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Oral History Transcript — Dr. Georg von Hevesy

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Interview with Dr. Georg von Hevesy
By Thomas S. Kuhn, Emilio Gino Segrè, and John Heilbron
At Segrè home, Lafayette, California
May 25, 1962

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Georg von Hevesy; May 25, 1962

ABSTRACT: This interview was conducted as part of the Archives for the History of Quantum Physics project, which includes tapes and transcripts of oral history interviews conducted with ca. 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the l920s. Also prominently mentioned are: Francis William Aston, Karl Auer von Welsbach, Niels Henrik David Bohr, William Henry Bragg, Johannes Broensted, Dirk Coster, Marie Curie, Charles Galton Darwin, Alexandre Dauvillier, Albert Einstein, Roland von Eotvos, Kasimir Fajans, Alexander Fleck, Fritz Haber, Martin Knudsen, Henry Gwyn Jeffreys Moseley, Hantaro Nagaoka, Walther Nernst, Ida Noddack, William Ramsey, Ricci-Curbastro, A. S. Russell, Ernest Rutherford, Erwin Schrodinger, Frederick Soddy, Edward Teller, Thomson, Georges Urbain, M. Volmer; Niels Bohr Institute, and University of Manchester.

Transcript

Session I | Session II

Kuhn:

Now, will you say something Dr. Hevesy, just so I can make sure that you are recorded.

Hevesy:

Well, it's a great pleasure to share your company. I will tell you what a queer way I got to Manchester. I was in Zurich. I was an assistant in the department of electro-chemistry in the Technische Hochschule in Zurich. My chief was Richard Lorenz. He got a call to Frankfurt. He wanted me to follow, but I didn’t feel inclined. Willstatter was the head of the chemistry department. Willstatter came to me and said, “Now in Germany the assistant belongs to the professor; in Switzerland to the laboratory. You stay here “But I didn’t go to Frankfurt and I didn’t stay in Zurich, because I didn’t know who will become the follower of Lorenz. It is unpleasant to have a new chief. But I got interested in ammonia synthesis. You know it was very great advance. Haber and Rossignal, his English operator, used catalytic processes to unite nitrogen of the air with gaseous hydrogen. This later became a very important industrial concept. So I went to Haber, to Karlsruhe. But Haber wanted me to do some other work, not to work on this catalytic process. He found that sodium potassium alloys, liquid potassium sodium alloys emit electrons when they are oxidized. And he thought this to be a very great discovery, which it was not. And he wished: me to investigate whether when molten zinc oxidizes, if production of electrons can be found. Now no one mastered electro-static techniques there. And I told Haber, I am going to England to learn technique. (Bose) and J. J. Thomson and Rutherford carried out this type of measurement, and I shall go and learn there and return. And Haber entirely agreed and found it a good idea. Now I had a choice between J. J. Thomson and Rutherford. And it was a former collaborator of Rutherford (Limmerling) who worked with him in Canada, who told me I must absolutely go to Rutherford. ‘He is a marvelous man.” So I decided for Rutherford. I went to Manchester early in January 1911.

Kuhn:

Were you sent by Haber to do this?

Hevesy:

No, no, not at all. It was my suggestion. But Haber agreed. I mean, it’s a good idea to go to England to learn these methods. Then in the summer of ‘10 I left Haber, but I left only for Manchester in January 1911. I found Rutherford’s place very busy, hard working. But a very dirty place. Namely, Manchester is very foggy, foggy and smoky. And of course everywhere you see smoke there, everywhere the smoke. Now the technique used in Rutherford’s lab was to fit up an electroscope. You have to build it yourself of cocoa boxes, gold leaf and sulfur isolation. And you charge the electroscope by sealing wax which you rubbed on your trousers. So it was a very primitive technique. But of course also a microscope to read the electroscope. Now the microscope was fixed and then you were not supposed to touch it. And of course you were not supposed to clean it. So years went on without apparatus being cleaned. But apart from the shortcomings it was a very fine lab, nice rooms, and lots of people working there—able people…. I remember Moseley very well, with whom I was on very friendly terms. I will tell you later about his work. And Charles Darwin was there. He was lecturing in theoretical physics. And Russell, who later came to Oxford. An Italian, Rossi, did spectroscopic work. He showed that ionium and sodium have the same spectrum. And then Geiger was there. He was an assistant. And also an assistant named Makower, who died since. Geiger and Makower published a book together. And also a chap Robinson, who worked on beta rays. Gray, a New Zealand man. Marsden who came from Australia. Fajans who came from Germany. And Boltwood was there for a while. He came from Yale. Rutherford invited him in hope that Boltwood, a great chemist, would purify ionium, but he failed as many others. And many visitors. Langevin came occasionally. Jean Perrin came.

Kuhn:

Bohr was not there?

Hevesy:

Not when I first arrived. Bohr came, it must have been the autumn of ‘11. No, it was the summer of 1912. In 1912 Bohr came to Manchester his first time. It was on a honeymoon. Everyone was astonished at such a charming wife he brought with him. Because people, were not impressed by him. Most people are not impressed by Bohr. They do not realize his genius. He was not talkative, somewhat reserved. Some people did. Rutherford did and Darwin did, and so on; but young people did not. Well, what were most outstanding events? Of course the discovery of the nucleus…Rutherford told the story that he jointly with Geiger observed small angle scattering. And when Marsden had to do some research work, he suggested he should look if it’s possible to find larger angle scattering. But Rutherford remarked that he never believed that he shall find such, “But try, let us try,” he said. And one day Geiger came very excited and told him, “We’ve found large angle scattering.” It was entirely correct.

Kuhn:

Were you there when that happened?

Hevesy:

I was there, yes.

Segre:

Marsden has told that story rather in detail at the Manchester Conference last year…

Kuhn:

But there must have been discussions about it, and apparently there were a variety of early interpretations…

Hevesy:

Well, you know. I had always the impression that Bohr had a great share in formulating the nucleus. If I remember well, the word ‘nucleus,’ term ‘nucleus’, comes from Bohr. And Bohr stressed the point that the mass must be concentrated in a very small space.

Kuhn:

Yet the first of the papers on the nucleus was probably before Bohr came.

Hevesy:

Oh it’s not Bohr, it’s Rutherford who published it, you know. But Bohr discussed with Rutherford…Nagaoka was the first with the planetary atom… Nagaoka must have been quite an able man.

Kuhn:

Did you know him at all?

Hevesy:

Yes, I met him. He was once in Manchester. I met him… I don’t know when he did the work, but he visited, he visited in Manchester. I think he was in Japan when he carried out the work, but he came to Bohr and Rutherford, and I saw him in Manchester. He was in very good shape, a little heavy man. Not like the average Japanese, much heavier, a round head, this Nagaoka.

Segre:

The question that the nuclear properties were in the nucleus and yet the chemical and the atomic properties were—

Hevesy:

This comes from Bohr no doubt… In ‘12 he had certainly the idea very clear. He might have it earlier already, but when I first talked with him in ‘12 he had quite clear the idea that the chemistry resides in the outer electron arrangement, and mass and atomic charge in the nucleus. No doubt about that… I don’t know how Bohr came to the idea, you know. But he actually arrived very early at it.— Oh I remember. It was a Sunday afternoon. I was at the house of Rutherford. Bohr was also present. I asked Rutherford: “Alpha particles clearly come from nucleus, no doubt. But where do the beta particles come from?” Rutherford answered, “Ask Bohr.” Bohr was present. And with no difficulty answered that electrons involved in transmutation process come from the nucleus, and all of the other electrons come from the exterior of the atom.

Segre:

It’s very interesting. ‘I asked Rutherford, and he said, “Ask Bohr.”

Kuhn:

Do you remember other conversations about the nuclear atom, from the time of your arrival?...Well, say J. J. Thomson, how did he take it?

Hevesy:

I don’t think J. J. Thomson liked the idea. J. J. Thomson didn’t like the ideas which didn’t originate from his head. As I told you of the mass spectrograph and all this. That is typical of him…

Kuhn:

Had you known of the Thomson atom before you came to the laboratory?

Hevesy:

Yes, yes. The Thomson atom is described in his book, Electricity and Gases, which already came out when I came to Manchester. This book must have been published in 1909 or ‘10 or some such… The interest of atomic models was not so great, as it became later on, you know. Here was a large field of electricity and gases. Tremendous work carried out in J. J. Thomson’s lab. Then out of this work hypotheses are put forward about the constitution of atoms. I don’t think that people get excited about these things. People got all excited in the atomic—nuclear problem after the discovery of the nuclear atom and especially after Bohr’s work.

Segre:

How much time was there between the discovery of the model and the interpretation of the hydrogen atom? The quantization of the model?...

Hevesy:

I think not more than a year.

Kuhn:

Now Bohr’s paper is July of 1913. And the nuclear atom paper is 1911…

Hevesy:

Yes, but you mustn’t forget that Bohr is not a man who writes from today ‘til tomorrow. It took him a year or so to write this paper. He is very particular in writing papers. Now, he gave the Rutherford lectures about three years ago, and now it took him almost three years to write it…So we can with great probability consider that the paper published the first of July was conceived the year earlier.

Kuhn:

Do you remember conversations about it? He surely had talked to Rutherford about it. He acknowledges conversations with Rutherford.

Hevesy:

Yes, yes. Oh yes, because the paper was sent to Rutherford and Rutherford forwarded it to the Philosophical Magazine. All papers in those days—. This is peculiar. It is very different today. But even some years later I remember that our papers on the discovery of hafnium, we sent Rutherford a paper, and he forwarded it to Nature or another periodical. So Bohr sent his paper to Rutherford. .

Kuhn:

Did you talk with him about this idea of quantization?

Hevesy:

With Bohr? Yes, yes, but more on the isotopy, on argon and these problems we talked a good deal. The interesting point is that Bohr sent his paper to Rutherford with a request, “Read it and forward it to the editor of Philosophical Magazine.” And Rutherford after finishing the paper wrote, “It is an interesting paper but it is much too long. It must be shortened.” It was Rutherford’s custom to describe very clearly and concisely the result of experiments. He writes a very different type of paper. When you have to explain lines of thought and alternative explanations and argue against possible arguments against, and so on. But in the meantime, Bohr sent his second paper to Rutherford. It was still longer, the second paper. Rutherford answered, “No, I mean it is impossible. You must shorten these two papers.” Then Bohr tried to argue, and then finally he took the train for Manchester. And he looked up Rutherford, and they were arguing the whole night. Finally Rutherford accepted Bohr’s argument and sent the two papers to the editor of Philosophical Magazine… This is history I haven’t witnessed in Manchester. Bohr told it. Bohr told it to me. This story of how he approached Rutherford and how Rutherford reacted on these papers.

Kuhn:

Was Rutherford himself much interested at any point in the quantum hypothesis?

Hevesy:

I don’t think so that he was very interested. He was to some extent interested… He was skeptical about the interpretation of a theoretical physicist. He was always joking about chemists and about theoretical physicists. Oh at chemists he was strongly joking: “Chemists are second class beings.” He was not quite seriously mean that but partly serious. He was always joking that he got the Nobel Prize in chemistry, saying that he had no idea about chemistry, had no idea what it was about.

Kuhn:

Was his feeling about chemists also involved in his relation with Ramsay?

Hevesy:

Oh, Rutherford was really on friendly terms with everyone. Two men he distinctly disliked, and those are Ramsey and Soddy. He didn’t say so. He didn’t say directly, but he spoke so smilingly about Soddy.

Segre:

Oh but they worked together.

Hevesy:

Yes long ago they worked together in Canada.

Kuhn:

Do you have any idea yourself? Had he always felt that way about Soddy, or was it because of the book Soddy started to bring out?

Hevesy:

No, no, this started before. Rutherford measured the deviation of alpha particles in an electrical-magnetic field. These measurements led to the hypothesis—not direct result—that alpha particles are very probably helium atoms. And he intended to test this. Soddy associated with Ramsay, procured radium and showed that helium is produced by radium. I had the impression although he never said so, that Rutherford found this not fair. While Soddy was working with him and Rutherford came up with this idea and stressed this very strongly, then Soddy goes away and works with Ramsay on this. This may have been one reason why he disliked Ramsay and Soddy. But apart from that, Rutherford was a straight-forward man, while Ramsay was not all that you heard about, you know. He was conceited and fussy. And Soddy was a very difficult man, an unusually difficult man.

Difficult with everyone. Robert Robinson for example was his colleague at Oxford, but his life, was made impossible by having Soddy as a colleague. He made such great difficulties in the faculty always. He was a very difficult man. So that Rutherford didn’t like him. But these were the only two persons I had the impression that Rutherford didn’t like. He much admired Bragg, Thomson… He admired the (prestige) of Marie Curie, but at the same time he feared her a little bit. When we were at the Solvay Congress—just a few young people—we said, “We shall look after Marie Curie and prevent her to come too near Rutherford.” And the explanation is that Marie Curie loved to talk shop and only shop. And her shop was chemistry. Rutherford, while occasionally discussing problems, liked to talk about all sorts of topics, you know. On politics, on human affairs, on economics, what it should be. Now here comes a highly honored lady who begins to talk that when she precipitates lanthanum if she adds ammonium sulfate it works much better. This was something Rutherford didn’t appreciate. Besides, the old lady was exceedingly keen, most remarkable. She lived with her chemical problems and only talked about these. Rutherford, while strongly very admiring of her, simultaneously feared her. It is not a contradiction. I can admire you very much; I can fear you simultaneously…

Kuhn:

Was it partly also that the shop was chemistry and not physics? Or was it just that it was shop?

Hevesy:

Too much shop is what he didn’t like. And shop to be pure chemistry! He had no interest. He had no interest how you precipitate lanthanum or cerium and that you mix sodium and so on. Now somebody comes and talks for hours and hours and hours, he didn’t like that. That’s an explanation. As it was he had great admiration for her, for Madame Curie. It was also I think at the ‘11 Solvay Congress, he wrote his wife. I remember a letter he writes that she is quite a pathetic view, Marie Curie. She looks so miserable. She works much too hard for her health. But I don’t know what is his view on Irene Curie and Joliot, I don’t know…

Kuhn:

Radioactivity called suddenly for a lot of collaboration in fields that had previously been relatively distinct. Now I’ve wondered what sort of problem this may have created.

Hevesy:

Well, the problem was always: Rutherford was interested to get pure radioactive substances. He wanted purely ionium. He invited Boltwood, you know. He wanted me to separate radium D from lead and such problems. The chemistry per se didn’t much interest him, you know. He wanted radioactive substances as tools. But not the chemistry of radioactive substances. Soddy had of course a great share on elucidating the chemistry. It was he who induced Fleck to investigate the chemical properties of radioactive elements, a very important work. This man, Alexander Fleck, was laboratory steward in his lab. And Soddy observed he was a very able man. He let him study, made him assistant later on. He carried a very fine piece of work, left for England’s Imperial Chemical Industries and ended as president of one of the greatest concerns in the world. That’ s a career, you know… Today he is Lord Fleck. Lord Alexander Fleck. That’s career, from lab boy to president of one of the greatest industrial concerns in the world. A very nice man.

Kuhn:

You spoke of having been with Haber, and when Haber got interested in the electron problem, there was nobody there who had those techniques. Or you speak of Rutherford’s having an attitude that somehow chemistry was secondary as compared with physics. Now, this speaks for a certain amount of real professional separation.

Segre:

No, because that was really the heyday of physical chemistry and of thermodynamics. You see Van’t Hoff, Arrhenius, Haber, Ostwald. Physical chemistry was almost the ruling science.

Hevesy:

Rutherford considered chemistry as a strange science, you know? ‘It was a science; it is not my science. I need the substances. I need hydrochloric acid or what it is. It is the chemist’s duty to produce these substances. But in chemistry as science I am not interested. And I’ve even some suspicion that this is a somewhat superficial science. It is not so effective as physics’…I am not sure it was a general attitude. And I am not sure the German physicists had this same view. But Rutherford had it undoubtedly. I don’t know the view of J. J. Thomson, how far he had a similar view of that. But I don’t think that J. J. Thomson was much interested in chemical problems.

Segre:

Did you ever come in touch with Nernst at that time?

Hevesy:

I got in touch with him, yes, yes. You know it is very interesting. Einstein was appointed an associate professor at the University of Zurich in 1909. I was there when he gave his first lecture. And after a while Nernst, who was a very famous man in those days, appeared in Zurich to consult Einstein. Nernst was interested in specific beat problems and wanted to apply quantum theory on specific heats. And Einstein had made already important contributions, so Nernst wanted to talk to Einstein. And that made Einstein famous. Einstein came as an unknown man to Zurich. Then Nernst came, and people in Zurich said, “This Einstein must be a clever fellow if the great Nernst comes so far from Berlin to Zurich to talk to him.” Isn’t that interesting?

Kuhn:

What was the inaugural lecture of Einstein?

Hevesy:

A paper on the ratio of the charge and mass of the electron. That was his inaugural lecture. Perhaps 20 people, not more than that, were present. It was on a paper by Bucherer on e/m… I saw Einstein several times in Zurich. One day he came to visit our lab. My chief was away, and I was showing him around. I happened to show him the hydrogen electrode, and he was very much astonished that such a thing existed. He thought that it was just a fiction, you know. That we actually can construct the hydrogen electrode, this surprised him. I remember so clearly some episodes… So I saw him occasionally. I saw also Nernst occasionally. I saw him in Berlin several times. He was a most remarkable man.

Segre:

When did you leave Manchester?

Hevesy:

I left Manchester in ‘14, early in ’14… I had been a few months in Vienna starting this tracer work. That was from January to April ‘13, then I returned to Manchester.

Segre:

So during the Bragg work and the Laue thing you were in Manchester?

Hevesy:

Yes, yes. Bragg was in Leeds and really the idea of X-ray spectroscopy goes back to Bragg, in fact. He was already clear that you can take an X-ray spectrum. Laue had made the experiment, but it’s not yet spectra. And Moseley went over. I remember he was in Leeds to talk with Bragg. He came back, and he made his mind up that he shall study the whole periodic system and determine the spectral lines. . I just wonder, when did Laue publish his paper? If I remember, when I came to Manchester Laue’s paper was published in ’11… Laue’s paper, Laue’s work, was not so much discussed as Bragg’s, for the geographical reason that he was in Leeds nearby, you know. And they were interested in Manchester in what Bragg is actually doing. . Bragg interpreted Laue’s findings in an ingenious way—great clarity, which characterized him.

Kuhn:

It’s in part ironic that it should have been Bragg, because Bragg had so very recently before given the very strongest arguments for X-rays being particles.

Hevesy:

Well I can’t tell about that. I was not in sufficient contact with Bragg for be able to tell how Bragg, how the conversion of Bragg actually took place.

Kuhn:

But did this create some sort of sensation at Manchester?

Hevesy:

No, no. The interests were altogether in a very different direction. X-rays had no primary interest in Manchester… Moseley was the first. Moseley built his own spectrograph… They had had X-ray equipment to illuminate—I mean just to investigate… Moseley was the first man…who did experimentally serious research in Manchester. He was induced I suppose by Bragg’s results. And then also another point, that was discussed in Manchester. I remember Darwin, for example, was interested, with others, in this business with tellurium, iodine and argon and potassium, these anomalies in the periodic system, and how far X-ray spectra may give information on these points. This and Bragg’s work induced Moseley to take up X-ray spectroscopy. He earlier worked on beta rays.

Segre:

But the regularity of the X-ray spectra; did it come as a surprise?

Hevesy:

No, it didn’t come as a surprise. But you still discussed, “Shall we find any irregularity, at tellurium or not? Probably not, but who knows?”

Segre:

No, I thought that the regularity of the X-ray spectra should have come as a surprise because the optical spectra are quite different from one element to the next.

Hevesy:

Yes, but it was quite clear that inside the atom conditions may be simpler for electrons… That was already clear… Those ideas undoubtedly influenced Moseley.

Kuhn:

Now, is it clear that these experiments were proposed with some knowledge of its being interior electrons that were responsible for the X-ray spectrum?

Hevesy:

Yes, yes, yes. It was not so clear as you put it, you know, but there was some information in that direction. No proof, no certainty, but it must be in that direction. .

Kuhn:

There was already Barkla’s generalization about variation of hardness with atomic weight—a qualitative generalization only. But it has looked as though Moseley simply tried to see what would happen now if you did real spectroscopy with this.

Hevesy:

Yes, yes, Barkla’s K and L line—they were already known.

Kuhn:

So that work could have started with the new tool of X-ray spectroscopy and without any particular reference to the Bohr atom.

Hevesy:

Yes, but Bohr was there, and these ideas were discussed. So I have the impression that Moseley was influenced by Bohr to some extent… I don’t think Bohr discusses the X-ray spectrum in his first papers. But to publish something and to discuss something are two very different problems. But I can’t guarantee—though I was quite close with Moseley’s work—I can’t guarantee how far Bohr had an influence on him or not. When Moseley told me he had embarked on an experiment, and I offered to assist him in putting up his spectrograph. And I remember very clearly it was a (cellar) locality. In the corner there was a big table. And he went over to the chemistry department. There was a very nice steward, Mr. Edwards. He told Mr. Edwards he would like a nice crystal. They had a very nice collection of all sorts of chemicals.

Mr. Edwards presented a beautiful potassium ferrocyanide crystal. And without hesitation Moseley accepted it. The crystal was put up, the metals were put in small sledges—very primitive, just connected by strings. The whole system was evacuated, and then using a magnet he directed a cathode ray stream into one element. I happened to have some tantalum. Tantalum was very rare. (There was a man there from Siemens, Bolta, who presented Moseley with tantalum. I gave him my tantalum also.) And beautiful results at once. Very remarkable. I intended to work with Moseley in fact. And we made out that in first of August, 1914, I should come to Oxford. I had been in Holland that summer, but first of August war broke out, so I cou1n’t go. He wanted me to bring rare earths with me from (Belgium) to be able to investigate the heaviest rare earth elements. Later he wrote me that he obtained rare earth samples from Urbain in Paris so I should not bother in bringing them.

So I traveled without rare earths but never reached Oxford and never saw Moseley again. He was a very nice person, very ascetic. We used to lunch together at the University faculty club, and his lunch was fruit salads, nothing else. He had fruit salad, that was his lunch. And he was living with a family, and he told me, “Well, I don’t like to dine with a family. I prefer just to eat bread and cheese for myself.” So bread and cheese was his dinner, and fruit salad his lunch. A very interesting and very nice man, very remarkable. A very able man, quiet. He told his results so quietly, without excitement—beautiful spectra. He was quite a young man. Oh I don’t know, he was twenty-four when he was killed. How shocking to kill such a man. He gave just a message, a telephone message, that a bullet had hit him. .

Segre:

Where were you during the first world war?

Hevesy:

I was in the Austrian-Hungarian Army… I had to go back from Holland and was drafted into the army.

Kuhn:

Your period at Manchester really embraces all the work right up to the announcement of isotopes, at least of radioactive isotopes, doesn’t it?

Hevesy:

Oh, well I mean this isotope notion came not from today to tomorrow you know, but it developed. Otto Hahn couldn’t separate mesothorium from radium. He tried and tried and tried. But he tells himself that it never occurred to him that something of importance lay behind. “I have not the chemical skill, I can’t separate them.” Then came ionium from thorium, which Boltwood tried under the wish of Rutherford. It didn’t work. We tried the lead. And so all this knowledge accumulated loading then to the notion of isotopes. Soddy called these ‘chemically inseparable elements.’ It was quite a good definition. But it is very characteristic you know that he wouldn’t acknowledge that deuterium is an isotope of hydrogen. Because he defined isotopes as inseparable. When you take the stuff and separate it easily, it can’t be an isotope. And he argued this point. There’s nothing to it.

Kuhn:

That one had been so prepared when Soddy’s paper and Fajan’s paper and the Russell paper came out in 1914, did people immediately take this up, in view of the background?

Hevesy:

Yes, yes, yes • What actually happened was, that Russell was in Glasgow. Yes, he was still in Glasgow and heard Fleck’s result. And then everything was clear. And Fajans heard it from me. Fajans wrote me and asked me on the way to stop to talk to him. And I told Fajans about Russell’s work and Fleck’s work. So really these displacement laws go back to Fleck’s work and indirectly to Soddy because he induced Fleck to work on this problem. Russell and Fajans published it, but really it originates in Fleck’s results…

Kuhn:

One suspects with this increasing practical inseparability of these substances as this piles up, there must have been all sorts of glimmerings of the idea.

Hevesy:

Yes, it came. When we started to use tracers with Paneth, we simultaneously tried to defend the application of tracers by showing these are actually inseparable. So hand in hand with the first application of the tracer went a defense of the notion of inseparability. You precipitate bismuth on a metallic surface… And if you add a bismuth salt, then it won’t separate, it won’t precipitate… But you can’t add any other element and prevent precipitation of bismuth. That was one of the lines of thought, and we did a lot of work in this direction. So we can only influence electrochemical properties of bismuth or lead or thalium by adding a stable isotope of the same element. There is no other…

Kuhn:

But did you think now that this was a general point of principle?

Hevesy:

Oh yes, no doubt about it. No doubt about it. There is no doubt about this. You can only use radium D as a label for lead because these are inseparable. It is the same with bismuth you can tell, this is quite clear, that it exists stabilized. . .

Kuhn:

And you saw that there were many cases of this?

Hevesy:

Yes, yes, we happened to know about a number of cases.

Kuhn:

Because in a sense the whole idea is already there. Did it bother you that there should be this class?

Hevesy:

No, it didn’t bother. Just people were very happy about it, you know. We were very happy that we have an excellent tool now. We can label this lead. We must only prove that these are practically inseparable elements,

Segre:

It is strange that you never met something with two oxidation states which don’t mix. You see, if you had tried something like an organic compound of lead, your tracer wouldn’t have worked.

Hevesy:

We surely tried also organic compounds of lead. * * * In experiments with a number of organic compounds, tetraphenol lead for example, they did not interchange. So we have drawn the conclusion that lead bound in an organic compound is not interchangeable. This is published in the (???)… It was published in ‘18 together with Dr. (???). He is retired now. He was at Cal Tech. No, there was no question about that.

Kuhn:

Now how is the transition? These early generalizations are, as you may say, exclusively for radioactive substances, which are isotopes of known stable elements. Yet right at the same time or already when this was going on, the two lines of the neon mass spectrogram are there.

Hevesy:

The two neons came somewhat later. Because I remember I was present when J. J. Thomson gave his Bakerian lecture at the Royal Society. It was in April, 1914, when I returned from Vienna to Manchester. I by chance happened to be there. But Thomson never associated the two neons with the notion of isotopes. I wrote J. J. Thomson after his lecture that the case of the two neons is similar to that of radium and lead. And J. J. Thomson answered—I still have his letter—that he doesn’t believe that any connection exists between the two neons and radium D and lead. Because the two neons can be separated by distillation, that was the point. It was Aston who really realized that stable isotopes exist… He had worked on the separation of the two neons… But this was mainly J. J. Thomson’s work; he was assistant, you know, on the experimental part. But the idea came from J. J. Thomson. But later he decided to build a better mass spectrograph and to try all elements. He started with chlorine and found these two beautiful lines, chlorine 35 and chlorine 37. I mentioned already that he wanted to show this plate to J. J. Thomson, and he turned his back. He didn’t want to look at it. Remarkable. It is a remarkable thing.

Kuhn:

Well now were you yourself pretty deeply convinced about the parallel already in ‘14?

Hevesy:

Oh yes, I wrote a letter. Otherwise I wouldn’t have written a letter to J. J. Thomson. I wrote J. J. Thomson that I was so interested in the two neons and drawing attention to the fact that we have such cases, radium D and lead (with differing atomic weight), but they are practically chemically identical elements. So these two neons are the same element in an inseparable state. So it was no doubt about it. We couldn’t have applied tracers if we wouldn’t have been convinced that these are inseparable.

Kuhn:

Did it still come though as a very considerable surprise to people with the mass spectrograph?

Hevesy:

It was a surprise to people. It was a surprise to people undoubtedly. Well with the two neons it was a surprise that they should give two parabolae in a positive ray discharge tube. But then when Aston came with his lines, it was a great impression on the other people. And then one element came after the other.

Kuhn:

Did Thomson continue to resist?

Hevesy:

I don’t think so that Aston pressed his point, you know. Thomson was disinterested. He left him alone. Thomson’s view was, it might be hydrides. But I remember when we were in Arosa, and Aston told me when we went home—it was at Christmas, it was in ‘30 or ‘29. “I’m going home, I shall tackle now lead again. I will make sure that this lead 209 is not a hydride.” So he must feel that this may interfere with his results. I remember very clearly just this point, that he told, “I will make sure the hydride problem doesn’t interfere with my lead results.”…I mean this is not general. It was just in this case, in the case of lead. He was sure that his results are all right, no doubt about this. But I only mention it that it is not surprising that J. J. Thomson held that hydrides were always moving about, since even Aston considered it a possibility that hydrides might interfere.

Segre:

No, because people did make many mistakes with hydrides. It was a common pitfall, it was known to be.

Hevesy:

Yes, yes, yes. But all Aston’s were correct. I can’t remember that he ever made a false conclusion. And then he measured the mass of hydrogen atoms with great accuracy, it was very important contribution. He had a whole branch of science for himself. That doesn’t occur often, though. Aston discovered-let us say xenon—then he went for a cruise for some months, come back, take another element, then he went for skiing for some months.

Kuhn:

You can’t imagine that happening now, can you?

Hevesy:

No, no. Took it easy. Yes, very different times.

Segre:

After the war you went to Copenhagen?

Hevesy:

I went immediately after the war. I went in the beginning of May ‘19 for the first time to Copenhagen to discuss matters. I arranged it with Bohr already in Manchester. I went as soon as it was possible to travel, in May ‘19 to Copenhagen. And it was arranged that Bohr’s Institute should be open the first of April, 1920. And I should be the end of March in Copenhagen. Then I went back to Hungary. I was there for a few months and carried out this work with Zechmeister. But when I came to Copenhagen there was no Bohr Institute. As usual such things move a little slower. His Institute was not yet built. And I was interested in the separation of isotopes and associated with Bronsted who was a very good physical chemist, a great physical chemist, who happened to visit Aston. So he worked and got also interested in the problem.

So we started to separate mercury isotopes, which was quite amusing. There was a physicist in Copenhagen, Martin Knudsen. And Martin Knudsen did some very fine work on evaporation velocity, and also showing if you let atoms pass through small holes in such a way that the hole is small compared with the mean free path, then the square mass relation comes in. So we used partly this method, diffusing vapor. We took another method. //We took a few hundred cc. of mercury, kept the mercury at 110 degrees. So the mercury distilled slowly, and the light mercury isotope more rapidly than the heavy one. And we kept a surface cooled with liquid air so that when the mercury vapor// struck this liquid air surface it was frozen, thus prevented from being reflected… And we repeated this and distilled again, and we got quite nice differences in composition of mercury isotopes. Of course today this is of no interest any more. I mean this was a first preparative clear-cut case of separation of isotopes. Then we did the same work with concentrated hydrochloric acid. We separated the chlorine isotopes also. And then happened a very remarkable thing.

I thought perhaps should we not have a look at the water. We had several liters of concentrated hydrochloric acid. We specially separated the chlorine isotopes, and we must have separated very markedly a hydrogen isotope. Bronsted told me, “Oh, a paper came out recently from Volmer and Stern, two very able men, who looked after isotopes of hydrogen and oxygen; entirely negative.” Volmer made, his mistake, I can’t remember—the way they diffused water vapor through porous membranes, to see if any indication exists of an isotope of hydrogen and oxygen. It was an entirely negative result. So it is no sense to look at this more. Well now a few years later I reminded Bronsted of this episode. He answered, “Well, it’s quite all right. One shouldn’t discover heavy water by pure chance.” One must do it like Urey did it from theoretical considerations.

Kuhn:

How long did it take before the Institute itself was ready?

Hevesy:

It took one and a half years. (I was still at the Technische Hochschule, working on Bronsted’ s things.) Bohr had also already a room there in the same building of the Technische Hochschule in Copenhagen. And I remember he was wondering about what shall he call the new institute. His institute. Two alternatives. Call it Institute of Atomic Physics, or Theoretical Physics. And then be decided for theoretical physics because he thought: first of all, it is too exacting, atomic physics was in those days something quite (extravagant); and then we can’t know, perhaps we’ll do other kinds of work which is not atomic physics. So it is more correct to call it theoretical physics… When the Institute was then set up, I moved in at once. I mean, I was only in the technical high school physical institute because I had to be somewhere, but I moved at once into the Institute. And we were quite a few. Kramers was there, and a Polish theorist, Rubinowicz was there. Two Danes, H. M. Hansen, who did optical spectroscopy, and Jacobsen, who is now there, was an assistant. Occasionally Oscar Klein came. And Franck came for a short time. Franck came. He was there at the opening of the Institute. I have still a picture of the opening with Bohr and Kramers and Franck and H. M. Hansen and Jacobsen and myself. We are there at the opening of the Institute.

Kuhn:

Well as soon as it got going, were there regular colloquium that involved the whole group at the Institute?

Hevesy:

No, that worked out slowly. You know, at the beginning everything moved slowly. All these colloquium came in later on.

Segre:

But there was no experimental work except yours which was chemistry?

Hevesy:

Yes, my work was experimental work, and Hansen did some optical spectroscopy. That was all. No other experimental work… Coster came there after Lund to Copenhagen. And I can tell you exactly, this was in September ‘22. And I got to know him, and I liked Coster very much. He was a very fine man. He was an able physicist, so I told Coster I would very much like to learn X-ray spectroscopy, if he would teach me. But, I had also another wish. I had a little bit queer idea that it should be possible to influence radioactive disintegration rates. Many people had such queer ideas. And I first tried to irradiate uranium with radon, and test the period of uranium… It was negative. I did the wrong end; I should have begun with the light elements but had no means. And then I thought how, if you would take an anticathode of radioactive lead and irradiate it for a very long time. Then would radium E still decay in five days half life or not. And I tried to induce Coster to be interested. This Coster was willing to do, but we couldn’t get a proper installation. And then, I told him, “Well, you must teach me X-ray spectroscopy.” And it was a few months after Bohr put forward his theory of periodic systems, in which he has shown that you have only fourteen rare earth elements. So element 72 must be an homologue of titanium. “Well, can we not combine this teaching of spectroscopy with looking after this element?”

Segre:

How did Bohr do these without Pauli’s principle?

Hevesy:

I don’t know, I have no idea…The first time I heard was in January ‘22. I went for a walk with him and he spoke about this point in January ‘22.

Kuhn:

Now this is already the point with respect to the rare earths?

Hevesy:

Yes. Altogether his periodic system, the whole system. In May ‘22 Coster came over. He was still with Siegbahn. Bohr wished to know Coster’s and my view on this point. He took just a footnote in his paper, writing that the element 72 cannot be a rare earth. Now, a paper came out from Urbain—who pretended to have found 72 to be a rare earth element—and Dauvillier, who published two weak X-ray lines. “Shall I remove this footnote,” he asked us. We thought, “No, he shall not.” After all, the optical spectra rare earths are so complicated that for new lines to appear is no proof it’s a new element. And as for X-ray spectra, well I was not competent, but Coster was. He said, “Two such exceedingly weak lines; to base the existence on this evidence is very dangerous. We saw later Masurium was ‘discovered’ on the basis of two lines, that don’t exist. So we suggested Bohr not remove this footnote. He didn’t do it. And then in September Coster came and we embarked on this X-ray—he was teaching me spectroscopy. And I procured zircon and purified it from other elements; only the zircon silicate remains. And the first sample showed element 72. This is really good luck. It was 1 percent hafnium… Of course it is not so simple. It was really much more complicated because by a queer coincidence the second order zirconium K spectrum coincided with the hafnium KC. Now of course you can always avoid getting secondary orders in the zirconium K spectrum by keeping the voltage of your X-ray tube below a certain value. But we had very primitive apparatus, and our voltage was going up and down. So it was very difficult. Then alpha two came and beta one came and beta two came. So it was quite clear, it was no mistake.

Kuhn:

Then you recognized the trouble with the second order K spectrum immediately?

Hevesy:

The difficulty we recognized, but we were of course quite uncertain before we obtained the beta lines. Especially, I looked once at the zircon source which I had in the lab. I had several zirconium sources, different sources. And all happened to show this alpha lines This was so suspicious. ‘Where you have zirconium you have this line.’ So this second order K spectrum business made one uneasy for a short time. It didn’t take very long. We had a big fight with Urbain. Urbain said, “Well, I found this element long ago.” But he had bad luck. Namely after hafnium was prepared, not a single one of perhaps 26 optical lines agreed with those of Urbain… Because Soddy wrote to me; he wrote, “If your spectral lines happen to be identical with Urbain’s you should withdraw your name.” But not a single line (coincided). It was very amusing. I wrote a paper on the chemistry of hafnium. This also went through Rutherford’s hands. I suggested that we should send the paper to an English periodical called Chemical Journal, not the Journal of the Chemical Society but another journal. Yes, the editor is a good friend of Urbain. I don’t know, he might not accept it, but try it.” I sent in the paper to a friend of mine who lived in Sheffield where the editor was Professor in Chemistry. He looked at the paper: “All right, but as for the word ‘hafnium’, we prefer the name celtium proposed by the French, who are our allies in the war. The Danes participated only in the spoils.”

Segre:

How was the business of lutetium and (Cassiopeum)?

Hevesy:

They are the same thing, you know. (Cassiopeum) was the discovery of Auer. This was also quite unfair, because really Auer was the first to discover (Cassiopeum), but the International Commission were ruled by Urbain’s great influence and simply didn’t accept it.

Kuhn:

Who did you say? Auer?

Hevesy:

That’s Auer von Welsbach, an Austrian chemist. Well, you are too young, you won’t remember—the Auer lamp. You know on the gas lamp you put such a thorium oxide filament, which gave a very intense light, and this is a patent of Auer von Welsbach… It was very interesting. You know, they produced it from (monoxide) which they got from Brazil. And they got it without paying for. Namely, when the German ships left Brazil, as a ballast bought sand. This contained (monoxide) sand. The Brazilians never realized that it was very valuable sand. So it was a very cheap—. And this (monoxide) sand contains about 6% of thorium, but a very high cerium content. So they accumulated a tremendous amount of cerium oxide. And Auer von Welsbach was wondering, ‘What shall I do with all this cerium?’ And then he made an ingenious—he had a very ingenious idea. He found that an alloy of metallic cerium and iron sparks when scratched. This was his patent. He used up a lot of cerium and earned a lot of money. He didn’t earn money with the Auer mantle—this lamp—not at all. But later on he was a more experienced business man and he made a lot of money with these cerium and iron alloys. [Break: Tape recorder turned back on in middle of conversation]

Kuhn:

They [Noddack, et al.] actually persuaded themselves that they had seen X-ray lines [of the homologue of manganese of atomic number 43]?

Hevesy:

Yes, yes. Very weak X-ray lines. The claim was based on these X-ray lines.

Segre:

Now how long they believed they had seen them, I don’t know. Between 1925 and ‘45, in 20 years, something should have been achieved. Especially since rhenium they had by the kilogram. And this stuff they could never lay their hands on.

Hevesy:

No, it is quite clear that they extrapolated. " ‘If somebody has discovered hafnium in zirconium, then masurium must be in samples of manganese. This is evident. We shall find it, and we claim already now that we found it.’ I can’t explain it otherwise. They thought, ‘Those elements are missing. We found the higher one, which is always less abundant. It is quite clear that the lower must exist.’

Kuhn:

When was that claim first made?

Segre:

In 1925, ‘24, ‘25, something like this. But if they had been smart, they should have let go after five or six years instead of keeping on insisting for 25 years. By the time they started to see the grams of rhenium and no masurium, a good man would have said, “Well let’ s start not to talk about it any more.”

Kuhn:

Well surely that is an important part of the background, isn’t it? For so little attention having been paid to this fission suggestion?

Segre:

I don’t know. They were not considered absolutely reliable people.

Hevesy:

What can you say about a man who, when a botanist draws attention to the fact that you can’t discuss (metabolism of plants) by disregarding (up-takes) of the roots, answered, “I will complain to the Nazi authorities that you object to my work.” That is an impossible man.

Kuhn:

I wonder if I can get you to talk about one other sort of question which really now isn’t the technical scientific question at all, and there may be nothing to say about it. I’ve been very curious about the number of Hungarians who are involved somewhere or other—

Hevesy:

Well I will tell you the story. This is so. I will tell you the story. I had as neighbor at a dinner party Mrs. Eckart, von Neumann’s widow. She married the physicist in La Jolla, Eckart I think it is. And she asked me, “Can you explain that there are such a number of able Hungarians in the United States?” I answered no, I can’t explain it. This was a very difficult—the number is too small. You can’t apply statistical theories. She answered, “No, it is entirely wrong. A scientist should be able to explain everything.” Which is a little peculiar view. “I know the explanation”—she had an explanation. The explanation is that in Hungary people went to coffee houses and discussed matters and sharpened the brain. And that is the explanation why these people who sharpened their brain became so able scientists. And I told her, “Well I doubt that Edward Teller was ever in his life in a coffee house.” She answered, “No, but his father was.” So she believed in the transheredity of acquired qualities.

Segre:

Was there in Hungary a scientific tradition?

Hevesy:

Yes, there were some people, for example Eotvos.

Segre:

But this was a sort of person who never influenced anybody.

Hevesy:

Yes, he was a grand seigneur; he was an aristocrat. But there were very good mathematicians. (Fejer) was a very good mathematician. Oh yes, Bolyai, yes. It was a really good mathematical school, and they had good mathematicians and they still have.

Kuhn:

But to some extent, what goes with it is that not in mathematics so much, but in physics and in chemistry, these are people who go almost immediately to Germany and almost invariably to Berlin.

Hevesy:

The mathematicians studied in Hungary partly, but the physicists, Wigner and Teller, studied in Germany.

Kuhn:

When did you decide to be a scientist? Was it to be chemistry from the beginning?

Hevesy:

I didn’t decide to be a scientist. I really started to become a chemical engineer. And only one day I found myself in science. I didn’t decide, I slipped into it… I went to Berlin. I wanted to become a chemical engineer. But I got an inflammation of the lungs, and my doctor told me, “Go to a university where you have fresh air.” So I came to Freiburg. And so slowly I slipped into science.

Kuhn:

Well then let me ask the question, because this, except for the inflammation of the lungs, is fairly typical. Why did so many Hungarians want to be engineers?

Hevesy:

Yes, yes. Science was not considered to be a serious occupation in those days. So one was interested in engineering. Well then, it was quite understandable it should be chemical engineering. Some of us studied electrical engineering possibly. This was a serious occupation. I know the father of Teller was unhappy about that his son didn’t go on to become a chemical engineer. He already picked out a position in Hungary for him, but he had the foolish idea to become a scientist. But after all the number of these people is very small…

Kuhn:

Why does it happen that they’re all so very bright?

Hevesy:

But those who are not bright you probably don’t see, you know. You see the bright ones. The dumb ones you don’t see.

Segre:

Well one thing you see. Anybody who emigrates has already been selected, because if you are say so and so, you can find a place in a secondary university in your mother country and you stay there.

Hevesy:

Some of them are very able. (San Giorgi) is perhaps the most able of these men.

Kuhn:

Was there any place in Hungary at this time where one could have gotten the chemical engineering education?

Hevesy:

Yes, but much less good. You couldn’t compare. These German technical high schools were the first-class institutions. It was possible to learn in Hungary, but less effective. .

Kuhn:

Was mathematics a serious occupation?

Hevesy:

No, no, but mathematicians are often career people, you know. They can’t do something else. They must become mathematicians. So it was less probable that mathematicians would say, “I will become a chemical engineer.” Where physicists or chemists, yes, it was possible to say, “All right, I shall do something reasonable and become a chemical engineer where I can do chemistry at the same time.”

Kuhn:

Was teaching of mathematics good in the Hungarian schools?

Hevesy:

Teaching of mathematics was good, but different schools were different. The school where I went, Latin was most taught…

Segre:

You didn’t go to the university in Hungary at all?

Hevesy:

Just one year. (I heard Eotvos’ mathematics. He was professor in experimental physics, yes.)

Segre:

He must have been a very tedious man.

Hevesy:

He was a grand seigneur.

Segre:

From his work I have the impression that he was a very boring man.

Hevesy:

Yes, yes. He was not amusing. He was very kind to me, I must say. That was beautiful work which he did.

Segre:

Oh yes. But I don’t know, somehow it makes me think of Ricci-Curbastro of the absolute calculus, whom I never met. But I heard him described by a lady—she was a friend of Amaldi. Everybody had a great reverence for Ricci-Curbastro. He was obviously a very great mathematician and so on, but everybody said that he was a most tedious man, the most boring man in the world. And all the stories of Ricci-Curbastro were that he would go the first of the year in a perfect black suit with gloves, sit in the chair to bring the new year greeting to all the members of the faculty in a certain order and so on. Somehow I got the idea that Eotvos was the same type although I had never seen him. [Discussion of Austrians as great musicians rather than great scientists.]

Hevesy:

Schrodinger was a queer man, a very queer man.

Segre:

I never met him.

Hevesy:

Terribly nervous. I met him the last time when he came to Freiburg. I was at the house of Mie… And Schrodinger came to see Mie. I told Schrodinger, “Excuse me, I have only five minutes; I have an important talk to give.” Mie’s predecessor died, and a talk was given, a memorial talk. I was the dean of the faculty so I was supposed to give the talk. So it was an important matter. It was a very few minutes. He is so angry—Schrodinger—with me. It was really three minutes only. A very nervous person. But an ingenious man.

Kuhn:

I think we should have our next session in Stockholm.

Hevesy:

I look forward to seeing you in Stockholm. It will be very nice.

Session I | Session II