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Interview of Charles Lauritsen by Charles Weiner on 1966 June 27, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4733
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Work at Caltech during the 1930s; when the Cockcroft-Walton paper appeared in 1932, he shifted from X-ray work to nuclear work. Development of ion sources and detection equipment, the building of a second tube at the High Voltage Laboratory, old tube is used in cancer therapy. Begins a systematic study of energy levels in light nuclei after discovery of artificial radioactivity. Interest in nuclear physics in Caltech. Nuclear work during the war, and the increase in level of support by Office of Naval Research (ONR) after the war. Also prominently mentioned are: Carl David Anderson, Robert Fox Bacher, Willard Bennett, Hans Albrecht Bethe, Niels Henrik David Bohr, Ira Sprague Bowen, Horace Richard Crane, Robert Andrews Millikan, Seeley Mudd, J. Robert Oppenheimer, Ernest Rutherford, Merle Antony Tuve; Conference on Theoretical Physics (1934 : London, England), Mount Wilson Observatory, Southern California Edison Company, University of California, Berkeley.
I want to start by asking how you decided to come to Caltech and how your interest in science started.
Well, that’s probably a little difficult to explain in great detail, I had been with a company in St. Louis making radios, and it became a little monotonous, so thought would like to go to school again. So drove out here from St. Louis and stopped here at the Institute, looked into things and thought I liked it. So applied here as a graduate student in 1926 and have been here ever since.
Where did you do your undergraduate work?
In Denmark mostly.
And was it of a technical nature?
Technical school, yes, in Denmark.
What was the name of the technical school?
Odense Technical School.
And what city was that in?
Was this the equivalent of a bachelors degree?
Something like that, yes.
Do you remember when you completed that?
That was in 1911.
Then when did you come over to this country?
I came here in 1916.
What did you study in school? Was it an engineering degree, or a science degree?
Well, it was structural engineering. Then later on I studied architecture in Copenhagen.
Did you have physics in the curriculum?
At about what level? It’s hard to compare.
Roughly on the same level as you have in universities here in general.
On an undergraduate basis.
But you weren’t a physics major, so it was a question of about a year or so of physics.
No, it was more like four years.
I see, And then you worked in architecture and structural engineering.
And came to this country in 1916, So you were how old then?
I was born in ‘92.
So you were about 24. And you came to St. Louis to work.
Well, had been in many places before I came to St. Louis.
But why the radio work? What type of work had you been doing before that?
Well, the first place worked was in Miami, Florida. I worked in an architect’s office, didn’t like that very much, so went to Boston, This was during the war, and the first job got in the Boston region was as a draftsman. I worked, among other things, on radio transmitters for submarines, so I got interested in radio.
That was your first interest in radio.
That was the first time, yes. This was during the war, the First World War, 1917-18.
And then what happened after this interest developed? Did you continue with the same work?
Well, after the war I went first to Cleveland for a short time and later to San Francisco, where 1 worked at the Federal Telegraph Company building radio transmitters and receivers for the Federal Telegraph Company network.
What was your job? Were you an engineer?
Yes, designing radio receivers for the commercial telegraph company.
Later on went to St. Louis and worked for a subsidiary of the Wagner Electric Company called the Kennedy Radio Company.
Are they still in existence today?
No, They were bought up by a subsidiary of the Studebaker Company and moved later on to some place in Indiana, Where was Studebaker located?
In South Bend.
South Bend, that’s right. They had a company in South Bend.
Were you married in this last job?
I was married in Denmark before I came over here.
Oh, of course, you were 24 when you came over. By this time did you have a family?
I had one son who came over with us.
You said before that you picked yourself up from the radio company job and got in the car and drove to Caltech. Why Caltech?
Well, liked it, It had a good reputation.
How had you heard about it?
Oh, reading mostly.
It had had a good name for not too many years before you came here, It was in ‘26, and think the name was changed somewhere in the early ‘20s, Had it already achieved that reputation?
That’s right, would think the name was changed about 1920— maybe before.
And did you have in mind a particular field of study?
No, really did not have any particular field, I was primarily interested in learning some things in general and especially in physics. I had no intention of staying here more than a year or so initially, but I liked what I was doing and so I stayed on.
Then you hadn’t come with a degree in mind?
You had come to take courses to learn something.
Who was the first person you saw here from the physics department?
The first one I saw in the physics department was Professor Watson.
And what sort of courses did you take?
Well, I took physics, electricity and magnetism, mathematics— the usual sort of first-year graduate courses.
Did you feel a bit strange? You were probably quite a bit older of course than the other graduate students.
I had to work a little hard the first year.
When did you come to know Professor Millikan?
Almost immediately. He suggested a research problem for me the first year I was here. In those days you usually started your research early. Nowadays you wait a year or two. He wanted me to start on field emission work, something that he had had several people working on before, so he suggested that I should work on field emission.
This is what you did. How did you go about working on it then after this suggestion?
Well, you build some apparatus, made some measurements, tried to understand what you were getting.
Did he have much to do with the actual work or did you work independently.
I worked pretty much independently.
Were there other graduate students that you had contact with who were doing similar work or related work?
Not in the beginning, not in the first year or two. Then later on when I became interested in high voltage tubes, I worked with Bennett. He was here as a research fellow and was interested in high voltage tubes. What I had learned about field emission was helpful in that connection, so we worked together on the first high voltage tube.
Let me get back to the program, to when you changed your mind from the idea of staying here a year to the idea of pursuing a Ph.D. program. You came in ‘26. You completed your Ph.D. program when?
How much course work did you have?
Well, I had three years.
You were actually taking courses all during this period?
And you started your research during your first year.
So the completion of your dissertation coincided with the completion of your course work.
Actually, completed my dissertation first, I finished that the first year was here.
But it wasn’t submitted as a dissertation.
No, but it was published.
Yes, think I have it on record: “Relations of Field-Currents to Thermionic—Currents.”
I think there was one before that. When was that?
That was ‘28. That was Millikan and Lauritsen. The next one was: “A New High Potential X-Ray Tube”—Lauritsen and Bennett. There may be another,
think there was one before that.
That first paper was published in January of 1928 in the Proceedings of the National Academyand was communicated December 8, 1927. So that was the dissertation then, By 1930 you had five publications. Is that usual for a graduate student? There were two of them on your own and three co-authored—two with Millikan, one with Bennett and one with Cassen.
That sounds reasonable.
Wasn’t it unusual for a graduate student to be actively publishing?
I wouldn’t say it’s unusual. It’s not always the case, but it’s certainly not unknown.
I was just trying to attribute it perhaps to the fact that you were older than the average graduate student and could perhaps get into research quicker.
This is probably true.
According to the bibliography the PhD. thesis was “Electron Emission from Metals in Intense Electric Fields,” That was 1929, It says, “unpublished,”
That was the field emission.
I see. And it was unpublished as such but you used the ideas in some of the other papers.
Yes, that’s essentially what was in the paper for Millikan.
How did the high voltage tube follow from this initial research in field emission?
Well, from understanding something about field emission, you knew something about what to avoid in a high voltage tube, such as sharp points, sharp corners and protecting the walls, things of that sort.
Where did the idea of a high voltage tube start?
I think it probably started with Bennett. Bennett was trying to build a high voltage tube) but had problems with field emission, in that they would burn up as soon as he turned them on. So we decided to start in on a different tack.
Why was he building them in the first place? Why was he interested?
We were primarily interested in studying X-Rays at that time, high-energy X-Rays.
As far as the physics of it went?
Was it apparent at that time that this was also a medical research tool?
Well, it was obvious that you could use X-Rays for medical purposes to see if high-energy X-Rays were better than low-energy X-Rays, because of their greater penetration.
Was this one of Millikan’s interests that he assigned this as a problem to you?
No, he did not, but he was responsible for getting medical people involved because some person that he knew had cancer, and he wanted to try high—energy. So he got Dr. Mudd interested in it.
Was that Dr. Seeley Mudd?
That’s right. So he became interested. Later on we got many patients from the county general hospital that we treated here.
Was there anyone on the staff of Caltech, any medical person who took a part in this, or were all your medical people outside consultants?
Well, I guess Dr, Mudd was, I think, listed as a member of the faculty after he started this work, and there were a number of other medical people working with him, and some of them were listed as faculty members at the time. Others were not.
I noticed that there was a medical board established and that Mudd was on it. He was the secretary of the board on the therapeutic use of the high potential tube. I got this from the Millikan papers. And then there was a Francis Carter Wood who was from Columbia University.
He was a consultant, yes.
I see. But first of all, the tube had to be built and had to be functioning before all of this came about.
How long a period was it before you got involved with Bennett in helping him on the tube solving the field emission problems?
This was probably in ‘27. He came here as a research fellow and we built the first tube in ‘28. We published the first paper in ‘28.
When the tube was built and was working, did you realize the significance of it? Did you have in mind applications beyond the general ones that motivated you to do it?
Well, from the beginning our main interest was simply the study of X-Rays. It was not built for the purpose of treating cancer patients, if that’s what you had in mind.
And then it was through Millikan’s suggestion that cancer became part of it.
Yes, that Dr. Mudd became interested in it.
What interests me is that from that point on, the money came in, apparently because of the medical applications which then could support the physics research involved in the tube. That’s the impression I got. Was there any other financial support besides medical money coming in?
I believe, at least in the beginning, Dr. Mudd financed the medical work.
I know in 1930 Kellogg gave $150,000 for a radiation laboratory.
That was for building this laboratory here.
Did the medical work within the laboratory play a part?
That was his main interest, yes.
Was it made clear to him that this was equally important as physics research?
I’m not sure about that. His main interest was in investigating the possibility of the use of high energy for cancer treatment. He was primarily interested in the medical aspect.
In your own work, did it make any difference to you in your studies whether or not there was a large interest from the medical viewpoint? Did you put much of your time into the medical applications?
Well, of course, it tied up the equipment while it was being used for treatments, but then when we built this laboratory and built the tube here, of course that took over the medical work, and then we continued our other work in the High Voltage Lab. Then very soon, of course, we changed from X-Ray work to nuclear work after the work of Cockcroft and Walton in Cambridge. They were the first to observe disintegration produced by accelerated bodies.
Differing from the radioactive nuclear disintegration.
That is correct. When you’re thinking about how nuclear physics started, of course you have to go back to the original work of Rutherford and others, using alpha particles; and of course it was through work of that kind that Cambridge had developed various techniques; so that when they built a high voltage tube very much like ours, they had the equipment for observing disintegrations like scintillation counters and cloud chambers, which were the first things they used. So they were well equipped for making those observations. As soon as they had done that, it became clear that this was a very important field, so we started in nuclear physics.
How did you hear of what they had done? Did you read their paper?
This was generally talked about in the physics group.
In other words, the example of the use of the same tube that you were using for the study of X-Rays and for medical uses—I’m trying to sum up to see if my understanding is correct—made it apparent that this also could be used as an accelerator to produce artificial nuclear disintegration, and it was that stimulus that made you start the nuclear physics.
I see. So it was actually hearing about it from them.
Yes. You see, the equipment is just the same except you put in an ion source instead of an electron source.
And had you, prior to that, no interest in nuclear physics?
Well, only in what had happened before—the work of Rutherford and others in this field with naturally occurring particles, alpha particles.
But you had done no research on it.
When you did start the nuclear work, did you consider this a switch of field, a big step, or was it just the logical use to which the tool could be put?
it seemed very logical very reasonable.
Did you have a feeling that you were getting into a new field of research?
Oh, yes. It was clearly a new field.
How did it feel, to have perhaps the only other machine in the world capable of doing this type of research?
Well, of course, that is not quite true, You see, Lawrence was building cyclotrons at about this same time, and he started into nuclear physics almost at the same time.
And then there was Van de Graaff.
No, no, that was the cyclotron.
No, mean in addition.
That came much later, at least somewhat later.
Did you know of Lawrence’s work?
Oh, yes. Oh, we were very closely in touch.
Did you know of Lawrence’s work before you knew of any other work? Cockcroft and Walton’s work came in 1932: the transmutation of light nuclei with artificially accelerated protons. Then Lewis, Livingston and Lawrence produced disintegration with artificially accelerated deuterons in 1933.
Was that the first they did?
No, Livingston and Lawrence had announced earlier than that in Berkeley. They had actually put the cyclotron into operation in '32.
I think they started about the same time we did. You see, we started out using protons, and I guess Lawrence did too. Then in the meantime, D. N. Lewis had made some deuterium and he gave each of us a little. Our first paper, think, is in October, ’33—at least the first paper with deuterium.
What's the title of that?
That's “Production of Neutrons by High Speed Deutons”, They were called deutons in those days.
How did that name get established, do you know? I heard some story about it.
Well, deuton was the first name used, and I’m not quite sure whether that was coined by Urey. At least it was by someone in this country. And Rutherford complained that the British always had a cold in the head so they couldn’t pronounce it, He wanted to call it deuteron. That’s the story I heard.
I think that’s the one that was in my mind, You had a paper also about the same time with Crane “On the Production of Neutrons from Lithium.” That was the second paper, I think, That followed the deuton paper, is that right?
Yes, That’s in ‘33 also, November of ‘33.
You saw that Lewis gave you deuterium. What kind of relationship did you have with the group at Berkeley so that he did this?
Oh, just a friendly relationship.
Did you write back and forth?
Yes, we wrote back and forth and we met at Physical Society meetings and visited bath and forth. We had very close contact.
Was there a feeling of sort of a west coast group in physics? Was the feeling closer because you were two western outposts?
Well, I would think we felt closer because we werecloser. It was just a matter of geography.
And so you knew of Lawrence’s work and you knew about the Cock- croft-Walton work. And the Cockcroft-Walton work was directly related to the tube that you had available here, and you put that to use. When did you start? Your paper was published in ‘33. Cockcroft and Walton published in 1932, and then the Lawrence work was around that period.
First, you see, we had to develop ion sources and detection equipment.
Now, there was a Wilson cloud chamber available here, wasn’t there?
Yes, but we did not have one at that time. Carl Anderson did in the cosmic ray work.
What did you use as a detector then to start with?
We used electroscopes.
And then when did you get around to getting a cloud chamber?
Well, that was very soon after. We started building a cloud chamber almost immediately.
By “we”—who else was involved?
Well, the first paper I find in here was published in French by Crane, Lauritsen and Soltan. Soltan was an international research fellow, and this is the first paper I have here.
I believe that’s the one where you used the helium ions.
No, that’s deuterium. That was published in Comptes Rendusin October, ‘33.
And when did you use the helium?
That I don’t remember but it’s probably one of the subsequent papers.
I think this one has something to do with helium, If I can read the French correctly it says, “In a previous note we have discussed and talked about the emission of neutrons, etc. from the bombardment of helium ions.” So that was a previous paper and this was the deuterium, so there must have been an earlier one. That’s what I’m trying to track down, I don’t have it here, but the implication is that there was an earlier one.
Maybe so. (shuffling through papers)
I’ll have to reread that paper carefully and see what specific reference they made, But, at any rate, you say this nuclear physics work was not carried out in the Radiation Laboratory. It was carried out in the High Voltage Laboratory.
In the beginning, yes, because this equipment here was then beginning to be used for cancer treatment.
I see. Did you build a different tube?
When was that? Do you remember?
I should be able to tell you. It was in the middle ‘30s would think, Here’s a paper in ‘33 on some work that was done here in the W.K, Kellogg Radiation Laboratory on X-Rays, high voltage therapy. That is dated September, 1933.
I’d like to get back to that later and talk about the differences between the High Voltage Laboratory and the Radiation Laboratory in terms of their origins and later functions. But before do, I’d like to ask a question on the paper that you published with Crane and Soltan. That was published in the Comptes Rendus.
I see I have an English version of it, too.
Yes, think it was published in Physical Review, as a matter of fact,
That’s right—September of ‘33.
Now, in a paper from the same period you made a statement, In the conclusion, you talk about a variety of excited states that had been found so far, and then you said, “A comprehensive knowledge of the energy levels in the nuclei should throw much light upon the question as to how far the identity of the alpha particle and other constituent particles are preserved inside the nucleus, and as to how far the previous structure of a nucleus is preserved throughout a transformation.” Now, this is interesting. Is this a hint at the later concept of the compound nucleus? Were you thinking along those lines?
Yes. It’s one of the things we’re still arguing about.
But I think this was rather early in the game. Were you conscious that this was a basic question?
What was the reaction of your colleagues here to the work that you were doing and the results you were getting?
don’t recall any. The only other people here that were interested in it at that time were the students that were working with me, like Crane, He was a graduate student here.
Is this the same Crane that’s now in Michigan?
Yes, Dick Crane.
It’s interesting that this concept was developing based on one of the first experiments that you reported on.
Well, think that was clearly one of the things you would like to know about. Which paper is this in?
That’s the one published in the Physical Reviewon page 514 in 1933.
Yes, have it here, You were asking if we had done work with helium, That one is about helium.
Then you did work with deuterium, What was the advantage of the deuterium?
Well, deuterium gives you a lot of energy in a disintegration so that you can reach very high excited states, and even higher with tritium.
And what was the voltage that you were able to achieve with your tube at that time?
We seemed to have measurements here up to about 975 kilovolts, I guess it is.
So it was in the million range.
Close to a million.
How does this compare with other tubes? How about the English work?
It was much higher than the Cockcroft-Walton tube. Their work was, I believe, below half a million volts. They had, as I recall it, two sections. These tubes were built out of gasoline pump cylinders. You’ve probably seen pictures of them. They used two sections. We had four. So we had a little more energy.
Now, when you began to use the tube for nuclear physics, what happened to your work and your interest in the medical applications? Were you still involved in that?
Well, the first thing that happened was that we built another tube down in the High Voltage Laboratory, so we had one tube that could be used for medical work and another that we could use for our own work. But of course it still tied up the Laboratory. You couldn’t do both at the same time, But you could have an electron source in one and an ion source in the other,
The thing that was responsible for the building of the second tube was the desire to do nuclear physics work?
Yes, that’s right.
And this followed from the results that others had achieved?
That’s right. And then of course when we built this laboratory here, then all the therapy work was done here in the Kellogg laboratory. And then we built a Van de Graaff accelerator down in the High Voltage Laboratory.
I see. What about the origin of the High Voltage Lab? Was that here when you came?
Yes, that was built guess around 1920, ft was one of the very first buildings.
And that was in connection with the electrical transmission work?
I believe it was a question of Millikan convincing the electric companies that if they were going to build a laboratory they build it on this campus with the advantage of a physics department here, ft would serve the research needs of the physics department and the research needs of… Edison Electric, was it?
And so when you came, the High Voltage Lab was well established.
Yes. It’s Southern California Edison Company. And they built it in order to test transmission lines, That’s the reason for the big door, You probably never saw it. This whole end here, this side, was practically open with a very big door, and the transmission lines went down to the other end of this block. But that work had all been completed before got here, and the only thing that the laboratory was used for at that time was some insulator tests.
They had a continuing series of tests on insulators under combined mechanical and electrical stress and different weather conditions—salt spray and rain and so forth. They were still doing that over here, but this was the kind of thing that only required attention maybe once a month, and very soon that stopped, too, so that the whole laboratory was available for anything that we wanted to use it for.
Was there a problem of financial support, though, for this new work?
Well, I don’t think it cost very much,
To build the tube?
The first tube don’t think cost a hundred dollars.
Well, then essentially you took over the High Voltage Laboratory.
Yes, that’s right.
Was there ever any plan to turn that into a radiation laboratory?
No, not really. It was more or less an accident, that we got into that therapeutic work, and resulted in building this laboratory so that the High Voltage Laboratory was again available for anything we wanted to use it for. And the electrical engineers later on did do some work over there, not very much.
It’s very interesting. You had a combination of a laboratory with a tremendous potential for this type of work and you had the tube that you had built for other purposes; and when this new field opened up, you were right on top of it. You had the stuff to work with. At this time was there any contact between your work which involved high energies and the high energies involved in the cosmic ray work?
Well, only after Joliot had produced artificial radioactivity by means of alpha particle bombardment, Then we did the same thing by means of protons and deuterons that were artificially accelerated, and thereby with artificially accelerated particles we produced artificial radioactivity. And the first activity we produced was carbon and it presumably produced positron emission. And in order to verify that, we got Carl Anderson to check that in his cloud chamber.
We had already measured the activity by means of electrometers, so we knew that we had artificial radioactivity. Then in order to be sure what it was, we got Carl Anderson to put it in one of his cloud chambers and observe the positive electrons.
I see, At that time you didn’t have a cloud chamber.
What year was this—do you recall?
It must have been ‘33 or ‘34, I would think.
We can leaf through your papers when we have some more time and see when the first mention of a cloud chamber in your work occurs and we can then assume…
I don’t know whether it occurs there or not, but it was within a few weeks of the announcement by Joliot, Here’s one paper: “Radioactive Elements of Low Atomic Number.” This was not, however, the first paper, but it’s one of the first papers, and there’s a cloud chamber. This was in ‘36, We’d done quite a bit of work before that. Here’s radioactivity.
That’s in the paper on gamma radiation from lithium.
Yes, that’s from ‘35. know our first paper was within a few weeks after the announcement by Curie and Joliot.
What effect, if any, did the knowledge of Anderson and Neddermeyer’s work on the positron have on your own thinking? Did you see any implications then for the work that you were doing or for nuclear theory as it was then understood?
Well, you see, they had just shortly before discovered the positron.
It was in ‘32 essentially. Then in ‘33 they produced electron pairs from the thorium C double prime. What I’m interested in is your impression of the reaction of people around these parts and perhaps on the larger scene to their work. What were the implications that people here thought this might have for further nuclear research?
I’m not sure that I understand your question.
When Anderson announced the discovery of the positron, this evidently had some effect on the physics world. just wonder if you have any recollections of what the reactions of people around here were to this announcement.
To the announcement of the positron?
Yes, to the work he was doing, Were you aware of the work he was doing?
oh, yes, very much, Well, it had of course a great effect on theoretical physics because, you see, before that, many people thought that this positive particle that showed up in Dirac’s theory was a heavy particle, a proton, and Oppenheimer showed that this could not be so. Then after Carl Anderson had found the positive electron, Oppenheimer and other people developed the theory of pair formation, which of course was very important for studying these reactions. Oppenheimer and Plesset think published the first paper.
Was there much excitement around here at the time?
Oh, yes, very much,
This was, I guess, one of the major milestones in the early history of Caltech.
Sure, yes. I remember Bohr was here very shortly after, and he was very much interested.
Did you have contact with Oppenheimer when he was here?
Oh, yes. I had contact with him on the first paper I wrote on field emission because he had been working on a theory of barrier penetration, hydrogen atoms in a strong electric field, from which he calculated the field that was affected in field emission, and he derived theoretically the same equation that I had found here experimentally. When he came here he showed me his calculations. He had exactly the same formula that I had derived experimentally. As far as remember, his theoretical paper appeared in Zeitschrift fur Physik the same month that my paper appeared in Physical Review.
Had he done that work prior to coming here?
Oh, yes, he did that at Göttingen.
I imagine he was pleased when he came here and could find confirmation Each of you could find confirmation of the other’s work.
Yes. That was in ‘27 or ‘28.
think in ‘29 he was in Europe because I just came across a letter from Millikan to Oppenheimer, an exchange of correspondence while he was in Zurich. Millikan had asked him for an explanation of his view on the Dirac theory, and Oppenheimer in his answer explains his views on its limitations and so forth.
Right. That was probably ‘27 or ‘28 when he was here first.
I’d like to ask what happened then from the early ‘30s when you had done very active work and this whole series of papers, especially in 1935 relating to different disintegration reactions, You worked a lot with Crane and Delsasso and Fowler. You mentioned that Crane was one of your students, How about Delsasso?
Yes, he was also a graduate student.
see. And Fowler?
It’s interesting that all but Fowler and Delsasso remained in the West,
Well, Delsasso did not, He went East. For the rest of his life he was at Aberdeen Proving Grounds.
But he’s in Los Angeles now.
No, that’s his brother, He died a couple of years ago or a year ago.
This explains the difference then.
His brother was in Aeronautics.
There was a whole series of experiments done in 1935, all of them published in the Physical Review—cloud chamber studies, gamma radiation from lithium, protons from disintegration of lithium and so forth. This really continues up through ‘37, ‘38, right up through that whole period. Can you characterize what happened in the period? We’ve spent a little time now talking about the origins of it and how you got into this work and some of the early experiments. But how did things proceed then? Was there a certain pattern? Were you leading a research group? Were you working always with a group of people? Did you have a plan of research that was pretty clearly defined?
Well, we very soon started a somewhat systematic study of energy levels in light nuclei and the group gradually increased in size.
The composition of the group would vary with graduate students, There would be some who would come and some go.
How about other faculty? Who else on the faculty worked with you on this?
So it was your group as such.
Did the equipment remain relatively simple?
Well, it’s still fairly simple. Of course, it is getting more complex all the time, As mentioned before, after the therapeutic work was transferred here to Kellogg, we built a Van de Graaff accelerator down in High Voltage Lab. That’s where we did most of our work until we stopped the therapeutic work, which must have been around ‘39 or so. We had an agreement to continue this work for five years. Actually, think we continued for about seven. By that time we had treated nearly a thousand patients and so we discontinued that, and then we moved the Van de Graaff up here. Have you been in the laboratory there?
No, 1 should really.
Well, that’s the one we call the number one, We now have four, you see.
But in this period prior to the transfer of the Van de Graaff from the High Voltage to the Radiation Lab, you had your high voltage tube and the Van de Graaff then both functioning at the High Voltage Lab.
Yes, for a while we did, yes.
Now, during this period what was going on elsewhere was the gradual increase of energies being achieved by accelerators, by Lawrence, and beginning to be done at other places. Did you feel that things had changed in this field, that there was a race for energy going on?
Well, of course, before very long, people became interested in high energy or particle physics. Mesons were discovered and people became interested in particle physics, high energy physics.
I see, and yet of course Anderson continued on cosmic rays.
But that is, of course, an entirely different field.
When do you feel that high energy became known as a separate field of inquiry?
That’s very hard to say because in cosmic radiation you already had the high energies and many of the mesons were discovered in the cosmic radiations. You already had very high energy.
Let me interrupt myself to ask you this: If someone asked you what your field was in physics, did you consider yourself a nuclear physicist?
It was clearly nuclear physics.
And you would have said this in the ‘30s.
When would you have started saying this?
Well, guess as soon as we realized that we could make transformations from one element to another.
The field was defined as nuclear physics as early as that.
Well, the point is I think that it’s only in retrospect that we look for the origins of high energy in the ‘30s. I guess all the high energy phenomena were still considered in the general category of nuclear physics. It was only after people began specializing with very large accelerators after the war that it begins to take off as a specialized field.
Well, wouldn’t you say that you talk about the field as nuclear physics as long as you think of the particles as hanging together, as long as they remain for practical purposes protons and neutrons, but when they come apart, then you can talk about high energy physics.
Well, maybe, but you could say that when they come apart you were then exploring nuclear structure.
Nucleon structure, not nuclear structure. Then you’re studying nucleon structure. This is the particle physics. n all the work that we do we consider the proton and neutron as solid particles that do not come apart or change.
That makes a good distinction.
They can change into each other. A proton can change into a neutron and vice versa, but they’re still the same nucleons. But when you get up to a few hundred million volts, then you can no longer treat them that way. They don’t behave that way any longer.
In the work that you did in the ‘30s you seem to have had a large number of graduate students working with you, and you said this group increased. Was this a reflection of a generally increasing interest in the field of nuclear physics?
I think so, yes.
Do you think people were attracted here because you had the Van de Graaff and you had the high voltage tube and you had been known for achieving results? When they came did they express an interest in working with this equipment? Do you feel that the great availability of the equipment and the labs was an attraction?
Oh, think so—yes. This was particularly true of the post doctoral fellows. They came usually for a specific purpose. just happened to look at a paper here by Bonner and Brubaker. Bonner got his doctor’s degree guess at Rice so far as remember, and he came here for the specific purpose of using our equipment for studying neutrons.
What kind of research support did you obtain in the ‘30s?
Well, we got a little bonus from the medical research.
There was something left over to do physics with.
A little. And Millikan usually managed to get a few thousand dollars. Before the war it didn’t cost very much to do this sort of thing.
What was the average size of your group? know it changed, but mean was it on the order of six or seven people?
Maybe so, something like that. From the middle ‘30s to the beginning of the war it was probably about five or six.
How about conferences during the period? Do you recall any special complications of one kind or another that you feel were especially significant or where you learned something or where exciting results were announced or where you exchanged ideas that were particularly significant?
Well, the first one recall we didn’t go to but we submitted a paper. That was in Cambridge. think that was one of the very first.
Yes, This was a conference on nuclear physics to which I was invited by Rutherford, and Crane and wrote a paper because we couldn’t get away. I have it here and can’t find the date.
1934, Here it is: “Gamma Rays from Artificially Produced Nuclear Transmutations, Papers and Discussions of the International Conference on Physics, London,” It must have been just the proceedings of that conference.
You say you couldn’t get away. Was it a question of teaching responsibilities?
I think so. I think it was during the school year, so far as I can remember.
How did you find the relation between teaching and research here? Of course, you had graduate students who were doing research with you. But did you teach undergraduate courses?
At that time in the 30’s I was teaching a graduate course. I did teach freshmen one year and sophomores one year.
Did you feel that you had enough time for research?
Well, you always had the evenings. We did most of our work in the evening and at night.
Why is that?
Well, less disturbance, fewer students around to ask questions. I don’t know why this isn’t dated but apparently it’s not.
Well, anyway the date of the conference was 1934. I know that from other sources.
Oh, yes, here it is on the front page: “Papers and Discussions of the International Conference in Physics ‘34”—that’s right.
Who did go from here? Do you remember?
Nobody. Anderson had a paper then and Neddermeyer, I think, but they were probably in the same sense as yours. They submitted papers but they didn’t go there.
They may have gone, but I didn’t know it. I doubt it very much.
I doubt it.
It wouldn’t be his field.
No. I’m not sure anybody went from here.
I’ll talk with Anderson. I’ll check. But do you remember any conferences you participated in during this whole period?
They were mostly Physical Society meetings.
Would you go to the East Coast to attend them?
The first one I remember was in Madison. remember I gave an invited paper on the radioactivity of boron and copper.
I see. Did you go every year to the meetings? Was it about one a year that you attended?
Not in the East certainly. But we usually went to the meetings here on the West coast—Stanford, Berkeley, and so forth.
Were those the centers of physics research in your feeling during that period—that is, Stanford, Berkeley and here?
What institution in the East did you regard as most important in the field of nuclear physics?
Well, guess the first one that got into the business was Merle Tuve’s Lab in Washington, at the Carnegie Institution,
The Department of Terrestrial Magnetism.
You see, they had this Tesla tube in an oil tank.
How did you know of their work? Did you communicate with any of them directly?
Now, here’s the important question: Whatever happened to those letters? Did you save any of your correspondence?
So you knew what Tuve was doing; you knew what Lawrence was doing…
Yes, Tuve, Dahl and Hafstad were the three at Terrestrial Magnetism. Later on after they got tired of swimming in this oil, they built a Van de Graaff, first in the open air, and then much later in a pressure tank. And suppose the next development that we got interested in was Herbs development on the Van de Graaff machine in a pressure tank at Madison.
This was in the ‘30s? Any other developments that you know of that you think would be significant in that period at other institutions?
There probably was if I could think of it. There were not so terribly many in the mid-3Os, not like now.
Whom do you regard in retrospect as having made some major contributions, say, in the theoretical sense?—people that you felt had some influence on your own thinking during the 30’s?
Well, in theory the Bible was Bethe.
This is his three papers in Reviews of Modern Physics?
What did you do when you saw that? Did you read it?
Sure, This was our Bible.
What was so good about it in your own view?
Well, thought it was the best thing that had been written on the subject up till that time—very clear and comprehensive.
It seems that Robert Bacher was here in ‘30 or ‘31 as a fellow.
thought it was before that, He was not interested in nuclear physics,
But at Cornell he did one of the three pieces of that Reviews of Modern Physics.
He and Bethe, yes—that’s right. But, as remember it, he was not interested in nuclear physics when he was here the first time. He was interested in spectroscopy.
Well, he did a lot of work on the hyperfine structure with Goudsmit and some papers with Sawyer and others.
Well, who else here was interested in nuclear physics?
Yes, I forgot. Anyone else?
I think not.
What was your relationship with Oppenheimer? Of course he was a theoretician, but you told us of the one instance. Was there a close collaboration or occasional exchange of ideas?
Well, when he was here I saw him every day; and when he was here after the war, he had the office next door, so saw him there several times a day.
Was he interested in your experimental results?
But you didn’t do any papers together.
Yes, we did at least one but I’m not sure just when that was. [On the Scattering of the ThC¹¹ Gamma-Rays, Phys. Rev. 46, 80, 1934.]
But in general your conversations with him then referred to subject matter and discussing the theoretical aspects of what you were doing here?
Well, notice in the abstract here of that paper for the London conference, we mentioned that we agree satisfactorily with theoretical predictions of Oppenheimer and of Bethe and Heitler. This had to do with pair formation. Now, we wrote a paper together on something.
When did things here change as far as the interest in nuclear physics? Now I think we would characterize one of the major research interests of Caltech physics department as nuclear physics. When do you think this change occurred?
I don't know that there’s been any change.
I mean with more people involved in it other than yourself.
Well, that increased gradually, and then of course after the war we built more machines, After the war it increased rapidly. That was, of course, partly due to the fact that we got money from ONR-money became more plentiful.
Let me ask you what you think the effect of the war was on the field of nuclear physics? Was it a question of marking time? Was it a question of accelerating what had been developing in the 30’s?
The effect of it here was to stop it because we all went away to various places.
You worked on the rocket work.
We worked on rockets at Los Alamos, but there was no nuclear physics going on here during the war. The old machine was here and we had started work on a new one, and both of those were removed to make room for war work,
Everyone actually physically packed up and moved out?
Yes. One of them was moved over in a corner, and the only use we had for it during the war was that several times it was used for decompressing divers who had been down too deep or too long. At that time there were no decompression chambers in the neighborhood here, so they brought them up here in ambulances from Long Beach, where they usually got in trouble. Then we’d decompress them in the Van de Graaff tank.
So that, too, was used for medical research.
Finally, I complained to the Navy and they put in a decompression tank down at Long Beach, These things usually would happen in the middle of the night. They’d call me at two or three o’clock in the morning and tell me that an ambulance was on the way up. The second Van de Graaff was not finished but we had the tank installed, and when the Navy got in trouble with the aerial torpedoes, they asked us to do something about that—so we took that tank up in San Gabriel Valley up to the San Gabriel Dam and used it for compressed air storage and for launching torpedoes down there in the water to find out what was wrong with them. This was after the Battle of Midway when they lost all their torpedoes.
That’s a whole story in itself: the rocket work and war work. But for the present, how did things get started up again after the war?
Well, after the war we started to rehabilitate old generators and continued our work. We got our tank back from San Gabriel Canyon and started building a new generator.
Were there any grand new plans for nuclear physics work here after the war? What ‘m getting at is: Was it just a question of an interruption and then continuity or was it a real change in level?
The real change in level came after we got the ONR support in, I think ‘46, and they have supported our work ever since.
The ONR money then enabled you to get new laboratories essentially.
Yes, and especially newer equipment, you see, because by that time equipment had become pretty expensive—amplifiers, fast circuits, crystals and things like that, which we never could have afforded before.
Was there a feeling then of competition for good research men? During the war everyone was brought together in a central place, Los Alamos, and a few other places. And then after the war they dispersed. Was there a feeling here of competition in trying to attract some of the well-known people here, new additional faculty?
I don’t think so. Of course there’s always competition for good graduate students, but I don’t know exactly what you mean by competition.
Well, sense that Berkeley and Chicago were in competition after the war and they tried to get.
We always had more than we could really use, than we could really take good care of.
Then of course you started attracting some theoreticians in the field of high energy. think of Feynman coming in ‘50-’51.
The first one we had after the war was Robert Oppenheimer. Then when he left we got Christy, and he was very helpful and very interested in the nuclear physics. More recently he’s become interested in astrophysics.
Then of course you get practically into the present period with all the familiar names that are here now, One other question: You mentioned astrophysics. During the ‘30's certainly Mount Wilson was very active. Was there much contact between you and the people in astrophysics?
There was some contact. We usually went to their seminars, but their seminars were on astronomy. And after the war, we started a series of evening seminars about mutual problems; and that started the collaboration between physics and astronomy.
I see, the sort of stuff that Bethe would do of different reactions of the stars and so forth.
That’s right—chemical abundance.
Fowler’s work, for example.
And then in your earlier period, perhaps the people in the department who were interested in spectroscopy would have had a lot more to do with the Mount Wilson people.
To some extent, I’m not so sure there was very much of that before the war. They had some very good spectroscopists up at the observatory.
Well, they had Bowen for one.
Well not before the war. He was here before the war. But of course the astronomers were interested in his work because that was mostly forbidden transitions he was interested in. But there was no strong collaboration between nuclear physics and astronomy until we started these seminars at Bowen’s house. We met once a week at Bowen’s house to discuss nuclear problems and astrophysical problems.
Who would be there?
Well, of course Bowen was there, I can’t remember exactly. Baade was usually there and Minkowski. There would be half a dozen astronomers and maybe three or four of us from down here.
I intend to talk with Bowen about these informal get-togethers. They’re sometimes very productive.
They never get into the published record of what goes on.
That’s right. This was very helpful to us, Bowen was very helpful, very interested. And by that time Bethe had already made his suggestion about where the energy came from in stars.
There are a lot of other things we could cover, but I think that for now maybe we’ll cut it off. have gotten a great deal out of it. There are many things that we covered that may appear obvious to you but that are new to other people, and that you just don’t find in the published list of papers. And so I think it has been worthwhile.
Well, I think it might be interesting for you to look around here and talk to some other people.
Gamma-Rays from Artificially Produced Nuclear Transmutations, H.R. Crane and C.C. Lauritsen, Papers and Discussions of the International Conference on Physics, London, Vol.1, Nuclear Physics, 130 (1934.)