Oral History Transcript — Dr. Nikolaus Riehl
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Interview with Dr. Nikolaus Riehl
Nikolaus Riehl; December 13, 1984
ABSTRACT: Work with the Auer Society on rare earths, luminescence, and radiation; an "invitation" to go to Russia in 1945 and work on uranium metal production. Otto Hahn's discovery of nuclear fission; the reactions of German physicists to this discovery. Great care taken while working with radiation. National Socialism and science in Germany; competition within the German uranium project, Werner Heisenberg; the interests of the Auer Society during the war; Riehl as one of the instigators of nuclear power in Germany; on the technique of smoking cigars. Riehl at the Munich Technical University as of 1955 and work with Heinz Maier-Leibnitz on a "swimming-pool" reactor. Also prominently mentioned are: Barwich, Adolf Hitler, Philipp Hörnes, Lise Meitner, Timofejew-Ressowsky, and Zimmer.
TranscriptSession I | Session II
Riehl:Until the end of World War II I was with the Auer Company, a large very fine firm which no longer exists.
Walker:How about Degussa?
Riehl:Do they belong together? Yes, at that time. After the war in 1955 I was sent back to Germany from Russia and didn't know quite what I should do because the Auer Company at which I had a very fine position as Director of Research and Development no longer existed. All of these activities in which I was a specialist, that is, radioactivity, the production of uranium, the production of rare earths and luminescence, had been carried out by Auer. The field of luminescence was my principal area of activity for a long time. I wrote a book in this field that in its time was translated into Russian, Japanese and English. All this in the year 1940. At that time I was the person who invented the fluorescent lamp which is sometimes called the neon tube. This work was done in cooperation with the Osram firm. The Auer Company was no longer able to work in these fields after the war and as a result I was not quite certain about what I should start working on. Fortunately, at that time, after I returned from Russia, the government of the Federal Republic decided to construct a research reactor here in Munich. Professor Maier-Leibniz who was in charge of this activity asked if I would be willing to come to Munich in order to help him with the construction of the reactor. Needless to say I was properly pleased at this invitation and as a result was glad to cooperate in the construction of the reactor. This was followed soon after by an invitation to the Technical University in Munich, at that time known as the Technical High School and so I have remained here ever since.
Walker:It is very nice here in Munich, isn't it?
Riehl:Beautiful here? Yes! Yes! Moreover here it is a bit freer, life being a bit more untidy and not so exactly Prussian as I experienced in Berlin, a bit disorganized. One sees holes in the streets here and everything is a bit disorganized but that actually has its good side.
Walker:You often speak in your reminiscences of Mr. Wirths. Which individual do you mean?
Riehl:There are two Wirtzes — the Professor Wirtz who was in Haigerloch and Dr. Wirths who was a colleague of mine and whom I have mentioned a great many time in my memoirs. Later on, he was technical leader and director of Nukem, a company in Frankfurt that was founded by Degussa. The interrelationship of Auer and Degussa which is mentioned in my memoirs and which led to my being plunged into work on uranium, which was a natural interest for me and for Degussa, particularly very pure uranium. Our problem at Auer was to produce the purest possible basic materials, our fundamental specialty. We had started with the rare earths, separating them from one another with the use of fractional crystallization and other things. We also produced luminescent substances in very pure form, achieving a purity of a power of ten to some significant figure, depending on the circumstances. We also had experience in the production of pure thorium that is pure thorium and thorium metal. Actually the production of a metallic form was not our specialty, but that of Degussa. The Auer Company belonged originally to Geheimrat Koppel who was Jewish. In the year 1933 or 1934 the Auer Company, as we used to say, was Aryanized and the bank consortium which owned Degussa combined the two companies. Herr Koppel left. He was a wonderfully generous man, Koppel was. He financed and supported the Kaiser Wilhelm Institutes substantially. He was a very clever, big-hearted man and left for Zurich, Switzerland in order to escape the Nazis. It is really tragic. He did so much for Germany. In any case, that is the way we became a possession of Degussa and how it happened that I decided to make pure uranium for reactor purposes. We could do the wet chemical side exceedingly well since we had enormous experience in that field. On the metallurgical side, however, that is, in the production of the metal at high temperatures with the use of calcium as a reducing medium, we had little experience and used the experience of Degussa, with whom we worked in cooperation. After the war, Degussa resumed this interest and founded the firm Nukem but then later Alkem. My colleague Dr. Wirths was the spiritual leader of Nukem. So much for that! There remains the question as to whether you have interest in applications, for example, in the field of radiation damage, or is that a bit far away from your interest.
Walker:Everything that happened in these years is of interest to me. I cannot put all of it in my dissertation, however, I would be glad to hear about it.
Riehl:I was a guest professor at New York University in New York City for a half year.
Walker:When was that?
Riehl:That was in 1965. That went very well. My English wasn't very good at the start but gradually improved. All was better. Unfortunately, I am somewhat deaf and understanding the spoken language often caused me difficulties. This is true in German and even more so in English, particularly if the individual speaking to me as has a Texan accent. For example, a friend wanted to tell me that he was now longer in the "military." However, he spoke the word military in such a way that I couldn't understand him at all, since I could not guess the area about which his conversation centered. I was in New York sufficiently long that I was able to take some English lessons which were of help. On one occasion I met an assistant on the street who asked me at the outset, "How is everything?" To me, however, it sounded like, "How row ow." I thought this over and decided that he was asking me something very important about President Johnson or something of that general level and kept asking him to repeat. Unfortunately, he made the same statement very doggedly and in the same way and then about the seventh time I realized that it was nothing more than the equivalent in German of "wie gehts.” Yes, that was terrible and I was dismayed. As you can see, I had a good deal of experience in trying to understand. Let us go back. We were discussing, when I got onto this line, questions about radiation damage. Actually, this is not really nuclear research in the true sense but applied nuclear research. It is technically very important but properly speaking it lies in the field of solid state physics, rather than nuclear physics.
Walker:However, it is also interesting. Tell me more about what you did with the Garching reactor. Incidentally, I have also spoken to Maier-Leibnitz.
Riehl:If you have talked to Maier-Leibnitz, that's good enough for me, since he knows everything about the reactor and all things connected with work with the reactor -– neutron physics, radiation damage, and experiments with neutrons. Maier-Leibnitz had a couple of very neat ideas with respect to neutron spectroscopy. For example, one of our colleagues in the group, Koester, did a beautiful series of experiments with very slow neutrons with the use of a natural spectroscope. He projected the beam of neutrons for a very long distance in the gravitational field so that those with different velocities had different trajectories, the slow ones falling farther than the faster. This not only allowed him to measure their velocities but to do experiments with neutrons of different velocity. Today he is a professor at the Technical University and also Technical Director of the reactor. Maier-Leibnitz held that position previously but that is long ago since both Maier-Leibnitz and I are both emeritus. The staff at the Garching Institute has extended its work using accelerators and related things. All this is excellent but Maier-Leibnitz had been the important individual in the creation of the center. We were both professors of technical physics, he having been there much longer than I, since I did not join until 1957, after returning from Russia.
Walker:As you know, one can read historic letters and reports, but not really know what the individuals involved were really like. I would like to ask you about your own experience with individuals such as Heisenberg, Bothe, and so forth. What relation did you have with them? A more explicit question: The work of Heisenberg is regarded as secret. You, however, knew where the uranium went. What do you actually know?
Riehl:I can give you a precise account of those matters since I lived with them. The situation was as follows. Hahn published his work on the fission of uranium in 1938 or 1939, together with Strassmann. Strassmann was a very suitable co-worker for Hahn. He was very exact. It should, in fact, be emphasized that it was a fortunate accident that fission was discovered by Hahn. He was the true master of radioactivity, the entire field. He proceeded with extreme cleanliness and with extreme concern about contamination with foreign radioactive substances, all of which was very important for the work. Without this experience, and this true mastery that bordered on the genius that Hahn possessed, the discovery would not have been made. For example, he applied methods to determine whether the fission product of uranium was barium or radium. One suspected radium or radium isotope. Hahn had enormous experience in settling such issues — I, incidentally, worked with him very intently alongside him — and saw how he enriched radium with barium and thereby determined what isotope was present. If one has an emitting substance and does not know whether it is radium or barium, one can use fractional crystallization with appropriate enrichment of a known substance. If, for example, one does not know whether it is radium or barium and adds sufficient pure barium for crystallization.to occur, the radioactivity will crystallize with the barium compound. Conversely, if it is radium, it will concentrate in the liquid solution so that one can distinguish between the two. Hahn understood these techniques completely as well as the theory going with them. I used many of them later on when I was at the Auer Company. Incidentally, I got along very well with Hahn, since he had a good sense of humor and was a very broad individual. He always referred to me as my friend Nikolaus, even though I was a student of Meitner.
Walker:I would like to ask you to tell me more about this.
Riehl:Yes. I was a student of Meitner, however, I had much more companionable and humorous relations with Hahn. This, in fact, was true long after I had graduated. He was an uncomplicated individual. Lise Meitner was somewhat nervous and so forth. She was always a bit difficult. Later on, when she was somewhat older and I was also older, we got along much better. However, the relationship was not a very easy one when I was a student. The difficulties were mutual. It seemed to me unconventional to have a woman as a boss. I was terribly young at that time when I was completing my doctors work, being between twenty and twenty-three years old. She, as head, was a bit impatient and domineering. We never actually quarreled but it was not a true friendship. With Hahn, however, and until his death we maintained a true friendship. We both knew the merits of Strassmann and, in fact, no one ever disputed his merits. It is, however, not relevant to make an issue of what detail Hahn or Strassmann thought of first. It was very important, for example, that Hahn determined that barium was present and that another fission product had to be a gas, that is either xenon or krypton. In the second instance, Hahn used a method that was entirely his own, namely, in the production of high-emanating preparations. They knew that radium produces emanations in the form of a gas. Early on one isolated the emanations by dissolving the radium in the form of a salt, whereupon the emanations were released. Hahn, however, had a very beautiful method that was entirely his own, namely to use exceedingly porous forms of thorium hydroxide or iron hydroxide which possessed a large surface area. One incorporated the radium in this material, drying out the precipitates slightly. The gas would then be absorbed on the surface of the pores. Hahn applied this method to determine whether one of the fission products was a gas. In this way, he demonstrated that either krypton or xenon had to be present among the fission products. This example demonstrates the way in which the vast experience that Hahn and his previous colleagues had generated played a very large role in ascertaining the correctness of the hypothesis that fission had taken place. Let us, however, get back to the question which you have raised, namely, how does it happen that these basically secret facts were not retained as secrets. First, the existence of fission was published. This then left the problem which the German physicists faced: What shall we do next? Should one keep further details secret since it was soon clear that one had here the potential of making a bomb or in any case an energy source in the form of a very intense reactor? The conclusion drawn by the German physicists was that it was best to be completely open so that it would no longer be completely secret. Dr. Fluegge wrote an article for the journal Naturwissenschaften which was precisely accurate but did not contain all the details.
Walker:Did you actually work with high levels of radioactivity?
Riehl:Yes. In our activities at the Auer Company, we often worked with extremely intense preparations, particularly of radium — with many grams of radium.
Walker:It is really a wonder that you have lived to such an age when you worked so extensively with such dangerous substances.
Riehl:Indeed so. It is a small wonder. I should say, however, that all my co-workers in the mesothorium division or the radiological division, as we call them in Auer, all died fairly young and, indeed, all of the laboratory workers, of different illnesses. It is well-known that there is a very specific death caused by radium. This knowledge is gained by research with rats and related animals whose organs receive weak damage. We know that damage by alpha rays produces tumors and bone sarcoma and other dreadful things. If, however, the individual has had rather general damage, he or she usually dies of some more general illness, as occurred among my colleagues. All are dead except for the head of the division and me. I am thinking here of the period as a young man when I was the deputy head. At that time I had to deal with enormous amounts of radiation, however, I was always informed where and what the source of danger was. I was, indeed, a student of Hahn and as a result had a great deal of real experience in the field of radioactivity. I knew that from one thing one would expect alpha rays and from another gamma rays and that another would produce emanation. There was also the danger of producing a radioactive spray which would contain radium, for example. The incorporation of uranium is the worst of the hazards. Gamma radiation is not so bad. The worst result of it being perhaps a small radiation rash (Roengen Kater). In other words, I was always conscious of the nature of the source of danger. It is somewhat like the situation in war. Experienced lower officers know exactly how to comport themselves in a dangerous situation, whereas the young, inexperienced ones who run about get shot. It is important to develop professional experience in any field. We at Auer dealt with radioactivity on a technical scale at the level of grams and curies, that is, at dreadfully high levels. Hahn, in contrast, worked with small quantities. Honestly said, we at Auer worked in what might be called a swine-like manner. Whenever I sought Hahn after such a period of work, he would say to me, "Herr Riehl, you are not clean. I won't give you my hand." We finally achieved an agreement. I sought him out early in the morning when I came directly from my home. It could then be assumed that I had bathed myself properly and was clean. That was, indeed, a very happy solution. It does demonstrate, however, what great concern Hahn had for my work with very intense preparations, since he was much concerned about the possibility that in shaking hands with him I would transfer some contaminating radioactivity. His concern was not on the grounds of health, but about the cleanliness of his own laboratory and work. Let's get back to the secret history. It was agreed on fundamental grounds that we should publish the fact that a bomb could be made, however, nothing was said about plutonium and such matters. Moreover, nothing was said in Fluegger's article about plutonium. Only about uranium 235. It was stated that it was fissionable and was the lighter isotope. There was also additional work on isotope separation with particular emphasis on the separation for producing heavy water as a moderator. Norway had been occupied by Germany. Experiments were carried out there employing both electrolytic separation as well as with fractional distillation. With regard to the maintenance of secrecy, the issue was raised by the Ministry of Military Weaponry which referred the matter to Dr. Diebner, who agreed that further development should be declared secret and officially labeled so. Thus, the topic became secret but not nearly so secret as in Russia. Any material related to further developments carried the designation secret on it. If, however, one wished to be relieved of that burden for some special use, one merely cut off the special designation and the document was no longer secret. In other words, one was very light-hearted in relation to the classification. In this connection, Weizsacker took one occasion to 90 to see Niels Bohr in Copenhagen and describe what was going on. I might add that I made a special trip to Sweden during the war in order to see scientific friends that I had there. In fact, it was the only trip I took outside Germany. While in Sweden I talked quite openly on the general status of the situation regarding our work on uranium. You may well ask why were we so open about this. The point is that essentially all, if not quite all, were fearful that Hitler would pick up the matter, place the topic on the top secret list, and then use enormous force to require the scientists to work on the development of an atomic bomb. Actually, German industry and science, as a result of Hitler's "genial" leadership was so weakened that this was unlikely. It was not weakened in relation to matters of producing chemical bombs, tanks and artillery, but in all other areas, particularly those that contained a bit of science at a higher level. Neither Hitler nor his colleagues understood such matters. They had at the base, primitive souls. Abstract thinking was too difficult for them. As a result, even though classification and interest was proposed by the Military Weapons Ministry, the support became less and less until finally the matter fell into the hands of the National Research Agency. The responsible individual at that stage was Professor Gerlach, the well-known German experimental physicist. The topic remained secret but not very strongly so. In fact, the longer the war went, the less interest in the matter was displayed by the government. Hitler focused his attention on the V-1 and V-2 weapons, that is upon rockets. The interest fell so low that when I asked for seventy kilograms of copper required for a transformer to be used in connection with an oven for melting uranium and other products, I had to wait eight months for delivery. Copper was very scarce in Germany. There was very little to be had. I heard on many occasions that Hitler would visit research institutes to inquire if they had some wonderful military equipment to offer. If the response was yes, he would ask, "What material do you need?" If the answer was copper, the response was, "I am not interested." This will give an indication of the shortage of copper. And so that is the history of secrecy. Contributions of German physicists were held back as a result of the environment in which the country found itself as the war progressed.
Walker:A specific question. How much did you know about what Heisenberg and Wertz were doing? What were they investigating and so forth?
Riehl:I knew exactly what they were doing, not in all details since I did not work with them, however, I supplied them with these uranium cubes which were employed in Haigerloch also. They were made by me and Degussa. I was the central supply.
Walker:Were they plates or sheets?
Riehl:We did make plates, however, the investigations at Haigerloch employed cubes.
Walker:Did Diebner do something with the cubes?
Riehl:Diebner was the referent for the Ministry. Incidentally, he is no longer alive. The installations of the German physicists were different. Some believed that they could develop a nuclear reactor but none desired to make a real atomic bomb. Most physicists felt that developing a reactor that functioned was something in the nature of a game, since there was so much energy to be released from such small quantities of matter. That properly fascinated every physicist. For this reason, it is false to say that the German physicists basically opposed releasing nuclear energy. It is not completely true. Any normal physicist or engineer would be bound to be fascinated by the topic and its development. It is, however, true that the overwhelming variety of German physicists and many engineers had no desire to provide Hitler with an atomic bomb.
Walker:You always say "most." Can you name exceptions?
Riehl:Exceptions! I did not know anyone who wanted to make a real atom bomb for Hitler. Reactors yes. Reactors evoked much interest. That was something new.
Walker:But you did know that if you had a reactor you could make plutonium.
Riehl:Yes. Yes. There were, however, many obstacles in the way of going further. Most of us, or at least many, knew that the war was lost. It was just a question of when. I was convinced from the first day of the war that it was lost. Let me give an example. I knew a co-worker of Degussa, a doctor whose name I have forgotten, who was involved in the production of metallic uranium. He once asked me, "Herr Dr. Riehl, do you believe that the end result of the uranium we are making will be the production of a bomb." I responded, "We will produce no bomb. You know how heavily both industry and science are over-burdened because of shortages. To produce a bomb one would have to go very far: isotope separation, diffusion membranes, then a very large quantity of uranium. The amount of uranium we have available is not sufficient. All they have been able to do in Haigerloch is to enhance the production of neutrons slightly. Their reactor does not go critical, however. In the main everything is in bad shape. You can rest assured that we will not provide Hitler with an atom bomb between now and the end of the war.” In this way I put him at ease. Yes, so much for the preservation of secrecy. That is about as much as I can say.
Walker:The relationship between Heisenberg and Diebner interests me a great deal.
Riehl:They were good.
Walker:Was there a professional competition between them?
Riehl:No. No professional competition, absolutely none. You see, Heisenberg was a very great scientist but he was not interested in technical matters. He was the leading physicist in Germany, but he had no interest in technical problems. After the war, for example, his interests shifted completely to other problems, fundamental problems of physics and the like. Professor Wirtz, on the other hand, was much interested in such technical matters. At that time he was not yet a professor but an assistant. Wirtz was much devoted to technical matters, but Heisenberg, for some particular reason, does not talk much. All the Germans tend to be that way at times. There was some matter of friction or a bad relationship of some kind or some other dispute that has generated his silence. You must realize, however, that at that time during the war, the Germans were very much interested in survival. Many were in danger as a result of Hitler's practices. Others had to leave the country, for example, those who were completely Jewish. One could protect people who were half Jewish and individuals, such as me, who were a quarter Jewish. One simply did not make an issue of it.
Walker:I didn't realize that.
Riehl:Yes. My mother's father was Jewish but I could simply hide that, the matter being easy because I was born in Russia. That would have made it difficult to prove anything one way or the other. In any case, we were all in danger, whether because of our political outlooks or because of a Jewish background. In fact, Hahn had something or other in his background, a Jewish ancestor. The details are known to his grandchildren but I do not remember them. That was never mentioned, however. The only serious problem was with Lise Meitner. She was Jewish on both sides of her family and as a result was forced to make an illegal crossing into Holland. That pained her a great deal, since she did not want to leave. I made a visit to her in Sweden during the war and she was very reserved with me until she noted that I really came to see her as a matter of principle. I wished to visit her and pay my respects. I had no other goal in mind. She was, however, very reserved. Later she thought a bit and said to me, "Mr. Riehl, you cannot imagine how I have been betrayed. I have been betrayed, indeed, by my best friends in Germany." Do you have another question?
Walker:What do you think of the book of Barwich?
Riehl:My commentary on Barwich's book is as follows. I went to Russia, or rather was compelled to go to Russia without any illusions. I knew Bolshevism from revolutionary times since I lived there and along with it. I was then eighteen or nineteen years old, that is, practically grown, and I had no illusions because of seeing matters first-hand. I was, later on as a captive, much surprised that they treated us captives so well. In other respects it was really terrible, the living standard, terrible. But not for us. We had everything. It was terrible for the Russians. And then this lack of freedom, continuous control. The Russian people themselves are wonderful, but the system was awful. It was particularly bad at the time of Stalin but now it is somewhat better. However, it was really horrible in the time of Stalin.
Walker:I have one more question. I plan to devote my thesis to the general subject of German nuclear energy development and its applications between 1939 and 1959. I thought that, in the process, I could obtain both from Barwich's book and from you some information on your experience when you were forced to go to Russia. That is a very important matter. Do you know, incidentally, if there is any information available concerning developments in the German Democratic Republic after 1955? Is there material that you know of?
Riehl:Oh! So you are interested as well in the German Democratic Republic.
Walker:Do you know anything about what went on there which I could add to my story?
Actually not. Essentially no specialists in the field of radioactivity or nuclear research remained in the Democratic Republic. Gustav Hertz remained after returning from the Soviet Union. He was Jewish and was so bitter about the times of Hitler. During those years he worked for Siemens. The head of the Siemens family had to go to Hitler in order to protect him. He, however, is not a nuclear physicist. He separated isotopes. That is his field. In fact he did that in Russia using uranium hexafluoride in a diffusion system. That is his expertise and Barwich worked with him. Barwich was the son of a so-called independent socialist. They were not Communists but rather left-leaning Social Democrats, a party that existed in Germany before Hitler. He grew up in this atmosphere of left-leaning Socialism. He went to Russia at the end of the war, more or less voluntarily, along with Hertz. Hertz also went voluntarily. Hertz had had enough of Germany, as did Volmer, that is Professor Volmer. There was a significantly wonderful man. Volmer and I were very good friends. In fact, if I live until next May, I will go to Berlin to present a laudatory memorial in behalf of Volmer. It will be the hundredth anniversary of his birth. The people in Berlin begged me to come. It is to be something in the nature of a festival. They said to me, "You are the only person who still knew him." That is true and so I shall give one more lecture in my old age, speaking about Volmer in connection with my memories. He was a very fine man, as was Hertz. Barwich, coming out of a socialist background, thought that in going to Russia he might find something especially attractive. There was, however, nothing. His book describes, with some starkness, his disappointment. Beyond that it is somewhat long-winded. He tends to write long, as you probably noted. He stayed in the Soviet Union for a long time and returned much later than I, years later, and came to West Germany since he was much disappointed. He went from East Germany to West Germany but said little to anyone about his experiences, perhaps because he stayed so long. And then he died, but not until he had written this book. His wife wrote privately about living conditions in Russia and everything she said is precisely right, everything that she has written.
 Professor Riehl had previously lived in Eastern Europe.
 N. Riehl “Ten Years in a Golden Cage, Experiences in the Soviety Uranium Industry.” Manuscript copies in the German Museum in Munich.
 S. Fluegge “Can One Make Technical Use of the Energy in the Atomic Nucleus?” Die Naturwissenschaften, 27 (1939) 402-410.
 Karl Wirtz and Werner Heisenberg carried out nuclear reactor research in Berlin-Dahlem.
 Kurt Diebner was Director of Reactor Investigations in the Military Weapons Ministry.
 H. & E. Barwich, The Red Atom (Scherz: 1970).