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In footnotes or endnotes please cite AIP interviews like this:
Interview of William Fowler by Charles Weiner on 1972 June 8,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Early education and career; graduate training at Caltech, with C.C. Lauritsen’s group; collaboration at the Kellogg Lab and structure of Caltech physics department after 1939, Relationships with Oppenheimer and Lauritsen. Fowler’s and Caltech’s war work, Lauritsen’s role in setting up Office of Naval Research for federally funded post-war research.
I think we agreed from your outline and mine, a good place to start with would be family background. I know you were born in Pittsburgh. I’d like to know something about the profession of your family, your family life —
Yes. Well, as you’ve just said, I was born in Pittsburgh in 1911, but my family moved to Lima, Ohio, in 1913 when I was two years old. My father was a bookkeeper-accountant with what became the Buckeye Pipeline Co., which was moved from Pittsburgh primarily because of the Sherman Anti-Trust Act which said that oil companies dealing in Ohio oil had to have their offices in that state, and Lima was at that time the center of one of the original oil fields in the state of Ohio. While my father was very adept at arithmetic and was a whiz at adding and subtracting, multiplying and dividing, doing fractions, he had very little interest in scientific matters. His hobbies were primarily sports and gardening. My mother was of course the housekeeper, but I suspect that in a way there’s more connection with my scientific career in her side of the family — my teaching career, let me say. Her paternal grandparents taught school in a National School in Northern Ireland. I’ve been back to the little place, it’s called Taniokey and is near Clare in County Armagh. They lived in the central part of the building and the boys’ school was a wing on one side and the girls’ school was the wing on the other, and her grandfather, my great-grandfather, taught the boys and the great-grandmother taught the girls, and they taught there in that school for some 60 years. Then in fact one of my grandfather’s sisters also became a school teacher. She married a school teacher, and they inherited the positions there at Taniokey National School, and they taught for another 40 years. So school teaching has been in my mother’s family. On the other hand, her father, although he wanted to be a teacher, found things very difficult in Ireland. This was in the 1870’s or ‘80’s, as I remember, and so he came to the United States, settled in Pittsburgh, but never had the opportunity to teach and actually became a grocery owner. My mother’s mother, my grandmother, came from a family that owned the Summers Steel Works in Wolverhampton, England, so there was some engineering on my mother’s mother’s side. Her mother was a very enterprising young woman. She came to the United States on her own at the age of 19 as a seamstress, married my grandfather, and that’s about as much I think as I can tell you of those antecedents. As a boy, I think the major influence toward the scientific career was the fact that I had lots of toys, starting with tinker toys as a very small child, erector sets, stationary steam engines and electric trains. I had a series of electric trains leading up to a very large one that my father got for me, actually 2 inch gauge, which was quite a train. I really think back, that the fact that I was provided with mechanical and electrical toys at an early age had a lot of influence in stimulating my interest.
At what age?
It started with the tinker toys when I was three, and I was still playing with electric trains when I was in high school. In fact, the very large one that my father got me must have come when I was about ten, but I had smaller versions before that and became very much interested. The train that he bought me, this large one, was a second hand one, and I remember I had to repair it and we had to buy new gear for it, so there was all that sort of thing, which I suppose is characteristic of the early start of many people who’ve gone into science. On the other hand, I did not go into radio in any way, and did not learn any electronics, and so that’s another side of the problem. One other great influence in my early life was the fact that our family home was only one block from the main line of the Pennsylvania Railroad. I was just fascinated with trains, still am. Lima was at that time a division point on the main line of the Pennsy, Chicago to Pittsburgh to New York, and it was a division point in the sense that the steam locomotives were changed in Lima, and the yard where this was done was only about half a mile from my home. So I spent a great deal of my boyhood in that yard, getting to know the drivers, and whenever I could get a ride while the engine was being shunted around the yard, and every time the Broadway Limited came in (it went through in the early evening going East in those days) I was out there. When the train would come in, stop momentarily, pull off an engine, have another one put on, that was the big thrill of my life. I got a great interest in locomotives and in model locomotives, and to jump ahead 60 years, when my friends in England held my 60th birthday celebration last year, they gave me a model locomotive as a present. It’s still over there. I haven’t brought it back to the United States yet. (Tank Engine #696 was brought to Pasadena in September 1972.)
A model, a large one?
Yes. It’s 20 inches long, ten inches high (scale 3/4” to 1’, track 3-1/2” wide). It’s a little tank locomotive and I’m very proud of it. I’ve had it operating and it’s lots of fun when under steam.
How old were you in this trainyard period? High school?
No, no. By the time I got to high school there wasn’t much time for that. No, all of this was before high school. I was not supposed to go to the trainyard. That was considered dangerous. But I did nonetheless. I just couldn’t stay away from the yard. There was also a lot of freight activity and shunting, as well as changing engines on the mainline passenger trains. So there was something going on all the time. Of course, that’s all gone now, with the diesels replacing steam locomotives. In fact, it was some time when I was 12 or 13 that everything changed. They no longer changed the engines in Lima. They made the run all the way from Chicago to Crestline, Ohio, without changing in Lima, so the activity in that yard decreased. I’ve been back in recent years, and there’s nothing there at all any more, what with the diesels.
Did you have brothers or sisters?
I have a brother two years younger and a sister eight years younger. They are still living in Lima. My brother went to work for the Lima Locomotive Works. That was another thing — although it’s in an agricultural area, it’s an industrial city in a way. Not only the Pennsylvania Railroad goes through Lima, but the Nickelplate, the Baltimore and Ohio, the Erie, and the Detroit, Toledo and Ironton, Henry Ford’s railroad that brought iron ore from southern Ohio up to Detroit. Also the Lima Locomotive Works was there, and in fact my brother still works for them although they no longer make locomotives and they’re no longer called the Lima Locomotive Works. It was Lima Baldwin Hamilton for some time, and now it’s called Clark Equipment. It’s a subsidiary of Clark Equipment and their main activity is power shovels, and my brother’s an engineer. He graduated from Ohio Northern, which is in Ada, very close to Lima. He went to work for the Lima Locomotive Works, did not do postgraduate work, and he’s worked up to a very responsible position in the engineering division of the present company. He’s largely theoretically inclined, and in fact his present work is on the design and testing of the new ideas for these long booms that you see on cranes, which have to be made as light as possible but as strong as possible, and that’s more or less what he does at the present time.
Did he share in these activities that you’ve described as your pre-high school activities?
I would say, not very much. My brother had considerably different interests, it seems to me, and there was the usual thing that brothers about two years apart — I don’t know whether it’s usual really — weren’t all that close. I had very close friends of my own age and slightly older, and my brother — actually, he was a rather unique boy. He didn’t make friends easily. He was very easygoing, much more so than I am, and he had his own world that he lived in. Actually we were not awfully close as boys. In fact, I would say we’re much closer now. In fact, we used to fight quite a bit as youngsters, until he grew to be considerably taller than I, in spite of the fact that he’s two years younger. Now he’s 6 foot 4 and I’m about 5-11, so we soon stopped fighting, when he got bigger than I did. But I had a great interest in sports. I played baseball and tennis. We lived right next door to a playground. In fact, at the grade school that I went to there were tennis courts and ball diamonds and track. I was never very good at either tennis or baseball, but I spent quite a bit of time especially playing tennis. My brother was never interested in sports. He spent more time, as I can remember, reading and wandering around in the woods and getting into what my father and mother considered to be general devilment. But he did not take part in the ball games with the rest of the boys in the neighborhood, and so we weren’t as close as we might otherwise have been. Then my sister was considerably younger. She was born when I was in the second or third grade. So I really lived in the same home with her only for about ten years.
Did you have any close friends who shared your interests?
Only in sports. I did not have any close friends who eventually became scientists, that I know of.
I mean in the tinkering activities, trains, that kind of thing.
No. I did that almost entirely on my own, as I recall. Oh, when I got a train all set up and had all the switches running the way I wanted them to, I would get my friends to come over and watch, but I remember I was very jealous. I would never let anybody else play with the trains because I was certain they were going to break something — you know. No, there was not very much participation, either with my brother or with other friends, in those activities.
The general economic situation of the family I guess was good? It must have been, to afford this kind of —
Yes. My father had a good job, and it was never — we were never rich in any sense, but there was enough money that he built very early a very nice home, modest, I would say, modest to the extent that my brother and I shared the same bedroom all through our life together there. When my sister was born, and eventually she grew up, my mother’s sewing room was changed over to my sister’s bedroom. There was one bathroom. That’ll give you some idea. But we always had good food and there was always money on Sundays for my dad to take me to the ball game if he wanted to. So it was a good life.
In grade school I see by your notes that you were a good student.
Yes, I was quite a good student. In fact, I went all through the first six grades with nothing but the equivalent of A’s. They used the l,2,3,4 system — I got all ones, I remember. So I went through all grade school and I think in junior high school I had a few B’s, and then in high school I remember, because I got a cup on which my name was engraved, I had the highest grade point average in the high school for four years. I remember I got one B, the first year, in general science, of all things, but I made very good grades, and in looking back on it, I see the one great fault in the whole system of education then, probably in a way now. I largely think I was able to do this because I knew really what the teachers wanted for the answers. Now, it was true that I could do arithmetic correctly and all that, but in essays and English and history and so forth, and on examinations, I rather feel that I just had a sense of what it was that the teachers wanted for the answers, rather than any real ability that would be indicated by the type of grades that I got.
At that level though, that’s pretty much how we find it.
Yes. Exactly. So I’m not saying anything new. The same thing happened when I got to the university. I finally wound up my senior year with the highest grade point average in Ohio State, but there again, I’ve always looked on it not so much as showing exceptional intelligence — it’s just that somehow or other I was able to do what the teachers wanted done on examinations and so forth. But I don’t know whether you want more about high school. I was quite active in high school. I was president of my senior class, president of the Hi-Y, played on the football team and actually won a letter my senior year, although my old friends from that time always tease me and say I was the worst end that Lima High School ever had and that’s probably true. I brought along my high school annual which might interest you. There’s the picture of the class officers.
Where’s yours? Oh, that? Class president, I see.
Class president and, I don’t know what that one’s in there for —
It might be good to get a Xerox of this, just for —
Also, teachers who influenced me in high school, quite considerably. This man here, R. W. Edmiston, “Pop,” we called him, taught physics and chemistry, and my junior and senior year, I worked essentially with him. He let me do special experiments in the lab, and the other great influence was — were two mathematics teachers, one who was quite old, Miss Blanche Andrews, who taught me college algebra my senior year, and Miss Mary Noland, who, the year I took algebra as a sophomore, was just starting. She got me interested in algebra. Of course, anyone with my interests at the time, when they first take algebra they just think it’s the most wonderful thing in the world, but Miss Noland was really quite a good teacher and Miss Andrews was the same. But the man who had the greatest influence on me was this chap Edmiston, there. Then I was business manager for this yearbook, it was called THE ANNUAL MIRROR, and I was on Quill and Scroll —
— which is the literary magazine?
Yes. Really journalism. Journalism. In fact, I was very much interested in writing, and at the end of, or during my senior year, Pop Edmiston acquainted me with the fact that the American Chemical Society at that time gave prizes for essays written throughout the country, I guess, but the competition was within a state. So I entered the state competition, and won third prize, as I remember, and got $1400. Well, in those days $1400 was a small fortune, and as a matter of fact, my father told me when I said I wanted to go to college, “Well, you know you’ve got a brother and a sister who are still home. You’re going to have to earn your own way.” My father had left school at the age of thirteen. I actually wanted to go to Oberlin because it had a great reputation as a school of science, as you will remember, but the tuition was just too much, and since I could go to Ohio State as a resident of Ohio by only paying laboratory fees or something like that, no real tuition, it was finally decided that I would go to Columbus. I hitch-hiked. One of the great things in those days was that you could hitch-hike. I did all the things that a kid working his way through college did. I waited table. That was a very interesting part of my life. I’m very grateful to the fraternity and the sorority at which I worked. I waited table for two years at a dental graduate fraternity, and they were a real rough bunch of characters but they were awfully good to me. Then I waited table my last two years for a Jewish sorority, Phi Sigma Sigma, and those girls were just wonderful. The reason I changed from the fraternity to the sorority was because the cook changed, and she really befriended me. I remember her name was Mrs. Untermeyer. She was black but she was married to a white man, which seemed at that time a very interesting thing to me. He used to come and pick her up. But there were always problems that I wouldn’t get there on time to serve dinner for the girls, and she would set the table, and she just was marvelous, so I had her as kind of mother away from home — she was a wonderful woman, just a wonderful woman. I’m sure if she had had an opportunity to do something more with her life she would have been successful. She was very intelligent, very wise and very kind. So when she changed jobs from the dental fraternity to the sorority, I went along with her. I worked in the Columbus Central Market on Saturdays. We’d go down Friday night, and I worked in one of the little markets down on the sidewalk outside the main market building, where a chap who only operated on Saturdays sold nothing but ham and cheese, and he just had a little shop practically no bigger than this office. On Friday nights we would hang all the hams from hooks on the ceiling, and bring in the great big cheeses, and all we sold was cheese by three pound cuts, and we sold the hams, or you could buy half a ham. I spent all day Saturdays I remember cutting the cheese, while he cut the ham. It was in the Depression, ‘29 to ‘33 — so even wealthy people would come to buy at the Central Market. We had an incredible amount of business. I’d work 24 hours, from about midnight Friday to midnight Saturday, and I’d get five bucks, which was something in those days. I did a little better in my last year. I got a job selling tickets at the Ohio State football games in the fall, and that actually paid a little more and was a lot easier, took much less time.
How did these activities, the waiting on tables, weekend jobs, affect you in terms of your scholastic —?
Well, when I look back on it, I don’t quite realize how I or anyone else could have done it. I even belonged to a fraternity. I joined Tau Kappa Epsilon when I was a freshman, and actually lived in the fraternity my last three years. It wasn’t very expensive, — although it was in a sense a luxury. By doing these other things I was able to do that. One real break that I got, all during college, was that during the summers I had a job back in Lima as director of the playground that I’d played on as a boy. As I think I mentioned, my father was very much interested in sports, also in Sunday School activities, mainly because he was then able to coach the boys’ teams in the Sunday School Leagues. He also served as treasurer of the Sunday School for almost 25, 30 years. Through my father’s influence, I was able to get the job as playground director, and that paid me $100 a month for four months each summer, and with that plus not having to pay for food, I was able to get by. But the answer to your question, how did one maintain a scholastic record, well, it’s just that that’s about all that I did. That’s about all I did. I did not take part in many activities at Ohio State. I just realized that I couldn’t be running for president of the class and that sort of thing. It was an entirely different business, in a very big state university. I wasn’t interested in that sort of thing any longer, so I just worked on my studies all the time, in addition to doing these jobs when I had to do them. I had a couple of girl friends, I guess, but I did much less socializing in college than I had in high school, much less, just because of the fact that it wasn’t possible to do it. In my senior year I was elected President of the Ohio State Chapter of Tau Beta Pi and attended the National Convention in Washington in the fall of 1932 where we were all introduced to the engineer president, Herbert Hoover.
Can I take you back a minute to high school? On that American Chemical Society competition, let’s talk a little bit about how you picked the subject, what it was, and also what this reflects about the kind of interest in science or science-related subjects which goes beyond electric trains.
Yes. Well, it’s rather difficult for me to remember. I would suspect that Pop Edmiston suggested to me a subject. Anyhow, what I finally chose was to write about the production of cement. I wrote an essay on the production of cement, and on the design of the kilns, and how the rock is crushed and so forth. That’s what I did and it was mainly a matter of going to the library and reading all kinds of papers and articles on the subject. So that, however, got me very much interested in ceramic engineering, and at that time Ohio State had (probably still has) a very good department of ceramic engineering. After all, there’s a large industry in Ohio in the production of bricks, and so through that I got interested in ceramic engineering, and when I went as a freshman I enrolled in ceramic engineering.
Now, the thing that saved me, if you want to put it that way, was that every week the freshmen met in a big auditorium and the various department heads in the engineering division lectured to us on a professional career in civil engineering, mechanical engineering, electrical engineering and so forth. Well, the very last one, the very last one was a lecture by Alphons Smith, whose name is well known in physics as the author of a very popular college textbook in physics, and who was at that time head of the physics department at Ohio State. He came and told the freshman engineer class about the fact that Ohio State was setting up a new option in engineering called engineering-physics, and in fact it turned out then that Leonard Schiff and a man named Howard Gundlach who is now at Oak Ridge and I were the first three graduates in engineering-physics at Ohio State. Once I heard about — well, of course, had been taking physics from, of all things, a book called — a book by Duncan and Starling. It’s a very old book, and if you contrast it with what we’ve been doing in modern times in the teaching of physics, it’s just incredible. It was an English book written for engineers, for engineering students, and I’ll never forget going all through Duncan and Starling.
But although I’m sure in terms of modern standards it would be considered a very bad textbook, nonetheless it fascinated me. And so when I finally heard that there was going to be a course in engineering-physics, why, I just decided overnight that that’s what I wanted to do. And quite frankly, I had found that in the ordinary physics course that you had to take a lot of courses in what we would now call the humanities, and for reasons that I really can’t recall too clearly, I didn’t want to do that. When I found that in engineering-physics you could take courses in electrical engineering and mechanical engineering and actually work in the electrical engineering laboratory in particular, which was a very fine one at Ohio State, that really convinced me that that’s what I wanted to do. I was still very much interested in engineering and in electrical things, and in fact I remember that my last year, in spite of all these other things I was doing, arranged to have Saturday mornings in the electronics lab. By that time, I wasn’t working on Saturdays. I was selling tickets in the afternoon during the fall.
But I remember, all through the year I arranged with Johnny Byrne, who was a young instructor in the electrical engineering department, to use the electronics lab, just to do whatever I wanted to do. And he had enough confidence in me to permit that. Another person who influenced me and who helped a great deal was a man named Mack. I think it was Charles Mack, in the chemistry department. I took quite an interest in chemistry, especially when I got to physical chemistry. I was very much attracted by physical chemistry. At that time, there was great interest in the properties of surface films, and Mack was specializing in that, had a laboratory where you could produce surface films and compress them and do all the sort of thing that you do on three dimensional objects, but do it in two dimensions with corresponding greater simplicity. So I also arranged with him that I could use his lab, I think on Thursday afternoons when I had some time off from regular courses.
This curriculum gave you an opportunity to do many things. Let me ask — either in your freshman year in college or prior to that, had you been aware of what was going on in science, either through popular publications or through occasional journals, knowing what the current research interests were in one field or another of science?
No. Not as a freshman. I didn’t become aware of the fact that physics was becoming exceedingly interesting and active until I was a junior. That must have been 1932, and I would say the first thing that happened, as we all know, was Urey’s discovery of deuterium, and then, of course, Anderson’s discovery of the positron. I think the Cockcroft-Walton experiment was done during my junior year.
April or May of ‘32.
That’s right. So — and one could just tell by the interest in the Ohio State physics department that there were really great things going in physics. My senior and junior years, I went to the seminars, and you could just tell the great excitement — but that did not happen until my last two years. The end of my sophomore year, I decided that I’d like to go to Cal Tech. Now, I think the reason was that in high school we had used Millikan’s textbook, and everybody knew about Millikan. I don’t quite remember whether I’d become discouraged or whether I was just being very ambitious, but I do remember that at the end of my sophomore year, I wrote to Cal Tech and asked them if I could enter as a transfer student and could I be free from paying tuition. Well, of course, no one was taking transfer students they didn’t know anything about and giving them tuition, so I got a very polite letter saying no, but maybe I’d be interested in applying for graduate school. But then, during my junior and senior year, hearing, especially of Carl Anderson’s discovery of the positron and the role that Cal Tech was playing in all this exciting business, I just became convinced that I wanted to go to graduate school at Cal Tech, and that was all there was to it.
So I applied to Cal Tech and was admitted, but that was right at the worst time financially, 1933, and I was offered room, board and tuition, no cash. Well, I came anyhow, but it was really rough. It was really rough then. I remember what my father told me at that time — he just couldn’t understand. He had left school at 13, and my mother had not gone much further. She left school at 15 or 16. My father just couldn’t understand why, when I had graduated from Ohio State — I had been to college — why didn’t I take a job? What was this about graduate school? He’d never heard the words graduate school in his life, you see. So he said, well, he had helped somewhat while I was in college, whenever I really got into trouble. It never amounted to much more than about $100 a year, but that made a lot of difference. Also, when I was in Lima in the summer working on the playgrounds, I lived at home, and they still bought my clothes. But when I told him I was going to go to California and go to graduate school and that I wouldn’t be making any money, he said, “Well, there’s nothing I can do any more. You’re entirely on your own now.” So I came out here. Maybe we’re getting ahead of the story, but the solution turned out in a rather unusual way. The first thing is, I went to Ernest Watson, who was really the head of the division of physics and mathematics, astronomy and electrical engineering, in those days, although Millikan was the nominal head.
I went to Ernest Watson and told him I wanted to start doing research immediately and that was one of the very first things I did. He asked me, “Do you have any interests, have you heard of anything that you’re interested in?” and I think I said the words “Nuclear physics,” because I had heard of that at Ohio State, of course, and so he sent me over here to work with Charlie Lauritsen. Charlie had quite an active group of graduate students at that time. There was Louis Ridenour, who’s now deceased, Lewis Delsasso, now deceased, Dick Crane, who’s at Michigan and Walter Read, who is at Oak Ridge, and there were others I don’t remember.
I have a list for the year ‘34. There was a John Read.
Well, he was not a graduate student, he was —
— teaching fellow —
— yes, he was an Englishman who came over to work with Charlie. As you probably know, the way the Kellogg Radiation Laboratory was funded at that time was through cancer therapy with radiation. Charlie Lauritsen had built a million volt AC X-ray tube — treatment with high energy X-rays was quite experimental at the time, and Dr. Seeley Mudd, who subsequently became quite a benefactor of Cal Tech (he had inherited quite a bit of money from the Mudd family), was head of the medical unit here that was doing experimental work in cancer therapy. I got a graduate research assistantship as one of the operators of the X-ray tube during the morning hours. Then any maintenance on it, and there was plenty, had to be done by all of us graduate students, but with Charlie always helping, of course. When things were working well, in the afternoons, Charlie had the tube available for research, and John Read (a post-doctoral fellow from England) in particular, was doing some very interesting work. Charlie had developed a crystal spectrometer, so that even though he was using an AC tube, he could isolate a particular wavelength of X-rays, and they were testing the cross-section for absorption due to the Compton effect. I don’t know whether Charlie ever told you this, but Read and Charlie showed that the Klein-Nishina formula was the correct one rather than the Dirac-Gordon — (Read & Lauritsen, Phys. Rev. 45, 433, 1934).
— this was done while you were here?
Yes. It was pretty well finished, I think, but it was I think one of the most significant things that Lauritsen did, and I recall, because you mentioned Johnny Read who went back to England and, I think, has continued in radiation therapy in England, as far as I know. I considered that piece of work, showing that the Klein-Nishina formula was the correct one, or fitted the data better, was really one of the most significant things that Charlie did. Then about that time, about the time I came, the Cockcroft-Walton experiments were well known, and Charlie and Dick Crane had changed a second experimental X-ray tube that Charlie had — not in this building, not in the Kellogg Building, but in the high voltage laboratory which is now the Sloan Lab — over to the acceleration of positive ions. They were accelerating hydrogen and helium and deuterium, and actually starting to do nuclear physics at the time I came. I remember, Charlie wasn’t here when I actually showed up at Kellogg. He was in Denmark, and Dick Crane was more or less in charge. Dick and Charlie had gotten a sample of deuterium from Gilbert Lewis at Berkeley, but Lewis had told them that he was not going to be in the business of supplying all the nuclear physicists in the country with deuterium, and this was it.
He did very well.
He did very well. So my first assignment was to set up electrolytic cells to separate deuterium. I remember we had to get a great big three volt DC generator, it could supply something like 500 amps, and I built these great big cells. We started out just electrolyzing water and collecting the residue, which was enriched in deuterium, and that was my first assignment. That worked fine. Within six months we had — down on the floor of the high voltage lab — quite a little operation which produced all the deuterium that Charlie and Dick needed. Then —
Was that an elaborate procedure? Was that something that could have been done at any other laboratory?
Oh, it wasn’t very elaborate at all. It’s just a matter of putting a lot of current through water, and you have to have two electrodes. The hydrogen goes to one, the oxygen goes to the other, and the light hydrogen is electrolyzed somewhat faster than the heavy water.
The reason I ask is, it seems it was such a rare commodity in the period, and if it was this simple, I’m wondering why other people didn’t start making their own right away — or maybe in the early stage it was difficult? I know Rutherford for example, was desperately in need of that before he started producing it, and many other places too.
Well, quite frankly, I think this was typical of Charlie Lauritsen and of Crane. They realized that they had a need for deuterium and they just said, well, we’re going to make our own, and we’ll put this new boy to work and he can learn the business at the same time. That was quite typical of Charlie. He never let anything that looked difficult stop him. He was a great one for doing things on his own, and doing it as cheaply and as simply as possible. I’m sure you’ve heard this story many times, but Charlie — I can’t remember Charlie ever buying very much new material. He always scrounged around in various shops for pieces of brass or steel, and would make the most marvelous things. He was a very, very skilled operator at the lathe and the drill press, and I learned all of that from him, because I had not done that. Well, I had had some training at Ohio State in the use of the lathe, that’s true, but I learned a million and one tricks from Charlie that I would never have learned otherwise. So there was that attitude — well, here’s a problem, let’s do what’s necessary. I remember Dick Crane went down to the junkyard and found this old generator and they bought it for $100. It was a marvelous thing. Three volts, 500 amps. It was really something.
The switchover of the existing tube had occurred before you came?
Yes, before I came, and they had done quite a bit of work with helium first, you see, with alpha particles, because they thought — I don’t know quite why, they decided to use alpha particles, but they did. They used helium. They bombarded beryllium. They produced neutrons from the 9Be (α, n) reaction, and then they had started using hydrogen. Then it became very exciting to use deuterium because you could make all types of radioactivities, — the Curie-Joliots had shown that you could make artificial radioactivity by alpha-bombardment, but deuterium always produced intensities much larger than you could produce with ordinary hydrogen or helium. So that was the main reason for going to deuterium. Well, about that time I asked Charlie for some kind of a thesis assignment, and he and Dick were producing radioactivity and were measuring the activity with Charlie’s electroscopes. But in one experiment they had taken some nitrogen-13 activity that they had produced by bombarding carbon-l2 with protons, over to Carl Anderson and Seth Neddermeyer who had put the bombarded target into their cloud chamber, within the ten minute lifetime of nitrogen-13, and actually seen the positron tracks. Carl and Seth had a magnetic field so it was possible to measure their energy.
So a spectrum had been obtained, using Anderson and Neddermeyer’s cloud chamber. So Charlie gave me the job of building a cloud chamber. Actually me and Louis Delsasso. We built a cloud chamber that was somewhat of ingenious design for the time. It had a big sylphon bellows, as the working mechanism. But after we got that built, then in the top glass through which the tracks were photographed we built a well, and the end of the accelerator actually projected into this well, so the target that was being bombarded was right in the cloud chamber. Then there was just a very thin-walled diaphragm between the target and the cloud chamber, and the tracks, the electrons and positrons actually then came into the cloud chamber, and we had Helmholtz coils that produced a uniform magnetic field. And so my thesis was on radioactivity in the light elements, and oh, we either discovered or co-discovered or found very shortly after other people did, all of the radioactive mirror nuclei, carbon-11, nitrogen-13, oxygen-15, fluorine-17. Whether we did it first or whether it was done first at Berkeley doesn’t matter. Then we did a lot of electron activities, lithium-8, boron-12 and so forth.
The thing that came out of this was the similarity between proton-proton forces.
That’s right. That’s right. We found that in these mirror nuclei transitions, that the energy of the positrons increased with the charge of the parent nucleus. See, we had a series, carbon-11, nitrogen-13, oxygen-15 and fluorine-17, and the energies, the end point energies ran from something like one million volts up to 1.8, and it became very clear that the transition between the parent nucleus and the daughter nucleus, these mirror nuclei, that the whole difference was essentially just the coulomb energy, so that one had to say, to fairly high precision, that the nuclear energies were independent of the proton and the neutron. So this was essentially one of the first discoveries of charge independence of nuclear forces. I remember that we, and this brings in a whole new element of my graduate training, called this progression in energy, with charge of the parent nucleus, to the attention of Robert Oppenheimer. I think it was pretty clearly Robert who first realized the implication of this. I remember, he discussed it with Charlie and me, and I immediately went off and started making models of nuclei with uniform charge density and radii, and getting the expressions for the coulomb energy. That was done eventually by other people, but when I published my thesis results, remember that Robert suggested that, “Well, you’d better do this in a very general way now, don’t introduce the concept of a nuclear radius, we don’t know very much about that.” So we actually wrote it in terms of a mean of the reciprocal of the distance between protons and in fact, looking back on it, I remember now, that was a very elegant way of expressing the coulomb difference between the parent nucleus and the daughter nucleus. We also had to take into account the difference in mass between the neutron and proton, but that’s an old story. But that brings up the fact that a great influence on my life as a graduate student was Robert Oppenheimer. As you probably know, he had a joint appointment at Berkeley and CalTech. He came to CalTech in the spring, what corresponds to our spring quarter —
— about April some time?
Yes. Berkeley ended early, so he was able to come down here and spend the third quarter here, spring quarter, and of course, he always brought his students with him, people like Willis Lamb and Bob Serber and Wendell Furry. Leonard Schiff was not his student but he was a research fellow.
Got his PhD at MIT, Schiff.
Yes, and then went to Robert as a post-doc. In fact, that brings up one point that I perhaps should mention before I forget about it. While I was at Ohio State — because he also enrolled in engineering physics, I got to know Leonard Schiff very well, and we became very close friends, and of course remained so until his death. I did some studying with Leonard once in a while. He lived in Columbus. His family lived in Columbus, and I visited his home many times after I got to know him, and did some studying with Leonard. Of course, he was quite young, much younger than most of us. He was kind of a child prodigy. So he made my work at Ohio State much more interesting because I had someone to talk to who was very much interested in the things I was interested in. He didn’t want to take humanities either — although Leonard did not work in the laboratories as much as I did, and was more interested in theory, and became a theoretical physicist, so — but it was a wonderful thing. And then the other chap, Howard Gundlach, he was more interested in the engineering side and went into engineering at Oak Ridge. Before I forget about it, going back to high school things, there’s a very amusing thing in the annual here that shows that my friends had a premonition at least that I was interested in science. “Bill Fowler commits suicide after failing by .000000019 inches to measure the distance between Tyngyanakhskaya, Siberia, and the planet Venus.” I just happened to see this about a year ago. I had never been aware that it was there. Here’s a remark about my brother, “Art Fowler attains seven feet.” He was growing.
The title was “Ten Years from Now,” where you’ll be, what you’ll be doing. Does that mean you were known for your interest and apparently also for your own personal high standards?
Yes. It’s really funny.
Let me ask, on this college yearbook, I mean college period — you talked about the relationship with Schiff, that you were able to work with him. His main interest was theory. Did you, either through conversations with him or in any courses or supplemental reading, get some good doses of theory? If so, did it include stuff related to the new developments in quantum mechanics which had just taken place in the mid to late twenties?
I did not develop any great interest in theory. I took a few theoretical courses from Alfred Lande who gave the theoretical courses at Ohio State that I took at that time. His lectures were rather formal, and as I recall, I didn’t really understand very much of his approach to the problem. I got the most in that regard out of a course on X-rays by Dr. M. L. Pool at Ohio State. He became quite a well known nuclear physicist. Anyhow, he gave some lectures on Bohr orbit theory, and that, of course, was just fascinating. But I did not develop any great interest in theory, and was convinced when I came to CalTech that I wanted to be an experimental physicist, and then of course, here, I took courses in quantum mechanics under Houston, and under Epstein. It’s rather surprising, I didn’t get any very deep interest in quantum mechanics, other than what it meant in terms of what we were doing in the lab at that time. I remember trying to solve Schrodinger’s equations for the beryllium-8 nucleus, to try to understand the gamma rays that we were finding at that time from the bombardment of lithium-7 with protons.
But I never developed a really deep interest in what you could call the philosophical aspects of quantum mechanics, and never have. Never have. In fact, I would say that in a way, I find it nowadays very difficult to follow many papers that use modern quantum theory. One other thing that I think is worth noting is that neither in college at Ohio State nor at CalTech as a graduate student did I have any courses in astronomy. So all of the astronomy and astrophysics that I’ve learned has been self-taught. On the other hand, here at Cal- Tech, in addition to Oppenheimer, the other major influence as a teacher was Richard Tolman, and of course from Tolman I took relativity, both special and general, and his course was just a delight. And since he taught some cosmology in the general relativity, I got it at that time, a little interest in astronomy. And of course, there was the fact that one of Charlie Lauritsen’s closest friends was Sinclair Smith of the observatory, and there were all the people from Hubble on down at the observatory, so it was pretty hard not to be aware of astronomy. But it really wasn’t, quite honestly, until Hans Bethe came out with his paper on the CN cycle that I developed any real interest in astronomy. That was a turning point. After I got my Ph.D. here in 1936, I became a research fellow for three years, and during — this is the three years before the war, ‘36 to ‘39 — during those years, among other things Charlie and I were studying excitation curves, cross-sections versus energy, for the carbon and nitrogen isotopes bombarded with protons. Then in 1939, Bethe pointed out that these reactions formed the carbon- nitrogen cycle and that they possibly were the mechanism of hydrogen to helium conversion in the sun. Now, subsequent developments have been that we think the carbon-nitrogen cycle works in stars somewhat hotter than the sun, but that’s what first spurred my interest in astronomy, when we found out that something we were doing was relevant to what’s going on in stars.
But you didn’t have much opportunity to pursue it.
No. Then the war came. Also, we didn’t have much opportunity to pursue it because by that time Charlie decided that we just had to give up the use of AC acceleration, and so we decided to build an electrostatic generator, following pretty closely the Ray Herb pressure-type rather than Van de Graaff’s original design. It was a vertical rather than horizontal machine, however. We had previously built a vertical, open-air Van de Graaff. So Tommy Lauritsen and I — started in 1937 and throughout ‘38 and ‘39 — were building a pressure electrostatic generator, which by the way is still operating. I think it’s the oldest operating Van de Graaff in the country now — it’s used by Ward Whaling in beam foil spectroscopy. So we didn’t have much chance to follow it all up before the war, and then the war came, and this lab was turned over to work in rocket ordnance. But then after the war, a decision had to be made, primarily by Charlie although I can remember discussing it a great deal with him, as to whether we would stay in low energy light element nuclear physics, or whether we would build a cyclotron and go into high energy physics.
I think primarily because we saw the possibility in low energy nuclear physics of studying reactions which were relevant to astrophysics and astronomy, Charlie decided to stay in the field. Then we had worked very closely with Ike Bowen during the war. He had been head of the photographic measurements section of our group in the rocket ordnance development. And Ike had been also a very influential teacher as far as I was concerned, because he gave an extremely good course in optics. And so when Ike became head of Mt. Wilson after the war, he organized some seminars in his home where he invited the staff members from Mt. Wilson and the gang from Charlie’s lab on Fridays to discuss things and hear presentations by various people. I’ve still got a notebook with all the notes I took at that time. We did that for guess almost a year, I can’t remember really how long it lasted, but that was my first introduction to stellar structure, stellar evolution and matters of that kind. And I got hooked at that time and have been primarily interested in that aspect of science since then.
This gets down the overall framework. I’d like to go back and pick up details. Starting with your arrival here, in the fall of ‘33. You said Ernest Watson — after you requested from him immediate involvement in research — sent you over to Charlie Lauritsen.
You came without any fellowship or assistantship at the time, and yet as soon as you went over there you became an assistant?
No, I already had I guess what was called a graduate fellowship, room, board and tuition, but then in order to — everybody who had such a fellowship had to work some place, and so at the same time that I went to Watson and said I wanted to do research, he knew that he had to find some laboratory in which I could earn my room and board.
I thought that was in addition?
No. No, there was no additional money.
Because in 1934 in the bulletin they list you and Dick Crane and Nichols and Jordan as “High Potential Radiation Research Fund” — in that category of teaching fellows and assistants. In that case, what you’re saying is that the High Potential Radiation Research Fund paid for your tuition and board, but there’s no stipend.
No, as I remember, I began to get a stipend maybe in ‘35, or — I remember, the main thing was that Charlie arranged so that I could move out of the old dorm, and I moved into the Atheneum which was much more comfortable. I’m certain I did not get any cash until maybe my last year as a graduate student. However, when I became a post-doc, I did receive cash; I think I started out at $1500 a year, something like that. But I think what it all means is that the fund paid for my room, board and tuition as a graduate student but in exchange for that I had to operate the X-ray tube and help maintain it, and there was a great deal of maintenance that was always going on. It was a real jerry-built device.
This shows that you’re listed on the High Potential Fund through your PhD, anyway. I just wanted to clarify. Then you were accepted and needed as part of that research group. What was the nature of the collaboration? Was it quite clear, the division of labor? You were junior, Crane was a year ahead of you —
— yes. In the beginning, I took instruction from Dick Crane as to what to do, and even after Charlie came back, since I had been working with Dick on the separation of the deuterium, I continued to work with Dick, oh, I can’t remember whether it was for a full year. But in addition to the deuterium problem, I just hung around. I was very much interested in what Charlie and Dick were doing and anything I could do to help, in the measurements or recording or in just running the accelerator for them while they were making the measurements, I was just fascinated by what they were doing. And they were glad to have someone to keep an eye on the control board, or if necessary, to take down some numbers, you know. But it was clearly that Dick and Charlie were doing the experiments and I was just the new boy who was trying to learn.
You’re associated with him on ten papers.
Well, that came later. That’s after I built the cloud chamber, which was mine and Delsasso’s, and there was a long series of papers, Crane, Delsasso, Fowler and Lauritsen. Delsasso was very clever with his hands. During the war he had a very responsible position in army ordnance, at the Aberdeen Proving Grounds and eventually at White Sands. Del was extremely good in constructing things. But he realized that I, if I was going to be an experimental physicist, needed more training in shop work, and so he actually helped me a great deal. But in constructing the cloud chamber, I did most of the actual machining. Although I said that I learned a lot of tricks from Charlie Lauritsen, I also learned a lot of tricks from Delsasso who really was a wizard at the lathe when he used it. So I remember that I did most of the machining, and Del taught me how to solder, which I had never done before, so there was the period then when I was building the cloud chamber. Then I kind of looked on it as mine, and the actual operations during the period when all those papers was published, I was always there when the cloud chamber was operating, and Del developed the photographic system.
We used a little 35 mm French camera and the mirror system for getting two pictures of the tracks, stereoscopic pictures. Most of the operation was a very slow business. We would run for periods of 12 hours at a time, because you couldn’t bombard the targets too intensively because you’d just fill the cloud chamber with tracks. You had to adjust the bombardment so that you’d get just a few good clear tracks every time. Then there were hours spent in measuring the curvature of the tracks; from the curvature and the magnetic field which we had measured separately, we could get the momentum and thus the energy. Now, in the beginning Dick Crane measured quite a few of the tracks, but then I gradually took that over, I remember, and finally when we began to get into what eventually became my thesis, I was doing all of the measuring of the tracks. Those papers, Crane, Delsasso, Fowler and Lauritsen, were primarily, you’ll note, on gamma rays. It gradually developed that some of the early work we had done using Compton electrons gave quite erroneous results, due to the fact that the Compton electrons had to be produced in a thin piece of lead that served to convert the gamma rays that were produced in the target, into the Compton electrons, whose energy could then be measured.
Well, of course the Compton effect had, first of all, the disadvantage that not all of the energy of the gamma ray was given to the electron. Part goes into the scattered quantum. And the second thing is that the electron is scattered in the foil, and also scattered in the gas of the chamber, so that the measurement of the curvature isn’t all that precise, due to the scattering. What finally came out of it is that we began to notice that pairs were created in the foil, electron-positron pairs, and, of course, there you just measure the energy of the pairs and add a million volts, and that’s the energy of the quantum that produced the pair. And that gradually became the technique that we used during that series of papers. That work was mainly on gamma rays produced in nuclear reactions, but when it finally came time for me to do a problem of my own, I concentrated on the radioactivity which was being produced.
What contact did you have with other people outside of the group, either CalTech or other? For example, you started to build a cloud chamber after using the Anderson-Neddermeyer chamber. Did you learn anything about cloud chamber technique from them, or from experts like Blackett and Occhialini who were doing things in England?
No, not from people in England. I remember that Delsasso and I and Charlie discussed cloud chambers with Carl Anderson. I must also point out that Walter Jordan had either built or borrowed a cloud chamber, I can’t quite remember, and he had done a thesis using a cloud chamber. So there had been some cloud chamber experience in the laboratory, and, of course, Charlie, as was customary with him, had his own ideas about how to do things, and I’m pretty certain that it was he who suggested that we should use one of these big sylphon bellows; we used the compressed air supply to expand the bellows and compress the chamber and then open the exhaust valve for the bellows, so that you got the fast expansion.
We went ahead and built it, roughly according to Charlie’s ideas. I remember that I made a sketch. I made a sketch and took it in one day to Charlie and said, “Do you think this will work?” and he made some comments on it, and Delsasso and I argued a great deal about how to put this together, and finally that’s the way we made it. But I think I can honestly say that we went about the thing in the way that Charlie wanted us to. I do remember reading Wilson’s paper and being amused by how clumsy his way of actuating the cloud chamber was, you know — they had a bung that they pulled, I remember. And it was clearly the case that we needed an automatic cloud chamber that we could actuate every 15 or 30 seconds, so none of the things that I read in the literature about what had been done in the Cavendish, at least by Wilson, were very helpful, although the general principles of cloud chamber operation were all made clear there. But we went ahead to try out this idea of using the sylphon, and glass rings, on the side, so we could shine light in, a glass top, so that we could take pictures of the tracks through it, and Helmholtz coils around it. It was quite definitely designed to fit the whole new series of experiments that Charlie could do with accelerators.
In the gamma ray experiments, the target chamber was outside of the magnetic field, so the gamma rays just went in between the Helmholtz coils, and through the glass walls, and into the lead foil that was about a quarter way or a third of the way across the chamber, perpendicular to the direction of the gamma rays. So that two-thirds at least was available for viewing the Compton electrons and the pairs. One other great advantage was that unless the photography was very good, sometimes we couldn’t tell whether a Compton electron had started in the thick glass wall, and then gone through the lead, and then — the idea was, if the photography was good enough, we would see a track that originated in the walls, because you’d see it on the closer side of the lead foil. Our photography wasn’t always all that good, and I’m sure sometimes we counted tracks as starting in the lead foil when really they had started way back in the glass walls or the wall of the target chamber, and thus had an energy, by that time two energy losses, which had very little connection with the primary energy of the gamma ray. It wasn’t until we began using pairs that it all became much more straightforward, and I think we got much more reliable results. Assignment of the origin of a pair to the lead foil converter was unambiguous.
You mentioned the Cavendish in terms of cloud chamber technique. On that, Blackett and Occhialini had developed good techniques.
But it seems that at that time, about ‘33, ‘34, there was a dispute regarding Ernest Lawrence’s idea of the disintegration of the diplon, as he called it. The results in this laboratory played a role in helping to mediate between his view of it and the view of people like Cockcroft at the Cavendish. Do you recall anything about that? Where Merle Tuve finally had to do a series of experiments to put the issue in perspective, and there was rather a bitter debate on, I think, at the time of the 1933 APS meeting which was probably out here.
Yes, well, you’ll find that all described in the article that I wrote for the memorial issue for Charlie Lauritsen. The main controversy was whether in the bombardment of carbon with protons, one produced nitrogen-l3 radioactivity. You see, when you bombard carbon-12 with deuterium, you produce nitrogen—13 and a neutron, and that (d, n) reaction has an enormous cross-section, and of course, at that time any hydrogen beam was contaminated with the natural amount of deuterium in nature, namely one part in 7000. So I guess it was primarily Ernie Lawrence who questioned Crane and Lauritsen’s claim that they got a capture reaction in carbon — the carbon-l2 (p, γ) reaction to produce nitrogen-13. Lawrence suggested that really wasn’t right, and what was happening was just that there was a deuterium contamination in their beam and that’s what they were seeing.
Now, the way that Charlie and Dick satisfied themselves that this wasn’t the case was by running excitation curves; in spite of the fact that they had an AC tube they were able to plot the rise in cross-section, or rise in production of nitrogen-13, versus the maximum energy, on the tube, and they showed that the excitation curve for the activity that they produced with protons, as a function of energy, was of an entirely different nature than that produced by deuterium. In fact, they actually realized that their curves for the production of gamma rays and any radioactivity, when they bombarded with protons, implied resonance phenomena. Now, that had in particular been done on lithium. The 7Li(p, γ) reaction showed resonance at 440 kilovolts, and Charlie and Dick had shown that even with an AC tube, you got quite a different excitation curve for that, for the lithium-7(p, γ) gamma than they did for example from lithium-7 (d, n). So there was this controversy. I wouldn’t say that it was all that bitter.
There was considerable reluctance, even on Oppenheimer’s part, to accept radiative capture as a mechanism for the production of gamma rays. He just couldn’t believe that gamma ray emission could compete with the scattering, and it wasn’t until the Bohr concept came along that the proton essentially, when it was captured, produced a long-lived resonant state which had time to emit gamma rays, that the process was understood. So Merle Tuve came into it because by that time Merle Tuve and Larry Hafstad had a Van de Graaff working, and when Charlie pointed out to Merle that the excitation curves for the proton irradiation were quite different than the excitation curves for the deuteron irradiation, Merle said, “Well, I can do that much better than you can because I’ve got discrete energies, and I’ll try it.” Merle had also been, I think, convinced that Charlie and Dick were measuring something that was produced by the deuterium contamination in their proton beam, and Merle did not have any really very good detecting apparatus at that time. He and Hafstad had mainly worked on the construction of their Van de Graaff, so Charlie lent them one of his electroscopes. I remember that, and — well, you can find it all in the literature. They took it back to Washington and they found a very sharp resonance in the carbon-12 (p, ) reaction, and showed that it differed entirely from the smooth curve that you got with the carbon-12 (d, n).
Do you remember discussions on this back and forth, were you involved in any?
Oh yes. There was a period when this question of — down here, the main discussion was, we have to believe that something is going on here that is not deuterium contamination. Charlie was just convinced of that and he Robert Oppenheimer. About that time — and I frankly can’t remember just how it went — Fermi discovered resonance in neutron capture, slow neutron capture —
— late ‘34, beginning ‘35.
Yes. Well, I have always felt that resonance in radiative capture was certainly known here before we heard about Fermi’s results. Now, you see, there had been some evidence of resonance effects in alpha particle capture; if you look at Rutherford, Chadwick and Ellis, you’ll find a little section devoted to some work that had been done, not at the Cavendish, but I think by Paneth — where there was clear indication that radiation produced by alpha bombardment showed what they called resonance. So although I think the credit is mainly given to Fermi, and one wouldn’t want to take any credit away from him, nonetheless I think independently Lauritsen and Crane discovered resonance effects, and they had a very difficult time convincing Oppenheimer, just because he felt that it was theoretically impossible. And then of course Breit and Wigner came out with the Breit-Wigner formula based on Bohr’s general ideas, and then it was clear as a bell that the cross-section could be very large, even though the width of the resonance was quite narrow. So essentially what had been found in the lithium excitation curve and in the carbon excitation curve was all borne out by subsequent events. Now, of course, that controversy was well in our minds when Bethe came out with the carbon-nitrogen cycle, but that has nothing to do with deuterium, and by that time Charlie and I — Dick had gone, as I recall, to Michigan — were producing gamma rays and radioactivity by proton bombardment, and it always showed these resonance effects, you see. Then when we got our own Van de Graaff and could do very careful excitation curves, we had started on measuring the cross-sections at resonance, and the width of the resonances, and all that sort of thing. So when Bethe came out with the carbon-nitrogen cycle, we kind of felt a proprietary interest in this group of reactions because we had been working on them, and Charlie had had such a hard time convincing people that (a) you produced radiation with protons, and (b) getting the idea of resonance radiative capture accepted. So that all tied very closely together.
Of course, conversations with Oppenheimer keep coming in here. Did they occur just by him dropping into Charlie Lauritsen’s office and chatting? I understand their offices were next door during that period. Or was it through some more formal colloquium, seminar, even through some of the courses he gave?
Both. Both. A lot was done in Charlie’s office, although when we were running, as we called it then and still do, Robert would come in the lab, and a lot of the discussions were held right in the laboratory while we were making the measurements, and whenever Robert would show up we would just kind of put things on the back burner, and enter into any discussion he wanted to talk about. There was another case. It’s not nearly as well known. We found that when we bombarded fluorine with protons to produce oxygen, alpha particles and gamma rays — that we produced pairs that seemed to come directly from the target and weren’t just produced as secondaries in foils that were in the path of the gamma rays. So we began to realize that there was some kind of pair formation in the bombardment of fluorine with protons that didn’t go through the intermediate stage of the gamma rays being produced and then the pairs being produced as secondaries. And we started calling those “nuclear pairs” around the lab, and it wasn’t until Oppenheimer and Schwinger finally realized that what was happening was that the first excited state in oxygen, up around 6 million volts, has spin zero and even parity, so it cannot couple to the ground state which is also spin zero and even parity, by a single electromagnetic transition. If it had been under a million volts, the way this state would have decayed would have been by double gamma ray emission. But being over a million volts it was able to emit a pair, and Oppenheimer-Schwinger worked out the probability of that happening, and it was much greater than double gamma ray emission.
So we found that spin zero to spin zero transitions resulted in direct pair formation. But that was the thing. We had this experimental evidence, and in the beginning we just couldn’t understand it at all. Robert always took the attitude, when something like this happened, that we were doing something wrong and didn’t understand what we were doing, and that was a very good point of view because there were many times when we did do things that were wrong. But in this case, when he finally became convinced — we could show that the excitation curves for these pairs were different from the excitation curves for the pairs produced as secondary gamma rays. And we could see in the cloud chamber series, that these pairs started right in the target that was by that time protruding into the cloud chamber, and other pairs would start in a little foil that we had about an inch from the target. And then we developed techniques using Charlie’s electroscopes and absorbers and converters, as we called them, to differentiate much more easily, much more conveniently than we could with the cloud chamber. But once Robert convinced himself that there was something there, then he started thinking about it, and I don’t know, he turned up one day and said he understood it and that he and Schwinger had worked it out, and they wrote a little note to the PHYSICAL REVIEW, I remember, pointing out that you could have such transitions and that our excitation curves could be understood in that framework. But then also in addition, to answer your question, Robert gave courses, gave seminars, and he came to the Kellogg seminars during the spring term, and pretty much dominated them.
Once Robert was down here, and his students, Lauritsen’s seminars, which were held every Friday night, were pretty much dominated by the theoretical group, which was a very good thing for us working in the lab, because although Paul Epstein was a very fine theorist, he had very little interest in nuclear physics, and Houston was still running his own show in atomic physics, and Smyth was primarily interested in classical electromagnetism. So we depended entirely on Robert for theoretical instruction in modern nuclear physics. He always gave a course when he came down in the spring term. The course was quite informal. If there was something we were doing in the lab that he was interested in, he would discuss it. Well, it was a little more formal than that, but he wasn’t afraid, he never hesitated, maybe one of the lectures out of the three each week to discuss what was going on in Kellogg and a great deal of the time what was going on up at Berkeley. We learned much more about the developments at Berkeley through Oppenheimer than we did by direct contact with Lawrence and the group in his lab –- although I did get to know Ed McMillan and Luis Alvarez and Bob Wilson pretty well as a graduate student and then as a post-doc. By the time I became a post-doc, there was quite a bit of dialogue between myself at least and McMillan and Alvarez and Bob Wilson. And I went up to Berkeley quite frequently. Also through letters, mostly with Kranz Kurie who was doing quite similar work with cloud chambers. But it seems to me there were meetings all the time that we were going to, and there was quite a bit of contact. There was quite a bit of contact, and eventually I knew enough about the business myself that I was able to– I used to have quite a bit of dialogue with them quite independent of Lauritsen.
That would have been the closest laboratory to you and to the others, the group. Now, of the other institutions in the field, you think of Cambridge, and Tuve’s laboratory, Berkeley, here, and other groups that were getting started in Michigan, Rochester, MIT and so forth. But of all those groups apparently Berkeley was the one closest.
It was the closest one.
I don’t mean just physically, but I mean the ones you really got to know.
Yes, and the contact with the others was I would say almost entirely through the literature. Now, it’s true that Dick and Charlie went to a meeting in London, ‘34, and there they got a lot of direct contact with Cockcroft and Walton and I’m pretty sure they went up to Cambridge, and so there was a lot of transfer of information I’m sure at that time, both ways. But while I was a graduate student and a post-doc, there was very little — well, there was quite a bit of contact with Merle Tuve’s lab. Well, I did take some part in that, come to think of it, although that was mainly through Charlie. I do remember, there’s one thing that Charlie and I did where we found two groups of protons from bombarding lithium with deuterium, and we thought they both came from –- gosh, I’ve probably got it all wrong now. We thought that both of these groups came from the bombardment of lithium-7, and by that time, Tuve and Hafstad had isotopic targets, and they showed, if I remember it straight now, that one group was from lithium-7 plus deuterium, the other was from lithium-6, and I remember getting into that argument with Hafstad and Tuve at the Washington meeting. The main contact was through Charlie. Charlie and Merle were very sympatico, much more so I’d say than Charlie and Ernie Lawrence. So I often had the feeling that Charlie and Merle kind of ganged together because they realized that Ernie was doing such remarkable things, although they disagreed with a lot of the things that were coming out of the lab.
There was one aspect of this controversy involving Lawrence and Tuve. Ernie had the idea that the deuteron was breaking up, you know, and that that’s in some way the way in which the radioactivity was being produced. Actually, in some very early experiments he did, he felt that — he found that he was producing the same radioactivity no matter what target he bombarded with deuterium. Well, this turned out to be carbon contamination. But he thought that it was something characteristic of the deuteron, and so this very same reaction, the carbon 12 (d, n) that made nitrogen 13, he kind of got caught on it, you see. That’s why he also thought that Charlie was being fooled. The whole thing was all tied in together and it finally all got straightened out. Ernie was the first one I can remember to say that, well, he had been wrong about deuterium breaking up, but what he was really saying was what came to be called the Oppenheim-Phillips reaction you know, and there again, Robert and Melba Phillips in that case worried over what Ernie’s people were finding, and they finally came up with an explanation. In a way, Ernie wasn’t so far wrong, that you didn’t have to get the charge of the deuteron all the way into the target. You could transfer the neutron, and then the proton flew off. That was called the Oppenheimer-Phillips effect, in those days, just because of the fact that the proton in the deuteron didn’t have to penetrate so far into the Coulomb barrier meant that the cross sections were correspondingly higher, at a given low energy. So the deuteron was breaking up, but both the proton and neutron weren’t flying off. The neutron was being captured, you see. Direct capture it is now called.
I found three way correspondence, Tuve, Cockcroft and Lawrence on this issue.
Yes. Well, don’t trust my recollection too much, because the interest here was primarily in whether you could produce these radioactivities with protons, and that was kind of incidental to the controversy concerning just how were the deuterium mechanisms going, you see.
Two questions about Oppenheimer before I get back to the research program here. You mentioned that on those Friday evening seminars he’d more or less take over. Was the subject necessarily nuclear physics each time? It seems to me Oppenheimer’s interests were in what we would now call quantum electrodynamics, cosmic ray phenomena.
Oh yes, Robert would discuss anything that he was interested in at the time, but it was related some way or other to nuclear physics — the cosmic rays, the mesons, although that may have come somewhat later. But he would tell us all about those things. And that was part of his great charm, of course. Robert knew about everything that was going on, whereas the rest of us had our noses pretty close to the grindstone in keeping the machinery going and doing our own experiments, but here was this chap who knew all about everything. Of course, he was at that time — it was about that time that he was doing his work in general relativity, on neutron stars. Of course, I don’t know whether it’s realized, at the same time that Oppenheimer and George Volkoff were doing their work on neutron stars, and this must have been around ‘33 or ‘34, I’m pretty sure, Tolman was very much interested, and there are several papers by Tolman which were much more model-dependent.
Tolman had a couple of papers on neutron stars that were much more model-dependent than the way Oppenheimer and Volkoff finally did it. But I can remember, there were lots of discussions involving Lauritsen and Tolman and Oppenheimer. The three of them would come in the lab and be arguing, and the rest of us would just stop what we were doing and listen to what the great men were saying. Whenever Tolman was around, the conversation almost inevitably drifted towards cosmology, and general relativity, and then when Robert wasn’t here, Tolman dropped around the lab at least once a week when I was a graduate student and research fellow. He never took quite as much interest in nuclear — well, he didn’t take anything like the interest in nuclear physics that Robert did, and he never did anything professionally, except he was very much interested in having chemistry — he was very much interested in the equilibrium between nuclei. In fact, he did some of the very early work — if you heat up matter to a given temperature, what’s the equilibrium concentration of the nuclear matter, not just the chemical equilibrium that he had studied a great deal. So in that sense he was interested in nuclear physics, but he never got as much interested in details of what we were bombarding and what we were observing. Although he always listened and was amused by some of the things that we were finding.
But Richard was always discussing cosmology and general relativity, and then of course later on, this was considerably later, Bob Robertson played that same role, when he finally came back from Princeton. He had been a close friend of Charlie’s and he became quite a close friend of mine, and Bob used to pop around the lab every week. Again, the discussions always drifted to what he was doing in cosmology. So it was through Tolman and then eventually Robertson and their close friendships with Charlie that I had the contact with that whole part of physics that I otherwise wouldn’t have had, and it didn’t come about because Mt. Wilson was here, although Hubble used to come to the Athenaeum quite frequently, and I remember having breakfast with Hubble. I remember that was the first time I learned about his red shift observations directly from the great man himself. Hubble told me that “his constant” had the value 550 Km per sec per megaparsec which is about ten times what it is now. Those were the days. Those were the days.
Another question on Oppenheimer — did you take any of his courses?
Yes, oh yes.
Nuclear physics. He gave a course in nuclear physics, Robert did, yes, I remember he derived the Breit-Wigner formula for us.
You must have been a post-doc by the time you took it.
I probably was, yes.
Was he effective as a lecturer? Talking with Carl Anderson he said how difficult it was... the early lectures, almost everyone dropped out of the course. He was about the only one who remained in it.
Well, that may have been the case at one time. I would guess Robert was already teaching when I came here as a graduate student, and it’s true that I didn’t have as much contact with Robert in the first year, and I didn’t, I guess I didn’t take a formal course from him. It probably was after I got my degree that I began to go to his lectures. But by that time, there was certainly great interest in what he was saying, and as I remember, certainly the notes that he gave us, I’ve still got them some place, were quite good. I thought the lectures were very good. I think maybe Robert had learned a great deal. It’s true, he always talked a little bit above one’s head, but that’s a very good thing. He made you really try to think through what he was saying. He never went through a derivation or anything completely, in the way that Epstein had done for us, you see, or Smyth. He always left a few steps where you had to do it yourself. But I must say that I felt that Oppenheimer’s lectures were extremely good. Then I always had this opportunity when he was around the lab to ask him questions, if I didn’t understand something, you see, and maybe that, it probably made quite a bit of difference, the fact that I could talk to Robert and ask him questions, and then listen to him discuss things with Lauritsen and Tolman.
You did a paper with him in ’38 on the scattering of energy loss of — the only one I know of that you did with him.
That was not with Robert Oppenheimer. It was not with Frank Oppenheimer. It was with Jackie Oppenheimer. It was Jackie Oppenheimer, and Frank by that time had come as a graduate student under Charlie. He was married to Jackie. They didn’t have any children yet. Jackie wanted something to do, so I put her to work measuring, remeasuring all these old films that we had, primarily to look for the scatterings of the Compton electrons in the gas of the cloud chamber. You could see the cusp where, or the change in direction, where the scattering occurred, and by measuring the probability of the scattering angle as a function of track length, we were able to say something about the cross-section for scattering at high energies. That got us involved in multiple scattering, for which Williams had developed the theory about that time, and so she did all the measuring. Jackie was quite a smart girl and she understood what we were doing, so when it came time to publish it, we published it together. But that wasn’t Robert, no. As far as I know I never published a paper with Robert.
Professor Fowler inserted this note later: Indeed I do have this just backwards. We thought one group came from lithium-6. Hafstad and Tuve showed both came from lithium-7, indicating a low flying doublet-p structure in that nucleus.