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Interview of Hilde Levi by Charles Weiner on 1971 October 28, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/5038
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Graduate studies in Berlin in the early 1930s with Beutler; Ph.D. in molecular spectroscopy, 1934. Contacts in Denmark lead to stay at Niels Bohr Institutet as James Franck's assistant working on photo-synthesis, 1934-1935. Levi changes fields after Franck leaves and Otto Frisch and Georg von Hevesy arrive: she builds Geiger counters with Frisch, then works with Hevesy on induced radiation experiments. Lengthy discussion of how Hevesy's active work style and inspiring attitude engaged people at many different institutions, including herself. Collaborations among Bohr's Institute and other groups, e.g. Enrico Fermi's Institute in Rome, August Krogh Institute, and the Finsen Institute. Anecdotes about Bohr and Hevesy; an account of the beryllium sources handmade by Frisch and Levi. Levi's work in Sweden at the Wenner-Gren Center Foundation during World War II. Discussion of Bohr, Krogh, and Paul Bergst as leaders.
Let me start by saying that in our conversation last summer, end of July I guess, you mentioned a number of things. We were just talking casually and you told me that you got your Ph.D. at the Kaiser Wilhelm Institute in X-rays, spectroscopy.
No, molecular spectroscopy.
And that the exam was 1934.
I think maybe I should get a little background on that, find out who you did your work with there, how you chose that kind of a problem, whether you had any responsibilities there other than doing your —
No, I hadn't. My doctor father, as one said in Germany in old times, was Beutler, a rather well known molecular spectroscopist who later also emigrated to the United States but died rather young. Hans Beutler, that's right. And he sort of directed that work and supervised it. It took about two years. No, I had no other responsibility. I was just a diligent student doing her work, and was quite a strain and hard sort of a little unpitiful boss to have. I am grateful for that, because he taught me a lot of things that I try to teach my students now, and that was all to the good. My exams I took in Berlin. I think I was the last Jewish student to get a Ph.D. in Berlin University, with Pringsheim as my physics teacher and Lauev as my theoretical physics teacher, or taking the exams with them. Bodenhof was in physical chemistry. And at that time it was compulsory in Germany to take philosophy as a subject for a Ph.D. in the natural sciences. I had to take that, and I took that with the famous Khler, the man who worked with apes, you know, and was well oriented in the direction of physical methods in psychology. He later went to the U. S. He was at Swarthmore for a long time. He was called "Ape Khler" generally. That exam I took in January of 1934, and then I applied for, not even a position, just for permission to work in Copenhagen. I wanted to get out of Germany as fast as possible, and I had some acquaintances here, and it was just, you know, the courage of the, shall I say, stupid, or the courage of the not very informed —
— naive —
— yes, naive, that's a better word, that's right. And I applied to get here, and I was accepted, I think mainly because my thesis was in the field of spectroscopy that interested Ebbe Rasmussen very much, who was working in the same field, and he knew it. And I think another factor which was relatively important was that Bohr was negotiating with James Franck at that time, and James Franck was coming to Copenhagen, and the wise people thought, it might be a good idea to get James Franck a young slave, because after all a famous German professor was used to having quite a number of slaves who worked for him, and one thought that this girl here with a thesis in a field that interested Ebbe Rasmussen and also interested James Franck, and a girl that didn't cost anything because she didn't asked for money, was a very good solution to that problem. So they said yes, I was welcome to come. I started in early 1934 and James Franck came very shortly afterwards, if I remember correctly, almost at the same time, and I was assigned as an assistant to James Franck.
Let me backtrack a minute. When you talk about research support and you talk about getting out of Germany, what opportunities would there have been for you, if you can imagine without the Nazi so-called racial laws, even without that, did non-Jewish students find employment opportunities in those years preceding the year you got your degree?
Well, I don't think it was so easy, but I think it would have been possible. However, I would say that a certain discrimination against girls was relatively common in Germany too. I observed it already during my studying time. It was harder to get in as a girl, in physics, for instance.
You say harder to get in, in what sense?
It was considered for instance — not quite trivial to be accepted in lab courses. Where there were a great number of applicants they would sort of push the girls aside a little bit. But I think it is very difficult to really distinguish clearly between what was a slight discrimination against girls, and was anti-Semitism, because after all, I was a Jewish girl, and anti-Semitism was beginning to play a part. So it's hard to say, if I had some trouble, was it for the one reason, or was it for the other reason? At least there was difficulty. And I don't think it's at all possible to make this theoretical assumption, what would have happened if Hitler hadn't come to power, because the mood in the population and the university was building up towards this trend, so you had these difficulties, even before 1933.
I get the impression from what I've read about the academic situation that universities were very overcrowded in the years before Hitler really came to power, and that was one of the things that he used as an argument later. He reduced the number of the people in the university, first of all by dismissing — but also by having various work corps.
That is right. But the first years after Hitler came to power I sort of was already out of Germany.
In the period while you were there, was it your impression in seminars, laboratories, courses, that there was tremendous pressure?
No. Not to the same extent as nowadays, for example. I mean, of course there were many students, particularly in Berlin where I was, there were many students. But it wasn't any pressure to the extent as we know it nowadays, where we really have to sort of double and triple and quadruple courses, and — not to the same extent. I don't think so.
I'd like to talk about Berlin for a few minutes. What about the contact in the years 1930-1934, your period in advanced work I gather?
What about contact with physics elsewhere? Did you have many people coming in lecturing? Were there colloquia you were able to attend?
Yes, particularly at the Kaiser Wilhelm Institute where I did my experimental work. I think that contact with the world around them was even greater than at the university proper. But it wasn't as international as we nowadays know. I think the Germans considered themselves at that time rather self-sufficient, and there wasn't so much contact with other countries. But it may be of course that as a student you didn't realize it so much. We were not brought up in the kind of international atmosphere that students are brought up in, in this country, nowadays, for example, with foreigners working. It may also have changed a little bit. It may be a little different from place to place, from institute to institute. There were some foreign co-workers at the Kaiser Wilhelm Institute. I do not recall that I ever met foreign co-workers at the downtown Berlin University. That may be my fault. But as a student, I didn't. Sometimes a foreign lecturer. You would go to just one lecture by a famous foreigner. But not in any way what you all international contacts in Copenhagen.
That's a unique phenomenon, Copenhagen. It's based on international contacts, it's not accidental. Were there regular colloquia or seminars, where there was an opportunity to participate with some of the established people?
Yes, absolutely. Definitely so.
There are always the famous stories about the Berlin colloquia, the front row with all the famous people sitting — was that going on?
Yes. And of course, the students in the back row, naturally. But you had the opportunity to hear these people discuss, of course, but students kept in the background. But there were student colloquia too once in a while where a younger person would present something, naturally.
Who were the principal people? Was there any particular group of distinguished people who were the main characters on a continuing basis in these colloquia?
Well, in the Kaiser Wilhelm Institute where I worked, Haber was the boss, and Fritz Haber was such a great personality and such an explosive type of a man that he would of course dominate the whole scene and people were just shivering. I mean, the typical old-fashioned manner, the boss that everybody was afraid of, or at least many were afraid of. So that was always in the German style of the professors being the bosses and doing the talking and the students sitting in the background and listening.
Would one of the professors present a paper?
Yes, very often. As a rule I think so, yes. I don't recall that in very great detail. I just recall a few. There were colloquia between the various Kaiser Wilhelm Institutes.
The proper name for your institute was what?
Kaiser Wilhelm Institute of Physical Chemistry, so-called Haber Institute, that's right. But then of course, the students who tried to make a doctoral thesis there, they were rather busy, and while we did go to seminars when there was something very important, we didn't go nearly as much, and there wasn't nearly as much communication between people at that time as we have nowadays. I mean, you just started out and you were quite busy, and my boss, Beutler, he had a special tendency of making you work. I mean, it was just hang on.
You were working pretty much alone, on your own projects?
He gave me a project. I mean, it was sort of a part of the general subject he was working on and he just handed out a piece. It was characteristic of all doctoral theses in Germany. You had a boss and he had a lot of things he wanted studied, and he sort of gave a bite to every one of his doctoral students and let them work on this project and supervised it, and the degree of guidance you got was entirely dependent on the individual boss. Some would give a lot of guidance, and some would give very little. Beutler was somewhere in between. He was very kind and helpful but he would let you struggle for quite a while before he came and said, "Well, you might try this and that" or "Such a thing might be wrong." He had a wonderful principle that I often quote to my own students. When I went to him and said something didn't work and I couldn't find out, or even worse, when I came to him and said I thought something was wrong with the instrumentation, he would always look at me and say, "Well you must always start on the assumption that the fault is yours." He would never permit that if something didn't work, that the student would say something is wrong with the apparatus or with something else. The first approach was always, something is wrong with what you do — which I find is a very useful approach, which is sort of out of fashion nowadays. Youngsters nowadays, when something doesn't work, they will primarily come and say "The machine has broken down," and they will not start out with the assumption that they themselves did something wrong. I tell them the story sometimes and say, "Well, it might be an idea that maybe you might not feel that the machine did something wrong, but I did something wrong."
That's the beginning of analysis.
Yes, and he was very hard in this direction. He would let me struggle for quite a while and I should really sort of prove to him that it wasn't me that there was something wrong with. Then finally he would come and help me find out why.
How many other students were there at the time?
I can't recall that. There were several doctoral students at the institute. I can't recall the number of them. Dr. Beutler had only me at that time, he didn't have several. But there were other co-workers at the Institute and Haber himself who also had a doctoral thesis going, so I don't know —
Your degree was in physics, but were people there also getting them in chemistry?
Not in chemistry but in physical chemistry. It wasn't pure chemistry. There was no pure chemistry at the Haber Institute. It was physical chemistry.
To me it's interesting to get some of the background. At what point did you enter doctoral work? What had you gone though before in order to get to that point?
I think eight semesters of study in physics and chemistry.
In other words, having been admitted to the university and then having completed about eight semesters —
About eight semesters, yes. I'd taken all the courses that are prescribed or were at that time compulsory, before you could be accepted for a doctor's thesis. You had a little book where you had confirmed which courses, which lectures, which lab courses you had taken, and there was a certain curriculum which was the minimum requirement for admission at an institute for a doctoral thesis. Of course the different professors in the field knew each other. They knew the students that were planning to go up, and they talked between themselves, was this a relatively student or was it a fool, and then eventually you were accepted.
These are regular courses you're talking about at the university. Then when you started on specific research for a thesis, you're assigned or accepted at a particular institute.
Two categories of questions more on this. As to the subject matter, the content — when did you start on the actual research work?
And the courses you started, when?
I took my so-called Abitur, as it was called, in the spring of 1928. And went to the university immediately. But I think I came out to the Kaiser Wilhelm Institute to start on a doctoral thesis in 1931, which means six, seven semesters.
In the courses, was there any particular focus of interest in the physics course that you saw beginning to emerge? For example, did they include any discussion of the quantum mechanics that had been developed in the late 1920s?
Yes, it did, and it didn't mean very much to me, because I have never been very mathematically minded and not much interested in theory, so I thought it was rather boring, not interesting, and hard. Theoretical physics was the weak point. I was absolutely a do it yourself girl. I was experimentally interested and loved to fiddle in the lab, and was relatively skillful in the lab, but I hated mathematics. So I didn't take any more theoretical physics than was absolutely required. And I think the molecular spectroscopy simply came up because that was — well, if I'm permitted to say so, the fashion of the time. I mean, this was just simply what physicists did at that time. It was the period where spectroscopy maybe was at its peak. That was the topic of the period. And since the student as a rule, there may be exceptions, but as a rule didn't have an opinion of his own, what you really tried to get was a good boss. You didn't want to get a project — as I say, there may be exceptions, there may be very brilliant students who already at the time of beginning a thesis had an idea of their own and wanted to do that. This may have existed. But the average student would not look for a project; he would look for a pleasant boss. And you tried to get in a place where you thought it would be nice to work and where the boss was pleasant in that way. I got in there, and that was very nice. It was much nicer than downtown Berlin University, particularly because the trend of anti-Semitism was already developing, and it was much more difficult in Berlin University. There was much more friction, while the Kaiser Wilhelm Institutes after all were private institutions, a private organization that wasn't so much under political pressure, and it was an advantage for a Jewish girl to try to get placed out there. You were a little more at peace, a little longer in peace.
How did it manifest itself at the Haber Institute, because Haber's own subsequent history is an interesting one?
And a tragic one. It didn't manifest itself. There was nothing at the Kaiser Wilhelm Institute. I cannot recall any difficulties because of my origin at the Kaiser Wilhelm Institute. It did not exist. But on the other hand, it came there, it arrived there very abruptly. I mean, they threw Haber out in 1933, immediately. Well, it got there very fast. But until the time — and fortunately, my good fortune was that my experimental thesis work was almost finished in 1933. I just had to clear it up, and then I used about six months, I don't remember exactly, but about a half a year, mainly the second half of 1933 when it was extremely unpleasant to be anywhere, I used for home study to prepare myself for the oral examinations. And I went to the oral examinations in January, 1934, and left the country immediately afterwards.
How did it affect the Institute? Who was dismissed?
Beutler was dismissed, Haber was dismissed.
Beutler was your thesis adviser, so how did that affect you?
He left later than I did. Yes, he was a very patriotic, very German German. Just in the same manner as Haber was. I mean, Haber and Beutler just never thought of the possibility that they could be touched at all. After all, Haber was the hero of the First World War, and while he thought it was horrible, the idea that he could be involved, he could be touched, didn't occur to him. And Beutler was also a participant in the First World War. [crosstalk] That's right, and he had ever so many excellent decorations and things from the First World War. They all would argue, "Well, that's horrible, but it won't hurt me." My personal feeling and I cannot explain it, it's a purely emotional thing, it had nothing to do with intelligence or anything else, it was just purely emotional — my reaction was, this will not work, I have to get out as fast as possible. I couldn't take it at all. Of course, I had nothing to my credit that could induce me to say "Well, it won't hurt me." I mean, I was a Jewish girl, nothing else; of course it would hurt me. I was very busy getting out. But at that time, Beutler, oh, I mean, oh, he wouldn't even dream of it. He put on his fine decorations from the First World War, his Eisennes Kreuz of the first class, "Look at me, I'm a hero of the First World War." And Haber the same way. And it hit him terribly, when it turned out, not so very long after, that this would not protect them, but they wouldn't believe it. And I think it killed Haber. I mean, this is a very well-known story — it killed him. He just couldn't bear it, that he would be thrown into the same heap, you know.
The laws went into effect at the end of March, and unless you had something to your credit, having been a participant in World War I or something like that, you were immediately very shortly after that dismissed. Bethe for instance was notified that his job was over and he had to go back to Munich. This happened to a number of people. So Beutler and Haber had this other extension, in a sense — Franck did too.
No, not very much. Franck put in his application for dismissal — he resigned. I mean, he took the initiative.
These were people not immediately affected, but what I'm trying to get at is, what about people who were immediately affected? You had started to answer but I didn't give you the chance — whether they were staff members, faculty or whatever, who were dismissed prior to the time you left.
No, I don't think so, not at the Kaiser Wilhelm Institute. And not the people I sort of knew very immediately. Pringsheim, for instance — I do not recall when he left Berlin, but he still was there when I took my orals in the beginning of 1934. Now, you can look up when he left, but you see he still was there, so I think the so-called cleaning out process after all took some time, and they kicked out a few people very promptly and then gradually worked their way through. Of course, several people stayed a little longer. Haber was still there. Now, I don't want to give historical records if I'm not absolutely sure they're correct. I do not recall with certainty whether Haber still was on his post, in early 1934 when I made my orals, because he didn't give me an oral examination, because he was not a professor at the university, he was the director of the Kaiser Wilhelm Institute. He could accept students for thesis work, but he would as a rule not be the man who'd make the orals. Bodenhof was the man, the professor of physical chemistry, to whom I had to go to make my orals, and Pringsheim was the professor of physics at the university to whom I had to go to make my orals, you see. So I don't really recall, but I have a notion that the dismissal of Haber must have happened a little after I left. You'll have to check this.
As a matter of fact, just before I left New York the man who's written a biography of Haber said he's going to deposit all his notes and papers in our library.
And Beutler I think left considerably later. I would guess that Beutler didn't leave until 1935 or 1936, you see — he would just struggle and say, "I ignore that, they won't tell me," and all that stuff.
Did you know people who were on grants who because they were Jewish had their grants withdrawn or not renewed?
I don't know.
I wanted to check on that because there was a statement someone made at the same time about that and I was just curious.
I don't know.
You weren't on a grant, your family was paying?
My family was paying, that's right.
We seem to be going back, but it's all necessary, interesting. You say you were interested in tinkering, in lab work — where did this come from? Was there anything in your family, the profession of your parents, which led you to this kind of interest in science?
No. My father was a businessman. I don't know where it came from. I don't know. Well, of course, I have a theory that would horrify Women's Lib, but I have a theory that my interest in physics and this kind of work actually goes back to a very excellent teacher I had in school whom I loved dearly. You know, very often that's the way girls, boys also for that matter — if you have an inspiring teacher in a field, that's of very great importance, and I think this man sort of had the ability to waken my interest in the field he taught.
This was in the Gymnasium?
That was in the Gymnasium, yes. I think that was just the thing. Also, as a youngster I was interested in photography and before I knew better I thought I would try to become a photographer, even maybe a scientific photographer when I go to the university. Then I found out of course this was not a field you could study at the university and I started in physics and became interested and then went on. I liked it. I liked to be in the lab. I like to be in the lab today.
You still do, I gather, from our surroundings.
Yes, and instrumentation interested me. I would just fiddle, you know, with wiring and things and high vacuum technique I loved very much. I thought that was wonderful. And high vacuum technique was an essential part of my thesis. I thought it was fun.
And as you pointed out, it helped get you established. That particular line of work helped get you established here. You mentioned when we talked this summer that it was through a friend of yours who was connected as a member of the International Association of University Women, that the recommendation came from her that you should write to Denmark.
Had you thought of any other place, or was it just because she suggested Denmark that you decided to follow up on it?
I think I had Denmark in mind. Also I had as a teenager a boyfriend who was a Dane. He was, as a matter of fact, the son of a very famous father. It was the son of the — at that time director of the Serum Institute named Thorvald Madsen. And this boy was sent to Germany to be trained in business, and he happened to be in the same firm, which was a very large firm, where my father was. So my father invited him home, and for a number of years we were very close friends, and sort of fitted very well — in part I had a boyfriend who was a Dane and my teacher and acquaintance within the University Women organization suggested — well, I knew Niels Bohr, after all. I mean, you can't get a degree in physics without knowing something about Bohr. That fitted all very nicely together. I said, "Fine, I have a boyfriend, there's Niels Bohr," and I had entrance through the IAUW women — it fitted very nicely, and it was my first try, and it was successful. So I didn't have any need for looking around in other directions. I was just very lucky.
For all concerned. Did you write to Bohr?
No, I wrote as a matter of fact to the president of the federation, of the Danish section of the federation, and she contacted Julie Winter Hansen. Who was an astronomer, and she had a position at the observatory in Copenhagen, and she knew of course Ebbe Rasmussen very well and she knew the Bohr Institute, and she just handed my application on to the Bohr Institute. Then came this argument — well, maybe — and they knew my thesis, of course, Franck knew my thesis.
This is before you arrived.
Yes, but I mean, they knew my thesis. I don't recall in detail but I'm pretty sure that I sent them a copy of my thesis with my application.
You mentioned also that [Hans] Kopfermann was here at the time and he knew your thesis.
That's right. Yes, because he was on leave of absence from the Kaiser Wilhelm Institute, from the same Kaiser Wilhelm Institute. He was a member of the Haber Institute and he was on leave of absence with a Rockefeller fellowship in Copenhagen. So that all sort of — well, it was a very lucky coincidence, I think, for me in every respect. It was very nice, and Kopfermann knew me and of course Ebbe Rasmussen knew Kopfermann. They had talked and maybe Kopfermann said, "Oh, she's quite skillful with her fingers, let her work," and that sort of thing —
Rasmussen was in Germany in 1933.
That's right. No, I didn't meet him. I think he was at the University, wasn't he?
He was with Friedrich Paschen.
Yes. Well, I remember Paschen. I didn't know him but I heard him lecture and I have met him, in the student-professor relationship. I was very impressed with Paschen.
It was just that time that Paschen was being kicked out and replaced by Stark.
That's right, must be that time. But I have heard Paschen lecture. He was a very elegant man and I was very impressed.
But this kind of a tie then, was established because Kopfermann who had known your work at the Kaiser Wilhelm Institute was in Copenhagen at the time, Rasmussen had been in Germany, Franck was coming, your thesis was on that general line, and they told you to come whenever you were ready.
Exactly, that's right. And my father paid for me. That could be done still in 1933. He just sent me a monthly allowance and I worked.
Your exam was January, 1934. When did you come, March?
When did Franck come? I could probably check that in another way.
You'd better check that. I would think, very shortly after. Well, I don't know for quite sure but I would think it would have been in April or May or something, during the spring, Franck came.
What did you do when you got to the Institute?
I looked around. I think I did was sort of hang around Ebbe Rasmussen. Because that was fascinating. He did studies very similar to what I had done. He had a huge grid at that time and did spectroscopy and he had an interferometer and all sorts of interesting things, and I just sort of hung around. Maybe a fiddled a little bit with him. It may well be that there were a couple of weeks where I sort of tried to be a little handyman for Ebbe Rasmussen. But I wasn't really put to work, because they were waiting for James Franck and they wanted me to be James Franck's helper. So they didn't put me to anything very demanding. Just wait a little bit, he will be coming. And then Franck came very shortly after. It can't be more than a couple of months until Franck arrived, if it wasn't even maybe less. You can check back when he arrived.
How did you find the facilities at the Institute, compared to what you had been used to in Kaiser Wilhelm Institute?
I thought it was wonderful. I mean, the Kaiser Wilhelm Institute is a very pompous building and all that kind of stuff, but that didn't interest me. As far as instruments are concerned, Ebbe Rasmussen had more and more fancy instrumentation than I had at the Kaiser Wilhelm Institute. I had never before worked with a large grid. I had worked with an old fashioned spectrograph, you see. So the equipment was more sophisticated in Ebbe Rasmussen's laboratory and I thought that was very interesting, very funny. Also I remember that his analysis of photos of his spectroscopy work were very elaborate, more elaborate than what I had had. I worked a little bit with him, not really but just sort of — and I mean, they weren't very strict. After all they didn't pay me. They thought I should have a little bit of a good time. You know, Bohr was infinitely understanding.
How soon after you came did you come across him?
Oh, immediately, the day after or something, immediately. Now, here they had colloquia, of course, very frequently, and here were all sorts of foreign guests, and I was invited to come in and sit in and listen to them, and that was very new and very strange, and very different from Germany.
In the sense of openness and the informality of it?
Yes, that's right, although at that time they still spoke German a great deal of the time.
Well, people told me they were beginning at that time, after Hitler came to power; the deliberate switch was to English.
Yes, but I think slowly. There were still a lot of German speaking people. And when the refugees, after all when Frisch came and Weisskopf came and Placzek came, their common scientific language was German rather than English. So I would say that German was spoken much more than English. But that changed.
They came later of course.
No, no, not very much. Frisch must have arrived in 1935, because my switch from spectroscopy into atomic physics occurred at the moment when Franck left. Frisch had arrived and Hevesy was expected. I had a conversation with Niels Bohr, and he, in the well-known manner in which he would suggest something he thought was right, he put in such a way that it ended up being one's own wish —you know, that was not a trick, but the way in which Bohr would try to show somebody which way to go was quite unique. So that in the end you almost believed yourself it was your own idea, not his idea, you followed. Franck was leaving in 1935, which was a great sorrow to me because like everybody else I adored Franck, he was a fantastic person — but he was leaving for Baltimore and Hevesy was about to come. Bohr was terribly interested in getting some induced radioactivity started at the Institute, so he told me how interesting it was to study induced radioactivity, and he was talking about the Halieu (Fereesi) experiments, and this information was pouring in at the Institute, in 1934 and beginning of 1935. So he said, "Oh, Frken Levi, wouldn't you think it would be terribly interesting, and you know, Frisch is coming and maybe you could help him a little and you could work together —"And my heavens, I mean, I was a very young person. I was entirely used to and was growing up in the authoritarian system of a German university. It wouldn't even occur to me to say no, I wouldn't want to, or I wanted something else. It was just unthinkable. Also, the way he made it so interesting, it was not sort of a matter of obedience, it was just being very quickly convinced that this was frightfully interesting and you should do that. I said, "Oh yes, of course, I would like to." I started with Frisch building Geiger counters and amplifiers. Then Hevesy arrived.
Before we get into that story, just to trace the work with Franck, when he did arrive how soon afterwards did he get down to work and you participate in it?
Very fast. Very fast. Franck wasn't long in getting something started. And I mean, the interesting thing was that Franck arrived here, and I think this is certainly to the history of physics of great interest, Franck arrived here so to speak with I think the mental attitude that he would not be in a position to continue the line of work he had had in Gottingen. He would be on his own, he wouldn't have half a dozen students to work for him, he wouldn't have the same equipment that he had left in Gottingen, so he would have to start on something fresh. He knew that he had one little girl to help him, and he knew that there was some equipment which allowed [him] to work in spectroscopy, but not anything of the kind of the Gottingen Institute. Therefore he had made up his mind, at least this is what I recall, that he would start on a new area, and the new idea was his beginning to work on photosynthesis. And when we started working, he suggested that what he wanted to do was to study the absorption spectra and emission spectra of chlorophyll. And we went out in the yard and took some leaves from the bushes, and started extracting them with alcohol and got a green fluid, and began to look at absorption spectra of chlorophyll. And after all, that is the turning point in Franck's field of interest. I mean this is the beginning. Now of course, I should be a little bit careful because I do not know whether Franck in Gottingen had already begun to think of photosynthesis or not. But this might be possible to check. I'm not sure, I think that this work sort of was provoked by the changing working conditions and the changing situation and he thought, "Well, I can't continue along the line I have been working till now, I have to start something simple and knew with the means that are available."
Did he have in mind that he would be staying for a long time or was it all very temporary?
I don't really know. I think that Franck would have loved to stay, but Franck was a very wise and clever man, and it is very possible that he realized when he came that this would be a transitional affair, that there was really not any basis for him to stay in Copenhagen, because after all I think he was a very great man and it was natural that he should lead an institute and head a large group, and I think that Franck and Bohr both agreed that this was a transition, just to make it easier.
Bohr was able to get a stipend for him from a combination of sources — and it could have continued.
Yes, I know that, but after all, that was too small a platform for Franck to be on, and I think, my notion is, that Franck loved to come here and hoped to stay a couple of years, but I don't think that either of the two thought that this was the final station where he should remain for the rest of his life. This is something I only have a notion, and no real knowledge about, but I doubt very much that it was ever considered as something permanent.
When he was here not only did he start this line of work you did with him, but did he participate in colloquia, on general issues?
Oh yes, very much so, and he was also very very much interested in the atomic physics line of, for instance, induced artificial radioactivity. He made experiments along that line. Oh yes, there are records about induced radioactivity experiments that he carried out with Ambrosen at that time, so he did — oh yes, he very much participated also in the other work and of course in the colloquia and so on. I mean, naturally. But his own fiddling in the laboratory in the basement of the Bohr Institute at that time, that was with the extract of chlorophyll from plants and attempting to measure absorption and emission, in order to investigate the energy needed in the photosynthetic reactions.
The first paper on that topic I found was submitted in October of 1934.
So that was one of the first fruits then of that work.
Then there were others that came.
Right, and I gave the notebooks and all the documents I have about that, I gave to the University of Chicago a while ago because the University of Chicago apparently to my knowledge is trying to collect a little bit the documentation of Franck's work and they have some sort of archive I think.
It's a big one with Bob Rosenthal.
That's exact — I didn't talk to him but I, I don't know how it got about, it went through Robert Platsman, of the University of Chicago And — well, at any rate I know that Bob asked me I think one day whether I had some things left from that time. I said, "Oh yes, by all means, I have lots of notes and things Franck has written and I have our laboratory notebooks." So I packed them and sent them to Chicago.
Rosenthal told me not to talk about it but he was getting the Franck papers.
Yes. I sent them as a matter of fact all I had, from the time of my collaboration as an assistant to Franck.
Now, in that collaboration, you assisted and worked with the instruments. Did he also work with the instruments?
Oh yes. He is a fiddler too. He was at that time at least. Oh yes, he loved it. I mean, it was a delightful relationship, because it was sort of a grandfather-grandchild relationship, and we got personally very close. He had a wife who was ill and he travelled quite a bit in between, and I stayed in his home and kept his wife company. It was much more than — I mean, the professor-student relationship vanished. I don't think that Franck ever was such a very typical German professor. I think he always had a much more personal human relationship with his pupils. And certainly here in exile, both of us being uprooted and strange, this was not at all the professor-student relationship, this was a grandfather-grandchild relationship which took place both in the home and in the laboratory.
When it came to writing up results, how would that be done?
Oh, he would do that, of course. I mean, after all. But we would have endless discussions. He would discuss very much with me, but he would do the writing. Oh, naturally.
How about the viewpoint, his and yours, about whether the situation in Germany would change in a positive way, that maybe all this would go over after some time.
No illusions of any sort.
Both of you?
No, none of us would think it possible — it was only a question of how long it would last, but it would last long.
We can check the dates, but Franck wasn't really in Copenhagen that long, so this relationship you're talking about, working and friendliness —
— about a year, I would think.
And during that it was pretty much what you did all the time, working with him. You didn't work with anyone else at the Institute?
No. I wouldn't. What I was in doubt about was just something I did a little bit later. We must come to that, but that was definitely later, when Lise Meitner came, but that was later.
Did Frisch arrive while Franck was still here, or was it just afterwards?
Don't quote me on that. We have to check that again. I am not quite sure. But I think, I recall that Franck and Frisch were there simultaneously, at least for a little while. I think they met here.
I've talked with Frisch so I have the exact dates.
I would think so.
The reason I was asking was not just to find out about dates but to find out the connection of various work.
There was a certain overlapping. The Fermi work had started. Bohr had the first news about neutron activation. I mean, that was coming in, and —
Well, it would have been yes. As a matter of fact, let's take a look at the first paper, I have a list of the papers and the first paper you did with Franck was fluorescence and so forth.
— that's right —
— then it continues, and Frisch has a paper just about the same time on induced radioactivity of fluorine and calcium.
He's working with E. T. Sørensen on the velocity of slow neutrons.
Oh yes, I think I can recall.
It's just about that time that Hevesy's name starts coming in, and he's working on artificial radioactivity of scandium —
— rare earth elements, yes —
— which led to the radio-potassium.
That's right. That was the beginning of our work. But you see, this was sort of preceded by the necessity of building the instrumentation needed to do that kind of work. And that's what we started, at that transition period when Franck was about to leave and Frisch had come in and Hevesy was about to come in. Now, I do recall that Franck and Hevesy were present at the Institute at the same time, I don't think for very many months, but they did for a little bit, because I remember some very funny stories and some very funny incidents where Franck and Hevesy sort of — what should I say? Hevesy was a very poor experimenter and a sort of sloppy man in the laboratory, while Franck was more of a perfectionist and a very experienced and fabulously good experimenter, and they had been together in the lab at the same time. And I recall very funny incidents when Franck saw Hevesy doing something which he thought was just horrible, the way Hevesy did it, and he would say, "Yes, but Lieber Herr Kollege..." — I remember that very clearly. So there must have been a period of a couple of months or so when they were in the same building at the same time and sort of kidding each other. But Franck was on the verge, he was about to leave and Hevesy had just come, so it isn't so that they really worked at the same time. The one was just starting, the other was just stopping, but there was a period when they were together.
That must have been an interesting period. Frisch also was here at that time.
And Frisch was here also.
If we were to talk about Franck and say whether or not he was influenced in his research interests by anything else going on at the Gottingen Institute, the answer would apparently be no, in the sense that because of the transition, either because he had started in Gottingen or because he was ready for this problem under the circumstances — there was nothing at the Institute that turned him onto that problem?
I don't think so.
Was there anything that was continued along that specific line after he left? I'm just trying to see whether that little interlude had any other repercussions in terms of research.
Well, I think as far as Franck is concerned, very definitely.
No, I mean at the Institute itself. No one else picked that up? Because when he left, you —
No, I was transferred to Hevesy. I started something new. No, I think Franck took that problem with him, and spent the rest of his life on it, after all, and I was transferred to another section of the work at the Bohr Institute and actually never came back. I haven't had a spectrograph in my hands ever since.
I want to ask you about your timing, your schedule, but for my purposes we're ready to get on to the follow-up of the conversation with Bohr regarding the interest in induced radioactivity. So, what's the schedule?
Well, I don't know. We can continue a little bit more if you like. There is a lunch room downstairs. We can go down and have a sandwich. But let's continue a little bit.
I'm perfectly happy; I just wanted to give you the option at this point… Well, during this transition period, you mentioned about the conversation you and Bohr had that you took as your own decision.
Well, I knew all the time I was being placed, but I liked it, sort of.
You had been aware of that work being done elsewhere?
Oh yes, of course, I mean it was the talk of the house. These were very exciting times, and while Franck and I were down in the basement doing our little green soup and measuring fluorescence, which we did, the talk of the house, I mean the emphasis of the house was of course on all these new discoveries, mainly I think the Joliot work and the Fermi work, and as you know undoubtedly from our other records, Bohr received a stream of letters from all over the world telling him what people were doing all around, and of course it was a relatively small group and they had very frequent discussions. We had our lunch table every day, and Bohr would of course come in and tell almost day by day what he had heard from the other laboratories around the world — from England, from Italy, from France and so on, what they were doing, and that was constantly discussed. And naturally, before he even asked whether I would like to help Frisch, I had heard all that talk, so it wasn't any surprise and it wasn't new, but it was of course a new field, and the initiative to drop an old field that I had worked on for several years and start something new had to come from a superior, sort of, it had to come from the boss. I mean, that was just the way it is, with young people, and you must remember I was in the first place relatively young, I was a refugee, and I was a guest in the house. You keep your mouth shut and do what you're told.
You don't mind.
I didn't mind it either. I mean, you don't take initiatives in this sense. But it all happened very easily, because by the time this talk about the new discoveries reached a certain degree of intensity, they started — I mean, there was no waiting period, sort of.
It was quite natural and easy for the Institute to get into this.
How soon after the conversation with Bohr did you start working with Frisch?
Oh, I think almost immediately.
You started building counters.
We started building Geiger counters, which was the first thing.
Were there none?
And the amplifiers to go with them. Nothing of this kind was available.
There were no counters.
In Jacobsen's studies of radioactivity in the earlier period, didn't he have some kind of counter?
That's what he used, I see.
No, there was no Geiger counter in the house.
So the thing to do was to build it, and Frisch knew how to do this?
Frisch knew, yes.
So you essentially followed his guidance?
Yes, we worked together very much, but again Frisch was the superior one in knowledge. I do not even recall whether Frisch is very many years older than I am, but I think he is. He was a little further ahead, and also he had worked in another field before. He was not a spectroscopist. He knew more about what he was supposed to do. I had never worked in atomic physics, in radioactivity, let's put it that way.
He'd just come from Blackett who was an expert on detection techniques.
That's right, so Frisch built and he put me to work. Also I didn't know even the elementary electronics we used at that time. He had to teach me that. I had no use for it, no opportunity to build an amplifier or make high ohmic resistances, nothing of the type. He taught me that. And he was very fascinating.
So it was tuning up period essentially.
That's right. But it didn't take long. I mean, you hardly had a detector when you began to make experiments. There was no time to improve the instrumentation you had, because you were very busy to measure the things you wanted to measure, so the experiments on induced radioactivity began very soon.
It seems to me you needed two things, detection instruments, counters — but you also needed sources. How did you solve that problem?
Yes. Oh, that was the famous radium emanation beryllium sources we had at that time, and the sources were made at the Radium Station, where they had several grams, I don't know exactly how many but I think they had three or four grams of radium, and a considerable part of that as a salt in solution, and used the radon for cancer treatment. And Bohr of course talked them into leaving whatever they didn't need themselves for the treatment of patients, for scientific purposes. And that was done, and I think it is an amusing historical anecdote. We have talked about it very often, that Frisch and I made radon beryllium sources, a large number of them, and we made them all by hand, and we did all of the things at that time that nowadays everybody would die from immediately. This does not always only apply to beryllium. I mean, we pulverized beryllium by hand, and sort of separated the factions, different coarsenesses of grain, and only the very, very finest that really was like dust were suitable for radon beryllium sources.
Weren't you aware of hazards?
Oh no, we had no idea. There was absolutely no precaution taken then. We did that in a good old fashioned mortar.
Oh yes, of course, and separating the fractions and filling the finest grain beryllium we could produce into small glass ampullae which we had drawn ourselves, and we brought then over to the Radium Station. Jacobsen and Ambrosen at that time, and I think also Hffer-Jensen — he came into the picture at that time. They were all working at the radium supply of the Finsen Institute. Then they pumped, whenever they had enough that they didn't need for patient treatment, they pumped the radon from that radium chloride solution at the Finsen Institute into these glass ampules and sealed them, more or less. Sometimes they were sealed, sometimes they were not tight. And there you had your radon beryllium neutron source.
You were stocking up on that, apparently, when you say you produced a lot of them. Did you do this as you needed them?
Well, we were stocking up on them, of course. We didn't want to waste our time. Once we made a portion of beryllium, we made enough to last for a while, and we would get a neutron source, oh, maybe twice a week or so, and we used the famous well down in the basement of the Institute to store the sources when they came and to make our irradiation. Then we worked on slow neutrons, making slow neutrons out of fast neutrons in a huge paraffin block. You know this experiment. I worked on that a little bit too. The first experiments Hevesy made were after all induced radioactivity of hafnium and scandium and the rare earth elements. This is all published. And well, that was done in this way: we had built detectors of various types, we'd make the preparation for the sources, we got the sources, we made the irradiations and measured half-lives and tried to find out what was what. That was the work during the first year, I would say.
The first year of Hevesy?
The first year with Hevesy and Frisch.
The first paper with Hevesy on which your name appears is April, 1935.
That's right. So that was pretty fast.
Actually it is because the paper with Franck was submitted in October, 1934, and then this paper April, 1935.
Well, Hevesy was a fast publisher, you know that. And also, I mean, that was at a time when almost every experiment you did gave you a bonus, particularly in that group, because the group around Bohr, they knew what experiments to do, what questions to ask.
Because they were well-informed, you mean?
Because their background for knowing the atomic physics behind it was so fantastically good. I mean, Bohr wouldn't suggest an experiment or wouldn't ask a question that you couldn't rely on to give you an answer that was important, and Hevesy also was a very high calibre man, and that would give bonus each time. That was a wonderful time.
Was there any feeling of competition with other groups, I mean in a positive —
No, I don't think so. I think there was, for instance, no feeling of competition with the Fermi group. I mean, both were very eager and very busy doing work, but not in order to compete. And the line that Hevesy took up was, as a matter of fact, a line that Fermi couldn't have taken up, because as you certainly recall Hevesy had worked on rare earth elements for a long time. He was in the possession of these elements. He'd go to his little cupboard and pull out the strangest compounds of elements that — well, of course, I once knew that they existed, but I mean, it was very strange, and I'm sure Fermi didn't even have them. Who had dysprosium and praseodymium and holmium? He had them all sitting there. He brought them with him from Freiburg. He had them, through his collaboration with Auer van Welsbach who had worked on rare elements before. So he had it. So it was quite clear that Hevesy could take a group of elements in the periodic system and work on them that he had always been interested in; that were not really a competition to Fermi's work. Because Fermi didn't have these compounds. He didn't have these elements. So this was very peaceful, and nobody rushed in order to come first, anything of this kind. That didn't exist at all. I mean, this was an unknown feature in the Bohr Institute.
What was the main means of communication with the people in Rome?
They were the principal people also doing this, is that right?
Yes, at that time, definitely. I think Fermi was the —
They were very well organized.
Yes, and I don't know whether this correspondence exists but I would imagine there must be quite a correspondence between Bohr and Fermi.
No, surprisingly, there's very little. I think that Placzek was the go-between in this.
That is very possible because he traveled tremendously, yes —
This was his nomadic period and he had worked very closely with the people in Rome, and with people here, and went back and forth.
Yes, maybe he was the person who carried the news. That is very possible.
I get the impression from talking to people in Rome that he was their contact with Copenhagen, Amaldi particularly.
I see, yes, oh yes, Amaldi, that's right.
I'll see Rasetti in a few weeks so we can talk about that.
But of course they did other experiments, that Bohr had suggested, and so on, but the radioactivity experiments were with elements from the periodic system that Hevesy had a special interest in and that was his little baby for a long time. And that of course gave also an enormous bonus. I mean, that was fascinating work.
What was the relationship of the, say Frisch was doing his own experiments, working with Sorensen I think, and with others occasionally. Was there close discussion based on the line of experiments he was doing, slow neutron work eventually?
Yes, I think there was as a matter of fact only one group and we all were members of that one group, and it was sort of a little bit branching out, I mean what Jacobsen did and what Hevesy did and what Ambrosen and a few others, no, I don't recall — and Frisch of course. Who else was there? I think Halban came later.
Halban came later and worked on fission? No before that, but McKay.
Oh yes. McKay. That was a Britisher, a young student, I don't know, I think he wasn't a student, I think he had his degree. He came from Britain to work with Hevesy. But you know, Hevesy had sort of one leg, one extra leg, which was the deuterium work that Hevesy had started in Freiburg and which he took along and Hevesy kept on working with heavy water, and drew with him a few persons as a matter of fact who still would continue. There were some more. I looked through Hevesy's own papers. I could tell you —
This gets into the biological work.
That's right, and that was biological, but it was deuterium exclusively.
Yes, Linderstorm-Lang (?) and then maybe Lundsgaard (?), but that's strictly biological.
That's strictly biological. These are the Danes. And very famous ones, by the way. No, but he had some —
— Hahn of course he worked with —
Yes, but L. Hahn came later, and Hahn worked with isotopes. You know there is a period here in Copenhagen when Hevesy and myself together with the others worked on induced radioactivity. At that time, not a bit of biological work, because after all these were rare earth elements and potassium and hafnium, there was absolutely no trace of biology in that. Now, another thing is that Hevesy started at that same time the production of phosphorus, by means of the same radon beryllium sources that we used to make the experiments in induced radioactivity.
He used scandium in this case.
No, he used, now let me see, carbon disulfide. Wait a minute, yes, you make phosphorus P-32 from sulphur and a neutron, isn't that correct? I think so, and what he did, he would put down in the famous well a huge container with several liters of carbon disulfide and all the sources that either were too old, too far decayed to be useful for the induced radioactivity work, or also extra sources he could get, he would put down into that bottle of carbon disulfide, with the idea of making P-32. He would then separate P-32 in the well-known fashion, and that was a little sideline in the beginning. However it appears quite clearly from the history of radioactive tracer that Hevesy at that same time, while 90 percent of his effort went into studying induced radioactivity, the atomic physics of the rare earth and potassium and so on, at the same time he began to think of making the radio isotope of an element that would be useful in biology. And that ran parallel. Then, we for the first time had succeeded in extracting some P-32 out of this huge bottle of carbon disulfide. The first P-32 he was able to make wasn't much; I assure you on a modern scale. He had already established his contacts with Chievitz at the Finsen Institute, and they began to inject that P-32 in some mice. But that was a sidetrack during the first year, while the induced radioactivity, the physics experiments was the main track. And that changed then gradually. He began to neglect the physics side and to push the biological application of radioactive indicators, and that was after maybe half a year — Hevesy got some P-32 out of that bottle very soon, and he used an even bigger bottle and requested that more of the sources and stronger sources were put in, and he got absolutely swallowed up by the possibility of making some elements that would be useful in biological work. After all, you know, that had simmered in his mind all the time. And the use of deuterium in biological experiments was a very important topic.
He was doing that in 1935 with frog skins.
Yes. Yes, he continued, even later. He did go on with a little bit of work using heavy water.
Now, that leads to the whole collaboration that was developed between the Bohr Institute and Krogh's Institute and others, Finsen Institute, and this was supported by Rockefeller Foundation.
Yes, a little bit later. Do you know the year when the Rockefeller money came? When did —?
Yes, 1935. In late 1934, a grant was received of 150,000 kroner from Carlsberg for the establishment of a high tension laboratory.
And at that same time discussions had been going on with the Rockefeller Foundation which led to this collaborative effort in which the Rockefeller was not supporting physics, but the application of physics to biology, and the plan for the cyclotron was included in that because that would be a biological tool.
That's right, and it is very true and I think historically very interesting that the motivation for the cyclotron building was very strongly biological.
That's what I wanted to get at. It's quite clear in the proposals that in fact it did produce isotopes that were useful biologically.
Yes, and it was a little clause. It was very funny, later in the years when the physicists were not very enthusiastic to make isotopes for biological use, you could always clamp down by saying, "Now remember, a good part of your wonderful cyclotron came from the Rockefeller Foundation with a clause that you are supposed to make isotopes for biological experiments." We had much fun with that. I mean, it wasn't anything, a quarrel about it, but you know the physicists of course thought that their experiments were much more interesting, to them at least, and they grumbled a little bit when Hevesy came and wanted them to make isotopes for his mice and his biological work, and they thought it was foolish, but he clamped them down, "Be sure to remember, you have to."
As a matter of fact, Lassen and I looked into the books to find out how many hours were really used for producing isotopes. We have some figures on it.
I see. Not so very many.
No, but there were runs.
But you see Hevesy was never satisfied. He had an enormous appetite.
Well, he consumed almost all of Ernest Lawrence's isotopes.
That's what I wanted to say. He had such an appetite that the Copenhagen cyclotron couldn't satisfy him, so he contacted Lawrence, and you know, they sent all this radio phosphorus in airmail letters back and forth — no, not back, only forth. It was one way. So as a matter of fact, he couldn't clamp down on the physicists enough to his taste to produce isotopes.
It took a while for the machine here to start so he had to depend on external sources.
Yes. That's very true. And the Rockefeller Foundation was at that period very much interested in supporting the biological aspects.
On this I have the complete documentation — every letter that went back and forth including Hevesy's reports. This is a whole separate story.
And I think that August Krogh, as you may also have found, has played a very important part in that, because after all Hevesy wasn't a biologist. You must remember that. August Krogh was. He was the biologist in Copenhagen who recognized at the same time and together with Hevesy and with Bohr the enormous role that this tracer method would play in biology, and was very active in support, and he was as a matter of fact, the biologist who pulled most and had very excellent relationships with the Rockefeller Foundation, because you recall maybe that the old institute out of which we have moved out now, at Juliane Maries Vej, was after all built by the Rockefeller Foundation for August Krogh was a very famous man after all too. He could also push the Rockefeller Foundation. He also told them, "Now, look this is so important for biology."
Yes, I saw some statements of his. I think the major negotiation at that stage went through Bohr.
Because the major expenditures had to be made at the Bohr Institute in terms of the cyclotron and for Hevesy's support, and people like Weisskopf and others were supported on the same funds because in fact they were helpful in the development of the facilities.
What you said about motivation, though, the motivation being biological, that's certainly Rockefeller's motivation. But it would be interesting if we could get to the origin of the cyclotron idea, who wanted it and why? I mean, it was during the period when everybody was getting interested in cyclotrons, but I doubt very much that Bohr wanted to have a cyclotron in order to produce isotopes.
No, I don't think he did. I thought this was just one of Bohr's terribly clever moves. I mean, he was fantastic.
That's a pattern of course, other people —
— I think the primary wish to have a cyclotron and do work was based on physics, both in Bohr's mind and I think in Jacobsen's very much, definitely. But I mean, Bohr was just so ingenious. While he wanted this primarily also for physics, he also saw the implication of this, and his interest was so wide. Bohr was really deeply interested in other fields besides physics, and he saw that this would be of immense importance for biology. And I don't think it's sort of a diplomatic trick. I think it's just simply the recognition that here meet two things that are equally important, let's pool them and let's get the money for them.
His philosophical views supported it too because this is just the period when he was lecturing on physics and biology.
Yes, and "Light and Life," is from that period. He was vitally interested, and he saw this enormous crossover of interest and the possibilities in using the results of physics in biology, and he thought it was fascinating and he wanted to push that, and he did it. It had the very pleasant feature that it would make the raising of money even easier. That he could say "Well, we need this both for physics and it has such and such implications for biology." Well, that made it so much more attractive to support it. That's just the genius of Bohr. That has come up thousands of times.
This raises another question. In 1935 on the occasion of his birthday — this radium gift.
That's right; I just wanted to talk about that.
I know very little about it, except that I gather some private citizens took up, as a way of honoring Bohr, at least that was the excuse, took up a public solicitation, a collection, to raise money to buy him —
— a gram of radium —
Which was rather expensive.
Yes, 100,000 kroner. That was a lot of money at that time.
Now, do you know anything about the background of that? First of all, why that as a birthday present? Was that really what people determined Bohr needed most, or was it his idea, and what were the uses to be and so forth?
I cannot answer your question whether this was discussed really with Bohr. I simply don't know. And I don't know who might know, because the people don't exist anymore. It's not impossible that Mrs. Bohr might know. I don't know who consulted whom. But I know that out of this circle of friends, both scientific and non-scientific friends of Bohr and the Bohr Institute, there was a desire to do something really big on his birthday. Now, who started consulting whom, what one could do to honor him on his birthday, I do not know. But it was definitely — and I do not know either whether one ever asked Bohr specifically — I don't think this is necessary. I think there were enough people around to say, "Well, if you want to honor Bohr, do something that will further his science." And at that time the thing that was really the most needed was a neutron source. So probably people in the inner circle suggested, well, that is the thing that would further Bohr's research, the Institute's research enormously; it is horribly expensive; if you want to give him a good birthday present, all right, give him a horribly expensive present that he now at this time really needs in his research. Now, who was primarily? There is one man whom I do not know whether you have met on your way, that was Poul Bergse — does he occur in your papers? Poul Bergse. He was the director and owner of a huge factory, metal factory, lead mainly they work on. He was a businessman and an amateur scientist — maybe it's not even correct to call him an amateur scientist. He was an engineer and he was very fond of science and liked it very much, and he was very wealthy, and he played a big role in Denmark — oh, up to a very old age. He became very old, and later he was famous as a speaker on the radio on scientific matters. He would popularize science and support science a great deal. He was quite popular. And Poul Bergse and Bohr knew each other very well. I wonder, you might try and find somebody who knows — I wonder whether Bergse was among those who were not scientists but had enough knowledge of science and knew what was going on, and were on the other hand industrialists, in the business world, had a lot of money and huge enterprises — whether he wasn't maybe one of [catalysts] who sort of sponsored that idea, raised the money, and what Bohr needed was a neutron source.
Yes, I think the names are mentioned.
Bergse has written several popular scientific books. Oh, he was very active.
There was another man, Berlme.
He was involved in the earlier period in establishing the institute.
He was very active, very eager. I wonder, you must ask someone. Mrs. Bohr may recall.
— she needs a name —
— yes, something to release the memories of that time.
I find when I mention something specific, then she remembers, but to ask in general —
— she will not remember. Try and find out. I think Bergse must have played a very important role.
Also that gives a way to check the correspondence, now that I have a name, to go back to the letters because I might have passed him over not realizing.
Yes, I think he was very important. And there was somebody in the Thrige Foundation also but I don't recall the name. The Thrige firm later on.
There was a lawyer on their board.
Yes, but you see Thrige is also an industrial enterprise. They built the magnet for the cyclotron, and they sponsored also quite a lot. I think they gave a lot of money also contributing to that — [not to the radium source] to the purchase of a gram of radium.
I may even have, in my rush in August in getting things together; I may even have found the list of contributors. I think I may have that, a xerox of it.
There must be a document of donations.
I think I have that. But I don't remember having anything to do with the (informal) origin of it. But what you tell me is a good hypothesis, logical, and with this name maybe I can dig it up. What happens then when the radium was purchased? Was it stored?
It was never purchased and stored in that fashion, because when Bohr knew that the money was available, he knew also what he wanted to do with it, namely he wanted a neutron source. He didn't want the radium. There was lots of radium in the Finsen Institute. That wasn't the point, and the nuisance of the radon beryllium sources was their short half-life. So what he needed was a source with a long half-life. I do not recall the details of these discussions, but I know that once it was clear that he would get the money, there was no doubt that what he wanted was a radium-beryllium source, and they contacted Radium Belge at that time which was the obvious source to buy radium from, and I recall that the only discussions that went a little back and forth, that was whether it was an advantage to have one gram of radium in two or maybe three sources of various strengths so that different experiments could go on at the same time. I do not recall any argument or any details from that discussion, but I do remember that the interest in it was, not one source, but if I'm not horribly mistaken, I think three. And I think what they did then was, they made one with 500 milligrams of radium beryllium mixture, you don't get 100 percent yield from it, so they lost a little bit, so the final result was not a whole curie, it was a little bit less. And I think it was divided in a big one and two smaller ones. And they gave the whole project to Radium Belge and they left it to Radium Belge to produce these sources, and that was done. The sources were in a platinum capsule, and the platinum capsule was again in a shielding brass holder of something and so on and so forth, and they came as readily mounted radium-beryllium sources to the Institute. They were kept in the famous well.
The well, does that exist anymore?
I think it does exist. You should go down. I don't think they filled it up but I think they closed it quite thoroughly. It may be a little bit of a storage room. They may keep some things down there. Yes, I think you should look, it's a historical place. I mean, I have spent a good part of my life on that winding staircase going up and down to the well.
Was it very large?
It was about, oh, a meter and a half or so in diameter. It was four meters deep or something of that sort, and a little winding iron staircase went down, and when we started to use it — it was originally also meant for spectroscopical work, and I think it was — now, be careful, I am not quite sure, but I think it was never used for that purpose.
It was built in the Institute originally, wasn't added later?
No, I think it was built originally, and it was meant to store a grid. I mean, I think it was meant for spectroscopy, and in fact never got that far. Then, in 1934, 1935 when this work began with radium sources, we put a table in the bottom of the well and there wasn't much room, there was hardly room for two people next to the table, and started all our irradiation work in the well. Of course, that was excellent — after all, you got the sources out of the way. You wanted to detect radiation, on top of it in the basement floor, and after all, these were quite strong sources, and they would give you a terrible background in all your detectors. So the sources had to be put away.
Did you get much contamination in the laboratory?
I don't really know. It is definitely so that leaking radon beryllium sources were rather frequent. It is very complicated to make a tight glass ampulla, once you have filled the glass with the finest grade powder of beryllium, the neck you wanted to seal up then was never perfectly clean, and these tiny tiny grains of beryllium powder would make that the melting together of the ampule wouldn't be quite successful, and you could have tiny leaks there. So leaking sources were not uncommon, and necessarily that would cause some contamination, naturally. The well was contaminated. Of course it was. We were all human beings — we also dropped one. I mean, one would go on the floor. What can you do? Of course the consciousness of radiation danger was very modest. I mean, I was never afraid. I would never think of anything, and we would move about and work in the immediate neighborhood of strong neutron sources and gamma sources without even giving it a thought. Just as we worked happily with beryllium powder without giving it a thought, you see. And I have written in some of my articles about Hevesy, I have made some sort of little ironical remarks about the fact that you didn't die so fast, or didn't suffer so much radiation damage in the good old times as you do nowadays. But this is of course not true, because we know that some of the pioneer workers in this field actually did suffer very serious injury from the radiation they were exposed to. So it's a little bit of a snappy remark. It wasn't meant so, but it is a fact that the rules for work with ionizing radiations nowadays are many times stricter than we ever observed.
But there your major concern was not to get contamination that would spoil the experiment? That was the main interest to you?
That was the main interest, yes. But we did actually expose ourselves much more than you would ever allow nowadays in the laboratory to be exposed. And I also recall that Bergse, just exactly that same Bergse, was one of the first who sort of talked about and was quite energetic about radiation risks. He came to the Institute quite often and talked, and he began to talk about that we were too easygoing and we should be more careful and we should think of radiation damage and so on. We just laughed at him. Thought it was nothing at all. I mean, the physicists were always that way.
It was only I guess later with the Berkeley people after many years of the cyclotron that they first realized they had to get some screening.
Yes. But it's not really justified. I mean, Madame Curie was undoubtedly a victim of radiation, and later Loewy — you know, he was a very close friend of Hevesy's, a medical man in San Francisco I think, he died of leukemia. But, well — it probably at least wasn't improved by his very strong exposure.
Let me tell you what I still would like to talk about, and you're going to have to be the judge of the time. One is to talk about your own status during the subsequent years, how you were supported at the Institute and so on, and to trace your work during that whole period. Another is, I'd like to explore some more the physical biological collaboration. There were some congresses and so on held, see if you recall anything about those.
That's much more interesting.
Then the third category is to talk about the reactions to specific physics events, whether or not you were involved in them. You were talking about the excitement in induced radioactivity, but then there were other things that were happening — if you happen to recall any of those. Those are three things. Then I would like to talk in a brief way about the occupation — you know, we did talk about that.
Oh, the German occupation.
Yes, and the time of your final leaving for Sweden and very briefly about your work there and how that influenced your subsequent career.
That's a lot of things.
Now, it's after lunch, we're starting again. Maybe we should first talk about the physical-biological cooperation in terms of the arrangements Bohr had made to work with the Krogh Institute, and how Krogh himself was involved in this, and Hevesy appeared to be the main channel of this cooperation, that it was thorough him that it all became possible, so I was interested in it from two points of view — how it did develop over the years, and how it affected your own work.
You're right. Hevesy was the sort of catalyst of this cooperation. As a matter of fact, he was it to such an extent that it almost became funny, because Hevesy is a very active person and he is a person who can put dozens of other people to work, on his ideas, and he did. The moment isotopes began to become available; he established contacts practically all over the city. I mean, we made a lot of fun out of that. He started at the Finsen Institute. His first experiments, when for the first time he had made some radioactive phosphorus, P-32, he injected it into mice, which were kept at the Finsen Institute. It's the work that is published together with [Ole] Chievitz — but then he had a hundred ideas of what more he could do, and he established a little sub department practically everywhere where he could get by with it. It was in the Rigs hospital he had some contacts, with Krogh's Institute he had the contact, in the physiology department, you have mentioned Lundsgaard, and he was the professor of physiology. He had a little group working at the dental high school. He had a group working at the Carlsberg Laboratory, which was with Linderstorm-Lang. He worked with a botanist out there. So it was really sort of amusing, how he chased around all over town. Now, the reason was that he was full of ideas, but fundamentally Hevesy was not a biologist. Hevesy was a physical chemist, a chemist with a bent to physical chemistry. He knew fundamentally very little about the biological or medical fields. He wanted to apply this method. So he had to go around and ask the experts in these respective fields for their cooperation. Now, Hevesy was very inspiring and very temperamental. So before these people knew, they became embroiled in the experimental work for exceeding what they maybe in the beginning had thought they wanted to get involved in. And this really was very funny. It belongs to the Hevesy anecdotes — the way in which Hevesy managed to engage people into this work that fundamentally sprang out of his ideas. And then ended up putting sort of the load of the work on other people. It was one of his great talents.
He supplied the materials.
He supplied the isotopes and I think he very often supplied the fundamental idea, in that he went to these people and said, "Wouldn't it be an excellent idea to study this and this problem by means of these isotopes?" People would say "Oh yes indeed, it's fascinating," not knowing at that time that they would get stuck with the work. This was really fantastic. Not only in Copenhagen — I mean, he very early extended his reach into Stockholm, for instance. He had work going on in Stockholm long before he moved to Stockholm —actually very fundamental, very important work, namely the nucleic acid work, was started in Stockholm, while he was still here. So there weren't enough people he could put to work in Copenhagen even. So he would reach out, and that was very funny. For me also a very interesting and fascinating part of it was that actually, nobody made measurements except me. So he would start work, he would start projects and biological experiments all over the town, and he would bring back all the samples and all the material that was to be worked up to Blegdamsvej to work them up (chemically) and measure them and do a lot of the work. It was terrific, but at times it became a little bit slave work. It was just simply fantastic, and the amount of measurements I made for him was terrific. I have sent to Dr. Hollaender in Oak Ridge just boxes and boxes and boxes of notebooks that we would fill, which contain all the experimental work belonging to the project he had spread all over town. Bohr was I think a little bit amused, but approved of it very much because that was exactly what he thought it should be. And well, I think I forgot to mention all of the physical chemists, because Hevesy also had some collaboration with Bronsted at that time, who was right next door in physical chemistry. So it wasn't just biology. At the dental high school, enormously — the work with Holst, you can easily see that, turnover study in teeth and enamel, I mean, things that you think relatively remote. But he was just so overflowing with ideas, how this technique would be applied.
That's the point I'd like to know about. What was his motivation? Was he interested in the concept of the indicator, the isotope, or was he interested in the biological process? Was this proliferation that he was responsible for aimed at solving biological problems and getting biological information? Or was it aimed in his mind at really exploring this physical chemical phenomenon of isotopes.
I think it started at the one end and ended at the other, because I think when he started it was more the impulse to show how extensively useful this tool would be. And he did not really, I think this is an open secret, he did not really know very much about biology, and many of the people he started cooperating with were very much amused by his ignorance. But he was such an ingenious man that his guesses were ever so often right. So without knowing too much biology, he would suggest a problem, he would even suggest a solution to a problem which was not really founded on his knowledge of biology, but just his instinctive sniff of where the answer would be. Although Hevesy has published, has done some work that later turned out to be wrong, basically because his knowledge of biology wasn't sufficient, the large majority of the projects he started were successful and meaningful, although his basic knowledge of biology at that time was very poor. Hevesy was a fabulous reader and he had an absolutely incredible memory. He was a walking telephone book, in science, and he had the ability to learn, to absorb, to make himself familiar with fields that he had never studied before, and he would just gobble that up, and in a relatively short span of years, he had actually acquired the knowledge that he lacked in the beginning, and I think then his work was not so much to show the many-sidedness of the tracer technology. Then he became really interested in the biological problems with which in the meantime he had familiarized himself, and really became interested. I think there are all the stages.
Did that transition occur before he went to Sweden?
Yes, but I would think that he became more and more of a biologist, and maybe in his later years, as a matter of fact, first really knew what he was talking about. He turned even into radio-biology. You know, he began to work on the effect of radiation which you will not find in his first biological experiments. So he ended even in becoming a radio biologist, and also there I think he acquainted himself so thoroughly with the problems that even the, let's say, basically trained biologists had to admit that Hevesy knew quite a lot about it by that time. So I think all the stages are represented.
Now, is work has affected other institutions. How did it affect the Bohr Institute itself, other than that it kept you busy, obviously?
It affected the Bohr Institute only seriously or noticeably in the first years, until the occupation, I would say, until about 1940. Hevesy would try to find room to put animals, and he did. I mean, we had rats and we had rabbits and we had all sorts of strange things that didn't belong in the Bohr Institute at all, because he had even more ideas than he could sort of place around in town, so he did a few things at the Institute, and not so few — particularly L. Hahn, his younger co-worker, came in very importantly. He did a lot of animal experiments at the Institute.
Was Hahn a refugee?
No, I would say quite to the contrary. Now, turn off that gadget... L. Hahn was the person who did a great deal of biological experiments on animals and a few others did too, like [Ate'n?] [Etienne?], you've seen his name in the publications, and this went on until 1940. By the time of the occupation, some of the co-workers of that period had left to return to their respective homelands, and I moved for a while out of the Bohr Institute and moved into the Carlsberg Laboratory to be a little bit out of sight, and you know, Hevesy left for Sweden also in the fall of 1943, and then this biological work at the Bohr Institute was interrupted for a while, and I think by the time it was interrupted, there was already a feeling, both in Hevesy and Bohr, and I have no doubt they talked about that even already at that time, that it was a little absurd and a little bit out of place, that Hevesy tried to maintain a group working in biological work in an environment that was so utterly unbiological as the Bohr Institute. I mean, put biological work in a biological environment and not in the Institute of Theoretical Physics, and I think this has been slightly discussed at that early time, maybe in the beginning of the 1940s. But then the situation in Copenhagen was such that no fundamental changes could be made. You lived from one day to the other. You never knew what would happen, and you wouldn't really undertake something fundamentally changing the situation. But then when the war was over and work could be resumed, it had already been resolved, that the biological work that Hevesy had started and in part carried out at the Bohr Institute should move out of the Bohr Institute, and be moved into an environment where it belonged. And that went so far that even before we returned, I think it must have been after the liberation of Denmark but before we returned from Sweden, that August Krogh made a trip to Stockholm and visited, among other people, me, and asked whether I would be willing to accept a position at his institute, with the special purpose of being the physicist and being specialist in isotope measurements to help the biologists learn that technique and apply it.
It symbolizes more than that. It symbolizes this field moving out of physics.
— yes, and Krogh had recognized and Bohr of course and Hevesy too, this was so important a tool for biology that it should be made at home in biology and should not be borrowed from the Bohr Institute. I think it was the right moment to make the move. So when we came back, Hevesy didn't really come back. Hevesy stayed in Sweden and commuted for a number of years. But I came back and [some of his co-workers also moved back], so that the biology group was gradually taken out of the Bohr Institute, beginning in 1946, the biological group of Hevesy moved out of the Bohr Institute and moved into the August Krogh Institute. No, it wasn't called that at that time. It was called the Zoophysiological Laboratory but August Krogh was the boss and he was in the process of retiring. He retired almost at that same time. But he saw to it, before he retired, that this move was made. He thought that was right, and I am utterly convinced that Bohr definitely thought it was right, and Hevesy also agreed that it was right. And that ended this funny period, where you had a small group of people doing biological work in the Bohr Institute. It was really out of place. I mean, the facilities weren't right and the atmosphere wasn't right, and it necessitated a certain dabbling in a field, because most of the people were not biologists. I am not a biologist, Zerahn was not a biologist, several of the others were not — some were chemists, some were physical chemists. We all dabbled in biology and Hevesy got good advice from all over town, and it was not satisfactory scientifically. By moving this whole thing into the biology division, we were under the guidance and protection and advice of true biologists, so we didn't make all the mistakes that necessarily are made when physicists and chemists and engineers try to do biology.
Considering the subsequent history of the Bohr Institute too, some change would have had to be made, because with the whole nuclear energy development during the war —
— sure, it was necessary —
It changes things at the Institute itself in terms of physics.
Yes, of course. So it was only natural that this moved out, and it lasted a little while. We didn't move all at the same time, but I mean, the decision to move was made, at that time.
Mostly it was people involved, not very much more, because the facilities at the Bohr Institute were never really extensive for biological work.
No, but for instance Hevesy's co-workers Ottesen and Zerahn stayed longer at the Bohr Institute than I did. But it didn't take very long, they all moved over then —
— but I mean, you're not moving a cyclotron or anything, you're moving people basically.
And moving a research project also. We went over and picked up the isotopes that were made in the cyclotron and brought them over from the Zoophysiological to the Bohr Institute. But that was not very much, because at that time we got a lot of radioactive isotopes from America.
No, I don't think so. They were too short-lived. The short-lived isotopes were made at the Bohr Institute and brought over, that was sodium or potassium, chlorine and so on, and the longer lived phosphorus and sulphur and so on were sent over from America.
Well, there's something I wanted to ask about the problem of sources between the period 1935-1940 or even 1943, of how it changed. In 1938 you're getting the cyclotron running. At the same time Bohr has this gift of the radium and at the same time there's this whole procedure of the ties with the Finsen Institute.
Yes, that went on. That continued.
Did you have enough? Or did you have a constant problem with sources? Was there always a shortage, even with all these sources of sources?
You must ask different people. For the people who worked for Hevesy or with him, it was absolutely enough. Hevesy was insatiable. Hevesy would have said it was not enough, because if he had had more, he would have maybe have started still another project.
You were talking about Hevesy's insatiable desire for sources.
For radioactive isotopes. I think there was — I would say — a large number of investigations were going on, and it was enough, but you must also remember that the detectors we had at that time were much more primitive. You were used to and didn't know better than making the greatest possible use of every tiniest quantity of a radioactive isotope you could get hold of. This sort of lavish use of isotopes we have nowadays, that was unknown. You would spend hours and hours measuring samples that were very weakly active, and that was a matter of course, because you would use your supply to every drop. And the instrumentation we used was much more stingily built. I mean, you would work with a much higher space angle. You would use every disintegration much more carefully than you do nowadays. Therefore I think it was enough, because he could hardly have made more experiments or started more projects, even if he had had more (isotopes) available. Now, then, as the whole thing developed, he simply became more and more lavish with it.
Also it seems to me that the war would interrupt the supply from California, for example.
Yes, it did.
And I assume that's where the cyclotron came in handy here.
Right. That is true. They would make phosphorus at a much bigger rate than they did before or after, and the same was true in Stockholm.
Now in Stockholm, that cyclotron, I've just been digging into the history of it and talked with von Friesen in Lund who was the one who actually built it for Siegbahn, in Siegbahn's Institute that cyclotron was producing isotopes. Was that the one that supplied you while you were there?
I think so. Now I'm not very well informed about whether Hevesy had, but I don't think so. Isotope work, was started — of course, thanks to Hevesy, in a hundred places all over Stockholm, as it had been here in Copenhagen. I cannot recall whether Hevesy still could, at least for some time, get some phosphorus for example from Berkeley. I can't remember how long that postal communication was open. But he did get Stockholm-made phosphorus too, and I think it was predominantly that which he used.
You in a paper published in 1945 acknowledged artificially radioactive potassium that you used in Stockholm which was which was supplied by the Nobel Institute for Physics, the cyclotron, and (Manne) Siegbahn and Atterling, are the people you mention specifically as providing the sources — at least, for the paper, supplied your work.
Yes, that was potassium. That's a short-lived element again, you know.
Just going back to your own status during this whole period, when you first came to Copenhagen you came on your own funds. Then presumably you started getting some support.
Yes. That didn't last very long because the permission to send money out of the country (Germany) didn't last very long. I think I had been on my father's funds for not even quite a year and then that was stopped. He wasn't permitted to send me money. Then Bohr applied to at the Rask-Ørsted Foundation for money and I have been paid out of the Rask-Ørsted stipend for years. As a matter of fact, up to the war and during the war, even during my absence, the Foundation kept me on that stipend even during the period I was in Stockholm, and our friends here in the country maintained our apartment and paid our little bit of taxes or the telephone or whatever had to be paid, out of a fellowship from the Rask-Ørsted Foundation that lasted, simply went on. We pretended that nothing has happened. And this fund stayed, and I think was then later supplemented by a grand from the Rockefeller Foundation.
You probably got some support from Rockefeller also before you left for Sweden.
That may well be so.
I think I saw your name on the list.
Bohr always wiggled with this money in his own fashion. Nobody knew. I mean, Bohr had money from here, from Rask-Ørsted, from Carlsberg, from Rockefeller, who knows where, and this money was largely pooled. Maybe somehow Mrs. Schultz kept it apart in the papers, but in reality the money was pooled, and he just used it as he saw fit. And I don't know, I really don't know how he did, but I think my money came for a long long time from Raskøsted Foundation and then was supplemented a little bit. After all, the money got less and less value and he had to give a little bit more. But you never asked Bohr where he got the money from. He was a tremendous fund raiser, as you know.
But never asked for enough, that's the problem.
Oh, I don't know. People weren't so spoiled at that time.
Well, this is what some of the people feel, that he was always cautious to keep his proposal down below the amount that he needed, and then his colleagues would criticize him for not asking for the full amount that was really indicated. Maybe this is in the postwar period. How about in Stockholm? Did you get that kind of state support that was going to unemployment office people?
Yes, that everybody else got, that's right.
How much was that?
It was, if I recall it right, 300 kroner per month, Swedish kroner, and that was sufficient. You could live on that.
It was sort of welfare?
It was a sort of welfare, and it was (the same) for all people who came. It was independent of what kind of work you did. A scientist didn't get more than an office worker or anybody else. So it was the standard support that was paid out by the Swedish state to all working refugees, regardless of whether they were Danes or Norwegians or whatever they were at that time, and it was sufficient to live on.
You explained about sharing a flat.
Yes, of course. We lived very comfortably. I wish that no refugee in the world would have a poorer life than we did. I mean, we didn't miss anything. We ate and drank and we lived under decent conditions, and we were properly dressed, who could want more?
Well, you had to go to a little trouble to get there.
You explained to me when you were describing it in fascinating detail your escape in the boats, going across to Sweden. Shortly after you got there, you got a phone call from Professor Runustrm to invite you to work — what was it, the Wennergren Institute —
— for experimental biology.
So you then became the staff member. What was your capacity?
I guess in America you could call that a research associate.
I see. Did he have a specific project that he wanted you to work on?
Yes, he did, and a paper came out of that, that is in the Bohr Birthday volume, on the permeability of red blood corpuscles. That was something that he had going; and again, you see, you are in this situation — I don't know whether it's just me, I don't think so — I think many people had this attitude: well, you just made it, and you were offered a straw to (hold) on, and you didn't come in and say "I want to do such and such." Maybe a few people did, but I don't think the average did, and the idea was that you tried to slide into a place that had become vacant because some of the Swedish co-workers had been drafted into the army and so on, that was after all the status of many of the Danish refugees in Sweden, that they just for a while took over the places that were left empty because the young Swedes were drafted into the army. And the same at the Wennergren Institute. You see, there had been scientific projects going on by somebody and suddenly they were called into the army or had other things to do, and it was natural, you came there as a guest, you were grateful for having something to do and something to live on, and Runustrm said, "Well, this has been going on, would you like to go on? It would be ever so useful, "you know, and they say some nice things, "You are so qualified to do that kind of work, would you?" And of course you say yes, and you slide in there, where the work happens to be. You don't say "I want to do such and such." At least I wouldn't and I think very few would. And in this way, you get into another group, with a certain number of projects going and so on. You get in and you try to help.
You find out that you're interested in it after a while?
Well, it doesn't take very long till you become fascinated by the project. I had never thought of being interested in it my life before and I hadn't worked very much with blood corpuscles and I thought it was very interested.
You put in a regular schedule then?
Oh yes, it was absolutely the same as here.
I have a question which takes us back to Copenhagen, about the physical-biological congresses. There were two that Rockefeller paid for, and I've seen files but haven't had a chance to study them so I know very little about it except the list of names. There were very few physicists who actually participated, although they were in attendance I can see certainly but in terms of the subject matter, it seemed to be very much biological. I don't know very much about the motivation for the conference, whose idea it was, what was covered, what was accomplished?
I wouldn't be able to say whose idea it was, but I would be inclined to think it was Bohr's. Bohr was very interested. I mean, Bohr was fascinated by these problems, and I think probably it just emerged from the fact that here the Rockefeller Foundation was supporting the biological application of physical methods, and Hevesy was around and all these contacts were established through Hevesy. I think it just occurred to them, it was relatively obvious that such a conference would be interesting. And Bohr has been in that lane before. Isn't the first that famous meeting in Helsingr with the anthropologists, wasn't that even earlier? Was it in the beginning of my time or wasn't it even before my time? When were the Light and Life Lectures?
Well, there you are. So that was before. So he has been in that line even before.
This would be quite natural for him. Do you remember the conference itself?
The 1932? No.
No, the first Physical-Biological one, 1936 I think.
I recall it, but not so terribly much. I don't know why I don't recall more of it, but it is possible that if I looked a little bit at the programs and so on, it would come back to me.
I have copies of that so I'll study it and see what kind of account I can prepare.
Yes, and then I may be able to see, so many things happened at that time. I mean, not only scientifically, but politically and in my own existence. I mean, it was a very decisive turning point, and so it is understandable that I don't remember everything equally vividly. I guess I was preoccupied with my own fate and with the fate of my family and with political developments and changing bosses, changing problems.
There was a little bit of uncertainty in all off that.
Oh, in all of that, yes.
About your family, when did they leave?
Very late. 1938.
You say they went to New York?
No, they went to Belgium — then after the war, New York.
In the few remaining minutes that we've allowed ourselves, in terms of other events that were going on at the Institute, how much involvement did you have? In other words, once you were involved with Hevesy on a regular basis, did you have much chance to get involved in a discussion or to be aware of other things? For example, around 1935, 1936, Bohr is developing his ideas of the compound nucleus. This is apparently brewing for a while, also precipitated by results coming from Rome, and then by late 1938, beginning 1939, you have fission. I was curious if you recall some specifics about that, whether there were discussions in which you were involved?
Oh yes, very much. I mean, involved and involved. Of course I didn't contribute in any scientific way, but I sat in and listened, and experienced it together. I mean, this was a very exciting time too, and all the experiments that others at the Institute made interested us tremendously. We would constantly discuss with Frisch the experiments on fission and the period when Lise Meitner came to visit, and Bohr came to me and said, "Well, if you should have a few hours at your disposal, it would be awfully nice if you went down and helped Mrs. Meitner a little bit," and so on. It was always that way. And of course I did. I know there was a lot of running going on at that time, the cyclotron being in one end and therefore the irradiations being made in one end of the house, and the detectors after all being as far away as possible, and these were all very short-lived processes and compounds there was really physical work to be done, like really running fast with some samples that came out of the cyclotron, getting them down to the Wilson chamber or to the counters and so on, and there was great excitement, and everybody was recruited to help. And this went on day and night, and I was in it too. You see, I wouldn't sort of sit upstairs and do Hevesy's experiments and make measurements and feed chickens or so, I would take all the time off that I could to be down in the basement where these experiments were made, and participate in it and discuss it and wonder what was happening and so on. Not as sort of a contributor to the experiments but as a participant in the game. I do remember that very clearly from that time.
Do you remember, during the period when Bohr was in the U.S. with Rosenfeld and this was a period of great anxiety about Frisch and Meitner publishing the results, getting the experiments done, and there were exchanges of cables and so on, do you remember the particular atmosphere?
Was there a misunderstanding locally in terms of the urgency of the situation? Bohr seemed to be in much more of a hurry than the people in Copenhagen were, because he was aware of the American scene.
Yes. We didn't know so much of the other side. I think the atmosphere in the Copenhagen Institute was much more coined by the fact that we knew how terribly interested Bohr was, how eager he was to know, and Frisch and Meitner worked very hard. As I say, that went on day and night. The moment they got something, they felt a terrible urge to tell him, not because they thought somebody else on the other side would do something. It was not a competitive affair; it was just simply when we got something very exciting here we would tell Father Bohr just as fast as we can. But not at all in a feeling of competition. I think — I don't want to say too much, but it is my notion that Frisch and Meitner were not at all aware of the competitive character off the situation. That was much more on the other side of the ocean. So they were terribly excited, but not out of competition.
Did you recall similar excitement for example when Bohr was working on the compound nucleus idea, when that came out? That was of course a theoretical contribution, but was there any interest in the results coming from Rome? You remember there was supposed to be a meeting, one of the Institute colloquia where the results from Rome were already known generally, and Miller came back from Rome —
Yes, I remember, he had been there as a Rockefeller fellow.
He came back, his wife was sick, then he brought the very latest news and it was apparently this that precipitated ideas. So do you remember that particular meeting?
No, I don't think so. I don't think I remember that. There were many meetings and many conferences, and it's a little bit sort of flows out in my memory. I can't quite remember what happened at which meeting, which year was it. Of course if I sat down and looked at it and studied it I could maybe reconstruct it but you have done that long ago, so —
Of all the excitement that you can think of in the years from early 1934 to when you left in 1943, would the fission thing stand out as the most exciting development, in terms of where people at the Institute really got worked up?
That was a very exciting period, but I think when the members of the Institute started on the induced radioactivity, that was very exciting too. You know, when the first radon beryllium sources were made and we started irradiating things and we started to count that was very exciting too. You know that little anecdote that is described in various places about the dysprosium that we activated, you read about that? Hevesy had left for Budapest, as he used to quite often, and he had dug down in his cupboard with all these little glass with rare earth samples, and gave me a glass of dysprosium oxide and said, "Try if you can activate that," and I did. He wasn't there. And I put it down the well and I irradiated it for a while and I took it up, and measured it, and it didn't say anything, and I put it away, sort of. That wasn't very interesting! I had a weak activity and it decayed slowly, but it wasn't very interesting, and I remember talking with Frisch about it and saying, "That wasn't anything." And it just sat there for a couple of days. Then we needed the little container it was kept in because we wanted to measure something else. We poured the dysprosium out, and we poured it back into the bottle Hevesy had given me and put it aside, you see, relatively conscientious as we were, we put the empty container over the counter, to see whether this was all right, and it just roared up, you see. After we had taken the dysprosium out, the counter was able to count what was left. Before that, it was just absolutely blocked. And later what turned out to be the most sensitive indicator for slow neutrons was after all dysprosium. It had the highest cross section (for slow neutrons) and it was used later. (Dysprosium) Of course this was a great experience. That was terribly exciting. The funny thing was that when we did that, [I recall very clearly] I measured the empty container and it was terribly active, and not only was it active, but it became more and more active. With time passing the activity we actually measured became greater and greater, and I watched with Frisch and said, "I have never seen anything like that, what's going to happen?" Well, we discussed that for a couple of hours, until the next day, until then Frisch found out what the reason was. After the dysprosium decayed, you see, the Geiger counter began to be able to measure what was there. In the beginning it had only measured the holes between the particles. As it began to decay more and more, then eventually we measured the activity. Well, that's now a well-known phenomenon, but at that time it wasn't well known, because you didn't know any substance that could be activated to such a degree, it had never happened before, and — well, that was very exciting, and it was very funny experience, namely, actually, you were unable to detect an induced radioactivity because it was so strong that it was no longer detectable with the instruments we had at that time.
Yes, I can see that that would really give you a feeling of accomplishment.
That was very exciting. I was maybe more involved in that experience than I was later in the fission experience because it wasn't my experiment. The dysprosium was my experiment, you see. I had been put to do that. It was my responsibility, excited me naturally extremely. So I think that also during this period there was really something going on, and when Hevesy began to find out which of the potassium isotopes was the naturally radioactive one and so on, that was also very interesting.
That really is the answer. You know I think to be honorable we should stop so you can get back to your other work, and we've covered the ground, so thanks.
 The final exam before leaving the gymnasium
 I am not sure that this is correct, Haber may have left 1934, cf. p. 14. You can check this elsewhere! [?] Nov. 1988
 E.T. Sørensen was — as I recall — a student working for his degree. H.L. 1988
 Historically, in error, he had holmium!! 1988
 Historically, this is not correct! We know that Hevesy was very competitive and he wanted to study the rare earth elements himself. Cf. my book! As of 1988 H.Z.
 I doubt it. 1988 H.Z.
 On gold! H.Z. 1988
 1988. I doubt it! H.L.
 1988: Leo, earlier!
 1988: I know now that Hevesy was the primus motor behind this birthday present. Cf. my biography of Hevesy (1985).
 Because there was too much vibration from the traffic (streetcar) outside. H.L. 1988
 I think this also is an error. A medical man in California who wrote one of the first books about the application of isotopes and ionizing radiation in medical research adn diagnosis, Loewy — Baer or ? H.L. 1988.
 His co-workers Ottesen and Zerahn had been at the Institute eduring the occupation, they did not have to "move back." H.Z. 1988