Interview transcript

We sit here in lovely Lindau in the south of Bavaria and this is the celebration of the 50th anniversary of the Nobelpreisträgertagungen in Lindau. And I have Professor Rudolf Mössbauer, who received the Nobel Prize in Physics in 1961. And I’m going to ask you as the first question. Could you tell us some parts of the story which led to you becoming a physicist?

Rudolf Mössbauer: It’s a difficult story. First of all, I grew up right after the war, which was already some handicap. The story really was I had never seen a physicist in my life before I went to studies. That’s the first thing, and therefore I came from the mathematical side. And I had once a teacher for four months in my school in which mathematics was taught, and I suddenly got the idea this was useful. So I went to the university. Physics was the worst field in my school, simply because the teachers were no good. But I had the feeling there is more behind that than actually there was presented in school.

Therefore I went to the university. I enrolled in all four fields which were similar to each other, which were mathematics, which was engineering physics, which was pure physics and which was high school teaching. So it was not too much difference between the four fields. It was only at the pre-diploma, which is roughly equivalent of the bachelor’s degree, in which I then clearly had the feeling I’m a physicist and nothing else. And I then decided to study pure physics and nothing else.

Thank you. Now we move forward quickly to the work that was recognised by the Nobel Prize. And maybe it is not so quickly, because you received it at a very young age, I think?

Rudolf Mössbauer: Yes. Well, that you see from the 1961, when I received the prize, so it’s really quite early. And I’m supposed to be dead since 20 or 30 or 40 years now. But I even have a story related to that. In 1962, the year after I received the prize, I was at Purdue University in the States – I was in the States then – and an old professor, a real professor with white hair and lots of shadows on his side, approached me and he said, “Oh, you’re still alive!” And I was a young fellow really then. So I changed my field 23 years ago from what is now called the Mössbauer effect.

… when I got into the neutrinos I immediately got excited and it was my new work …

23 years ago I was Director of the German-British-French high flux reactor in Grenoble. And then I looked at all the neutron experiments, we had made thousands of experiments during this period. Well that appealed to me sufficiently well, but when I got into the neutrinos I immediately got excited and it was my new work, which since 23 years I fulfil. I underestimated the braveness of the people who were working in this field. I thought I had cleared up the electromagnetic field in a few years, and I am now also cleaning up in a few years the neutrino physics. We are still at the very beginning, even after 23 years today.

So it means that if you start very young and you make some important discovery or invention you actually can have a new career?

Rudolf Mössbauer: Yes. I had a completely new career. I mean the neutrinos have nothing whatsoever to do with the old field of research on which I was engaged.

But could we go back? I realise that it is asking you quite a lot to go back and to try to remember when you made this discovery, or the effect that has been given your name, the Mössbauer effect. Was there some special moments you remember?  Could you also say a little bit of what it is?

Rudolf Mössbauer: What it is, is essentially … I learnt how to get rid of the so-called width of the gamma lines which I was using, which were at that time some ten orders of magnitude and now up to 15 orders of magnitude. You got rid in one step by incorporating the nuclei on which I was working, in solids rather than in gaseous form as most people had done before. So I got rid of the width of the lines immediately in one big step, and this of course opened a new area in which you could make many specialised experiments which were not possible before. That was it in essence. It’s like throwing a stone in a boat. If you throw the stone during the summer period, the majority of the energy is going into the stone but a small amount is going into the recoil. And it was this small amount which prevented the overlap of emission and absorption lines, which made it quite difficult to observe the effect in the old times.

They searched for nearly 40 years on this and they didn’t understand why it didn’t happen. The reason was simply this recoil phenomena. If you do the same experiment on the boat frozen into the lake during wintertime, then the whole lake takes up the energy, you have no recoil energy and the emission and the absorption lines are exactly on the same spot. And this is part of the story, but it’s an essential story, which tells you the emission and absorption line are exactly on the same energy and therefore you are in business.

So then of course I have to ask you was this a trial and error discovery, or was this something that you sat down with a paper and pencil and thought about?

… it was really a trial and error discovery …

Rudolf Mössbauer: No, it was really a trial and error discovery. First I should have gone to high temperatures. If I would have done that I would never have discovered the effect. But I went to low energy simply because I felt higher temperatures and lower temperatures were about the same phenomena; it was about the same size of the effect. So I felt it was easier to build a cryostat, which we called a cryostat, you wouldn’t call it today a cryostat, but it was at that time a cryostat. So I went to low temperatures and therefore I discovered the effect, because I always found the wrong sign. It was a very tiny cross-section measurement at that time.

Nowadays you do it by Doppler shift experiments, which I discovered also later on but after my thesis only, which is a factor of 100 higher so that’s easy to do. But at that time I did a cross-section measurement and it was an effect of ten to the minus four plus or minus three times ten to the minus five, which is nearly impossible today to make. Even today I did it with tube electronics rather than transistorised electronics. But you cannot do it today, because we make lots of correlations, and every correlation wipes out the effect and therefore the effects are, even to measure intensity change of one percent or point one percent today, is difficult. Point ten to the minus four with an error of three times and ten to the minus five is nearly impossible today.

Can I ask you what you thought of this as pure basic research? Did you have applications in mind? I mean I know now that the Mössbauer effect is used in so many applies?

Rudolf Mössbauer: Yes.

But did you think about that at that time?

Rudolf Mössbauer: No. Not at that time. Of course once I had the phenomena, once I had the Doppler shift experiment, once I knew how to measure these narrow lines – I at first didn’t know! I had no idea how to discover the narrow lines. I had them. I plotted them in the first paper, but I had no idea how to measure them, that it was very easy to measure them. This I only found out by getting my first printed version of the paper. And I was sitting down, you read your first paper later on – you cannot read it anymore, but the first paper you still read. And I put my feet on the desk and I was reading my first paper, and during this reading the first paper it suddenly occurred to me I had forgotten the major experiment. I could do this Doppler shift experiment very easily.

But you need mistakes. You have to make your own mistakes …

And I dashed over across the hall into my former supervisor’s office and I said, “I take the next train to Heidelberg,” because I did the experiments at Heidelberg while my thesis supervisor was in Munich, which was also a good thing because it was a distance of more than 300 kilometres between the supervisor and myself and I always did my own things. I could have, by following his advice, I could have saved a lot of time. But you need mistakes. You have to make your own mistakes. And for that reason I was in a good position. So I said to him, “I take the next train to Heidelberg. My equipment is still there and I have to redo this new experiment,” which was easy to do. As I said it was effect of 100 bigger.

When you had understood that this had high potential for applications, did you yourself go into those applications? 

Rudolf Mössbauer: Yes. I went into the applications. I spent about, well, some years in chemistry, I spent some year in biology. These were the most important applications. You could really … Every field, whether it’s medicine or anything you can do today. But I realised, after having been then for five years Director of the neutron research reactor in Grenoble, that it was time to leave. Even nowadays, some 2,000 publications per year annually are being done, so it was hopeless. There were hundreds of laboratories which were involved in the kind of research, and largely working along hyperfine interactions. Isomer shifts, which is zero, M1s are magnetic dipole interactions and E2s are electric quadruple interactions. Most experiments are along these lines.

I even asked the Max Planck Institute at Heidelberg, where I have been doing my work at the beginning, to provide me with iron-57, because the majority of experiments, even nowadays, is done with iron-57 because there you can do it at room temperature already. By lowering the energy sufficiently well you can do it already at room temperature and ask them to provide me this isotope. But unfortunately they declined me. They declined us.

It’s very interesting because I know several cases of people who have you know found something out and then have spent the rest of their life just applying you know what they found out. So my next question would be when you decided that it was time to lead the application of the Mössbauer effect, was the Nobel Prize in any way involved in that decision? 

Rudolf Mössbauer: Actually not. I got the knowledge from receiving the Nobel Prize in 1961, through United Press, because I was in the West Coast in the States in California, and the East Coast was rather close, Stockholm was much further. So, but I had a very bad flu at that time. And we always had a flu each year for about one week. And it was really you felt all your liver and your intestinals you felt and you completely lost your voice.  You had to write to communicate by writing with your wife or with whoever took care of you, because after three days for three days it was completely lost, the voice. But then it came back and I already knew by then it was nothing dangerous. And I didn’t have any fever but I was in bed when I received the knowledge of the Nobel Prize and I didn’t care, I couldn’t care less then.

But that was 1961 and you did continue for some time …?

Rudolf Mössbauer: Yes, I continued until 1972, and then I became Director of the high flux reactor in Grenoble, then for five years went to do neutron physics, and after that I changed.

And that change was the Nobel Prize … Did it have nothing to do with that?

Rudolf Mössbauer: No, it had nothing to do with that. It was simply it was a field in which I wanted to change to go to something else. But the Nobel Prize had nothing to do with that.

No. That’s very interesting. Now, could I ask you also a question which we did not discuss before, but I mean you can say no if you want to? I mean you have worked in many places, I mean many laboratories, and also very different laboratories; some of the smaller, some of the bigger ones and so on. And you know there is a discussion about creative environments. Could you say something from your experience about …?

Rudolf Mössbauer: I can only say my own experience. I was first working at Caltech, which was in solid state physics and there work very few people are together. Actually I was essentially alone. I had some students with me, but basically I was alone. If you are depending on machines, on big reactors, or any at Grenoble, it was a big installation. But the bigger installations where I really did experiments of my own was … first of all we started in the neutrino work at Grenoble. We could get very close to the fuel element. We got to within five metres. But I could move, I could move the experiment, therefore we left Grenoble. And then we went to Switzerland and went to Goesgen. It was a pure electrical station but it was a power reactor. I stayed outside. Fortunately, I measured the distance between. The closest distance was 38 metres, the furthest distance was I think 64 metres if I remember, and we had in-between another position. So we did experiments there.

We had a group of maybe ten people. It was a lot of fights. I then went to the Gran Sasso Laboratory in Italy. And we had about 50 people there and I though the fights are continuing and they are getting worse. It was not the case. It was very quiet there and we had no fights whatsoever between ourselves. Simply because we had young people, very young people, at Goesgen in Switzerland and they were very ambitious. We had older people in the Gran Sasso Laboratory and they were not so ambitious. You could just say you didn’t understand that and they didn’t bother about this, while the young ones would bother about this. And therefore we had about 50 people all together in the Gran Sasso Laboratory and it was peaceful.

That was very interesting. I mean you say that if you have more grown-up scientists then sort of the general feeling is more peaceful. But a question about creativity. I mean would you say that the peaceful environment would give more new ideas or would that be the other environment where we have the young?

Rudolf Mössbauer: It didn’t really matter.

It didn’t?

… most major discoveries, not all of them but most have been made by people under 30 …

Rudolf Mössbauer: It didn’t matter so much. Of course with the younger people you get more fights and they have also strange ideas. I make maybe a remark myself: I think it’s the young people who make the progress in physics. If you consider all the major discoveries, most major discoveries, not all of them but most have been made by people under 30. There’s no question about that. And the older you get the more knowledge you acquire, but the least your temptation is to get into new fields. You just know too much. You know the reason for this and for that and for that, why it doesn’t work.

For instance, when I was a young fellow I remember I had a paper in my hands, which I mentioned before, in which Steinwedel and Jensen were the ones. Jensen got later on the Nobel Prize also himself for another area. And he had proven mathematically that it was impossible to find what I had found later in Heidelberg some 40 years back. But he had proven it mathematically, but I was too stupid to understand it. And that’s why I think young people, who are more likely to try something which is unconventional which older ones wouldn’t try because they know too much, are making the progress in physics.

Thank you very much, Professor Mössbauer.

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