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In footnotes or endnotes please cite AIP interviews like this:
Interview of William Fowler by Charles Weiner on 1973 February 5,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Post-war career at Caltech, federal funding for research, relationships among Caltech, Jet Propulsion Lab and Office of Naval Research. Work through 1950 in nuclear physics, astrophysics, element synthesis in stars, influence of Bethe, Greenstein; Bowen/Lauritsen seminars, astronomical observations. Fellowship to Cambridge (1954-55), beginning of collaboration with Hoyle and Burbidges; return to Caltech, further work on stellar element synthesis with Burbidges, personalities of G. Burbidge and Hoyle; contemporary views on cosmology.
This is a continuation of my last session with Professor Fowler back in June. We agreed at the end of our session last time, as we both noted from the transcript, that we were just at the point where the new story was unfolding, and that’s the nuclear astrophysics story. You did mention some of the origins of your interest in the earlier discussion. Let me summarize a couple of things that I remember. There are bits and pieces. For example, you were exposed to Tolman’s courses and his interest in cosmology came through; Robertson, when he returned to Cal Tech from Princeton, got involved in such discussions; when Oppenheimer was working on neutron stars, there was some overflow of that, that you were aware of. And because of the astronomy work at Cal Tech and the observatories, you met Hubble. You were aware of what else was going on. This was all in the thirties.
People like Sinclair Smith, for example, who was a close friend of Charles Lauritsen, and there were other astronomers. When Bethe’s carbon-nitrogen cycle came out, you saw the relevance of this to the curves and the work that you were doing in carbon and nitrogen with Charlie Lauritsen. This made some sense to you in terms of your own interest. In the late thirties you were concerned with the Van de Graaff construction, and then the war work came in. We also talked about the postwar discussion of what the focus of effort and resources should be at Cal Tech, and the idea of low energy nuclear physics, not going into the cyclotron kind of work, but emphasizing low energy nuclear physics. One of the factors was because of developments in astrophysics and astronomy. You mentioned the seminars that developed from discussions with Bowen and how these were held. Bowen has also told me about that. You mentioned very briefly that Bethe visited here in 1942. You didn’t put it as a major factor but you said there was some discussion.
Well, it was an important factor, I think.
We’ll get to that, I’m just trying to summarize. Then you mentioned in another context the proposal to the Office of Naval Research, that came out of Charlie Lauritsen’s work in helping set up the ONR, and how this proposal approach was something new to you. We said it would be good, and the transcript showed it would be good to find that proposal, and you did. This is one of the things you sent to me. I’d like to discuss it with you in detail because first of all, it pins down the amounts of money that were asked for, but specifically it introduces the idea of the astrophysics which was in the proposal.
I haven’t even looked at it, could I just briefly do so.
Let’s talk about that, because the date on the proposal is June, ‘46. There’s nothing that tells me for sure that this is the one that was submitted, we don’t have in the files…
Oh, it is the one that was submitted. There may have been minor modifications after the ONR program director came back with the suggestion that we propose an amount of money equal to what he had. That’s always done. But I’m sure that the basis for the proposal, the explanatory basis for the proposal is exactly what went in, and then for several years it went in very much in that form, the only exception being that the money continued to rise as the activity increased, and as the expense of doing the research increased and so forth and so on. But there was a steady growth, you see, from that first budget in ‘46 of the order of, what is it, $80,000…
It was 88, plus 5, $93,000.
Yes, $93,000. At the time, in the sixties, we transferred from ONR to NSF funding, that budget had increased to roughly a million dollars, something like $900,000. So there was a steady growth over the 15 years — well, it was even more than that. We were with ONR more than 20 years.
Through ‘66 approximately.
Yes, I think that would be a good number to get right. If you’ll turn that off we can look it up…
What’s the name of the report you’re looking at, so I’ll have a reference to get a copy?
This is called “Final Report to the Office of Naval Research, Contract NONR-220-47 for experimental and theoretical investigations of light nuclei.”
Maybe before I leave here I can get it?
Yes, I’m sure we can give you one. So the grant which was started July 1st, 1946, was finally terminated on the 31st of August, 1970, a period of 24 plus years. But actually the major part of the work had been transferred to funding by the National Science Foundation sometime in the middle sixties. I’m sorry it isn’t noted here. But just as a matter of interest, the first proposal was, as we’ve just said, for something like $100,000 for one year. Over the total 24 year period, the Office of Naval Research supplied something over nine million dollars to the support of this laboratory, and in that same period, toward the end, NASA supplied $300,000, the National Science Foundation, which took over the major support in the middle sixties, some 2.8 million dollars. That means that the total funding of the laboratory in that 24 year period was 12 million dollars, or on average half a million dollars a year. So what has been done has come out of that amount of funding. One of the things that I think is of interest and the thing that we’ve made some point about here, in the sense that we have supported ourselves in this laboratory — we would claim, because of the excellence of the program, we’ve been able to get support, but in addition we have paid overhead charges to Cal Tech which amount to almost exactly 20 percent of that total, namely, 2.6 million dollars. And so, that’s in a sense typical of a medium sized laboratory enterprise in this country, nothing like the budget of the Radiation Lab or one of the big national centers, which would be several times that, up to orders of magnitude greater. But I think it’s rather interesting to show the extent of involvement of the Office of Naval Research with the work that we were doing here, which really has little connection with the Navy mission, except in a very basic, a very long range way. Now, it’s rather amusing that the final termination in 1970 came about in a rather interesting way, and I think that it is of some historical interest. In the middle sixties it became clear that the ONR could not continue to fund a laboratory of this kind to the tune of a million dollars a year. So we were transferred to funding by the National Science Foundation.
Was this partly due to the Mansfield Amendment?
No, that comes later. No, this was definitely before the Mansfield Amendment. I think it was in ‘66. I think it was in ‘66. But the Navy agreed to fund about 10 percent. They wanted to keep about 10 percent of the work, and we didn’t have to spell out too specifically what that was to be, but it amounted to about $100,000 a year. But at the same time that we went to funding by the National Science Foundation, not quite the same time but within about six months, I was appointed to the National Science Board. And as a member of the National Science Board, I by law was not permitted to take any funds from the National Science Foundation. No part of my salary could be paid for by the National Science Foundation, and insofar as possible, none of my activities were to be supported by the National Science Foundation. So it was very convenient to have $100,000 from the ONR, which we could then quite conveniently say was supporting my part of the work here, and it did that and more actually. By that time I was not actually using the laboratory equipment, so it wasn’t fair to put any of the costs of maintaining and operating the accelerators against my account.
The main item was part of my salary, my graduate students’ stipends and my computer costs, and that was easily covered by the $100,000. But then along came Mr. Mansfield, and the amusing part of the whole thing, the history of which is well known, is that ultimately I received a letter from the senior civilian, the scientific officer in the Office of Naval Research, saying that I was irrelevant, and that as a consequence I could no longer be supported by ONR. So this convenient arrangement that had gone on for four years or so had to be terminated, and the Institute was faced with the fact that since I was on the National Science Board and couldn’t take any money from the Science Foundation, and now because I was no longer relevant to the Navy mission I couldn’t get any money from ONR, they were going to have to put up my salary and pay for my secretarial help and so forth and so on. The upshot was that the Institute made me an Institute Professor of Physics. These Institute professorships are endowed and I’ve always been suspicious that my choice as the first Institute professor at Caltech wasn’t because of any merit of my case, but because of the necessity. Anyhow that’s what happened. And the Institute does pay a fraction of the secretarial salaries and other people in order to keep our relations with NSF legal and above board. So maybe there are other things about the general support of the lab that you’d like to know.
Yes, let me take it at this point and get back to the origins. Within this memo, proposal for a research project with Office of Research and Invention, Navy Department, there are a number of things that are quite interesting to me, and now that we’ve done the overall thing I can get back to it. For example, first of all, who wrote it?
I wrote it.
You wrote it, after discussions with Charlie Lauritsen. He asked you to write the proposal?
The point is made explicitly in the first paragraph, second — “that this work will be a continuation of the nuclear studies in the laboratory which were interrupted by the war.” There was nothing special told about that. The first item, though, on the transmutation of light elements with artificially accelerated charged particles, there a specific reference is made to correlating the experimental evidence with results obtained at the observatory, and that was not done earlier, but it was a continuation of a program that was perhaps relevant in that sense to the astrophysics. I was interested that in this thing it is spelled out. The decision you told me about that had been taken is explicitly stated right here.
Yes. By that time we had made our decision to stay in low energy, light nuclear physics, and to concentrate in part on the astrophysical applications. The correlation with observations at the observatories was quite justifiable, because we hoped, out of our discussions with the astronomers in these Friday evening beer sessions at Bowen’s, to see that there may be or might be a correlation between element abundances that astronomers see in stars, with the cross-section measurement which we can make in the lab. These cross-section measurements are relevant to the rate at which elements can be produced. So if you have nuclear mechanisms which are producing new elements, I think it’s pretty clear that that may have a connection with the element abundances that are observed. Now, that was a very significant addition in a sense to what we had learned from Hans Bethe’s work.
Bethe’s work primarily had to do with energy generation in the sun and energy generation in other stars, and clearly there is a connection, as he pointed out, between the nuclear processes that are generating energy and how much energy a star gives off. And you can begin to say something about what a star must be doing nuclear-wise when you make observations on how bright it is. Large bright main sequence stars pouring out great quantities of energy are operating at high temperatures in their center, and thus for example we know that they must be operating on the CN cycle. On the other hand, stars that are not so bright and that are less massive operate on rather lower temperatures and we know thus that they are probably, and this is all borne out by subsequent findings, they’re probably operating on another mechanism which Bethe also invented called the proton-proton chain. Even prior to his publication on the work of the CN cycle by himself, he had published with his student Charlie Critchfield a paper on the proton-proton chain.
Now, let’s follow up how it came about that we were able to do anything. When Bethe published his own paper on the CN cycle he included a review of the proton-proton chain, and he concluded on the basis of the reaction rates, which were available to him at that time, that the sun was shining on the carbon-nitrogen cycle and not on the proton-proton chain. The upshot of all the work that we were subsequently able to do on measuring the reaction rates in the laboratory showed that in detail he was wrong about that. The sun turned out to be just below the crossover point in mass. That crossover point is for stars not much more massive than the sun, say about 20 percent more massive, but nonetheless the sun is below the crossover point, in the sense that stars 20 percent more massive than the sun shine mostly on the CN cycle while stars less massive than 20 percent more than the sun, including the sun shine mostly on the proton-proton chain. So our experimental results could be worked into stellar models having to do with energy generation and could determine the relative importance of the proton-proton chain and the CN cycle, which by the way, because it also involves oxygen isotopes — it involves two cycles — we now call the CNO bicycle, and we think that is hilariously funny, at least I do. At the same time that these processes are going on, hydrogen is converted into helium.
That’s the basic element synthesis in main sequence stars. At the same time in the CN cycle, although the total number of carbon and nitrogen nuclei aren’t changed, most of the carbon gets converted into nitrogen, in the very first operation of the cycle. So one very elementary thing that one could hope for is that some time astronomers would see a star which, in ways not to be described too explicitly, had brought materials from its center out to its surface. Then if down in the center the CN cycle is going on, most of the carbon and nitrogen at the surface should then be in the form of nitrogen, whereas in a star that hasn’t mixed, like the sun, most of the carbon and nitrogen is in the form of carbon. So a new broad line of activity came to be added to our thinking when we talked to the astronomers. We found, it seems ridiculous now to me at this stage of the game, we found out for the first time that astronomers could identify elements in stars.
You didn’t know that?
Well, knew it vaguely, but didn’t realize that they could make quantitative measurements. I knew that they could observe spectral lines of various elements in stars. In fact, it isn’t much of a joke. For many years about all astronomers did was measure the wavelength of the lines, and it came to full fruition almost simultaneously that they began to realize that the depth of absorption lines and the width could be related to the abundance of the element that was absorbing the light from the photosphere underneath, see. So what we found was that there were people in astronomy interested in making abundance measurements of elements in the sun and in other stars, and so there that was then a new correlation between what we could do in the lab, and what they could observe directly, and that almost seemed more fun than the long indirect correlation between the energy generation and what’s going on in the center.
Let me pin you down on when this occurred to you, when you came to this realization?
It came in the discussions with Bowen. Merrill took a very important part in that because he was already measuring abundances in stars, and looking for strange elements. In fact, he was the one who discovered technitium, you know. However, I might just say that, not very much came of it until Jesse Greenstein was brought to Cal Tech in 1948, because Greenstein came here when there were only one or two people in the astronomy part of the physics, mathematics and astronomy division, and he has built up what at any place else one would call an astronomy department. He became the executive officer for astronomy. He has just retired from that, by the way, and Maarten Schmidt has taken over. But when Greenstein came, he was greatly interested in the astronomical aspect of this problem. What was the nuclear physics doing to make new elements? And could you see evidence for it in stars? So from that time on, from 1948, on, there has been a considerable overlap in the interests of the people in this lab and the interests of the people in the astronomy department, and of a few people at Mt. Wilson and now at the Hale Observatory…But we did learn right at the outset from those conversations that there was something more to it than just energy generation; there was the whole business of element synthesis.
Do you recall whether the proposal to the Navy was after these Bowen seminars started? This was June ‘46. I know the seminars started in ‘46 but I’m not clear whether they were going on at the time you wrote this.
I would guess that I wrote notes on the Bowen/Lauritsen seminars about the middle of that time period. I could look up...
You said you had notebooks of the Bowen seminar?
Well, I don’t want to mix up your…
…right, and I’m sure, I would have a guess that they’re dated, and we could find out. But it was all going on simultaneously. We were starting to talk with the astronomers. We realized we had to get some money some place to fund the laboratory. So it was all rather simultaneous. But I still think it’s fair to say that this new idea came out of the discussions with the astronomers stimulated by Bethe’s paper. I may have become aware of it almost immediately — because nothing’s spelled out there in the proposal.
Let me ask a couple of other things about the proposal. There are two observations I noticed just in general. One is that the majority of the funds is for salaries, very little for investment in equipment. You even talk about getting surplus equipment if possible. I’m going to make a study of the final report, but how would you characterize the allocation of funds during the 24 year period you mentioned earlier? Was it true that the majority kept on going for salaries, or were there big chunks of capital expenditures for equipment that came in later? You didn’t need it originally because you had the generator in hand.
Well, at the time that proposal was made, there was one electrostatic generator in the lab, the one that Tommy Lauritsen and Charlie and I had built just before the war. I think it’s true to say that over the whole history of funding in this laboratory, starting with the ONR and now continuing with the NSF, that the major fraction of the funds has been for salaries. Now, that’s in large measure due to the fact that most of the equipment in the lab was built with the faculty and students actually doing some of the labor and the shop men doing the rest, and the only thing bought was the raw material. We have always been a frugal laboratory in that sense, that is, insofar as possible we made what we needed here in the lab, and our expenditures for supplies and equipment have been relatively small as a consequence, although many of those salaries, much of the salary funding went into the cost of building new equipment.
Now, there’s one exception to that, and we’ve noted it before, that when we decided to go to somewhat higher energy than could be provided by the three million volt “homemade” machine, which was the second of the three Van de Graaffs that we built here, we did ask the ONR to purchase a tandem Van de Graaff from the High Voltage Engineering Corporation, and they did that. As I remember the cost was very close to a million dollars, and that was a special grant from special funds that is not included in the 12 million dollars or 9 million dollars that I mentioned before. So that was the one and only one major equipment expenditure in the whole history of the lab. In that way, I would say we’ve been rather unique, and it’s a direct consequence of Charlie Lauritsen’s belief that there was a lot of fun to be had out of just not using equipment and writing papers, but in building as much of it as you could. I think that Charlie was a very special person in that regard, because in many laboratories, it’s all done by buying something off the shelf, as you know, dozens of laboratories purchase Van de Graaffs of all shapes and sizes from the High Voltage Engineering Corporation, and we could have done that when we built our third small Van de Graaff. We had the alternative then of buying it from the High Voltage Engineering Corporation but we decided not to. We built it ourselves. But when it came to building the big one to go into higher energies, Charlie realized that if we were going to do that, we’d have to beef up and increase the size of our engineering staff, and rather than do that he was willing to settle for purchasing it. And he had to work very hard to get the money for it. It came at a rather difficult time in funding.
Gee, it was the early sixties, construction started in 1960 and was completed in 1961, so he was asking for the money in ‘58, ‘59 (?), and there was a period when it looked like the Air Force, the scientific office of the Air Force, Office of Air Force Research or whatever it was called, was going to supply the money, but at the last minute, the Navy found the money and so it was supplied on top of our grant one year, and that’s the way that came about.
Let me raise another question. That answers the ratio of capital expenditures to salaries. There’s a very interesting final paragraph in the proposal to the Navy, let me read this because there are some rather definite, positive statements — I want to know about the discussions that led up to it and the thinking. It comes into the category of publication of results and the nature of research: “It is essential that all results of these studies be in the ‘unclassified’ category and that publication in scientific journals and announcements to scientific societies be permitted at all times. It is also essential that it be clearly understood that these studies are primarily fundamental in nature, and that the possibility of applications is of secondary importance.” Then finally, “A clause must be inserted in any contractual arrangement guaranteeing the Institute’s right to purchase from the government all equipment provided under the contract.” Well, the first two sentences are very interesting. One is the statement on “unclassified.” What was the origin of that? Was this based on prior discussion with Navy people or on decisions taken here? If so who was involved? It’s a statement of very positive —
— yes. Well, everyone at the end of the war was concerned about whether the research to be supported by the Office of Naval Research was to be classified, as was all of the rocket work in this laboratory under the Bureau of Ordnance during the war. But as you know there was a great deal of controversy in this regard on a national scale, in which Charlie participated, because he worked very closely with Captain Bob Conrad who was a very close friend of his. This was the Captain Conrad who really founded the ONR and had the idea that something like the OSRD was a marvelous thing and that the Navy ought to continue that, and Conrad fought very hard with Navy brass, with Charlie’s support and the support of others, to make those two points clear on the national level, that (a) the research was to be unclassified and (b) it was to be of a fundamental rather than an applied nature. So that last paragraph is just a reflection of that general idea, and was put in there to show people up the line in this new Office of Naval Research that one university at least, and I’m sure they got this from many others, was not going to take the money unless it was agreed in advance that the work was to be unclassified, and that it was to be of a fundamental nature. Now, I don’t think there was ever any real opposition to this in the Office of Naval Research. I forget who was the first chief.
No, Waterman was a civilian and he was made the chief scientist. Captain Conrad was not the first director of the Office of Naval Research. I think Admiral Bowen was. But there was no real opposition to these fundamental principles in the Navy personnel who went into the Office of Naval Research. There were qualms on the part of Navy personnel in CNO about whether this was really the right thing to do.
Chief of Naval Operations.
Chief of Naval Operations who had to set up ONR or whatever it was called in those days.
According to this, it was called Office of Research and Inventions.
Well, that’s the predecessor of the Office of Naval Research.
This was wartime?
No, it was kind of an interim. It may have followed — it may have been an office in the Navy during the war which was used temporarily to get these grants started, but it very soon became the Office of Naval Research. But what I’m trying to say is that neither in the Office of Research and Inventions nor in the ONR was there any opposition to the policy that’s requested there. But there were people higher up in the Navy, and I think it went all the way to CNO, who felt that this wasn’t the right thing to do. Why should the Navy be supporting unclassified research, even if it was of a fundamental nature, because what one had learned from the war was that research of a fundamental nature eventually had applications and this ought to be classified. Fission was a fundamental discovery. The atomic bomb was a very important application. So this was all tied up with how the Office of Naval Research was to be operated, how the Atomic Energy Commission was to be operated — was it to be civilian or military control, and so forth and so on. So Charlie and I just decided, and Charlie was trying to get that policy through at top level, that one way to help in the general problem was to just insist on it in this grant. Because there was a program officer, Urner Liddell, who was very anxious to get us in his stable, you see, and he would have to go to his — to the civilians above him and say, “Look, these guys are insisting that their work is not to be classified, I still want to support it,” and those men would have to go finally to some naval officer and to the security officer and say, “This is what these fellows want.” And that helped to get the ONR to establish the policy that they would support unclassified fundamental research. So it’s a part, a small part of what was a very important formulation of policy.
Policy by proposal.
What I’m saying is that through the proposals, we put pressure up the line, Charlie operating on a more global scale was putting it in at other places, and that’s eventually what happened. That’s eventually what happened, and we weren’t the only ones who did this. There was general unanimity among everybody, a large majority of people who had worked for one military agency or another during the war, that they were going to get out from under security and classification, and they were going to go back to doing basic rather than applied research.
Do you have any recollection of effort to put such clauses in proposals? I understand the feeling might have been the same –- no conspiracy to do that?
As far as I know, there was no conspiracy or coordinated effort, just a consensus here on the campus. I am fairly certain that if you could get early proposals from other groups on the campus, that you would find somewhat similar language.
That’s an interesting point for me to check out with other universities. For instance, I’ve talked with Marshak about the Rochester situation — I don’t know, we talked more generally, I’ll ask him some time whether there was a specific…
Well, I don’t really know specifically that other people did that, but I know that I felt very strongly about it, and put it in, and when Charlie read the first draft he left it in. You see, this was part of a more general problem that we had toward the end of the war. We were operating a project in rocket ordnance, Charlie was director of research and I was assistant director of research for the OSRD, which was primarily for the Navy, for Navy landing craft and Navy planes. Toward the end of the war we had to make a decision, were we going to continue to operate, was Cal Tech going to continue to operate and direct activity along those lines, or was it going to turn it over to the Navy? And there was no doubt in Charlie’s mind and my mind, we wanted to turn it over to the Navy, and we actually did, because as I told you before, toward the end we got very much involved in making engineering components for Los Alamos, for the atomic bomb.
And at that time we started transferring all of the Cal Tech personnel on the OSRD project over to naval civil service, and I spent, well, I would say the most miserable six months of my life, trying to get people to do that, because all the people at the Naval Ordnance Test Station, which was still largely a Cal Tech installation, wanted to stay and work for Cal Tech. We just had to get them to go through the miserable business of going through all the civil service procedures. But that was done. Now, that again was somewhat unique, because even here at Cal Tech exactly the opposite happened. There was another rocket project which had started with jet-assisted takeoff for airplanes over in the aeronautics building just right across the alley here, under Von Karman and Molina and eventually Clark Millikan — their decision was to keep that activity at Cal Tech, and of course out of that has grown the Jet Propulsion Laboratory. You may say well, that’s NASA and that’s civilian, but that wasn’t true right after the war. The Jet Propulsion Laboratory was funded by Army Ordnance and they were actually doing highly classified work, so classified that it had to be moved off the campus. It also involved much large equipment. But nonetheless there was a difference of opinion about this, and one group went one way and the other group went the other, and I of course think that what we did in transferring it all to the Navy was the right thing for a university to do.
Now, there are those that would disagree, and I must admit that in recent years I’ve become very much interested in what the Jet Propulsion Laboratory’s doing because of the space effort, and it made a great deal of difference when NASA was set up and JPL went essentially into space science, and all of the ordnance aspect was transferred to Huntsville. So the worst element of that solution, which I at the time just thought was terrible, that Cal Tech was going to continue to do classified work in ordnance -– the worst aspect of that was terminated when JPL was taken over by NASA. But as anyone can tell you, it’s still somewhat of a headache for us –- it’s true, the Institute gets operating funds, or gets a fee in a sense for operating JPL. I doubt if it pays for the additional people that we have to have in order to keep books for the government on the operations of JPL, which has a budget five or six times the Cal Tech budget.
The entire Cal Tech budget?
What about the interaction of people from JPL with Cal Tech in terms of teaching and research functions that are going on on the campus?
Well, that’s a story that I don’t think has been too happy a one. I would say that among the Cal Tech faculty, I have had much more than the average cooperation and interaction with JPL, more than the average member of the faculty. Now, there are a few members of the faculty who’ve had much more interaction with JPL than I have had, like Jerry Wasserburg and Bob Leighton, but on the whole it’s only been a small fraction of the faculty. Very few students have gotten their Ph.D. theses from work at JPL, although in recent years, students have gotten their Ph.D.’s from work in the space program, but that’s primarily been supported by grants from NASA independent of JPL. That is, Cal Tech can go to NASA for funds for independent work just as JPL can. So I don’t know, it’s a long difficult story, whether JPL has been good for Cal Tech is a question on which you will get answers on both sides. I personally think that it has. 1 think that the role that JPL played in the space program, the Mariner program for example, has enhanced Cal Tech’s reputation in a field that up until just recently has been of great interest to a great number of people in physics and astronomy, geophysics and geochemistry, and has been well funded. Now, NASA’s funds are curtailed and as a consequence they’re decreasing their funding in what they call supporting research and technology, SR and T. It may become, not only for Cal Tech but for other universities, a very severe problem. But we’ll see.
The reason I think it’s worth talking about, it’s not just a digression — it’s because you have three models here on campus, relating to Cal Tech, of relationship with auxiliary projects or institutions. The observatories on the one hand, the Navy Work which was sort of disposed of by the transfer, and then the JPL. So I think — we talked about the advantages of the observatory work, because the kinds of programs you were developing, your nuclear physics programs, were directly related to that and they were mutually reinforcing. Let’s get back to that. This little document can really lead into a lot of things… The thing in particular I’d like to comment on is that, just reading your bibliography, the first explicitly astrophysics paper I see, at least from the words in the title, is 1954, yet I know a lot of these nuclear reactions papers from earlier are related to it. But from ‘54 on is the first time you really started publishing with explicit reference in the title to it; secondly, you start then publishing in other journals which are more closely allied with astrophysical interests — for example the Astrophysical Journal. I’d like to talk about this period from ‘46 to ‘54 in terms of your own work. We’ve talked of…
Well, let me just add one point there, because I think it is important to tie down when we first began to have a productive output in regard to the nuclear astrophysics. The very first paper actually, and I grant you that there will be little explicitly stated, but the very first paper to come out was one in 1948, which described the building of a high frequency proton source, that’s what it was called. Actually it was a very small accelerator using our old X-ray supply that we had found in the basement of the Budge Laboratory, and it was built by the first graduate student who worked with me completely independently, Bob Hall. It was a low energy 150 kilovolt machine which was modified explicitly to measure the carbon-nitrogen cycle reactions at energies as low as one could get in the laboratory and still detect something.
You must understand that in the sun the effective energy for the interaction of protons with the carbon nitrogen isotopes, which still goes on even though it’s not the major source of energy in the sun, the energy is 30 kilovolts. Now, the cross-sections there are so small that we can’t measure them in the laboratory. The only reason they’re important in the sun is because the sun has so much mass interacting. But anyhow, the very first paper — and you’ll find in the introduction to it I’m sure some motivation — was the paper describing the building of this high current, low voltage source, where we hoped to get measurements down to about 100 kilovolts. And then the first paper from that didn’t come until 1950, “The cross-section for the radiative capture of protons by carbon-12 near 100 kilovolts,” R.N. Hall and W.A. Fowler, Physics Review, 77, 197, 1950. So that shows how long it took to make the very first measurements, once we had decided in ‘46 we were going to do it.
It took a little over a year to build this special piece of equipment, and that took — of course the publication was in ‘48 so it was probably finished early in ‘48, but then the measurements of that type, we soon realized were of extreme difficulty, because one has to measure these excitation curves or cross-sections or rates that are very small. For example, Bob Hall was measuring the carbon-12 plus proton reaction which you detect by measuring the positrons emitted by the nitrogen-13 produced, and he had to count those positrons one by one, and I once up that in all the measurements which he reported in his thesis and you see it came out just about two, three years later—he had measured a total of 1000 positrons over a period of three years. The whole business was to get counters that had low background so that the counts that you detected were really due to the reaction, and I helped him build a little counter with a bundle of anticoincidence Geiger counters around it. That was the main thing I did for the youngster while he was building up this accelerating tube. But I really think that what you said, although you probably had some historical reason for it, the first work came out in 1950, and the fact that that’s four years after the first proposal is merely an indication of how long it took to build this special piece of equipment, and how long it took to make the measurements.
And so in the meantime we were also doing things with our Van de Graaff, some of which are relevant to the astrophysical problem, but most of which weren’t, and that’s of course been true of all the activity in the laboratory. True, we have always looked for reactions that have astrophysical connections, but in addition we’ve made studies where there was a clear and important and significant contribution to pure nuclear physics to be made, or a problem that was soluble. You have to choose in the laboratory something that you can do, and get a graduate student involved — we had as many graduate students then as we do now. You’ve got to give them problems from which they can actually get results and report on in a thesis. Bob Hall was kind of the guinea pig, as a graduate student as far as I was concerned.
You were saying that Bob Hall was a guinea pig as a student.
Yes. He was the first one to work on a straight forward astrophysical problem, and the question was, was it feasible to give as a doctoral problem a problem that, in nuclear astrophysics, required building specialized and sophisticated equipment, both the acceleration and the detection equipment, and furthermore would it be possible for him in these very difficult measurements of quite small cross-sections to get enough material to publish or to produce the thesis? One of the things is, we’ve always insisted that all work in this lab for a doctor’s degree be publishable, and in fact I don’t know of any exceptions. Every student who’s got his Ph.D. in Kellogg has at least published his thesis, and many of them have published a great deal subsequently. I think it’s fair to say that we started on this program immediately in ‘46 but it wasn’t until ‘50 that we saw the first fruit. And then one will find that in 1951 a paper on the transmutation of nitrogen-14 by protons came out, and another paper on the carbon-12, p gamma reaction by Seagrave, the one on nitrogen-14 was by Duncan and Perry. And then in 1952, E.J. Woodberry, another student of mine, did carbon-l3 plus protons and Seagrave worked on carbon-13, and Schardt came along and worked on nitrogen-15 plus protons. These were all the carbon-nitrogen cycle reactions, and what we were trying to find out in all that work was whether — just where this carbon-nitrogen cycle came into the picture, in what type of stars did it work? And it was the result of all these papers that we were able to say, about ‘52 or ‘53, that the carbon-nitrogen cycle doesn’t work in the sun, it works in the more massive stars. And so that’s the way it went.
Meanwhile during this period, this is strictly internal. You’re building a method of getting the reactions you want and you’re studying the reactions which are of interest, which could have dated back to the interest from the late thirties, the carbon-nitrogen cycle interest. What about new astronomical results? It seems to me that the Palomar telescope was dedicated in ‘48, and started producing results not long after that; there’s lots of other things going on in other observatories and laboratories. Were there any new questions that were introduced which changed the agenda somewhat? You were following a program, a basic one, which was indicated as late as the late thirties. Was there anything new on this same issue?
Well, I have to say that we were so busy, so involved in checking on the operation of the carbon-nitrogen cycle that although there was a great deal of activity in Greenstein’s group, in making abundance measurements in stars, and although we knew that there was a connection there, we interacted on a very limited scale. In fact, the primary problem that Greenstein and got concerned about was the fact that we were finding from these experimental results that the carbon-nitrogen cycle, or what came to be called the carbon-nitrogen-oxygen bicycle, converted carbon and oxygen into nitrogen, and so Greenstein was interested in seeing whether he could find any evidence of this astronomically. That was the first problem. But on his part that took a lot of time and on our part it took a lot of time because, as you pointed out at the start of our conversation, it wasn’t until 1954 that was willing to put out a summary paper which was called “Experimental Theoretical Results on Nuclear Reactions in Stars.” That refers to all this work on this C-13, p gamma, the nitrogen-14, p gamma, the Carbon-12, p gamma and the nitrogen-15, p alpha, all of which you’ll find were studied starting in ‘48, and were reported on in ‘51, ‘51, ‘53 and ‘53. By ‘54, I was invited to contribute to a symposium in Liege. In fact I went to it because ‘54 was the first year that I went abroad, and after contributing to the symposium I wrote up this paper for publication in the memoirs of the Royal Society of Liege.
So that’s how that all came about, and at the same time, Jesse Greenstein was working — among other things, because he had other things to do too — on the relative abundances of carbon, nitrogen and oxygen in stars, and of course that particular thing you might say was rather disappointing, the main reason being that most stars don’t mix the material in their centers up to their surface. The energy is carried out by radiative transport. The only time one gets mixing is when the energy has to be transported by convection, and convection actually implies mass motion, and then you can get mixing between the center of a star where the nuclear reactions are changing things, out to the surface where the astronomer can make observations. But the convective mixing is rather special and doesn’t happen very often, and so only in rare instances does one see this great enhancement of nitrogen. It is difficult for astronomers to realize how little they can observe above stars.
Now, I might just say the other thing we found is that if carbon had been through the carbon-nitrogen cycle, it then came out we could calculate the ratio of the two isotopes, which are carbon-12 and carbon-13, the stable ones that are found in nature. It comes out that that ratio, if you originally dump in pure carbon-12, which we’ll see later is made in another way, into hydrogen burning, as we call it, after a while the carbon-12 to carbon-13 reaches an equilibrium ratio of about 4. Now, terrestrially and in the solar system we know that ratio is about 90, but sure enough, eventually the astronomers found stars in which on their surface they see that the carbon-12 to carbon—13 is 4 to 1 or 3 to 1, or 5 to 1, roughly 4 to 1. We think that that is indeed the result of the carbon-nitrogen cycle operating, and in those stars, in some way that makes them unique relative to other stars, they brought that equilibrium carbon up to their surface where astronomers can see it spectroscopically. So all of this was going on, which was in terms of our output nowadays incredibly slow, as you see. But it was the basic work in which we learned all the techniques, built the proper equipment, and finally in ‘54 were able to in large measure summarize what goes on in main sequence stars, where hydrogen is being converted to helium, either by the proton-proton chain or by the carbon-nitrogen-oxygen bicycle. Now, in that connection, we began to realize that there was a lot of measurements to be made on the proton-proton chain itself. And so subsequent to 1954, you’ll find a number of papers on reactions in the proton-proton chain. But you won’t see anything in the title of the paper that indicates that the reason we were doing it was because it’s of particular interest in stars somewhat less massive than 20 percent greater than the sun. Nonetheless the proton-proton chain is of crucial importance in the way the sun operates.
Let me ask about the papers you were doing prior to 1954, the ones that were building up that knowledge. How did they relate to the general subject of the study of nuclear forces, for example, the whole study of nuclear reactions which was relating to some other large themes in the development of nuclear physics on a world scale. In this period in the early fifties you have the Bohr-Mottleson model and many other things were happening. Some might call it a relatively dormant period of the subject, some might not, but there was an awful lot going on. Were these papers of interest to that other aspect of nuclear physics per se?
Yes. In a rather limited way. One of the things that we had discovered before the war was the mirror nuclei, and we had studied the ground states of mirror nuclei, for example, nitrogen-13 and carbon-13, and boron-11 and carbon-11, oxygen-15 and nitrogen-15, and in our previous discussions, I pointed out how in cooperation with Oppenheimer we had come to understand the systematic increase in the radioactive energy of the mirror nuclei, and thus had been one of the contributors to what’s called the charge independence and the charge symmetry of nuclear forces. So one of the things that we did very soon after the war was to follow that up by making sure that the excited states of the mirror nuclei, the sequence of excited states on the most elementary level, should be identical.
So a lot of the work that you find here on excited states and energy levels of light nuclei was devoted to showing in detail experimentally that indeed, for every level — I remember the main one was lithium-7 — for every level in lithium-7, there was one exactly like it in beryllium-7. So there’s even a paper in 1951, “Excited States of the Mirror Nuclei, Lithium-7 and Beryllium-7,” by two of our students, Brown and Snyder, and Charlie and I. We already knew there was an excited state of lithium-7, just about 480 kilovolts above the ground state, so we looked in beryllium-7 and sure enough we found one not at exactly that energy but very much the same. So we were working in some fundamental nuclear physics. It might by that time be said that it didn’t have the glamour of some other things that were going on in nuclear physics, but it still was a very basic contribution. We were measuring the excited states, where they were, what their widths were, how they decayed, and building up a phenomenological picture of the light nuclei in much the same way that early spectroscopists had built up the knowledge of the excited states of atomic systems.
Now, I might say that we thought at that time that if we measured all of the excited states of a given nucleus and of a series of nuclei, not only where they were but what their spins, their parities, their energies, their decay widths were, that we could in that way unravel the nature of the nuclear forces. We now know that what we were really investigating was a many body problem in which, in large measure, all you can get out of it is a kind of average potential of a nucleon in a nucleus. You can’t get in that way the details of the interaction between nucleons except in second order. Now, we made a conscious choice there. For example, some laboratories, such as Herb’s laboratory at Madison, decided to study—and this was under the influence of Gregory Breit — the proton-proton interaction. They’d bounce protons off protons. We didn’t do that. We were bouncing protons off somewhat heavier nuclei, still light nuclei, hoping that in the interaction between a proton and lithium-7, which after all is three protons and four neutrons, that we would learn something that Herb and Breit couldn’t learn by the much simpler interactions.
But there was always the hope that given what Breit did or what Herb did in studying the proton-proton interaction, and then using the deuteron to study the neutron-proton interaction, and then assuming charge symmetry, which tells you from the proton-proton interaction what the neutron-neutron interaction is, that we could check up on them by making those individual particle interactions fit the energy levels that we found in the laboratory in the light nuclei, or even in the light nuclei with 8 particles or 10 particles or 16 particles or 20, which is the highest we ever went to in the early days. You still have a many-body problem, and as a consequence there is no simple connection between the interaction between two nucleons and the interaction between a bucketful or a nucleus thought of as a potential well, in which the nucleons interact fairly independently. The exclusion principle comes into the problem in a powerful way as first understood by Viki Weisskopf. But we had the motivation in those early days that by what we were doing in the interaction of protons and alpha particles and deuterons and later helium-3 and tritium, with the light nuclei, we were going to get to the fundamental nuclear interactions. Now, of course, one knows the proton is not a simple particle, the neutron is not a simple particle, and one looks for those fundamental problems at the level of very high energy physics.
So more and more as we came to realize that although we were working on very interesting problems, it didn’t have really any hope of solving the very fundamental problem of the nature of the nuclear interaction. Other people going into high energy physics were clearly going to be able to do more on that than we were with our complicated bundles of nucleons, even in the light nuclei. So more and more, as we saw that development, we were inclined to spend more of our time in the nuclear astrophysics, where we were a) uniquely involved as the nuclear astrophysics laboratory, although there were other places making contributions too, and b) where we could see some fundamental consequence pertaining to astronomy. That’s about the way it went.
It’s the consequence of a decision which you made.
You can’t predict what the entire field will do, and then one aspect of your decision is the one to move ahead on it — there’s a whole series of new things now. I’d like to talk for example, following your outline, of Salpeter’s visit here in 1951 and the significance of that, and interactions with such people including those who came later. What this meant to you personally. This is then involving you in a larger world of astrophysics, and had great significance I think for your own work. That leads to your year in Cambridge as well. Then I’d like systematically to take the things that led out of that, including the larger issue — I think it’s very important. I want to talk about you specifically and about the laboratory as well, but you were involved in a tremendously important period of explosive growth in astrophysics and cosmology, and you were close to the people who were most prominent spokesmen, and you soon became one yourself. I’d like to get impressions for example about Hoyle and his style of work and the disputes, all that.
We can talk about that tomorrow.
Much historical information is contained in the "Final Report to the Office of Naval Research on Contract Nonr-220 (47)" - one of the Grape Aid Preprint Series in Miscellany - December, 1970 and in "Engineering and Science" 52, #9 (1969).
It is difficult to reconstruct the situation in retrospect. I know that I wrote the proposal. Charlie assured me that our research would be fundamental and unclassified. I insisted that it be spelled out in black and white.
I don't know who the civilians were. But people eventually involved in support of our program were Shirleigh Silverman, Mannie Piore, William Wright, Jerry Fregeau and Ducie Padgett. God bless them!
Caltech is an Institute of Technology, not a university but it is also not a college. I just can't use the word "Institute" in this context!