father had a small macaroni factory where the macaroni was homemade by Corbino and his family. There were seven children in the family, four boys and three girls. Two of the brothers, Mario and Epicarmo, both became professors at the university. Epicarmo, the younger brother, is still alive. He's a professor of economics at the University of Naples. When they were very young they were helped a lot by an older brother Leone who was a noncommissioned officer in the carabinieri. This man was apparently extremely intelligent, and he felt that the younger brothers were very gifted, and he helped them, and they had to study and try to learn, and that's what happened. Mario, too, was a very remarkable person, extremely intelligent and very much interested in science. Corbino was an assistant in Palermo and produced a lot of very good work.

The professor there at the time was Professor Damiano Maculuso, and an effect was discovered by Maculuso and Corbino It was at that time known as the Maculuso-Corbino effect. It was after the discovery by Zeeman of the Zeeman effect. And these in some way are related. It's a variant. Now it is quite clear that it's not a completely different phenomenon, but is something related to the Zeeman effect. About two years after Zeeman had discovered that the effect of the magnetic field--the split of the lines, the spectroscopic lines in the magnetic field--they measured the rotational power of a gas, for example, sodium, near a resonant line. And they found that the rotational power becomes extremely high--infinity--near an absorption line. And they measured this effect, and they discovered it and explained it very well; and this is related to the Zeeman effect. They are different aspects of the same phenomenon.

Weiner:

But he did this as a student?

Amaldi:

Well, of that I'm not so sure. It would be better for some of these details to look into the biographies. There are biographies of Corbino I will try to find some good biography of Corbino and send it to you. In that you would find more details about that. I think there is also a biography by Fermi of Corbino, but I should find out.

Weiner:

I just wanted to talk about that for a minute. But I'd like to get back now to your story. There's a lot of the story that I already know. But there are a few missing connections. For example, you were Fermi's assistant, but it's not clear how you became Fermi's assistant.

Amaldi:

No, I was never an assistant of Fermi. I was an assistant of Corbino actually, as also was Segrè. We were both assistants of Corbino. But when Corbino took us as assistants, he said, "The best thing that you can do is work with Fermi." But the situation was such that he [Fermi] couldn't take assistants. Fermi was much younger; it was not so simple; and Fermi had the chair of theoretical physics. So Wick was assistant of Fermi, not Segrè and myself. We were experimentalists. And also Rasetti was an assistant of Corbino. So we were all assistants of Corbino, but then we were working actually with Fermi, and Corbino was essentially taking care that we could do our work--that Fermi could do his work and that we could do our work under him.

Weiner:

So you went under his umbrella, so to speak.

Amaldi:

Oh, yes, certainly. All of us recognize that the action of Corbino has been essential to all the development of physics in Italy. There's no question.

Weiner:

This raises a question about Corbino's speech of declaration that there are two new fields of physics to go into--that spectroscopy is no longer going to be the field, and you have to think of the study of the nucleus and the study of large cells, living systems. This was the 1929 speech. And he even said in this speech that to do the study of the nucleus we need expensive equipment and big energies; and if this is not practical, then perhaps the living system and the cell itself. What interests me about this transition period is the fact that it was before the neutron, and it's not at all clear to me why Corbino and others felt that nuclear physics was the field where you would get results or where it would be fruitful. Do you have any feeling about that?

Amaldi:

Oh, yes. I remember very well that this was very much discussed at the Institute. And there is one page on that in my biography of Majorana, because really this idea of Corbino was also an idea of Fermi and certainly of all of us in the department of physics in Rome. I'm not able to say who started the first idea--whether it was Corbino or Fermi. But certainly this point--that it was very important to move to a new field, that spectroscopy was a very nice field but the exploratory work was in some way finished, that you had to move to something where the phenomena, the facts, were still unknown--it was very clear that this was urgent.

Weiner:

It hadn't anything to do with theory? In other words, the theory of spectra was known. So in a sense you were getting new facts, but they were predictable.

Amaldi:

Yes, yes. The idea was to look for new facts that were not predictable, and there was also need for new facts and new theories and so on.

Weiner:

I can understand how this would be the case with artificial radioactivity when you wanted to do a systematic study of it because there was no theory involved in it, and there was an opportunity to do experiments. You had the sources; you were tooled up; you had the special techniques that you had developed, all of you on various trips. And then with the discovery of artificial radioactivity, there was an opportunity to do systematic fact-gathering where there was no real theory accompanying it, where you would feel that it's very promising. I understand what one means by that, but I'm not clear how in the years prior to this anyone saw such an opportunity-in the years between 1929 when Corbino spoke and, let's say, even before the neutron, even before 1932. What facts can you gather?

Amaldi:

We actually started in 1931 to work in this direction and to shift our interest from atomic and molecular physics to nuclear physics. It's not clear to me what is your question.

Weiner:

In other words, what was so compelling?

Amaldi:

We started first with spectroscopy. The basic parts of spectroscopy were clear. There was the idea that with quantum mechanics, spectroscopy was a very important field but where you needed development of computational methods to compute the wave function and levels, but there was nothing basically new to be found. And the idea was too look for a field where there was something basically new.

Weiner:

So it was a combination of a negative feeling about spectroscopy...

Amaldi:

Well, negative in the sense that the exploratory work was finished. There was need for precision work and precision computation. That is beautiful but is not really new exploration.

Weiner:

You've discussed elsewhere the discussions that took place about the switch, but one of the things that interest me is the 1931 Rome meeting. That was a meeting on nuclear physics specifically. I gather that the idea was that to learn as much as you can about the subject, you call a meeting and bring in all the experts.

Amaldi:

Yes, a meeting was called, and I remember that Bohr was there, and Bohr was giving speeches explaining that probably it was necessary to renounce the principle of conservation of energy of the beta decay. He suggested that there was no conservation of energy and momentum. There was a number of discussions on this point. I remember that Millikan was there. I remember that Blackett was there and quite young, and Mott was there, slightly older but still very young.

Weiner:

The Curies were there.

Amaldi:

Many, many more people were there.

Weiner:

Goudsmit was there.

Amaldi:

Well, Goudsmit used to come to Rome almost every year. Goudsmit and Uhlenbeck were both great friends of Fermi, and they used to come to Rome almost every year for one month or so And so we used to see them quite often. They came also on their vacation. But the old Madame Curie was there, and Sommerfeld was there. There are a number of very nice pictures of this.

Weiner:

I have them.

Amaldi:

There are a number of very nice pictures of the people there.

Weiner:

Segrè gave us a set of pictures. You gave it to him, think.

Amaldi:

I gave them to him last October, guess.

Weiner:

That's right, and he let us copy some for our archives. This was earlier. Maybe there are more that you gave him.

Amaldi:

I gave him some more I think last September or October. We looked through them, and he said, "I'm interested in this and this and this, and then we had them copied.

Weiner:

The conference itself--let's get back to that. Was it mostly formal papers or were there a lot of informal discussions at the meeting? I think I've seen the formal proceedings.

Amaldi:

There was also a lot of discussion, of course. I was too young to take part in many of the discussions, so I was listening essentially. But I remember there was a lot of discussion. You have seen the people who were there?

Weiner:

Yes. I'm just curious: was it on the experimental side? I get the feeling that it must have been; in other words, that the emphasis...

Amaldi:

Was mainly on the experimental side. At that time there was also the theory of Gamow on the alpha decay, and that was the only sound piece of theory existing at that time on nuclei.

Weiner:

Gamow, as a matter of fact, was supposed to come to that meeting but couldn't, wasn't allowed to; and the people at the meeting sent him a greeting--a card--which he showed me.

Amaldi:

The theory of Gamow was one of the things that was discussed. It was generally accepted. It was considered a great success of quantum mechanics. And then Bohr was discussing very much the beta decay and the possibility to have to renounce the conservation of energy.

Weiner:

He apparently had been talking about that even earlier at the Faraday lecture that he gave in 1930. And in his correspondence it turns out that even after the neutron...The proceedings weren't published until after the neutron was discovered and when he corrected the proofs, he was still talking about the same thing. It's something that I'm trying to understand--why he didn't change his mind on that after the neutron. But let me go on to some of these trips that you took in the period, in particular in 1934 when you traveled to Cambridge. You went with Segrè, and your wife was pregnant at the time.

Amaldi:

Yes, our first child.

Weiner:

I'm just curious about your observations there--what you saw. There was Chadwick; there was Goldhaber.

Amaldi:

Oh, it was very nice. We went to the Cavendish. There was Cockcroft; there was Ellis; there was Oliphant, Goldhaber and Dee. And on that occasion in London we went to see Blackett at Birbeck College, and we met Szilard. Szilard was in London. And I remember that while we were there, the Solphus affair happened in Vienna. Solphus's murder was the first attempt of Germany to incorporate Austria. And I remember that we had a lot of conversation on that with Szilard. Then at Cavendish we met also some other people, like Bjerge, who was a Dane, and Westcott, who is now in Canada. He's mainly involved in nuclear energy, in reactor physics. And we were very much impressed by Rutherford, of course. He was an extremely impressive personality. But we were discussing a lot with Bjerge and Westcott because they were the only people at that moment working in Cambridge on neutrons.

This was just before the discovery of slow neutrons, but there was a very difficult problem. That is described in the book of Segrè, about the so called radiative capture of neutrons. It was very difficult to understand at that time how a neutron could be captured by a nucleus. Any estimate of the probability of such a process turned out at that time to be very small, much smaller than what was observed. When by bombardment of a nucleus with a neutron we had observed an isotope of the initial nucleus, it was the question to know--if it was a process of capture of the neutron, or a process of emission of a second neutron, a second neutron knocked out. And the proof that it was a capture of a neutron--at least with the neutron that we used at that time which was not of very high energy--came from a paper of Bjerge and Westcott and another paper of Segrè D'Agostino and myself. This was done in September. We had done this work when we came back from Cambridge.

Weiner:

How about Chadwick and Goldhaber? Were they doing anything on this?

Amaldi:

Oh, yes, they were doing this at that time, and we had some conversations with them, but they were very busy at that moment doing their experiments on the deuteron. And so we had some exchange but not so much as with Bjerge and Westcott. Of course, we met them, we had a conversation, and it was very interesting. u u

Weiner:

You had been thinking about this before you went. What was your reaction in coming from Italy? You had been in Leipzig before and then you were coming to the Cavendish for the first time. What was your reaction to the style of the research group? Did this in any way contrast with the sort of thing that you had been developing with Fermi and others in Rome?

Amaldi:

Well, I was very much impressed. But in a certain sense we felt much better...Well, I had been for one year in Leipzig working with Debye before, and Segrè had been in Hamburg working with Stern. And I don't know what was the comparison of Segrè, but I think it was the same as mine. We felt at Cavendish much more at home than at Leipzig. In Leipzig it was very happy. Debye was a very nice man, and I liked him very much, but the Cavendish was really a very, very attractive place. And we became great friends with Bainbridge from the United States. He was there working with Aston. Aston was rather old at the time, and Bainbridge was doing very good work with him. I remember that we became very good friends with him and his wife and enjoyed very much the company of the Bainbridges.

Weiner:

You spent the summer there. Your wife was pregnant...

Amaldi:

We had to come back, because my wife had to have the baby, and she wanted to have the baby in Italy, so we came back just before the baby was born.

Weiner:

There's a story that Segrè mentioned, that you knew it was time to go back when your wife could no longer fit between the posts on a certain street. That's how I knew about that. When you did this earlier traveling--you worked on X-rays, for example, for a while with Debye...

Amaldi:

I was working with the scattering of X-rays by liquids with Debye.

Weiner:

And then other people in the Rome group became involved with the Raman effect, for example. Now, how did these two things--this background-- influence the transition to nuclear physics? Was it work that was really used--for example, in the interpretation of the neutron, in the reaction to the neutron? How did the Raman effect work on the nitrogen 14 thing? Did this figure in it? Did it prepare you, or the group?

Amaldi:

Well, the work that you mention about the Raman effect of nitrogen was done by Rasetti. Well, Segre and I both learned to do experimental work from Rasetti. Rasetti was a very good experimentalist, and he taught us how to work. He was much better than Fermi as an experimentalist. And so we started all to work in spectroscopy, and later Rasetti went to Berlin, and he was working with Meitner. It was part of this idea to learn nuclear physics techniques--"the radioactivity technique," we said at that time. So we had prepared ourselves. But in the meantime we knew rather well spectroscopy and molecular physics and so on, and so we were still devoting a lot of work to spectroscopy. Actually, we worked with spectroscopy all during 1932, and then we changed from spectroscopy to radioactivity in a couple of months.

Weiner:

Was there a time when you were working on hyperfine structure?

Amaldi:

I was never working with . Segrè was working on it.

Weiner:

I'm talking about in general. Was this a kind of transition?

Amaldi:

It may be.

Weiner:

In his work anyway it would have been.

Amaldi:

In Segrè's work it was a transition, not in mine. In the work of Segrè it was, in a certain sense, a transition. But this was all still seen from the point of view of spectroscopy, to go deeper into the under- standing of spectroscopy. I was more involved at that time trying to compute, as we had done with Fermi--to prepare tables of wave functions of all atoms. We had the idea to compute what we called at the time the x-arum" a joking Latin expression, i.e. prepare a book with all wave functions of all atomic levels. And we started, and in 1932 a paper by me published by Fermi and myself on the s-wave functions of atoms. It's in the collected papers of Fermi.

Weiner:

I have that, yes. Well, in 1932 when the neutron was discovered, one of the interesting things is that Fermi in his talk in July of that year at the international conference on electricity made this statement it's in the collected papers): "We see the uncertainty still prevailing on the subject of the neutron." This makes me feel that there was perhaps still some skepticism about it when it was announced. What I'd like to explore with you is what the reaction was, if you can think back, when the neutron was announced. One possibility was that it was immediately evident. You told me about Majorana, for example.

Amaldi:

Majorana foresaw its existence before the discovery of the neutron, and this story is told in detail in my biography of Majorana.

Weiner:

You covered it in the interview with Kuhn, so I know that part of it.

Amaldi:

But that was written, and I have thought very carefully what have written, and it has been read by Segrè and by Rasetti and by all people that were there; and everybody thinks that it is the best that you can recollect.

Weiner:

So we won't try to improve on this.

Amaldi:

Well, you can always improve. But certainly when the paper of the Joliots came out, Majorana said, "Well, the Joliots have not understood anything." He was very critical. He said, "Oh, these Joliots, they don't understand what they do. It's so clear. They talk of gamma rays. That's clear. There is a neutral proton." Hecalled it a neutral proton. He did not call it the neutron. He said, "It's so clear. These papers of the Joliots are merely saying there is a neutral proton."

Weiner:

Had he read the Rutherford references to this?

Amaldi:

I'll tell you. The reason was this. He was a great friend of another man that was in the department. That was Gentile. Gentile had done some theoretical work on an idea of Rutherford. Rutherford, in order to explain the anomalous scattering of alpha particles at a certain moment, suggested the idea that there could be neutral particles of a mass of the order of that of the proton going around the nucleus. And he had done a fantastic sketch...He had sketched a certain scheme that did not work. And Gentile took this idea put forward by Rutherford in a rather qualitative way, and he wrote a paper showing that the idea was inconsistent.

So there was a paper done in our institute by Gentile which showed that this idea, put forward in a very fantastic way by Rutherford, who was a genius, was not correct. It did not work from a quantitative point of view. And Gentile was a great friend of Majorana, and so he knew of this old idea. That is what we know. That we are sure of. But what is also sure: that when the paper of the Joliots came out, he said to me, "That's quite clear. The Joliots have not understood. These experiments are just the proof of the existence of a neutral proton." Then after one or two weeks (I don't remember, but very, very shortly) arrived an issue of Nature with a letter to the editor of Nature by Chadwick which discussed some experiments he had done on the same line as the Joliots but better in that he could really give the proof.

The reply of the Joliots were sufficient to suggest that the existence of the neutron was a possible interpretation, but it was not a proof, while Chadwick proved its existence. So Chadwick had done a very essential step, but Majorana had done this, too. So we were prepared in a certain sense, and nobody was astonished at it, and everybody accepted immediately in Rome that the neutron existed and this was essential.

Weiner:

Then what is the uncertainty that Fermi mentions in July? Was it a question of the interpretation of it?

Amaldi:

I don't remember. I'm sorry I don't remember this point in this paper of Fermi's. I'm not able to tell you because I don't remember.

Weiner:

Right. Well, that's where we always draw the line.

Amaldi:

Well, I could try, but it would be a present reconstruction that would not make any sense. If I can imagine, Fermi was extremely cautious before saying anything of that type. I remember on later occasions when something for everybody was proved, he was always very careful not to say, "This is the only explanation." He would rather say, "You have to accept a certain fact as proof only when you have really explored all other possibilities." A rather amusing thing. Later in 1936 when I was working with Fermi, and we found out the neutron resonances, and it was rather obvious that the differences between the neutrons that showed the resonance were only differences in velocity.

But Fermi did not want to talk of velocity. He would say, "That is the most obvious explanation, but we should not adopt an obvious explanation as long as it's not proved." That's the reason why when we found all these resonances, we called these resonances with alphabetic letters. We called them Group A, Group B, Group C and so on--in order to avoid getting into the habit of thinking in terms of velocity. So we classified all these resonances, because many people ask me, "Why did you classify resonances with letters, calling them A, B, C, D?" I remember that if I tried to talk of velocity, Fermi would say, "Please don't talk of velocity. That's the obvious explanation. We should avoid to get used to it, because later we will believe, even if it is not true."

Weiner:

That's very interesting, the fact that he wanted you to discipline your thoughts to allow other possibilities.

Amaldi:

You had to discipline not to get used to it before it was proved, because when you get affectionate to an idea, then you are not any more free to be critical. That was the attitude of Fermi. That could be the explanation, but I don't remember this specific fact.

Weiner:

You know, talking about words and names, this idea of the neutrino At the Rome conference in 1931--you said you weren't involved in all of the discussions, but...

Amaldi:

Well, I was listening, but I was young.

Weiner:

Well, anyway, the word neutron was used in the other sense. This was before the discovery of the neutron. But apparently the word neutron was beginning to be used in that period more and more.

Amaldi:

Well, there is that paper by Chadwick, a very good one; you know that. And this was given at the meeting at Ithaca. I would take this paper of Chadwick as probably the best.

Weiner:

There are a few things on that I will probe with him.

Amaldi:

In these short three pages--I have a photographic copy of this paper--he really explains what was the thinking in Cambridge and how the idea of a neutron was older when it was discovered. That does not reduce the merit of the discovery of the neutron, but it is interesting.

Weiner:

Apparently nobody else was looking for it, you see. They were the only group looking for it, although the idea was common. That's the very interesting thing. In one of your papers, the one on highly excited alkali atoms...

Amaldi:

The Excited Atoms.

Weiner:

Yes, the "Effect of Pressure on the High Terms of the Spectra of the Alkalis," with Segrè The experimental effects observed were explained in a theoretical paper by Fermi.

Amaldi:

By Fermi, yes. We had discovered this effect, and we could not understand what it was. We asked Fermi, "What do you think?" and then he made the theory.

Weiner:

In this paper he talks of slow neutrons.

Amaldi:

We were working with electrons in such excited states, they were bound with ~1/100 of electron volts, extremely weakly bound, and moving 100 almost free, bound so weakly they were almost free and with very long wavelengths. And in that paper, in order to explain the effect that we had found, he made the theory of a collision of a very slow electron against an atom. And this is exactly the same theory that was used one and a half years later for slow neutrons against nuclei. This is very interesting. People don't usually know that.

Weiner:

This is the question that I have written down here. In 1934, the idea of the slow neutrons came out. Now, this paper was earlier than that. It was the same year but it was earlier. So was there a connection in his mind? Was it the theory of slow electrons that suggested the theory of the slow neutrons? Is there any way you have of knowing?

Amaldi:

I don't think so. This effect in atomic physics was found by Segrè and myself. I don't know if you know how we found it. We were studying excited atoms in an electric field--what is called the Stark-Lo-Surdo effect, similar to the Zeeman effect but with an electric field.

Now, we were studying this effect in absorption. That means we had a long tube containing the vapor to be studied and closed with two quartz win- dows, and we had an ultraviolet source, and we have sent the beam of this light through the tube. The windows were cold while the vapor was at 500-600 degrees, so there was the problem to avoid, that the vapor (of sodium or potassium) would distillate on the windows. To reduce this effect, we introduced into the tube a very low pressure of noble gas (argon or neon). We started to put this noble gas at a very low pressure, and we said we should not put more pressure because at that time everybody knew that if you have a foreign gas, then by collision you get the lines wider because you shorten the mean life of the levels.

So we were very cautious to use a very low pressure. Then at a certain moment we saw that the lines were very thin, exactly the same. So then we said, "Why don't we increase the pressure?" and we started to increase the pressure, and we saw that the lines were not becoming wider--they were the same. Then we said, "We should try to increase the pressure again." So from a pressure of a few centimeters of mercury, we went to one-atmosphere, and the lines were still quite thin. And then we tried two-atmosphere. We changed the tube in order to be able to support the higher pressure, and we found that the lines were still the same but they had shifted a bit. And then really we were astonished, because this was against all common ideas at the time.

Then we asked Fermi what was his opinion. He immediately pointed out that when the electrons are bound so weakly, the orbits are so big that at high pressure of the noble gas between the electrons and the rest of the atoms, there are of the order of 10,000 foreign atoms. So you have atoms with a dielectric medium inside. So we had to calculate the levels of the atom by taking into account the dielectric constant. The shift of the lines due to this effect has, however, the wrong sign. Then Fermi found that one had also to take into account the collision of the electrons against the atoms of the foreign gas; so that the electrons don't go around simply, but in some way they do a complicated orbit, because they are scattered. They are kept weakly on their own original orbit, but in some way they are scattered around it.

And then he made the theory of the collision of a very slow particle against an obstacle. But this was later the same as the collision of a slow neutron against a nucleus. The ratio between the wave length and the dimension of the obstacle was accidentally the same in the two cases.

Weiner:

Did the idea--not the specifics but the idea--of slow electrons suggest a model for the slow neutrons?

Amaldi:

I don't know, because when the discovery of slow neutrons was made, it was also a purely experimental discovery. At that time we were planning our work in a very effective way. So we were making a meeting every second day and saying, "Emilio does that, and Edoardo does that," and "Fermi does that." Everybody was supposed to do a well–defined part of the work.

We were all very precise people; if we had to start at 8:30 or any other time, we started exactly at that time. We were working as many hours as necessary. We planned the use of our time in a very precise way. After Segrè and I came back from Cambridge, I was asked with the help of Pontecorvo who had been one of our students and who had finished at that time, to try to prepare a kind of absolute scale of the activations of the different elements.

That means to find a standard condition of irradiation and to see how the different elements become active when irradiated all in the same conditions. This was the idea, because in the first paper that was published in the Proceedings of the Royal Society, we had just given a qualitative scale, by saying "very strong activity,", "weak activity" and so on. We felt it was unsatisfactory. Then we felt that we had to take, for instance, silver (I remember we thought of silver), to call 100 the activity of silver, irradiated under certain conditions, and then to irradiate all other elements in the same number of nuclei, in the same flux of neutrons, and to give to each element a different number corresponding to an arbitrary scale of activity.

Pontecorvo and myself started to do this in a very precise way, but we found out irregularities. We were not able to obtain all the same results irradiating under the same conditions--at least apparently the same conditions--the same piece of silver. First of all, we had to choose a standard, and the standard had to be reproducible. So we started to look if our standard was reproducible.

Weiner:

You calibrate your standards.

Amaldi:

Yes, we were trying to calibrate the standard. And at that time Rasetti was saying, "Well, you do mistakes I'm quite sure. Is it possible that you find different results? Well, you find different results. In the same flux of neutrons, the same amount of silver is irradiated, and you get different results." We protested and said that we were not doing mistakes but that the results depended on the presence of some material around. We used some lead to protect ourselves from the gamma rays of Rn present in the neutron source and we had always thought that its presence was not important for the activation due to neutrons. But by changing this lead, we had differences.

Weiner:

You put it in wood?

Amaldi:

We had made already before the irradiation on a table of wood sometimes, on a table of marble sometimes, and we had observed differences. And also the presence of lead makes a difference, because lead has a slowing down effect, not by elastic collision but by inelastic collision-- much smaller than hydrogen, but also lead has a slowing down effect, owing to a type of collision in which the neutron loses energy by exciting the nucleus of lead to a higher level, and then the nucleus goes back emitting gamma rays. But we did not observe the gamma rays. We observed only a certain slowing down.

Weiner:

When you put the paraffin...

Amaldi:

We had prepared a cleaner experiment to see this effect in lead. But the morning it was decided to do the experiment with lead, Fermi said, "Let us try paraffin, not lead." And with paraffin, the effect was much more evident.

Weiner:

Now, when he saw that, later that same day he theorized that this was a slowing down?

Amaldi:

Yes, that was in the morning, and in the early afternoon he said, "This is just an effect of slowing down." I don't think this was so directly connected with the slow electrons--I don't think so But I'm not sure.

Weiner:

I wasn't pursuing it for that. I was just trying to get to a different point on this. What was the reaction of the rest of you to Fermi's hypothesis later that day about the filtering effect of the paraffin?

Amaldi:

Oh, we understood that immediately. What we could not understand was when Fermi came and he said a very strange thing. He said, "In each collision on the average the energy of the neutron is reduced by 1/e, 'e' the basis of the natural logarithm." And that was difficult for us to understand. What was clear to us was that the energy in each collision was reduced in average to one half. This point--if the neutron energy reduced in average to one half or 1/e--gave rise to a lot of discussion in scientific magazines, because Fermi for a long time did not explain why he was claiming l/e, and any elementary calculation showed it was reduced to 1/2. But when Fermi said it, it was rather clear that it was a slowing down, but he never explained for a long time why he was claiming the lie factor. And I remember Goudsmit wrote a paper on that, and other people wrote papers, because many people thought that Fermi was wrong.

Weiner:

Did the difference...

Amaldi:

The difference was that in order to calculate correctly the effect of slowing down, the best way is to use instead of the energy, the logarithm of the energy. And if you calculate in a logarithmic scale, you find out the factor of 1/e. But Fermi did not explain even to us why he claimed 1/e.

Weiner:

And yet you were willing to accept

Amaldi:

He said, "I will explain some time, but we have now to work, and it's much more important to go on working than to explain l/e or 1/2."

Weiner:

Well, he had a practical result. Let me ask you. One of the practical results was that you could explain the difference between the slow and the fast neutrons, which would explain the case of aluminum, for example--the anomalies you were having with irradiated aluminum.

Amaldi:

Yes. But if it was a factor of 2-1 or a factor of e-1 coming in at each collision did not affect this as well as other results at this stage of our experiments.

Weiner:

But that gave you confidence in his idea.

Amaldi:

We were convinced of the qualitative idea. The discussion was about the numerical factor. This led to a rather long discussion in the journals.

Weiner:

But you were willing, forgetting about the numerical factor, all of you, to accept immediately the idea of the slowing down of neutrons although you had been convinced earlier--and everyone had accepted the idea--that neutrons had to be fast.

Amaldi:

Well, there were two things. One was that the neutrons were slowed down, and the second that the cross-section should go up by slowing down the neutron. So actually the assumption was a two-fold one. There were two facts that you had to assume to explain the observed effect. But we started immediately to do experiments and to check the various aspects. And in four or five months devoted to do experiments on that we had continuous confirmations. Thus at the beginning we were not sure 100%, but Fermi's explanation was a reasonable one. And immediately a number of experiments were planned to check it.

Weiner:

Do you have any idea how others reacted elsewhere?

Amaldi:

No, there was some discussion, but it was accepted. It was accepted because it was the most reasonable interpretation, I should say. One could explain so many things that had been observed by ourselves or by other groups, that the assumption appeared pretty soon really a very good one.

Weiner:

That leads to another question about someone else's theory. This is the compound nucleus--the Bohr theory.

Amaldi:

This came in 1936. Breit and Wigner and Bohr's papers were both published at the beginning of 1936.

Weiner:

Yes, I'm just using that as an example to get to another category here about how Fermi reacted to the compound nucleus theory. Did he think that he could come up with a similar approach, and what was his attitude toward models of this type in general? Did he have any feeling for that?

Amaldi:

Well, I think he accepted it; he found it was a very good idea.

Weiner:

You see, you mentioned earlier that he didn't want to have preconceptions. For example, he didn't want to think about velocities in one case, and this "hypothesis non fingo" approach. This apparently was useful, but was this his general feeling? Was there a turning away from theory for a while in the Rome group?

Amaldi:

Well, in that period he was essentially doing experiments. He was devoting most of his time to doing experiments. I'm not able to say though I feel he did accept it. His attitude was the following, he would say, "I should avoid preconceived ideas--as an experimentalist. A theoretician is different."

Weiner:

That's interesting to separate them.

Amaldi:

That's a very, very sound position. "As an experimentalist I should get proofs and limit myself to saying I have observed this, this, and this, and from this I can conclude this. Then I can do assumptions. But I should do a very clear distinction between assumptions and what is really proved as an experimentalist." For a theoretician it's an entirely different proposition.

Weiner:

A lot of experimentalists feel the other way around. They feel that the theory has to be very tight, but with the experiments one can...

Amaldi:

I should say that on many, many occasions I have the impression that he would not be very happy now about the attitudes of many theoreticians and also of many experimentalists. He would not be very happy, in my opinion. Because there is today the idea in many places, also by very good people, that you have to do a theory and then do experiments only to check the theory.

Weiner:

In 1936 you go to the United States to look around. It seems to me that this ties into the next series of questions on the development of higher-energy machines, accelerators and so forth, and this is a nice way to break it off. It leads up to the early war years, for example, and then the differences in the type of research that you were doing. So this is the logical point, I think, to stop.

Amaldi:

I don't know if I could add maybe a short comment about the fact that we did not find fission in the winter of '34-'35.

Weiner:

Oh, yes, we started to talk about that.

Amaldi:

think that that maybe is interesting.

Weiner:

Do you want to talk about it now?

Amaldi:

Just to add a bit. When I was in Cambridge, one of the points that I tried to learn was to build a linear amplifier. Wynn-Williams, who was a British scientist, had built a very good one, and I tried to learn from him how to build another one, and then I went back to Rome and in the fall I built one of these amplifiers. Then in the winter we started to use this amplifier to study boron reaction. Actually, I worked very much on the boron reaction and also on lithium disintegration by slow neutrons.

Then, since uranium and deuterium both had shown so many activities, we thought that there could be a kind of new family of radioactive bodies in which there are beta decays alternating with alpha decays. So we decided looking for alpha decays, with this amplifier that had been connected with a little ionization chamber. And in order to see also short lives, I put a piece of uranium in front of the ionization chamber. I irradiated the uranium there and then I took away the source of neutrons and looked for radioactive bodies emitting alpha particles.

Since I did not observe any alpha activity, I thought to look for extremely short lives and I looked for the emission of alpha particles when the source was kept nearly the uranium. But, of course, the amplifier was disturbed by the alpha particles of uranium. Before doing that I discussed the arrangement with Fermi. Fermi calculated with the Geiger Nuttall law that the mean lives that we could observe were certainly very short; then according to this law, the range of the alpha particles should be long enough to put a foil of aluminum in front of the uranium so as to eliminate the alpha particles from the natural decay of uranium. And so a foil of aluminum was put there, but the foil of aluminum that was stopping the alpha particles of uranium also stopped the fragments of fission.

So we went on doing these measurements for quite a while, and we did not observe any artificial alpha emitters, because it was rather natural to look also for alpha emitters, but we did not find any fission. Some time later, I found out that a similar experiment was done in Berlin-Dahlem at about the same time by Von Droste.

Weiner:

At that time?

Amaldi:

More or less. This was told to me once by Otto Hahn, and Lise Meitner knew about that, and maybe Otto Frisch knows. I never talked about this with Otto Frisch. We talked on many occasions of many things, but not of this. So maybe he knows, but I'm not sure.

Weiner:

While we're talking about fission, this paper by Ida Noddack had predicted fission in '34, and it was read by your group--at least by some of the people. Do you recall reading it? Amaldi: Yes. But on this point I'm sure that Segrè knows more than I. About resonances, or things like that, I know more than Emilio, but on this, Emilio knows more than I. I remember, but I feel that the best information you can get is from Segrè.

Weiner:

You see, he doesn't know the answers to this either. Nobody knows.

Amaldi:

He knows more than I.

Weiner:

But I mean on this particular point he still wonders and all of us do, you know, just why at that time their paper didn't make sense.

Amaldi:

Yes, that was what we thought, but we were wrong.

Weiner:

Well, then we'll pick it up from 1936.

Amaldi:

Yes, tomorrow night.

Weiner:

This is tomorrow night, and it's April 10th and about 9:30 in the evening, and we're resuming again the interview with Professor Amaldi. When we left off, we decided that we were just going to talk about 1936. That was an interesting year. The Rome group began to break up as it was originally constituted, and certain things began to change. Now, one of the interesting things is that you went for the first time to America in the summer of that year. I want to know that whole story-- about the purpose of the trip, about your reactions, what you did, how the trip was planned, where you went, what you saw, what your reactions were to all of these things.

Amaldi:

Well, during the winter of '35- 36, I was in Rome working with Fermi, and we had started the resonances of neutrons. Actually, we can say that we contributed to establishing the existence of resonances of neutrons, and then we studied these resonances as well as the details of the process of slowing down and diffusion of neutrons and the interaction of neutrons with matter.

Then in the summer Fermi went to Columbia to give a course, and I went also to the United States. It was my first trip to the United States. I stopped for some weeks in New York--I will say in a moment why-- and then I went to Washington, D. C. because I wanted to go to the Carnegie Institution to see the accelerator existing there, because we had started to consider the problem of constructing some accelerator to produce neutrons.

Until that moment we had only used sources of neutrons made by radon plus beryllium and the intensity of the sources was too weak. In the meantime, in the United States, but also in other parts of Europe, in Great Britain in particular, there were accelerators; and the intensity of the sources was so much larger than our sources that it was clear in a short time we could not compete any more.

So the main reason why the trip was essential was to go to Washington, D. C., to go to the Carnegie Institution and to see the accelerator that had been built there and to learn how to build something similar. Actually we built a different machine, but this was mainly our interest. But on the way I stopped at Columbia, and at Columbia I translated into English the paper that appeared later in the Physical Review by Fermi and myself on the slowing down and diffusion of neutrons.

I tried at that time to convince Fermi to translate also his theoretical paper, because our experimental paper was accompanied by a theoretical paper by Fermi. But Fermi refused to do that. He said that he did not want to waste time writing in another language. If the people were interested in what he had written, they could read it in Italian; and he refused in the most strong way to write his paper in English.

Weiner:

Did your wife accompany you on the trip?

Amaldi:

No, that time I was alone. At Columbia I have also done some experimental work together with Segrè. He was on his way to Berkeley, stopped for a few days at Columbia, and we have done a little experiment together at Columbia University with neutrons. Then I went on to Washington, D.C., and there I became a good friend of Dr. Merle Tuve.

Hafstad was there, too. And with both of them, we have done some experiments with neutrons; and in a certain sense I have introduced slow neutrons in Washington, D.C. Up until that moment they had never worked with slow neutrons. With Odd Dahl from Norway, Tuve had built the Van De Graaff, and they had done very nice experiments on the proton-proton scattering, and I knew of the existence of the accelerator because of this work on proton-proton scattering. And so I introduced what you could call the technique--it was a very simple technique--of the slow neutrons in Washington, and I learned (it was very useful for me) how to build an accelerator. It was 1 and 1/2 million electron volts, which was at that time considered quite a good accelerator. Today it is nothing.

Weiner:

Let me ask you a few questions about that. The Van de Graaff at the Carnegie Institution was just one of many different kinds of accelerators that were working in the United States. Why didn't you look at others like the cyclotrons?

Amaldi:

Well, we thought that probably the cyclotron was too expensive and too complicated a machine for us. At that time we were of the idea to make an accelerator much simpler. Actually what we did later in Rome was not a Van de Graaff, but have built a Cockcroft-Walton machine. But what I really learned there was how to build the accelerating tube. At that time we had no experience at all on this type of work, and the idea was essentially to learn how to build the accelerating tube.

Weiner:

It seems to me that the kind of building that goes into that is on a scale very different than the kind of building that went into your earlier work.

Amaldi:

Yes, it's true. But, well, we were quite prepared to make also a complicated construction within those limits. Later, in '39, we had the idea to build a cyclotron, and then went again to the United States with the idea to learn how to build the cyclotron. But in 1936 the idea was to build a small accelerator in order to dispose of a good source of neutrons. And actually when I came back, a Cockcroft and Walton accelerator was designed. Fermi was consulted from time to time about various things, but the machine was built at the Institut de Pubblica Sanità, (Institute of Public Health; we had not enough money at the University), and the machine was finished when Fermi had already left the country. But the machine was used by Rasetti and myself. Then Rasetti also left, and I went on with Trabacchi and some young people. We have done a certain number of experiments on fission, neutron-proton scattering-- all this was done with the accelerator that was built after my trip to the United States.

Weiner:

When did this shift of interest occur: neutrons as useful in scattering work, for example? I mean you began to do scattering work somewhat later - about 1939, 1940, I think.

Amaldi:

Yes. Well, in the meantime we had built this machine; it took some time. We all had also big troubles. Italian theory was almost destroyed by the racial laws and political pressure, so we had lost time. It was not so simple as just to design, to build a machine. We had lots of troubles mixed with this.

Weiner:

Let me ask you about the techniques that were required. Did you have to get outside help in terms of electrical engineering kind of experience for large machines?

Amaldi:

No, no We have done everything. All the design and everything was done essentially by me. Rasetti helped a bit. But I have mainly done it. It was not very complicated. I calculated the electrostatic lenses for the beam. Well, it was not too bad. Actually we had built at first a little smaller tube in our Institute at the physics department, with Fermi and Rasetti. It was made more on an empirical basis. And later this one was calculated and planned quite decently, in a decent professional way.

Weiner:

Well, the first one--was this the 200 keV?

Amaldi:

Yes.

Weiner:

Was that ever put into business?

Amaldi:

Well, we produced some neutrons, but no experiments were really done with this at 200. Well, some little experiments, but we never published any interesting results. With the other--the Public Health machine--we did some work later.

Weiner:

Who paid for the first one?

Amaldi:

Oh, the first one we have done with the means of our department. The means were very modest but were enough for such a construction.

Weiner:

What kind of argument did you have to use to get the funds for the other one?

Amaldi:

Oh, it was very simple, because the director of the Public Health Department was Marotta, and he was always ready to support things like that. He was interested in this type of thing. Professor Trabacchi was...

Weiner:

It was in his lab, wasn't it?

Amaldi:

Was in his lab. Trabacchi talked with Marotta, and it was, should say, very simple. They were full of confidence that it was worthwhile to build the thing. So there was no problem.

Weiner:

Was this larger machine, the one we're talking about, initiated after Fermi left?

Amaldi:

No, the design was initiated before Fermi left, and during the design period I consulted on many occasions Fermi to say, "What do you think about this and that?" And he was always very much interested. In the meantime, the political situation became very heavy and the machine was finished more or less at the time that Fermi went away. But I don't remember exactly if he left Italy before or after it was finished, but I suspect he left immediately after it was finished.

Weiner:

Your first publication on it is July-August 1939.

Amaldi:

Exactly. Fermi had left in December '38. And I went again to the United States in June,-July of '39. I left Italy with Rasetti. The reason for my trip was that I wanted to learn how to build a cyclotron, and I went to Berkeley for that, but at that time I did not realize that the general political situation in Europe was deteriorating so rapidly. I was sure that it was deteriorating, but I thought it was going much, much slower; so I had also the idea to prepare in some way my departure-- well, I wanted to leave Italy at that time, but I did not feel it was something urgent. I thought I could have one year or so.

But then the situation was worse, because at the beginning of September the war started in Poland, so the situation was much, much worse. So I went to the United States, and I was looking around for a future possibility to stay in the United States, and then I went to Berkeley. In Berkeley, Segrè was there. I lived in his house for all the month, of September, and during that period I looked very carefully at the cyclotron. I took some of the drawings, and I brought them back, with the idea of building one. It was never built. It was never even started because then the war started, and it was impossible to do anything.

Weiner:

What had changed your mind about the cyclotron? Because the only thing that I see that changed from the earlier time when you weren't interested in 1936 and this time is that things got worse. The political situation deteriorated, so it didn't look as if there would be support for it.

Amaldi:

Well, there was a possibility. It was the following. In 1939 and '38 the preparation was started for the International Exhibition in Rome, that was planned for 1942. I had proposed, and it had been accepted, that on the occasion of the Exhibition one could build a cyclotron and have this built with the money assigned for the Exhibition. There was a rather large amount of money that was appropriated for this International Exhibition. So it was not money given for building a cyclotron, was money given for the International Exhibition. I was planning to exploit this situation. That was all. And it was not yet finally decided at that time, but people felt that it was a good proposal. Well, why not? We had to spend a lot of money, and if a cyclotron was built, then it could have been later used by physicists. So this was the reason why I felt that we could try to build the cyclotron for the Exhibition and then have it.

Weiner:

Did they have any science at all in the exhibition? Was there any emphasis?

Amaldi:

There was a part devoted to science, modern science. And then the modern science it was quite clear that the cyclotron was one of the most important machines of that time. It still is now. And so when this proposal was made, people said, "Well, that's maybe a good idea. In order to make a definite proposal you should see if it's feasible to build it in Italy and so on." I proposed it in a rather vague way, but I said to myself, "Before the idea is accepted, I should study the problem to see if we can really do it. But if we can do it and if you provide the money, it could be an interesting thing."

Weiner:

They didn't pay for your trip, though?

Amaldi:

Yes, my trip was paid...

Weiner:

From the fair money?

Amaldi:

No, no I asked for money from the Academy. At that time the Accademia del Lincei was closed, and it had been replaced by what was called the Accademia d'Italia. This Academy was built on a scheme similar to the French Academy...

Weiner:

With more of a flourish and with uniforms...?

Amaldi:

Exactly, they wore uniforms and so on.

Weiner:

It became a sort of political appointment to that?

Amaldi:

No, not really political...

Weiner:

But some people might have been put there because of this...

Amaldi:

Oh, some people have been put there because of political reasons. In any case, it was a bit more for appearances and so on. But in any case, I asked them for money for my trip and they gave me money. So my trip was paid for by the Accademia Italia, and I went to the U.S.A., and I have learned something about cyclotrons. That was very nice, and interesting.

Weiner:

What were the prospects for future opportunities in the United States when you looked around?

Amaldi:

Oh, I had long conversations with Rabi and Tuve, because I was a very good friend of Tuve, in Washington; with Rabi at Columbia. I was on very good terms with E. U. Condon. He was at that time director of Westinghouse laboratories in Pittsburgh. I was in the house of Condon for a few days. Everybody asked me: "Have you to leave Italy?" "No." "Well, then please stay there." That was what everybody told me. They had so many problems to find jobs for people that had to leave in any case. There were Segrè and Rossi, and many of my friends that were looking for jobs. It was really difficult to find a job. And I was not forced; I could stay there although in Italy there were ideas I did not like. So many people said, "Well, if you are not forced, why do you want to come away? Stay there for some time more."

Weiner:

They, too, didn't see the deterioration of the situation.

Amaldi:

Oh, they saw it much less than me. With many people I had a lot of discussions. I was trying to convince them of the response why I was convinced that Europe was practically to the end. I thought not in a few months, I thought in a couple of years. These were my ideas at that time. But many people felt that I was exaggerating--that of course there was this terrible thing of the racial laws, but apart from the people that were directly involved, and apart from the fact that to leave in Italy was very unpleasant, why, after all, do you want to come away and so on? This was the type of conversation I had with many American friends.

Weiner:

That's interesting. In any case, there was no job though.

Amaldi:

It was very difficult. I remember, for instance, people like Bruno Rossi. He was in Chicago Compton was extremely fond of him and he knew the beautiful work of Bruno Rossi in cosmic rays, and Compton was trying to help him. But I remember I went to see him at Echo Lake. He was doing experiments at Echo Lake on cosmic rays, and I went to see him there. And he was living on an extremely modest scholarship, that was usually given to a student, and he had a wife. Really it was very difficult. So it was very clear, because I talked with so many people, that it was practically impossible. It was very difficult to find a job. It was difficult for the people who had to find a job urgently.

Weiner:

Yes, I know that. What was the general state of physics itself in the United States during that summer? What was your impression of Berkeley, let's say?

Amaldi:

Well, I was first of all at Columbia for some time. Then I went to Pittsburgh--I don't remember exactly all the details. I went to Washington. Then I went to Ann Arbor. Fermi was giving a course in Ann Arbor during the summer, and I met there Goudsmit. I remember that Heisenberg was going through Ann Arbor going back to Europe when I just arrived. It was around the 20th of August when I was in Ann Arbor, between the 15th and 20th of August. From Ann Arbor I went to Washington and from Washington I took a Greyhound bus, and I went by Greyhound bus to Berkeley. I wanted to see America in a Greyhound bus, and it was very amusing.

Weiner:

All the way, in the hot summer?

Amaldi:

Oh, yes. And when I arrived in the morning of September 1 at Salt Lake City (we got out at 5:30 in the morning, I think, from the bus), the people were shouting in the streets that the war had started in Europe. The Russians from one side and the Germans from the other had started to invade Poland. Then from there I went to Berkeley, and in Berkeley I remember it was the time that Alvarez and Bloch were measuring the magnetic moment of the neutron. I remember that Bob Wilson I met for the first time there. He was a student, a graduate student, quite young and very brilliant. And I remember--everybody said it was so clever--he had invented the o-ring seal to move things inside the vacuum chamber of the cyclotron.

Weiner:

Did you meet Lawrence?

Amaldi:

Oh, yes.

Weiner:

What was your impression of him?

Amaldi:

Well, I knew Lawrence before. I knew Lawrence already. I had met him on previous occasions. He was a strong personality in a certain sense. Then Placzek was there, too. We were great friends, because I had been working in 1931 with George Placzek. We had done some work together on molecular spectroscopy. We had studied the rotational spectra of ammonia in Raman effect. In the meantime I had asked for a passport for my wife and children. We had already two children, and the third one was in preparation. But when the war had started and I got a letter from my wife that she had got a refusal of the passport.

They said that they did not give passports. And then at the same time it was stated that all connections between the United States and Italy were interrupted. So I did not know what to do So I stayed in Berkeley all the month of September, and then at the end of September I came from Berkeley to the east coast with Placzek by car. He had a car, and we went back by car. And on our trip back we went to Detroit and to Niagara Falls through Canada.

At the frontier where we arrived there was the Canadian police. In the next car there was Weisskopf with his wife, and the poor people of the Canadian immigration office were very much worried, because in our car I was an Italian with a passport from a Fascist country and Placzek had an old Austrian passport--but Austria did not exist any more after the "Auschluss." In the other car Weisskopf was in a condition similar to those of Placzek and Mrs. Weisskopf had a Danish passport. Four or five immigration officers started to consult among themselves for a long time before we were allowed to get in Canada.

Weiner:

Did Weisskopf and his wife also start from California?

Amaldi:

I don't know from where they were coming. From that moment we went together.

Weiner:

Did you meet them by accident?

Amaldi:

I had known George Placzek since '31. I met him for the first time in Germany in Leipzig. It must have been there also that I met for the first time Bethe and a number of other people. Later I had met Weisskopf on various occasions in Copenhagen. Placzek, after I returned to Italy, came to Rome for some time, and we were working together in Rome before the neutron time. We were working on spectroscopy together as I said before.

Weiner:

But when you saw Weisskopf and his wife at the border, was it by coincidence?

Amaldi:

By coincidence. It was so strange.

Weiner:

In a big country, and you had visited Niagara Falls. How about Placzek, had he become established by that time, or was he also in an uncertain position?

Amaldi:

He was still looking for some job. He had not yet a job, if I remember correctly. He had left Great Britain, and he wanted to stay in the United States forever, as he has done later. But then I went back to New York and to Columbia. I went to live with the Fermis. They were living in Leonia on the other side of the Hudson. There were no connections with Italy, and then suddenly the connections were reestablished, and so I decided to go back to Italy, and I took the Vulcania, which was an Italian ship, back to Italy.

It was the first boat going back. It had been stopped in New York for one and a half months or so. But the day before the last day I had to go back, I went to Columbia with Fermi in the morning, and we met Felix Bloch, and since we were good friends of Felix Bloch, he said, "You should come to lunch with me." And he invited me to lunch, I remember, on the lower side of Central Park.

We went to a restaurant--I think it was the St. Moritz Hotel. And he tried to convince me not to go back to Europe. This is a very amusing story. I said, "Well, I cannot leave my wife. My wife is to have another baby in a few weeks. "Oh, well," he said, "you leave your wife. You leave your wife. You stay in the United States...Well, the war will last six months, one year, and then you go back. But you should not go back now." I said, "No, I am sorry. I don't think I can leave my wife in this condition and stay here, because she has not got a passport. I do not feel that I can do that. I'm very sorry." Then suddenly Bloch said, "Well, if you don't want to leave your wife in Italy and stay in the United States, then you have a lot of work to do. You have a lot of work to do because after what happened in Italy, because what has been done by Fermi has been destroyed, and you have a lot of work to do to try to keep something surviving." And he started a completely different line of arguments, almost with the same strength. I should say that later, on certain occasions, I have thought about what Bloch told me at that time. You know Felix Bloch?

Weiner:

Oh, yes. I talked with him like this last summer, in August. I didn't know about this, so we didn't talk about it.

Amaldi:

A few years ago I told him this story, and he was laughing. He said, "Do you know why I was in New York in those days? Because I went to talk to a girl that I wanted to marry--Mrs. Bloch now--and I had just decided to marry in those days.

Weiner:

But he was willing to talk you into leaving your wife.

Amaldi:

Leaving my wife, saying, "Oh, that's..."

Weiner:

That's amusing. What was Fermi's attitude? Did he get into any of this discussion with you alone?

Amaldi:

No.

Weiner:

About your decision?

Amaldi:

Well, I had a talk first with Fermi and then with anybody else about my desire to stay in the United States if there was some possibility. And he had been extremely sharp and clear. He said, "I am very happy if you succeed to stay here, but I will not help you at all," because he felt that he had to help the people that had to leave by necessity. That was all.

Weiner:

A funny position to be in.

Amaldi:

That was all. "What are you going to do?"

Weiner:

Did you discuss with him the future of the work back in Rome?

Amaldi:

No. I never discussed that with Fermi. The only person that I discussed with, but not because I raised the question but because he had done it by himself, was Bloch. In a certain sense he said a number of very clear and very definite things on that occasion.

Weiner:

As far as the responsibility that you had was concerned.

Amaldi:

Exactly. The responsibility I had to take and what could be done if I was strong enough, so to say. "It will not be easy, but if you can, you could do that." And he was the only person to consider this case.

Weiner:

What were some of the things that he indicated to you?

Amaldi:

In a certain sense Fermi had decided that Italy was closed. People who knew him well could imagine him saying at a certain moment: "Well, Italy had done these stupid things, these incredible things. Italy does not exist any more." I believe that he had taken a bitter attitude of this type.

Weiner:

What did Bloch identify as the particular areas of importance?

Amaldi:

No, he was not so specific as to say, "This is important; that is not important." It was just in general terms, that this was something that was worthwhile to try--that everything has an end. This was the important thing in a certain sense--that even such a terrible period has a beginning and an end; and after the end, something else starts. So the point was to go through, that was essentially it. It was not talking so much in terms of what could be done in detail.

Weiner:

Not so much students. Did he talk about students?

Amaldi:

No. That was implied in a certain sense. He did not mention these things. But it was interesting.

Weiner:

Now, the total time on this 1939 trip was how long?

Amaldi:

July, August, September and part of October--between three and four months.

Weiner:

Did you do any research during that time?

Amaldi:

No, it was impossible. People were too much upset. We were talking physics, but it was very difficult for me to do some work.

Weiner:

But there was work actively going on.

Amaldi:

Oh, yes, in all places. In the United States work was going on in a wonderful way. And in that period I met for the first time Herbert Anderson. He was just a student working very nicely. I remember with a great pleasure when I met Anderson for the first time. It is also a pleasure when I meet him now. I remember the impression of Anderson-- very young, very enthusiastic; he had just started to work with Fermi. He was extremely nice with me, very nice, because he was very much worried. He was very much worried by the fact that in some way they had got Fermi, and we had lost him. It was very nice. He was extremely nice in his attitude. It was very pleasant.

Weiner:

This was the summer of 1939, so they were working on...

Amaldi:

They were working on fission, and I understood quite well that they were doing some work that they did not like so much to talk about. You understand this. It's part of the business. We were working on fission in Rome and doing something very similar. Then we stopped, be- cause we said, "Why should we do? This is something that will become a very hot matter, and we are here. What do we do? All of these people don't understand anything. But, on the other hand, it does not make sense to try to do by ourselves here. And, on the other hand, if they understand it is important, then we are maybe forced to do some work that we don't like to do So it's better to stop the work on fission and work on the neutron-proton scattering. That's a very nice scientific subject but with no danger." So we started to change. I had a lot of discussion with Giancarlo Wick on that.

Weiner:

Let me get back to the start of the fission thing. When did you first hear of it, and how did you react?

Amaldi:

About what?

Weiner:

About the fission.

Amaldi:

About the fission or about the bomb?

Weiner:

About the fission, the idea of Hahn and Strassmann.

Amaldi:

I read the paper of Hahn. I read it when the paper of Hahn came out. We said, "That's wonderful." And actually I have done immediately with M. Ageno an experiment similar to that of Joliot and Otto Frisch of looking at the fragments of uranium and for a rather stupid reason we did not publish. But we had observed the same thing. We had observed these fission fragments almost immediately after the discovery of Hahn and Strassmann.

Weiner:

Before the Frisch-Meitner paper?

Amaldi:

Well, we had the news of this experiment. It was stupid not to publish, because we had similar results. Then we got news--I don't remember how, through some letters--that that was done somewhere, and we were so stupid not to publish. I should say we were discouraged essentailly by Rasetti, who said, "Oh, why do you want to publish? It's already been done." It was stupid, because various groups published it much later, and they are still quoted, and we did not publish. Oh, we have done lots of stupid things on many occasions. We had observed and measured. We were quite satisfied. But we did not publish.

Weiner:

Other groups did various work--had various approaches to fission. Did you then actively pursue it? I know you did some work...

Amaldi:

No, we went on measuring the cross-section of the uranium 238. We started a study of fission in uranium 238 due to fast neutrons. We talked about but never tried to do any real experiment for measuring the neutrons emitted in fission as was done by Anderson and Fermi; it was done by Joliot and Kowarski in Paris. We did not try to do that. We knew about that, but we decided not to do We felt this was the subject on which everybody was working, and we decided to work on the cross-section of 238 as a function of energy, and that was the argument on which I corresponded with Bohr.

Weiner:

And then this paper that you published on it... I want to get to this later. It's all the way up here. It's later here--on the fission. This is a '41 paper up here--this one. I want to ask you about some of these.

Amaldi:

What are these?

Weiner:

These are from Physics Abstracts. These are the abstracts of your papers. I'm going to get back to some of these.

Amaldi:

I've never seen them. This is done quite nicely.

Weiner:

The fission paper here was published in '41. In other words, you were still, from '39...

Amaldi:

Well, no. We published all these things in Italy in the Accademia dei Lincei, and then this paper was a kind of resumé of all that we had done.

Weiner:

I see. So then this is not complete, because on my list this is the only fission paper.

Amaldi:

No, no. We had three or four papers on fission.

Weiner:

But this was just a sideline in a sense. You corresponded with Bohr in 1942. Let's see: in '41 you wrote to Bohr about 238 and 239.

Amaldi:

I have lost these letter.

Weiner:

I'll show you the letter. I think I have it. I want you to look at this. This is just a catalogue card of the thing, from the Bohr papers. That's a rough translation.

Amaldi:

But, you know, I don't have this letter.

Weiner:

You probably didn't keep a copy, because that's the letter that was in Bohr's files. I just want to get your general comment on that. You write on these things in March of 1941, and then in August of 1942 and September '42, you're still writing. And then you dropped it. And you dropped it for the reasons we talked about.

Amaldi:

Yes, we changed. We stopped the work on fission. We were very much worried. We were afraid. We were aware that there was a big effort. Nobody had told us, but we were sure that both in Germany and in the United States there was certainly a big effort to exploit fission for a bomb, and we did not want to get involved in that. It was very simple.

Weiner:

By this time you were able to put your accelerator into operation.

Amaldi:

Yes, we used the accelerator. This was done very successfully.

Weiner:

You focussed on that then. Almost everything went on the accelerator.

Amaldi:

Yes.

Weiner:

There's an interesting paper that you wrote in this period that I want to get back to, and it's on the subject of artificial radioactivity by neutron bombardment. Now, it seems to me that this is a summing up paper. This is earlier, 1937. This is a paper, a very long one...

Amaldi:

In German.

Weiner:

Yes, in German. It seems to me that it represents a culmination of a lot of the work that you had been doing: "Artificial Radioactivity by Neutron Bombardment."

Amaldi:

Debye was the editor of the Physikalische Zeitschrift. I had been working under him on X ray scattering by liquids. We talked about it the other day. And when this work on neutrons was made, he asked me to write a kind of review of the situation on the artificial radioactivity, and so I wrote this paper. I know various physicists who used it as a kind of reference paper on the work that had been done. It was a kind of resumé of what had been done in Rome.

Weiner:

But it was at his invitation. So it wasn't something that you had been kind of leading up to naturally.

Amaldi:

Well, I was, of course...Well, you see in 1936 I went a few times to Germany, and I went to Berlin, and I went always to see Lise Meitner. I was on extremely good terms and friendship with Delbrück who is now at Caltech. Lise Meitner liked me very much. I was much younger, but she was a very nice lady, and she invited me on various occasions to give seminars. And also Hertz asked me to talk a few times in Berlin. So there were a certain number of people in Berlin--Meitner, Hertz and also Richard Becker. I was on very good terms with Richard Becker. And they invited me on various occasions. I gave a seminar on slowing down of neutrons, on neutron resonances and so on. Debye was not present at this seminar, but apparently somebody told him about this, and he wrote me one day and said, I know that the group in Rome is doing this nice work, but could you write a review article. It was a kind of invited paper for the Physikalische Zeitschrift. So I wrote the paper.

Weiner:

A review paper.

Amaldi:

A review paper. Well, there are a few things that are only written there, that have been written for the first time there. So there are little things that are original, but not very important. Some of the details are original, had never been written.

Weiner:

You know, this is interesting, because just about the same period Bethe with Bacher and Livingston wrote a review. Let me ask two questions. One is to ask what was the reaction to that? Was it read in Europe? And the second is: had the field of nuclear physics by this time arrived at the state that it was the time to write review papers?

Amaldi:

I think so Well, the articles of Bethe and Bacher and Bethe- Livingston have been extremely important. Everybody of my generation read and used the articles of Bethe and Bacher and Bethe-Livingston and Bethe also. These were three famous articles that were useful to everybody.

Weiner:

Did you use them at the time? Did you know about them right away?

Amaldi:

Oh, yes. The second one, by Bethe alone, contains a great part-- I'll say one-third--that is devoted to the work made in Rome by Fermi and myself especially on resonances. And on that I had a lot of discussion with Bethe--also because at that time Bethe and Placzek had written their paper on resonances, in which the theories of Breit and Wigner and Bohr were used. On all these things I had a lot of discussion with Bethe and with Placzek. I knew very well the experimental material; at that time knew it really very well.

Weiner:

They would come to you then.

Amaldi:

No, there was discussion, and I was asking them for theoretical explanation. You know, then there was discussion about, "Are you sure of that? How good are these experiments?" and so on. So we had a lot of discussions.

Weiner:

Where? Where does this occur?

Amaldi:

Well, for instance, sometimes in Copenhagen; in Rome with Placzek. Placzek went to Rome on various occasions. Between '36 and '39 he has spent a lot of time in Rome. And in Copenhagen. Then when I went to the United States.

Weiner:

Did you go to Ithaca then?

Amaldi:

I don't remember. I remember that I met Bethe in the United States, but I don't remember if it was at Cornell. I think it was not in Cornell.

Weiner:

Maybe some other place. But was this very close collaboration with theorists characteristic, do you think, of your work? I'm not talking about within the Rome school, but I'm talking about collaboration that you had with theorists outside of Rome. Or was it just around this particular group of people--just Bethe and Placzek? Who else? For example, in Washington, were Gamow and Teller involved?

Amaldi:

I met Gamow; I met Teller; well, Teller had been in Rome for some time working with Placzek. Teller was younger than Placzek, and he was working under Placzek. And Bethe was also in Rome. That was 1932 or '33-- when I was working with Placzek. Then a couple of years ago I met Bethe in Paris, and I asked him to give me what he could recall of the time he was in Rome; and among various things that he told me, he told me that at that time he was in the same room in the department of physics in Rome with Placzek and that at the time he was very unhappy because he felt that Placzek was treating Teller too badly--I don't know why. But you know how Bethe talks--very slowly. He said, "Only in recent years I realized that he did not treat him sufficiently badly." (laughs)

Weiner:

Very good. That's characteristic of him.

Amaldi:

In a rather professorial style. [Tape is changed]

Weiner:

Let me get back to another general question that I wanted to ask: the effect of the breaking up of the group in Rome--the fact that Segrè goes in '36 to Palermo and Rasetti later leaves and then Fermi. Let me just break down the question in one way. For example, after Rasetti and Segr left, there was just you and Fermi.

Amaldi:

Yes, and there was also Wick and Pontecorvo But in those years I was working with Fermi, and Wick and Pontecorvo were working together. It was the only period in which Giancarlo Wick made some experimental work.

Weiner:

Now, did they essentially take the place of Rasetti and Segré--you know, two leave and two different people...

Amaldi:

No, because we were working in parallel--in excellent relations with continuous discussions--we we were not working together. They had their line of research, and we had our line of research--all on neutrons. They started to study scattering, the back scattering of neutrons. And they concentrated all their effort on studying the back scattering of neutrons, while we concentrated our effort on absorption of neutrons, and so we found the resonances, and we measured the positions of the resonances. And what was more typical of the Rome work was the width of these resonances. And this was a very important point for the theory of Bohr of the compound nucleus, because of the difficulties was just to explain how one could have lines so thin, absorption lines so thin; and Fermi and I had measured these widths.

Weiner:

Were you in Copenhagen at any time during this period when these discussions...?

Amaldi:

Yes, there was a very nice conference--I think it was in 1936, in July or June--and I presented a report on neutron properties. I presented a report on the work made by Fermi and by me.

Weiner:

On the resonances

Amaldi:

On the resonances and on the slowing down of neutrons. At that time the conference was quite small. I remember Maurice Goldhaber was there and was quite young. Heisenberg was there and many other people. Well, one can find out, because there are records of this conference in 1936. I remember Meitner was there, and she was reporting on what they considered transuranic elements at that time. They were just fission products. And I gave a rather long talk on slow neutrons and resonances. Otto Frisch also gave some contribution on that. Placzek was there as a theoretician.

Weiner:

What was the reaction of people to the resonance question?

Amaldi:

Oh, well, Bohr gave a speech on the compound nucleus, and he had this model with balls falling down.

Weiner:

He already had the model.

Amaldi:

Yes, yes. He showed the model with the balls going down a little piece of wood. That was just the time.

Weiner:

But he already must have been in touch with you and Fermi by letter.

Amaldi:

Not so much directly. At that time the contacts between Copenhagen and Rome were mainly between me and Placzek. Placzek wrote to me rather regularly what was going on in Copenhagen, and I used to write to Placzek what was going on in Rome. The exchange was essentially through us. There was total communication. I was writing to Placzek, and everybody knew I was writing everything we were doing; and the same--Placzek was writing what was going on in Copenhagen. And in Copenhagen Frisch and Placzek were working on neutrons--and also Koch. He was a younger man working with them.

Weiner:

I see. So there was something for them to tell you, too, in the way of experimental results. It wasn't just a question of experiment, and theory coming back.

Amaldi:

No, Frisch was also doing some experiments in Copenhagen. Oh, yes. There was a paper by Frisch and Placzek on the cross-section of boron. That was developed at the same time by Frisch and Placzek and by Bethe and Livingston--the idea that the cross section goes 1/v, 1 over the velocity. But we had much more work power, just force.

Weiner:

You mean your group.

Amaldi:

Well, this was just Fermi and myself. But compared with other groups we were able to get more results, because we were working much more than the others.

Weiner:

You put more time in? You mean it's as simple as that?

Amaldi:

Yes, that simple. And not doing mistakes, and working from 8 o' clock in the morning till 8 in the evening taking measurements every two or three minutes, checking everything on the clock--and for months writing at night, working incredibly, with an incredible speed.

Weiner:

What explains this drive?

Amaldi:

This drive? I've tried to explain in the introduction I have written for the papers of Fermi.

Weiner:

You said you had to make up for the people who were missing.

Amaldi:

Partly that and partly because we were used to say: physics as soma. Soma was the word by Huxley in Brave New World for this pill against spleen. The men of 2000 and the girls of 2000 take a pill that is ca lled soma. It is against spleen. Did you read Brave New World?

Weiner:

Yes. In other words, because the situation was deteriorating in Rome...

Amaldi:

Exactly. So in a certain sense it was...

Weiner:

You buried yourself in your work.

Amaldi:

Working day and night, and the work was amusing. The work was nice and exciting, and the rest was disgusting, and then you concentrate on that. In part I think that was it. But we were able to produce many more measurements than any other group.

Weiner:

Yes, the output was tremendous, just tremendous.

Amaldi:

We measured a tremendous amount. I don't know if you've seen the dates in these laboratory notebooks that are at Pisa. Every day we have done a great deal.

Weiner:

More than that, I noticed that even when Fermi, for example, went on a trip to America--just on a trip when he was returning--there were still observations made: August 2nd, New York City; August 3rd, New York; the next observation is Rome. The only time lost is on the ship going back. Just amazing. Let me ask another question about this group, this style of work. What about continuity in terms of students? You mentioned a couple of students, and one thinks of a school as having some kind of a multiplying effect. But yet there was a feeling I get that it was a tightly organized group working very well in harmony, creating the kind of environment that would be useful for your work, and consisting very much of similar temperaments or compromising anyway to be that way. But that's good for four people, or good for two people. How was that carried out into...?

Amaldi:

No, it could not be done. It was not a group that could teach to many more people. We were just efficient in our work, and if we needed somebody else, we could get him. But this was in order to be efficient in our work.

Weiner:

You did have some students. Let's talk about how many you had.

Amaldi:

Well, Pontecorvo, Fubini, Fano, who is now in Chicago. We had lots of students.

Weiner:

What about other places in Italy, other places where physics was being done?

Amaldi:

Well, there was the group in Florence with Bernardini and Occhialini and the group of Rossi. They were extremely good.

Weiner:

But they were not doing the same sorts of things.

Amaldi:

No, they were essentially doing cosmic rays. And we were on extremely good terns with all of them. They went quite often to visit us in Rome, and we had exchanges. We used to go to Florence quite often to give seminars, and the people of Florence--Occhialini and Bernardini-- went to Rome to give seminars in Rome. We were on extremely good terms.

Weiner:

Would you say that your contacts were more, though, with people in your own field who were in foreign countries than with other physicists in Italy who were in different fields?

Amaldi:

Well, there were very few physicists in Italy in the nuclear field. The groups with which we were on extremely good relations were the groups of Rossi, Bernardini and Occhialini. And there were very few others who were doing the same type of work. Well, we had good relations with Carrelli at Naples that was still doing spectroscopy. We had regular contacts before when we were working on spectroscopy. But with very few people we had contacts. We had some contacts with Wataghin, who was in Turin. And then we had relations with some American physicists, some British physicists, almost no contact with French physicists. I would say good contacts with the people in Copenhagen and certain contacts with some German physi- cists. But that's about all.

Weiner:

You visited Berlin in the late '30s, so you had a feeling of the effect of the change of so many people leaving. Did you see any shift of interest in physics or any change...

Amaldi:

When?

Weiner:

In the late '30s in Germany when you visited. When was the last time you visited?

Amaldi:

It was in '35.

Weiner:

Oh, these visits with Meitner and so on--that was earlier.

Amaldi:

That was my last visit. Then I did not go any more. I went back to Germany only after the war, in '56 or so, maybe later. From 35 I did not go any more.

Weiner:

The communication of physicists in Italy during the '30s is another question which interests me. Were there meetings of the Italian Physical Society?

Amaldi:

Yes, there were regular meetings of the Italian Physical Society. We had very good relations with Persico who was in Turin. We had excellent relations with him.

Weiner:

How about journals during this period--as long as we're on this subject?

Amaldi:

Well, we wrote our papers for the Nuovo Cimento. All our letters appears in the Ricerca Scientifica. That was the journal of the Council of Research which provided money for the research. They appeared first there very quickly. In that period my wife was working there at this journal, so she was taking care of the things that we sent.

Weiner:

That helps.

Amaldi:

And then the two main papers were given to Rutherford, who was at that time President of the Royal Society, and were published in the Proceedings of the Royal Society as presented by Rutherford.

Weiner:

He helped there, too.

Amaldi:

Well, we, I remember, thought, "This is radioactivity." We have to ask Rutherford if he is ready to present it. He was very kind. He said, he was very pleased to present this paper. He was very satisfied.

Weiner:

What journals became of interest to you from the mid '30s on? Which ones became the dominant ones as far as you were concerned?

Amaldi:

Well, at the time of spectroscopy and quantum mechanics, the most important journal in the world was the Zeitschrift für Physik. And after that, the important journals were the Proceedings of the Royal Society and the Physical Review. These were the most important.

Weiner:

The Physical Review starting about when--do you recall?

Amaldi:

Well, it existed before, but certainly around '34, '35, '36, the Physical Review was then just starting to be a very important journal.

Weiner:

It would be interesting to do what you did with Kuhn. You looked in the library at the University to see when certain journals started. I'm just curious if there's a full run of the Physical Review.

Amaldi:

We have a full run from the beginning. We have quite a decent library.

Weiner:

I don't mean now, but then.

Amaldi:

We have from the beginning, right from the beginning. But in our department we have many, many journals from the beginning, also very old journals--Poggendorf Annalen for instance. That was born; it became very important; and later it disappeared. Our library has always been very good.

Weiner:

So you were in touch then.

Amaldi:

Oh, yes.

Weiner:

Well, that was obvious from everything you said.

Amaldi:

From all these points of view, Rome has never been a provincial place in a certain sense. The newspapers have always been there; the people have always read; there were always intelligent people--even if they did not produce anything.

Weiner:

I understand; it's an awareness you mean.

Amaldi:

People were aware. For instance, Corbino did not produce for years, but Corbino every week was reading what was appearing in Zeitschrift fur Physik and Physical Review. All journals that arrived he wanted to have on his table. He certainly read all titles and all resumés, all of somebody; and if there was an important paper, he has always read it. He was quite active as a politician, but he has always devoted some hours to physics, and he knew quite a lot, and you could talk with him with great pleasure. Fermi could always talk with him with pleasure. And he was asking intelligent questions. "I don't understand. You should explain me that." But it was always an intelligent question. He was not producing, but he was intelligent, and he could understand.

Weiner:

There's a role for such people. That's important. Let's get onto something else, because the time is running out. Talking about the effect of Fermi himself leaving in 1938--this is about the same period when you had to make a decision, and because of all of the things that you mentioned, you stayed--what was the reaction, first of all, among the physicists in Rome about Fermi's leaving?

Amaldi:

Well, when Fermi decided to leave he called me one day. He called Rasetti and me. We were very much afraid there could be microphones in the building. So we went into a room in which we thought there was certainly no microphone. And he told us he had decided to leave. He was very sorry, but he had decided to leave; that we were not to say it to anybody, but he wanted that we were informed. He told us. That was November '38.

Weiner:

What was your reaction?

Amaldi:

Well, we were very upset, but I could recognize that the situation was such that it was quite feasible that he had to leave.

Weiner:

Did he offer specific reasons at the time?

Amaldi:

Oh, no It was quite clear. Well, we were talking all the time that the political situation was deteriorating. Then there were these racial laws. While Fermi was not a Jew, his wife, Laura, was a Jew, and she was directly involved, and maybe the children. Nobody knew what would happen with their children. So it was quite clear. There was no need for Fermi to explain why.

Weiner:

But this was the major reason in his mind, or were there others, too? You know, had Fermi in a way decided that physics was through in Italy or that things would just come to no good?

Amaldi:

No, no, I think Fermi was completely fed up with this political situation, and he felt that this was going too far. Until that moment he could stay in spite of the many things he did not like, but that was too much. It was quite clear.

Weiner:

Once it became known that he was not coming back... not

Amaldi:

It was known with the exception of some friends until he was in New York, because he left to take the Nobel Prize in Stockholm, and from Stockholm he went to the United States. That was official; he went to lecture there, it was not so strange. Then after he was there, after a few months, he wrote that he wanted to stay longer. He never resigned. Every time he said that he wanted to stay longer, to stay longer. Then it was quite clear that he wasn't coming back. But he never did write any letter resigning. We discussed this point. He said very clearly that he would avoid to do any act showing that he was breaking all bridges, because he was afraid to damage us. So he told us, and I knew.

Weiner:

Was there any public reaction or any official reaction?

Amaldi:

Oh, once some newspaper attacked him badly, but they were attacking him already before he left. There were some Fascists who attacked him on various occasions.

Weiner:

They attacked him before he left. You mean because he was not sufficiently political?

Amaldi:

Yes, and it was felt by some people that this group of people around Fermi was very bad. There were some Jews: Segr and Pontecorvo The others were not. And everybody knew that we were on excellent terms. And then we were so much interested to travel around. We were around, and everybody knew that we had friends in England and America and so on. Everybody knew that.

Weiner:

Yes, you were physicists.

Amaldi:

We were interested in any other person who was interested in the same subject. All that was suspicious. It's incredible how many people can become stupid.

Weiner:

It happens in all countries.

Amaldi:

Yes. It is incredible.

Weiner:

Was there any deliberate attack on theory as such? In Germany this took place.

Amaldi:

Not in this form. There was an attack--not to Fermi--but after Fermi left, to Polvani. There was an attack in Tevere--I think it was Tevere. Tevere was the most extreme Fascist newspaper. Polvani was attacked because he had taken money from the Council of Research to build an instrument invented by C.T.R. Wilson--it was a cloud chamber--"in order to make a Jewish physics." This was the expression. Because Polvani had gotten some money from the Council of Research, and he had used this money for his assistant (Cocconi) to build a cloud chamber. And this thing was described in this Tevere as "a man who takes money from the Council of Research for building an instrument invented by an Englishman in order to make a Jewish physics."

Weiner:

I'd love to have that story.

Amaldi:

Unfortunately, I don't have .

Weiner:

So it didn't matter then that it wasn't theory. It was an experiment that required the cloud chamber for.

Amaldi:

Yes--but...there was never an attack, as there was in Germany, against relativity or things like that. Not of that type. But generally the situation was worse, because all of these things in Italy are made at the same time. The people tease and don't take too seriously.

Weiner:

In Germany it started much earlier. Lenard's attacks were way back.

Amaldi:

Exactly. Oh, well, I remember when I was in Leipzig, on many occasions I wouldn't say relations were difficult, but some relations were unpleasant.

Weiner:

Because of these attitudes you mean?

Amaldi:

Well, when I was in Leipzig I went skiing. I've always been fond of skiing and climbing--still now I am. And I took a Saturday train and went on the Czech frontier in Erzgebirge to ski. I was used to go to ski on trains with young people and so on, and the type of conversation was almost always very disagreeable. This never happened to me in Britain or America.

Weiner:

For example?

Amaldi:

For example, in these trains there were young people--boys and girls who would just laugh and so on--but when I talked, the moment I talked people noticed I was a foreigner. I was talking rather decent German, but of course with an Italian accent. They would say, "Well, where do you come from?" "From Italy." "What do you do here?" "Well, I am here with a scholarship, with an Italian scholarship, from my city. There are some scholarships for people born there to go and study abroad." "What do you do?" "I'm here at the University of Leipzig." "Oh, understand. You are here to steal the German science."

Weiner:

This was just a stranger staying this to you?

Amaldi:

Exactly these words have been told to me at least three or four times, not once, but in a kind way, accepting. They accepted that Germany was so much better than everybody else, and if anybody went there, it was just to steal their science. "Oh, you are here to steal the German science." Of course, Germany was the only country where science existed. Everybody on the train was convinced that nothing was going on in any other part of the world. I've never seen this in any other place, the profound conviction of these young people that only in Germany there was good science, and people came from other countries to steal something from thew., that because in other countries it is bad, "these poor people come and steal from us."

Weiner:

And yet I'm finding that the opportunities in German science by that time were very limited, and that actually it was on the downgrade. I don't know if I'm correct in this, but I get the feeling that the opportunities and the atmosphere were such that the slope was going the other way. I can't prove it, but it's a feeling that I get. This was before Hitler.

Amaldi:

This was before Hitler and German science was still pretty good, but one could find himself in unpleasant situations like that I said before. I was not impressed by things like that. I was ready to discuss and discuss without giving up, although nobody was convinced by my arguments. But this never happend to me in any other place. The first contact that one had was very often of this type.

Weiner:

There are a couple of things I want to cover in the remaining time that we have which is not very much, and this is: the effect of the war actually--what happened to physics, to you, after the scattering work. You dropped the fission.

Amaldi:

Well, at a certain moment after the bomb was exploded we discussed at length what to do. We felt that in the United States and other countries there were certainly piles. We could not have a pile. We could not probably compete with the others in neutron physics. And then we decided that the only thing to do was to concentrate our effort in cosmic rays. When I went back from the U.S.A. in October 1939 I was immediately called into the Army and I was sent to Africa. I was there during the War for not a long period, but for six-seven months. Then I was sent back to teach again. When I went back I tried to manage to collect all the young people in Italy at the University of Rome. At that time there were some assistants of Segrè in Palermo, some assistants of Rossi in Padua, Wick was professor in Padua; and I tried to gather them all. It was necessary to have at least one group to survive.

Weiner:

A critical mass.

Amaldi:

And so I succeeded to bring them to Rome. So all the people that remained in Italy concentrated in Rome, coming from these different groups that had been destroyed. Then Bernardini went to do his research activity Amaldi 39 in Rome; Occhlalini was in South America at that time--he remained there during the war. Bernardini was not yet professor in Rome, but he arranged to have all his research activity in Rome. And we decided that Bernardini and with Giancarlo Wick that had come from Padua to Rome, that the only thing to do to survive was to try to put all our effort in cosmic rays.

Weiner:

When was it that the people got pulled together in Rome? Was this just after the war?

Amaldi:

No, during the war. That's the sort of thing that you can do in Italy. When I came back from the United States, the dean of the faculty was a man that had signed the racial laws, just to describe the situation. He was a biologist. He was quite an authoritative Fascist. And everybody knew that I did not want to come back, and that I had to come back because I did not want to leave my family.

Shortly afterwards, I was called into military service and sent to Africa; I was not very well during that period because I was on very cold terms with many members of the faculty. But I went always to the meetings of the faculty. One of the first problems I had to solve was the following.

The mother of Wick was a well-known anti-Fascist, and she had been put in jail because she had been corresponding with Benedetto Croce--you know, the philosopher. She died last year--she was a very remarkable woman. She had been a very strong anti-Fascist, and she had been in jail. So it was a difficult problem to get the faculty asking Wick to come from Padua to Rome. Fermi had left; there was the chair of theoretical physics free; and I thought one should call Giancarlo, because he was a good theoretician And then the dean of the faculty called me, and he wanted to know from me if I was really ready to guarantee that Giancarlo was the best theoretician I said, "Of course, I can guarantee." "Then I will arrange with the Party how to manage." And we got Giancarlo Wick in Rome. It's strange; it's complicated. That would have probably been impossible in Germany.

Weiner:

That is hard to say. Did you get any work done with this concentration of people? Was any physics really done?

Amaldi:

Oh, there was excellent physics done. Well, during the war there was this experiment done on the mean life of the mesons--the Mu mesons which were measured. Conversi and Piccioni were two of our students at that time and Pancini that had graduated in Padua with Rossi joined them. They were very much under the influence of Bernardini when during the war they discovered the rather well known effect that carries their names.

Weiner:

But all of this wasn't published until just after.

Amaldi:

No, it was made during the war and published in Italian practically during the war. I communicated the results to Fermi by letter in December 1946 but most of the work was made by Conversi, Pancini and Piccioni during the war with very little means. At that time I was still doing some work on neutrons at the Public Health Institute.

Weiner:

Were you using...?

Amaldi:

I had started to study the diffraction of neutrons on nuclei with the help of a few young people and this was the last work that was done on neutrons. But during the war there was a lot of work made on cosmic rays. Bernardini took the leadership of a lot work on cosmic rays. I did the work on the diffraction of neutrons on nuclei, the determination of the dimension of nuclei and also the verification of the optical theorem. I think that's rather good work. But the most important work was on cosmic rays, also because it brought the discovery made by Conversi, Pancini and Piccioni.

Weiner:

This is interesting, because despite all of the pressures you were able to continue.

Amaldi:

Well, the discovery was actually done not in the department, because there was a bombing of the city of Rome in which we had some 95 bombs on the University. At the University it was no more possible to work, and so the equipment was brought to a different part of the city--in the cellar of a lyee, of a high school. The work was carried on also during the German occupation when most of our people officially disappeared. The work went on during this period.

Weiner:

This was your work...

Amaldi:

Well, the cosmic ray work, not the neutron work. This was not possible. That was also one of the reasons we decided we should do cosmic ray work, because we aren't too much depending on machines.

Weiner:

This way you're dependent on nature. And was there pressure on the group or for anyone to get involved in special war projects?

Amaldi:

No, there was no pressure. We were afraid of that. They simply did not think of us at all. Actually, we were sent to different places-- Africa, Greece, here, there, just as officers. The people did not consider the opportunity and the possibility to use physics for research for war. So we were never forced. We were afraid of that. That's one of the reasons why we stopped the work on fission. But actually they never tried.

Weiner:

When did Corbino die?

Amaldi:

He died in '37.

Weiner:

If Corbino had been involved in government and had supported the regime, then he would have perhaps recognized the role of physics.

Amaldi:

Well, after Corbino, Lo Surdo became the director of the department. He was not on very good terms with Fermi, and after Fermi left, it was not so easy, but we managed to go on in some way. After the war he told me once that in the First World War he had been in some technical service of the Navy.

He had worked in detecting submarines for the Navy by acoustical methods, by collecting vibrations under water, placing systems for determining the position of submarines, so he was in some way in connection with the Navy. And when the second World War started he told me-- and I believe it was true--he went to some admiral he knew in charge of technical service of the Navy and said that there was a rather good group of physicists at the University of Rome, and that they could be used for the war. But the admiral said, "Oh, we don't need them. The war will last a few months. We don't need any help." He told me that. It's probably true. But at that time we were absolutely unaware of that.

Weiner:

He old you this much later.

Amaldi:

Oh, we had all various adventures, and stories.

Weiner:

Now, you were talking about the reactions after the bomb. You were considering what would be appropriate, what field to get into, and you selected...

Amaldi:

Well, the bomb was a factor--the atomic bomb. But we realized there were reactors that had beams of neutrons that were millions of times stronger than we could dispose. Then why work in a field where there are people who can do in five minutes what we can do in months of work? It did not make much sense. But if you work on cosmic rays, cosmic rays are equal for everybody. Experimenting on cosmic rays is the same here as anywhere else, so why not do cosmic rays research?

Weiner:

Well, that's a very practical solution. Were there any questions of physics that were especially attractive?

Amaldi:

Well, cosmic rays was a very attractive subject. There were a number of problems connected with elementary particles, but just to use a natural source.

Weiner:

That's what I getting at, about the elementary particles. When did this concern with the need to study elementary particles and nuclear forces, and to get higher and higher energies in order to do so-- when did this concern become apparent?

Amaldi:

Oh, well, it was quite clear. I should say that when we were doing with Fermi in '36 the scattering of neutrons by protons we were aware that the most important aspect was the study the nuclear forces between neutrons and protons. And when I started work on fission and I started to work on the scattering of neutrons and protons, we were mainly aiming to the nuclear forces between two nuclear particles. I have written that. So the main interest for us was that.

So at a certain moment we decided to stop the work on neutrons. But I was mainly interested from the point of view that a neutron is an elementary particle, and then I started essentially to work on the interaction of mu mesons with the nucleus. So it was a different problem but essentially the same line of research. The technique was different, but the interest was essentially the same.

Weiner:

And so you felt that the cosmic rays gave you the opportunity to pursue the same interest?

Amaldi:

To pursue the same interest without being in a too bad condition with respect to the others. Now, the problems are not exactly the same, but the type of physics was the same. The essential laws of physics were the same.

Weiner:

You were asking the same questions of nature in a sense.

Amaldi:

Yes. Well, if you are interested in the interaction between elementary particles--now you could distinguish between weak and strong interaction--but at that time to study the interaction of a neutron with a proton or of a meson and a neutron is very close, very similar. Amaldi

Weiner:

What was the position you were in? You made this decision before the war had ended already.

Amaldi:

I don't know exactly what date. I would say the decision to move to cosmic rays was more or less taken at the time of the bomb. We realized that there was too big a gap between any effort that we could do in Italy on neutrons and what was going on in the United States or other parts of the world.

Weiner:

This may be a bigger story than you have time for now, but let's just get a feeling for it. How did you go about getting started?

Amaldi:

Oh, there were people doing cosmic rays in our department for years. Bernardini was doing cosmic rays, and all of these experiments were discussed by all of us, and so the techniques were known to all of us and so on.

Weiner:

It didn't require any investment of time and of retooling.

Amaldi:

No, we were all quite well prepared.

Weiner:

And so were you able to make this transition?

Amaldi:

It was no problem.

Weiner:

When did things get back to normal again at the University, what year, would you say? When you had laboratories again and things were rebuilt?

Amaldi:

We went on doing cosmic rays until we had the synchrotron in Frascati.

Weiner:

And when was that?

Amaldi:

This was in '59--and then the machines at Cern in Geneva.

Weiner:

So the investment in high-energy equipment wasn't made until '59?

Amaldi:

It was made in '54-'55.

Weiner:

So you were able to work with available resources to do some very good work during this period. How did you feel your position was during this earlier period, the late '40s, early '50s, in relation to the development of high-energy physics throughout the world as a separate, distinct field?

Amaldi:

We were rather integrated in the general development. Well, for instance, we had this work with emulsions exposed to cosmic rays in 1952. Around 1950 we started organizing expeditions of balloon flights, exposing big stacks of emulsions in very high altitude. And this was done with European collaboration, in which 10-19 European universities were involved, and Powell from Bristol had a very leading role in this type of work. And we were working all together, and we have done two expeditions from Sardinia. We have launched balloons from Sardinia and then later from North Italy. And at that time we went to all international conferences. We presented our results, and they were quite decent.

Weiner:

Respectable.

Amaldi:

Well, just decent and presentable and appreciated by everybody as quite decent work.

Weiner:

I didn't mean it in that sense. The answer to that is obvious. I'm talking about whether you felt isolated at all in the immediate years after the war.

Amaldi:

Immediately after the war I had a very unpleasant impression, and that was also one of the reasons why I changed to cosmic rays. Immediately after the war I went to the United States. I was invited to go to a conference in '46 at Princeton, the first international conference after the war, and there I met Fermi for the first time. Later on the same trip I went to Chicago I was with my wife, and we went to Fermi's house and we were living with them for some time.

I had been at Cornell and MIT since I made a tour around, and I went to give seminars everywhere on what we had done during the war. And the work that we had done was appreciated by everybody. So I was rather satisfied. And then Fermi asked me if I did not want to go to Chicago After all, he said, they had discussed me in Chicago, and they would be very glad if I would go there. And I was rather uncertain, and then I decided not, because in a certain sense...Well, I discussed this a lot, also with my wife. We felt that it was not the right moment in a certain sense. There was some hope to start something more decent in Italy, and I felt it was not nice now that I go away, and so I decided to stay.

But what was unpleasant to me was the following: When I went to Chicago and I talked about neutrons with Fermi, he was talking completely freely up to a certain point, and then it was quite clear he did not want to give more information--not because he did not want, but he could not because a lot of work was classified. I found that extremely unpleasant. I found that was one of the most unpleasant things--the fact that we could not talk any more freely. So I did not want to work in a field where the people were not able to talk freely.

Weiner:

So that figured in your decision.

Amaldi:

This was one of the elements. I like neutrons. But I like also mesons. I found it very unpleasant, especially with Fermi. We used to talk and talk, and it was quite clear that after the war he could not say everything any more. With another person, it could have been different, but with Fermi it was terrible. I don't blame Fermi-- of course it was the situation--but I found it very unpleasant.

Weiner:

Especially because of your close relationship with him prior to that. How do you think he was affected by his experience in the United States as a person? It's a hard judgment to make, but are you able to make any judgment on that?

Amaldi:

I met Fermi three, four, five--years before the war; Fermi at the beginning of the war; Fermi immediately after the war; and Fermi five years after the end of the war; in each period he was a different person in certain respects. Immediately after the war Fermi felt like many others who emigrated from Europe to the United States. These people felt very strongly their...

Weiner:

Loyalty?

Amaldi:

Loyalty to the United States. Especially Fermi. Fermi was an extremely loyal person. There's no doubt. Above any other quality, he would never have done anything which was not correct. But sometimes this extreme loyalty, which I can understand and appreciate, pushed him even into too strong and definite a position in a certain sense. He was extremely severe in all his judgments of all that had happened in Italy, not only the Fascists but also on the people who were not Fascists--immediately after the war. After some years I felt that in some way he had understood more.

Weiner:

Did he ever return to Italy after the war?

Amaldi:

Oh, yes, he went twice. The first time was in, I think, '48. And the second time was the last summer before he died, and we were together until he left for the States. We were in the Dolomites together.

Weiner:

As a last question, let me ask you to think back over your career and, if you can, identify what you think was the most satisfying period and the most satisfying piece of work that you did, that gave you the most personal satisfaction?

Amaldi:

Well, it was the period when Fermi was there--there is no doubt. Also because maybe we were younger. That's also a factor. You have more energy; there's more excitement. It is difficult now to say. But this was a period that was successful and very pleasant, and the relationships were very nice. I should say that we have talked about that on many occasions--also with Fermi and Segrè--and I believe that also for them this has been the unique period, even if they had other periods very satisfactory. The atmosphere in Rome has been extremely pleasant and nice. Things came out in a natural way. It seemed natural to find a new radioisotope every second day--pleasant but natural--and that was very nice.

Weiner:

I guess that would then correspond to your evaluation as to which of your periods were the most important in terms of science itself, because personal satisfaction needn't be the same as external results, but you say it does correspond.

Amaldi:

I think so, yes.

Weiner:

I think we've covered a great deal of ground. There are a thousand things we've left out. You know better than I. But I've gone over the time limit that you set, and your wife is going to be worried.