Oral History Transcript — Hanni Bretscher
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Hanni Bretscher; July 10, 1984
ABSTRACT: Interview about Egon Bretscher with his wife. Joins Ernest Rutherford at University of Cambridge in 1934. Work on nuclear cross-section measurements leads him to Los Alamos, at Niels Bohr’s request; collaboration with Edward Teller on hydrogen Bomb project. Plutonium work is discussed. Many anecdotes; comments on the Oppenheimer spirit at Los Alamos; the Trinity test, effect of Nagasaki bombing on him; his views on atomic energy in 1946 and 1966; retirement years. Also mentioned are: Chadwick, Klaus Fuchs, Otto Hahn, Hans von Halban, Lise Meitner, and Wolfgang Pauli.
Bennett:Can you tell us about your husband’s work in Switzerland, and why you both came to England, particularly Cambridge?
Bretscher:Well, my husband originally was a chemist, and it was some molecular structure which he wanted to decide) which led him to physical matters end he shifted over to the physics department, but he wasn’t really a physicist, and he learned his physics only in the early thirties. However, by ‘34 he seems to have learned enough physics that he was chosen as a Rockefeller Fellow, and originally he was going to work under Blackett. But his boss didn’t want to sign him to be able to go to Blackett, and said he could go either to Germany, or to Rutherford in Cambridge, and of course he chose Rutherford in Cambridge. And Rutherford accepted him. So he really drifted into nuclear physics by accident.
Bennett:So what was that sort of work that your husband was doing in the early thirties?
Bretscher:Well, I mean, he really learned his physics. He had some operations going, sound recording, which circumvented the existing patent, but it was just by chance he got onto that. He was the sort of person who jumped from chemistry to physics; even in physics Jumped around quite a lot, until he settled onto nuclear physics. I think that’s the best thing I can say.
Bennett:Can you tell us about why he made the change from chemistry to physics?
Bretscher:Well, I said, he needed to study physics to answer chemical structure questions, and he couldn’t do that in the chemistry department, so he moved over into the physics department, and funny enough, the professor of physics offered him an assistantship as a physicist, and he was absolutely incapable really of holding this job, but he seems to have learned pretty fast. When I first met him, it was quite obvious that he knew nothing about physics.
Bennett:What is it about (this attraction of) physics? We were talking a little while ago about the links between physics and philosophy.
Bretscher:Well, I would like to say nuclear physics in particular is an aspect of physics that, you could say, belong to natural philosophy, as it was called at the time, and so you had (to have) the approach of the philosopher. I can’t see any other motivation for doing nuclear physics than wanting to know about things without any other practical motive. [This was particularly true of] the time of the early thirties, the discovery of fission. Rutherford, as you know, never believed that it could be used, and of course as long as it was only splitting off alpha practical of atoms, it was very true; you spent a lot more energy to do it than what you got. So he was absolutely entitled (to his skepticism), and I’m sure he would have seen the implications of fission straightaway, Just as everybody else did.
Bennett:What do you remember about the tremendous advances which were being made in physics say in the year ‘32, when the neutron was discovered, and cyclotrons were coming in? It seems a pretty exciting time to be getting into atomic physics.
Well, don’t forget, my husband Egan only got into Cambridge in the autumn of ‘34, and this was ‘32. Of course we heard about it, the discovery of the neutron or we had known about it before. There are several stories we picked up. For instance, those from the technical assistant that helped Cockcroft and Walton to do their experiments, shooting alpha particles at elements, was later a technical assistant to my husband during the war years when Cockcroft wasn’t in Cambridge any more. He said Cockcroft always did a lot of things, not just one thing, and was always away busy on various jobs, when the apparatus didn’t work, and so the “slug work” was really done by Walton. Then, when it worked, Walton really was nice and let Cockcroft know -- even when, for the first time, he realized that there was a certain scintillation, which meant that an alpha particle had been coming out. Walton was left there alone, and he phoned Cockcroft to come and see.
Cockcroft must have been very aware of the situation, because Cockcroft, for a long time, didn’t get the Nobel Prize for that work, and the reason, as it turned out, was seen in correspondence of Rutherford later on. Rutherford put his foot down; that for this particular experiment, the Nobel Prize had to be given to both, and couldn’t be just given to Cockcroft, who seemed to be an already known name. And the Nobel Prize people sort of couldn’t make themselves give the prize to somebody they didn’t know, and so (the Cockcroft-Walton team) never received the Nobel Prize until after the Second World War. Actually, in consequence of some evening chatting, as one does in Los Alamos, we were talking about who had missed getting a Nobel Prize for good work, and Cockcroft and Walton were the people -- but then by that time we knew why they hadn’t received it. Egon felt they really ought to have had it, and he said, “They didn’t get it, because Rutherford wanted to be absolutely fair.” Then after the war, early fifties already, Hans Staub became professor in Zurich. He was being asked by the Nobel Prize people for suggestions, so he wrote to my husband, should he put Cockcroft and Walton forward? He understood it had to be Cockcroft and Walton. My husband said he thought probably it was fair, and so he did, and he was the only one who put them forward, and they got it (the Nobel Prize in Physics).
Bennett:Getting back to Switzerland for a moment, can you tell us a bit about conditions in Switzerland? I seem to remember that you said that in order to get on, it was necessary to go and --
Bretscher:Well, in Switzerland, we have full professors, what corresponds to an American full professor, head of department, perhaps, one of those, but there was nothing like lecturers or readers or anything like this. They just had assistants which were very poorly paid, and meant to have a chance to do a PhD. Then after that, there just wasn’t anything to follow up, so they all emigrated. When we first met, my husband said, “Of course, you have to be aware that you will have to emigrate to the States.” But then it was Rockefeller who brought us to England, and we liked it here. Rutherford asked my husband to come back to Cambridge, so it was all very pleasing to us.
Bennett:So you came over here for two years.
Bretscher:For one year, with the Rockefeller Fellowship. Then we went back to Switzerland. But (Rutherford) asked us to come back, and so we did in ‘36.
Bennett:So now I think we ought to go on to those years, from coming back from Cambridge to Switzerland, and what went on after that. You came back to Switzerland.
Bretscher:We wrote a letter very soon after we had got back, saying we would like to come back to Cambridge, and then we never got an answer to this, and my husband arranged that Cockcroft and Oliphant were invited to a conference in the summer of ‘36. When they arrived, Oliphant said, “Why on earth did you never have the decency to give us an answer, whether you wanted to come to Cambridge or not?” He said, “Well, of course I replied!” The letter must have gotten lost in the Christmas mail. And Oliphant said, well, it was tragic now because Rutherford had always been short of money in the Cavendish, and he had used some money which he had put away for his chemical adviser on something else, so there wasn’t any money; but he and Cockcroft would go back and see what they could do, and soon we got a letter from Rutherford to say that he could arrange for Egon to come -- unfortunately there wasn’t much money, but he could arrange for my husband to get the Clerk Maxwell Scholarship, as he and Dirac were the only ones to decide! He was sure he could organize it, if we were willing to come, only getting that money, no more. So we did come, and when Rutherford realized that I was going to have a child, he was very very anxious, was very charming, and took an interest that we should be able to live, and he said, “Well, now, I’m giving the Royal Institution Lectures, and if they give me money for an assistant for those lectures, then if you’re willing to be my assistant, I can make up your salary with that. And that’s what happened. We very much enjoyed our time in Cambridge because Rutherford was the most grateful of men. I mean, he always pointed out that Herr Bretscher has done this and that with the lectures, and it was very marvelous for my husband to work together with Rutherford on this.
Bennett:Did you decision to come to England, have nothing to do with the worsening political situation in Europe?
Bretscher:No. No. Not at that stage. I mean, I had liked very much the spirit of this country. I was particularly impressed that men like Bernal had no interference professionally, although the fact that he was a Communist. I mean, in Switzerland, people are so narrow-minded that that would not have been possible. So I liked that aspect. But other than that, I wouldn’t say politics came into our decision to come to Cambridge.
Bennett:When did you start to become aware of the situation?
Bretscher:Well, I mean, obviously we were very much aware of Hitler. In Switzerland, you couldn’t help it. We were just “inferior mountain race of Germans,” and our mountains were compared called by the Germans, “our Alps;” so it was uncomfortable, in a sense, the situation, but at this time it was Germans who would come to Switzerland, rather it was the Swiss running away. And of course, once we got to Cambridge, we got to know a lot of refugees. It was impossible not to be aware of it. In fact, we were a lot more aware than the British. I mean, that was the trouble with Fuchs, that he found the British rather -- well, not seeing Hitler really as the danger he was. In ‘36, ‘37.
Bennett:Yes. Would you comment on what you meant by Fuchs being able to see the danger of Hitler but the British not being able to? In what connection?
Bretscher:Well, I mean, obviously Fuchs knew very well what the dangers were, having been thrown out himself. Very often, the British attitude was, “Well, if Hitler would happen in this country, he would be on a box on Hyde Park corner.” It was a certain -- it just wasn’t quite realistic.
Bennett:When did you first meet Fuchs?
Bretscher:Only in New York. That was in ‘44, January ‘44. He was hanging around Peierls’ office in New York. We had arrived practically without any money, because during the war, you could take out only five or ten pounds, so we just about could afford a taxi to the hotel. Peierls had an office in New York, and we had to go and discuss our finances with gir1s, and there was this stranger Klaus Fuchs, hanging around much to my annoyance, because I thought he had no business. There we had no secrets, but nevertheless -- so there was my first introduction to Fuchs.
Bennett:We’re jumping a bit now. I think we can go back and pick up what we were talking about. Who actually stands out in your memory of the men of physics in those years?
Bretscher:Well, that would be probably Pauli, the theoretical physicist.
Bennett:What are your memories of him?
Bretscher:Well, as it happened, I did take his course in theoretical physics, and the interesting thing about him was that his mind was so very different from the ordinary person’s mind. He seemed to be able to deal with very difficult questions. I mean, he’s famous for having, written a good summary on relativity aged twenty which was really an achievement at that age. On the other hand, there were simple things, which are easy for us, which were difficult for him. The funniest thing that ever happened was that he drew an ellipse on the blackboard, and then he put the focal points onto the short axis, and stood away and sort of looked and didn’t know quite what was wrong about it -- but it was so absolutely impossible! So, yes, that was the interesting thing about Pauli, his absolutely different make-up.
Bennett:What was he like as a man? When you got to know him?
Bretscher:Well, he could make very good remarks. For instance, a friend of ours, Felix Bloch, was assistant to Pauli, and one day he wanted to talk to Pauli and went and knocked on his door, and there was no answer -- so, in the end, he just opened the door to make sure he wasn’t inside, and so he was, sitting quite engrossed in something, and then he was astonished, and said to Bloch, “It seems you don’t have any manners! But never mind, manners only keep people apart.”
Bennett:Was there any one else in this time that you got close to, in the scientific world, in physics?
Bretscher:Well, Landau the Russian physicist, who was for a while with Pauli -- and we saw quite a lot of him. He seemed to like us and we saw a lot of him. He very much enjoyed being a naughty boy. He even once, after a colloquium, when a few physicists were standing together and Scherrer? was one of them, he said to Scherrer, “Scherrer why don’t you leave your wife? You don’t love her.” Just like that. So he really enjoyed to be a naughty boy. That was Landau.
Bennett:Do you have personal recollections of von Laue? Or Einstein?
Bretscher:No. He may have been at the conference. I think he was, but not that I ever remember him. No, Einstein is a person I have only seen through a window in Princeton, when Pauli pointed him out. Photographs tell more than I can say.
Bennett:At Cambridge did you meet Lise Meitner?
Bretscher:No, Lise Meitner I met for the first time in Zurich, at that conference where Oliphant and Cockcroft came in ‘36, and she gave a talk on transuranic elements. And right there, my husband was sure it wasn’t right, but he wasn’t really saying so in the discussion.
Bennett:Could you expound on that story a little more, because in one sentence you’ve dismissed it, but it’s a lovely story to tell, and perhaps in doing so, if you could tell us, bearing in mind that the audience watching this may not exactly know what transuranic elements are. You were listening to Lise Meitner expound this theory of transuranics.
Bretscher:Well, yes. I don’t suppose I can sort of remember the details, but I think my husband didn’t say anything in the discussion because she seemed to be sort of rather touchy about things, and he didn’t want to openly attack her.
Bennett:What was she saying? Could you just give us a brief idea of what she was saying?
Bretscher:Well, I mean, she was claiming that she together with Hahn had found elements heavier than uranium, and some, I’m sure, they must have found, but she particularly talked about one that had properties like Barium and I think that’s what Egon hooked onto as chemist and didn’t believe that that could be.
Bennett:What did he think?
Bretscher:Well, he just doubted that that particular thing was a transuranic element. When he got to Cambridge, he asked Feather to make an experiment. Feather was actually involved in the jumps of electrons in the outer shells of different elements, and Egon said to Feather, “Here you have the ideal tool to find out whether that transuranic element is there, whether you can find the right jumps,” and Feather didn’t say he wasn’t going to do it, he just didn’t, and my husband got very frustrated over this. For a long time he said, “If he only had the sense to do something that really gives an answer to something!” But Feather actually did do the experiment as soon as fission came out. It was Frisch who was first showing that fission was happening. It was Feather who then did the classic experiment and published it, that the transuranic element wasn’t there.
Bennett:But if he had taken the advice of your husband --
Bretscher:-- then he would already have earlier known that it wasn’t there, and therefore that barium in fact must be barium. And of course, my husband talked about it quite a lot, and a young Canadian, Cook, had worked with Hahn in Berlin, and was supposed to come and work with my husband in Cambridge after that, and in the summer holidays, he came over to Cambridge, that was in ‘38, to find rooms and make arrangements to come back here in the autumn, and then he returned to Berlin, and obviously my husband told him that he didn’t believe in transuranium elements, that it must be barium. So Cook went beck and told Hahn that, and Hahn’s reaction was, “Well, you don’t mean to say that I’m such a bad chemist that I don’t recognize barium when I have got it in front of me?” That was the report. Nothing was heard after that until a few months later, Hahn published that he actually did find the barium, and how much he was influenced by that statement, I don’t know, that he went back to look.
Bennett:That does bring us quite neatly onto the discovery of fission, but have we left anything out? Niels Bohr, yes.
Bretscher:But he will come later.
Bennett:So, have you a question?
We haven’t actually talked about Rutherford. I mean, I was asked about people early in the thirties in Zurich, and that’s what I talked about. Now, of course there was a galaxy of people when we got to Cambridge. There was modest, nice Wilson. He was such a quiet man, and I never understood how this nice quiet man once even asked just Egon and me for tea, and he made the tea himself. He was such a charming, honest, human man. Aston, I only saw his mass spectrograph, but these two things were important things that were going on before Rutherford actually came, or had been started before Rutherford actually came to Cambridge. Of course, in Manchester he had done his model of the atom, the important work. While he was in Cambridge, they carried on then with the, (32),? as you said, both big experiments, the transmutation of elements with Cockcroft and Walton, and the finding of the neutron, both experiments obviously which Rutherford had “put the problem” [to the discovers]. He had predicted the neutron in 1920, in a lecture, and the story I heard was that when -- that, well, I’m sure, both at first made some experiments, which he couldn’t understand without the knowledge of the neutron.
Then Joliot and Curie followed on, doing more experiments, and couldn’t understand them quite but published them. And when this publication came, the story I was told was that Rutherford took the publication and said to Chadwick, “Here is something for you to read.” So he must have had suspicions that that all was going to be sorted out with the neutron, and indeed in a few weeks, Chadwick had found it, the proof of the neutron. Later on there was discussion, you see in Cockcroft’s book, where Madame Joliot Curie said that if she had only read the 1920 lecture of Rutherford and knew the suggestion of the neutron, of course she would have understood her experiment! Anyway, it’s typical that Rutherford, in either of those two cases, didn’t even put his name to it. That probably accounts for a remark I heard, when Egon had become staff of lab. We were invited for lunch at Rutherford’s house, just together with the Cockcrofts, and … I still see the way Rutherford turned towards Cockcroft and said, “I will make a quite a good physicist out of you!” Another achievement, not in ‘32 but ‘34. There were three main people working with Rutherford, Chadwick, Cockcroft and Oliphant (and Oliphant was actually Rutherford’s pet), and it was this collaboration with Oliphant that they found the existence of tritium, and of the helium with mass 3. It was quite an achievement too. Really very much has happened around Rutherford.
Bennett:Can you give us a little portrait of Rutherford as a man?
Bretscher:Well, I have already mentioned how he worried about people like myself and my husband being able to live, which we very much appreciated. And my husband, right at the beginning, when he came, tried to go and see Rutherford, and Rutherford was very unfriendly. But Egon realized he had just to go again and he went to Oliphant and said, he had no good reception from Rutherford, and Oliphant burst out laughing and said, “Well, of course you didn’t. It was five minutes before his lecture. He never can find his lecture notes, and he always gets very flustered.” So even the great man got flustered before his lectures. Yet the way he didn’t put his name to publications showed how generous he was. And there is another story which unfortunately isn’t known enough. When Oliphant tidied up all Rutherford’s papers after his death, he found some which were supposed to be kept quiet for some time still, and there was some correspondence on him getting the second Nobel Prize. He had had the Nobel Prize for chemistry, already in 1908, and much had happened since, so it was thought that it was time that he should get a Nobel Prize for physics as well, and he was approached over this. His answer was that he had had enormous encouragement as a young man, getting a Nobel Prize, but now the money would be better used on another young man rather than on him. Considering that he actually was short of money all the time, he was talking about being short of money, it’s Just an incredible reaction.
Bennett:Yes. One wouldn’t find it in many men, to turn down a Nobel Prize. That’s nice. Maybe we can go on, unless there’s anything else you want to tell us about Rutherford?
Bretscher:No. That seems to be the main story. I don’t think I can produce anything that would show more, how generous he was.
Bennett:I think we should go on to the immediate aftermath of the discovery of fission, and the little story about meeting Hahn. And what that --
Bretscher:Yes, well, all right, that brings us to early 1939. Bohr came over (to England) to give a talk at the Royal Society, on his work following up fission, and Hahn was around as well. We all had lunch at Cockcroft’s house, just the six of us. After the meal, when Cockcroft and Elizabeth had gone to make coffee or something, Hahn took the opportunity to tell Niels Bohr that he had been terribly upset about him taking the news of fission to the States and advertising it, because he wanted to give Lise Meitner time to be the only person who knew about it, and that she could work on it and establish it. Of course, Lise Meitner and Hahn were for ever so many years close collaborates, and then in the end, because she was Austrian, Lise Meitner still felt for a long time she was safe in Germany -- but in the end she wasn’t, and she had to go out, go to Sweden, so Hahn as a German felt terrible about this, and he thought he could sort of make up for Lise in some ways, and that was -- it didn’t work out like this. However, I think, you can’t “pass on” discoveries. That lunch was the first time I met Hahn.
Bennett:And you met Niels Bohr as well?
Bretscher:Yes, that’s right.
Bennett:What was Bohr’s reaction to Hahn’s --
Bretscher:Well, there wasn’t much he could say. He just was told he’d done something he shouldn’t have done.
Bennett:Was he apologetic?
Bretscher:Well, yes, but -- I mean, not having been explained, he really wouldn’t feel very guilty.
Bennett:What was your impression of Hahn?
Bretscher:Well, I thought he was very charming. He tried to help Lise, but I think it was a bit naive way of trying, going about it.
Bennett:But generally, as a person?
Bretscher:Well, you see, I just met him over that lunch, and, then many years later, he came to Harwell, and he actually stayed at our house. I don’t know why Cockcroft used to pass some people on to us. But Hahn was one of them -- Heisenberg was another one. By that time, Hahn was a charming grandfather, showing his grandchild pictures, and I didn’t even want to go back to suggest that Egon might have pushed him into fission.
Bennett:You mentioned Heisenberg. Did you know him?
Bretscher:Well, he stayed one night at my house. Egon had heard that Heisenberg was practically a concert pianist, and so he had terribly wanted to hear him play, and he couldn’t at that stage. Heisenberg seemed to be a quite nice natural person then. There’s a story that Pauli and Heisenberg had a bet one day, and if Pauli would win he would get a bottle of Moselle wine, and if Heisenberg was winning, he would get a pair of tennis shoes. So that shows his sort of outdoor life and natural way of living. But of course, there are other stories that I heard later.
Bennett:When did you first encounter Heisenberg?
Bretscher:Well, he came to give a talk in Zurich at one stage. I’m not quite sure. That was probably in the summer of ‘34, something like that. And well, how it is you look at people when they come to talk, and I was very tickled that afterwards, Felix Bloch, who was an assistant to Heisenberg, said that Heisenberg actually talked about me when he got back to Leipzig. Have I already mentioned the paper Feather and brought out?
Bennett:You mentioned it in passing.
Bretscher:Well, just to say that Feather at last did the experiment which had been suggested, and didn’t find the trans.
Bennett:The paper came out, verifying the experiment.
Bretscher:Yes, yes, the paper, it was a good paper, but it wasn’t THE paper.
Bennett:So we’re now up to the year of ‘59 and obviously getting closer and closer to the outbreak of the war.
Bennett:What do you remember of that year?
Bretscher:Well, perhaps I might say that the first time that I had an inkling that atomic energy might or fission might lead to something more than a physics fact was at a tea party at Dee’s house, where somebody came up with the suggestion that physicists internationally ought to be organized, that they all were going to make parcels of uranium end simultaneously send them to Berlin to Hitler and blow him up. That was the first time I heard something about what could happen! And that of course brought me “into the know” at a fairly early stage.
Bennett:Is there anything else around that period?
Bretscher:At that period, it’s really the war preparations. All the people in Cambridge went away for some sort of training, which had nothing to do with nuclear physics, but the fact that they were physicists and could be trained in radar work or something like this. And at that stage, well, we were obviously, as foreigners, left behind. And then it turned out that the others were never to return, since the war broke out before they came back. Egon was asked by Dee to take the high tension set, it was Dee’s baby, and he wanted Egon to have it and which gave him all the possibilities to do the work after that. Only one senior British scientist who was left behind to sort of look after things. Of course Bragg was still there as a professor, but I think certainly the nuclear physics side of the Cavendish was to be run by Feather.
Bennett:Were there any other ways, the fact that you were Swiss, affect your life at this time, and provide -- a chance to do this work?
Bretscher:Well, my husband had actually to report to the police every morning on his way back into the lab, to show that he wasn’t up to mischief somewhere else in the country. You wouldn’t call it normal with the blackouts and everything, but I mean, it’s was not different for us than for anybody else.
Bennett:So your husband now had access to all this high tension equipment.
Bretscher:Well, he was in charge of the high tension set, yes.
Bennett:What work did he then go on to do with that equipment?
Bretscher:Well, it was early in 1960 that Cockcroft, who had been scientific liaison, or whatever you call that, between France and England, came to say that things are happening in the Joliot Lab in Paris, and it would be a good idea if he started measuring cross-sections, and so that’s what he did. I mean, this is a typical Cockcroft act. He really was very useful in recycling ideas. He had a notebook. He was quiet, nobody much noticed he was there, he made his notes and reproduced the ideas where they were useful. Obviously it was a very helpful thing.
Bennett:Was it before the first Peierls memorandum?
Bretscher:Yes. I think so. I’m actually not sure about the date, because at the time we didn’t know about it, you see, so I don’t know.
Bennett:But it was an independent decision, to start working on measurement of cross-sections.
Bretscher:Well, I understood that it was influenced by what was happening in Paris.
Bennett:And is there anything that you can tell us about that work that your husband was doing?
Bretscher:Well, I only know that, in hindsight, it was very good work, because one reason that we were going to Los Alamos turned out to be that particularly Niels Bohr wanted to discuss with my husband how he had done those measurements, because they were very important to figure out things about the bomb. On the other hand, a lot of American labs had done the measurements as well, and had very different results, so obviously they wanted to go into the details. My husband very modestly, in the end, said to me, “I was lucky, I got nearest to the right value.” The collaborator French later on explained why he was lucky, whet thinking he had done to be lucky.
Bennett:Shall we go on now to Hans von Halban and Lew Kowarski when they came to Cambridge. What can you tell us about them?
Bretscher:Well, they were two very different characters. Halban was really a politician, and Kowarski was a sort of a bridge player, very intelligent, very wise person. One story makes clear the relationship of the two. Halban was extremely anxious that, from the start, the British ought to understand that he is the number one and Kowarski is number two. On the boat, he got information about London hotels, and he decided to book a hotel that gives the right background to his personality, makes the right impression, while Kowarski had to be put up at some minor hotel.
Bennett:How did your husband like working with them?
Bretscher:Well, my husband made it quite clear that he was having the high tension set and his group, and they were really independent I mean, they would talk to each other, obviously, but my husband was quite sure that he wasn’t going to be one of Halban’s stooges, because he didn’t want to be summoned on a Sunday morning because Halban had a brilliant idea or something, most important, and it was Egon he “had to see.”
Bennett:So they really were two groups.
Bretscher:Two groups working quite independently. Halban and Kowarski were in the Old Cavendish, and my husband was in the high tension lab, it was in the Austin Wing.
Bennett:I think we must have reached the MAUD Committee, how that was set up and what effect it had on the work your husband was involved in.
Well, I mean, the fact is, the work of my husband was really essential to his contacts with Halban and Kowarski, knowing what they were doing. My husband had always taken an interest in energy. He was very worked up always that coal was simply burnt and any rare element inside coal was sent up the chimney. He thought it was a crime. So when he saw possibilities that coal could be replaced, he was certainly very keen. However, at the time there was a limited amount of uranium known in the world. Moreover, at this stage, when we expected that only a very small fraction, 0.7 percent, could be used for 235, he thought that, it will make some contribution, which will be nice while it lasts. So he was thinking very hard if something couldn’t be done with the 238, and so he was the first one who really studied, giving it the thought, of what was happening. Halban and Kowarski were concerned, whether it would start, and Egon was interested in what else is happening, something happening with 238.
Then, he said, “Yes, one neutron per fission roughly is being captured by 238, and they go with a weaker radiation to 93 and another one to 94,” and so he wondered, “what about 94”? In the summer (that was before Halban and Kowarski came to Cambridge) already in Berkeley, they realized with the cyclotron there that they had been producing plutonium, but they called it just “94” at the time. So Egon then looked carefully into whether any one of those is fissionable, and the one theory that was around, the Peierls/Frisch report was based on that too, an application of the Bohr-Wheeler work, and so he figured out and found that 94 must be very fissionable. That had two important meanings for him: a) if the Halban-Kowarski reactor started up, that there was enough 235, I mean there was the possibility that you had to enrich it, but if it was starting up, obviously there was going to be less and less of 235, and there would be waste products which might capture neutrons, and so he was afraid that even if they managed to start it up, that it would get poisoned and it would fizzle out again. But if for every fission, at least one other fissionable element was being created, then it was all right. So that was one good application for 94.
The other one, which was used of course first, that it could be separated very much more easily from the bulk of the uranium because it was chemically different. And he started right away having a chemical group work on how that could be done. So it would be easy to get actually pure “fissionable material.” When he did his calculations, applied the Bohr-Wheeler theory, he also found that the uranium 233 should be fissionable, and that could be created out of thorium in the same manner as 94 was created out of uranium 238, and I think that, more than anything else, excited him terribly. He knew that there was an awful lot of thorium on the west coast of India, and he felt he really knew now how to get atomic energy going for a long, long time.
Bennett:And atomic energy he saw as being the ultimate goal. Weapons were necessary because of wartime, but --
Bretscher:That’s right. I mean, one couldn’t disregard the weapon, when one was involved a war with Hitler, but the excitement came out of producing usable energy.
Bennett:So the feeling was at the time that Germany probably had the capability to develop a bomb.
Bretscher:He knew they had very good physicists there, in spite of -- well, of course, some of their best had left, like Bethe, Peierls and lots of them had left, but there were still people left like Heisenberg, so yes, it was really only at the end of the war when they realized that there really was nothing. Otherwise they wouldn’t have got anywhere. Of course, at the beginning, they half even played with the idea that they could do something in this country. It wasn’t realized easily, what an enormous effort it was needing, which only could be done in the States. All this turned out in the end. I suppose Germany would have been very much in the same position as England, that while fighting a war, they couldn’t have handled a project like that.
Bennett:It wasn’t until --
Bretscher:-- very close to the end of the war.
Bennett:End of ‘43 or ‘44 that the MAUD Committee work and the British going “it alone idea” was dropped.
Bretscher:Well, that because the relationship was very bad. In the British outfit there were an awful lot of ICI people. In hindsight, it is quite clear that the Americans were put off because they thought any information they feed is right away going to British industry, whereas they kept it secret from their own industry, and that was one very strong argument for them, to keep things separate. Till, of course, there was the Quebec agreement, but before that, I think it must have been that Oliphant and Chadwick, particularly, toured the States together and got in touch with the scientists rather than the politicians, and that had a lot to do with the basis of coming to an America-England understanding. Of course, there was just a tiny little thing too. Halban was not at all helpful in collaboration, because he felt that Fermi was going to be number one, and he wouldn’t be number one anymore. I know that Kowarski would have loved to just have the whole thing moved over to Fermi and Halban didn’t want it. In December ‘60 my husband was quite sure that he could make a statement that plutonium was going to be important, and had all these implications… According to the report of the following MAUD meeting Egon must not have actually given the details of his calculations with the Bohr-Wheeler paper, and obviously Peierls hadn’t done the calculations because right away he said that from simple theoretical considerations, one can see it will never work. I mean, that was his impression. And Cherwell got up and said, “Who wants to win the war with an element nobody has ever seen?” And so, Feather having reported on the work as if it was his, so altogether it was a very very sad meeting for Egon.
Bennett:The situation in which Cockcroft -- did he actually accuse your husband of being a bad colleague?
Bretscher:Yes, well, in 1949, there was suddenly a request by Fuchs to see the report on the work my husband had done at Los Alamos on the hydrogen bomb. Well, he had of course a copy of his own work, and he had sent a copy of this, through Fuchs, actually out of Los Alamos to Chadwick. So well, he had this copy, and he didn’t see -- he always felt that the Americans possibly didn’t even like to report on that work while outside America, and as long as there was no national need for the British to know, he wasn’t wanting to disseminate that knowledge, and he refused to give that report out, and said if they wanted to give the report to Fuchs, Chadwick would have a copy, so maybe they could get this from there. And this is how Egon was called a bad colleague, and how Chadwick was involved who didn’t like it and heard about Bretscher being a bad colleague. This resulted in Chadwick having second thoughts about Egon being his successor at Liverpool, which had more or less been decided that he should take that professorship. But then after this, he made a statement in the Athenaeum which Oliphant brought to us, that Chadwick had suddenly said something about Bretscher was a bad colleague and it was then blocked in Liverpool to appoint him, to have him as Chadwick successor. Well, I don’t think Egon really minded that it had this effect, but at the time it was not such a…(?) So --
Bennett:We’ve gone a little bit ahead of ourselves. We want to talk about Los Alamos. Your husband was going to have to go and --
Bretscher:Well, I mean, he was asked. Oliphant previously was quite willing to arrange for him to go to Berkeley, to work on plutonium there, and at the time he decided against it. Then again he was asked by Chadwick if he would come to Los Alamos, and in this stage, he said he would, if he could take the family.
Bennett:What were your feelings about going there?
Well, I was quite aware that it wasn’t the safest thing to do, to cross the Atlantic. But then you didn’t know if it was safe to stay in England either. On the boat, we actually had a terrible accident. In the first night out on the Irish Sea, it was very stormy. Pasteur had been changed over into sort of a holiday boat it was called (?) for troop transport. We got a first class cabin which had been refurnished with bunks, six bunkers in there, and so it was plenty for putting up the Bretscher family, which were five members by this time. Well, the arrival was marvelous. It was really rather for refugees partly, but nevertheless, it was applying the American style. We found a loaf of bread which an American had baked knowing that the English, we didn’t get white bread, sliced bread and so they thought it would be terrible if we had to start on that. It was good whole meal loaf, homemade bread. We had a standard lamp from the Weisskopfs, We had saucepans from the Tellers. It was very nice, arriving in a country for the first time) and realizing that there were all people around to help you. That was very, very nice.
However, Egon soon found life very hard up there. He had been given the impression that they were short of senior scientists, and that didn’t seem to be true at all, and there were senior scientists around, they had certainly picked up all the younger scientists for their groups, so all he got was an office, together with Joseph Rotblat and they sort of sat opposite each other wondering what they could do. Well, Rotblat in the end got even a nervous skin trouble, and decided that there was nothing to do, he might as well go back to England. Egon was a bit better off because at least he had discussions over the cross-section measurements. Nevertheless he said to me more than once, “It I only hadn’t got you family, here, I could go back home.” But we had had to pay our own passage, for the family. I mean, Egon’s was paid but he had to pay ours. We couldn’t take any money along, so the only way of ever getting back was to stay there till we had saved part of the salary, enough money to get us back. So he just couldn’t go back. Well, as I said, that was the time when he saw most of Bohr, discussing with Bohr these cross-section measurements. I now think, I’m on ground that is well known. It was very, very difficult to understand Bohr. He was very wrapped up in himself, somehow. Even quite normal things, you had to sort of really listen to get what it was about. He was of course an extraordinary person, and it was worth making the effort to listen.