Edwin McMillan - Session III

Weiner:

This is October 30th [1972] and I am with Dr. McMillan once again for Round Two of our interview.

McMillan:

Before we go into the next episode of this story, I would like to fill in a few little personal things, as I find on reading the transcript of the first session that some personal contacts which had some importance to me seem to have been left out. So to complete the record — of course, it will never be really complete because it is impossible to remember all the people that you knew, and nobody would even want to have a record of all of the people you knew. One of the things I omitted was my trips into the mountains of New Mexico with Robert Oppenheimer and his brother Frank. He had a ranch in the headwaters of the Pecos River, near a small town called Cowles, which he called “Perro Caliente,” meaning “Hot Dog” in Spanish. And I made two, or possibly three, trips to this ranch during vacations. It was a very rugged life. They had a log cabin that we lived in. They kept a string of horses and while there I did quite a lot of riding in the mountains. I remember particularly one trip on horseback from Cowles all the way up to Taos in New Mexico. Many interesting incidents occurred on these trips, which I don’t want to go into, but I would like to record the fact that I did have this contact.

Weiner:

When were these trips? During what period?

McMillan:

I can find that out. They are mentioned in letters to my mother. I will fill that in when I get the transcript. [August 1935, June 1936; if there was a third occasion, I have no record of it.] I remember with a good deal of pleasure another trip with Oppenheimer and Donald Cooksey into Baja California. [January 1936] Another personal thing I wanted to fill in was to give the name of Carl Overhage. He was a fellow who came from Germany and who was a student at Caltech during my one graduate year there, and became a very good friend of mine. I have letters from him, and he was one of the people I went on camping trips with. On reading it over, these are the most glaring omissions I noticed. There are probably others I haven’t thought of.

Weiner:

Let me ask about the Oppenheimer ranch trips. Did you talk physics? What kind of atmosphere was it?

McMillan:

We talked quite a lot of physics. In fact, we talked about all kinds of things. But basically it was a rugged life. The horses were the key figures — the care of horses, catching them, riding them. The trip to Taos I mentioned was for the primary purpose to buy a horse, and there are stories connected with that too which I won’t go into. It had to do with the nature of the horse. He was quite a beast.

Weiner:

Would there be just the three of you?

McMillan:

No, these were longer than weekends. Some people may have come weekends. I know I stayed longer. We took some quite long trips, like the Taos trip, for example. It was a very beautiful mountain country. One tends to think of New Mexico as being a dry desert state, but these were high mountains with very beautiful Alpine meadows, clear streams. On one of these trips I climbed to the top of Truchas Peak. It was a fairly good climb.

Weiner:

All right, then. We will get on to the other part. We had talked last time in just a general outline about your work on the fission products after you learned through whatever means — I’m not sure — about fission itself. You have written up a good deal of the subsequent work about that. But let me try to get a few more details. In your Nobel lecture and other places you talked about — and other people talked about — the concern with the by-product of the range experiments. And then you asked Segre to do the rare earth chemistry.

I’m curious about how you get someone else in on an experiment. Was he interested, or was he doing something else that he had to drop in order to do that? Just how do you bring another person in? And also what was your state of mind during the period? Did you really feel you were on to something or did you tackle things and put them down and maybe pick them up a little later? None of that emerges in the published accounts. Maybe you can relive a few of those details without necessarily going into the whole technical history.

McMillan:

I believe Segre came into this simply because I had been discussing these observations with him and he was very interested. I believe that he volunteered to do this. A job like that isn’t the kind of thing that takes you away from something else. Most scientists have several things going at the same time anyhow. It was a matter of taking some of these samples which I would make and then subjecting them to chemical separations and, of course, he came up with the conclusion that this activity was a rare earth. This seemed very anomalous to me, and so I continued trying myself to find out whether this was really true or not, and was finding some differences from a rare earth when Phil Abelson came. He had this idea of the different oxidation states, which was the key to the whole thing. When it is in the low oxidation state it does behave like a rare earth. You have to use an oxidizing agent to get it into the higher state, where it is not like a rare earth.

Weiner:

What was the time schedule on this?

McMillan:

I can easily find the time span on this. We can get the gross time from the interval between submission of the papers, which were dated.

Weiner:

I have some of those. “Radioactive Recoils from Uranium Activated with Neutrons” is February 17th. Then, “Radioactive Element 93,” with Abelson is May 27, 1940. So there is a large interval. But Abelson had come in the summer, I thought.

McMillan:

What was that date again?

Weiner:

“Radioactive Element 93” was May 27, 1940. Your first one, your letter, was February 17, 1939. Segre’s followed that — I don’t know the exact date.

McMillan:

We can find it.

Weiner:

Yes, I have the reference here. It is in the same volume of Physical Review, about 500 pages separate it from yours. Then you jump from 1939 to 1940. I thought Abelson came to do graduate work in the summer.

McMillan:

No, he didn’t come to do graduate work. He came on vacation. Apparently, he had an early vacation.

Weiner:

It wasn’t the preceding summer? He didn’t come the summer of ‘39?

McMillan:

Oh no. That letter was published right after the work was done.

Weiner:

I see. Now what was your major concern in the period from this first paper on February 17 on the radioactive recoils from uranium — your next paper was June 12 on the “initial Performance of the 60—inch Cyclotron,” a big group paper, and essentially a letter — and then other stuff on the cyclotron follows. “Modified Arc Source for the Cyclotron” —I can’t give the exact date of that. Then something on elementary radiosulfur — we talked about how that came about, and also another paper with Borsook and Yost, which is already 1940. I am concerned about the main thrust of your work from February 17, 1939 when the letter on fission is submitted to May 27, 1940, which is a period of fifteen months.

McMillan:

Well, clearly I was spending a lot of time on the cyclotron, that is on the planning and the bringing of the cyclotron into operation. And I was doing the sulfur work as you mentioned. Somewhere along in there I was doing some other work on various radioactive isotopes — another isotope of uranium. I was trying to tie down the existence of a long-lived beryllium activity, Beryllium 10. That work didn’t get published until after I came back from the war, but it was started with Professor Sam Ruben of the Chemistry Department. He continued that while I was away. He didn’t make any new samples but was continuing measurements of the samples which I had prepared. And then he was killed in an accident in the laboratory. He dropped a container of phosgene. And when I came back in 1945 I dug out these old papers and wrote up this work. I was spending some time on that. There were perhaps other things too. I imagine that the cyclotron was taking the majority of my time. And all strung out through here — I have notes which I can find — I was going back and trying new things with this 2.3 day period.

Weiner:

So that it was a continuing interest.

McMillan:

It was a continuing interest. It was never dropped. I would try something and not get a conclusive answer and then I would come back to it. I had no intention of dropping it, but I suppose it is a little strange that I wasn’t concentrating on that more, looking back now to how important it was.

Weiner:

Yes. I was just thinking that also the plans for the 184-inch cyclotron were being developed. Weren’t you involved in that?

McMillan:

I was also involved in the design study of the 184-inch cyclotron. I think that during that period my chief activity was with cyclotrons.

Weiner:

Yes, for example, on February 13, 1940, Warren Weaver has correspondence with Lawrence on the new cyclotron, and I want to raise some of these things with you later. But this helps make the point that one of the main preoccupations of the Laboratory was its design, and the grant had not even gone through then. But getting back to 1940, also to get some other developments before we go into more detail on the collaboration with Abelson, that was the time that Enrico Fermi came to give the Hitchcock Lectures. Do you remember anything about that? We had talked earlier about Bohr’s Hitchcock Lectures, but I was curious if you were present at Fermi’s.

McMillan:

Yes, I remember Fermi very well, I got to know him very well. His Hitchcock Lectures were some contrast to Bohr’s in that Fermi was a clear, articulate speaker who was very much easier to follow than Bohr was. And Fermi also was a rather different type of physicist than Bohr. Bohr was interested in the deep principles of physics. He was really as much philosopher as scientist. Fermi was a very pragmatic type of theorist who related his work quite directly to the real world.

Weiner:

Were there opportunities then for private conversations discussing the research?

McMillan:

Yes, there certainly were.

Weiner:

Do you remember anything about that?

McMillan:

No, I remember no details whatsoever. I don’t remember any topics I may have discussed but I am sure I did.

Weiner:

It seems to me, for example, that if you were working on the 2.3 day activity still at that time, that would have been something Fermi would have been interested in. They were doing some very interesting work at Columbia at that time. I’m trying to establish whether he did any collaborative work with anyone here at that time.

McMillan:

In my memory, he did not. He talked about his own work but I do not recall ever discussing this particular subject with him.

Weiner:

Was this the first time you had met Fermi?

McMillan:

The first time I remember meeting him. It may have been the first time.

Weiner:

I have not yet looked up the subject matter of the lectures themselves but I assume they were on some aspect of nuclear physics.

McMillan:

I don’t remember.

Weiner:

I will look it up to see if we should find out what he did say and then maybe we can come back to it. As far as other visitors, one of the people who came through at that time was Gentner.

McMillan:

Yes, he did work in the laboratory.

Weiner:

I don’t think we talked about him last time, but he came in just as the fission news was breaking. I was curious to know if you had any contact with him. There were two interesting things about him. He arrived at a time when fission was happening, and secondly, I understand that everyone was very much interested in what was happening inside Germany politically. Since he was a non-refugee German, I was interested in what the response was to him, what kinds of conversations were held, what his involvement was in terms of his response to fission and the new cyclotron work. The purpose of his visit was the cyclotron — to see what they could do about such a machine in Germany.

McMillan:

He did work in the laboratory. He was an experimentalist. I believe he made Geiger counters. I believe he was a counter man.

Weiner:

Do you recall any conversations with him?

McMillan:

Not specifically. I certainly saw a great deal of him. I got to know him very well. And then Bothe came some time. Was that at the same time?

Weiner:

Not the same trip. I did come across a reference to Bothe’s coming. My feeling is that that might have even been later but I’m not sure.

McMillan:

Of course Bothe and Gentner are known for joint publications, so one associates the names. I know Bothe visited the laboratory in that general period. I think you are right that they weren’t here at the same time.

Weiner:

Bothe was the head of the Heidelberg Institute when Gentner was there, and Bothe tried to get money for a cyclotron in Germany, and Gentner went off to find out how to build one. But I was curious — you don’t remember discussions regarding politics in Germany or questions of that type?

McMillan:

I do not.

Weiner:

He mentioned that all over he was asked a lot of interesting questions in this period.

McMillan:

I do remember feeling sure that he and Bothe were not sympathizers with the Fascist government. I know that they were not sympathizers with that system, but I do not recall specifics.

Weiner:

So much for that part of the background of the period. Now I’d like to get back to Abelson’s coming here and to find out how you got together with him, how you became aware of what he was doing and what his interests were, and as far as you know, how he became aware of your interests. And then how you got together.

McMillan:

He was working on the same problem. He of course, being aware from the previous publications of the existence of this particular activity, was working in Washington trying to do the same thing I was doing. I believe he was working with weaker samples than I was and using somewhat different methods, but he was working on the same thing. When he came I believe he told me tout this. We discussed the subject and I said, “Let’s work together on this.”

Weiner:

You had not known and he had not known prior to this?

McMillan:

I do not believe so at all. At least I am not aware of any correspondence on this subject. Abelson, of course, had been a graduate student here, and I had known him very well indeed. So I knew he was interested along these lines, but the fact that he was specifically trying to identify that 2.3 day period, I don’t think I was aware of until he came. I think it would be good to ask him. He may be able to fill in the dates of this early summer vacation. [About May 8 — 27, 1940]

Weiner:

He wasn’t in an academic setting there so it could very well have been early.

McMillan:

You could take vacations any time you wanted.

Weiner:

But as far as you remember and as far as you see, physically, there was no correspondence earlier?

McMillan:

I don’t recall any correspondence but it would be very good to check.

Weiner:

How did the collaboration work on a day-to-day basis? There are personalities to be considered and style of work. You weren’t just asking a person here the way Segre did a particular study but you were both addressing yourselves to a similar project.

McMillan:

We were right together. We were direct collaborators and at any given experiment, we’d be both in. I would be preparing the samples and irradiating them and he would be doing the chemistry. I believe that I did some of that too. I remember, for instance, that when measurements were being taken, one of us would be taking the readings and the other one writing them in the notebook. It was a very close collaboration.

Weiner:

Did you have trouble getting facilities for doing the experiment? Did it have to be scheduled in advance?

McMillan:

No, there was no scheduling then, or it was very loose scheduling anyhow. I had access to the cyclotron any time I wanted it. And of course the other work doesn’t need scheduling. That was done in the corner of one of the laboratory rooms.

Weiner:

About how long a period of time was the active collaboration?

McMillan:

Just a couple of weeks of very intensive work.

Weiner:

Did that mean nights as well?

McMillan:

Some night work certainly, because when you make a radioactive sample and then follow its decay it doesn’t wait for the clock. You have to stay up at night to fill in the measurements through the night. Of course, the bombardments and most of the chemistry were done in the daytime.

Weiner:

How about others at the time. Did anyone else get involved? Did you have an opportunity to discuss this with others?

McMillan:

I was discussing it with everybody — anybody who was interested — but no one else was collaborating. We were not in the least secretive, if that is what you mean. Everyone knew what we were doing.

Weiner:

How about people in other institutions? Was anybody else working on it?

McMillan:

I learned very much later that in Germany Starke and Strassmann were working on the same problem. There is some mention of this in Otto Hahn’s scientific autobiography, but I was not aware of this at all.

Weiner:

Also, you mentioned somewhere — perhaps in your Nobel address — that when you returned to the problem in early 1940 (you indicated before that you were intermittently working on it from the time of the first publication on February 17, 1939 until the next publication with Abelson on May 27, 1940), one of the things that had changed was that the knowledge of the general fission process had developed to a great degree. A lot of people were thinking about fission and there were explanations of the mechanism of fission and so forth. I was just wondering about how much discussion on fission was going on here, and how much of it you participated in when you became aware of these other developments. You know that Lou Turners article in the Reviews of Modern Physics, which think I was January 1940, was a review paper on fission. It had a fantastic number of references to everything that had been published on fission. So I know that there was a great deal of literature, but I am curious how this reached you. Were you involved in such discussions?

McMillan:

I wasn’t working on fission myself but certainly knew what was being done. Of course, the point of the fact that fission was better understood was simply that what knowledge we had made it extremely unlikely that a fission process would give one product with an extremely short range compared to the others. So that the explanation of this particular activity as being one anomalous fission product that just happened to behave differently from all the others became a more and more untenable hypothesis.

Weiner:

Was there any particular understanding of fission that merely paved the way for the next step?

McMillan:

I don’t know what you mean by the next step.

Weiner:

You say that as more knowledge accumulated about fission you realized how difficult this other problem was. But was there any specific paper or any specific thing discussing one or another aspect of fission which gave you some clues?

McMillan:

I don’t think there was a specific thing. I think it was just what was happening, just observing the kind of things that were being done, and the kind of theories that were being made to explain this process. What about the Bohr liquid drop model? When did that come out?

Weiner:

That was earlier, but the paper on the mechanism of fission with Wheeler was in Physical Review, volume 56. Your paper on May 27, l940 was volume 57, so this must have been the end of 1939. What I am trying to establish is the point that the general knowledge of fission that was building up was the thing that affected you.

McMillan:

Certainly, every time I would come back and think about this, it would still stranger that one fission product should happen to stop in the sample while the rest all went away.

Weiner:

Did Abelson’s arrival precipitate the whole return to an actual experiment?

McMillan:

That’s right.

Weiner:

Prior to that, you hadn’t returned to it except for thinking about it?

McMillan:

No, I told you I have a record of a long series of experiments over quite a period when I would come back to it and try some chemistry. That notebook will give all the dates. I find looking at it that I don’t learn too much from it because my notes were pretty sketchy, but at least I can tell when I was doing things.

Weiner:

That is what I wanted to know. After Abelson left — we can’t really pinpoint the dates — but we know that on May 27th the letter was submitted. Do you have any feeling of how long after that he was around?

McMillan:

I believe the letter was submitted very close to the same day that he left. My memory is that we got this thing written and I got his approval of the particular wording. I remember I had a few arguments with him about what we should say in it, but as I recall, we finally got an agreement as to the wording and sent it in, and that he left essentially right after that.

Weiner:

The normal acknowledgments are expressed at the end of the paper — they are to the Rockefeller Foundation and Research Corporation — and I assume that is because of their support of the cyclotron.

McMillan:

That’s right.

Weiner:

Was this the only laboratory where those results could have been obtained, given the existence of the cyclotron?

McMillan:

No, other places had cyclotrons. To do the experiment with the kind of techniques that we were using required reasonably strong samples. It would have been difficult to do, say, with the radon beryllium sources. It would have been possible, but that requires rather more sophisticated measurement methods when you are working with very weak samples. But the samples we had were of the type that could be measured on an electroscope or on an ordinary ionization chamber with an amplifier in a fairly simple fashion. One of the chief problems in working with induced radioactivity in uranium is that uranium has its own radioactivity and, of course, its decay leads to the whole chain of the uranium series, which appears as a background in what you are trying to measure. So it requires a much greater degree of care than if you are working with samples strong enough that you can ignore the natural activity of the uranium. But there were many cyclotrons in the world, so it could have been done many places.

Weiner:

I was thinking not so much of the question of comparing it with other cyclotron laboratories, but if one didn’t have a cyclotron how difficult would it be. What was the response when you did get the results? Apparently there had been a couple of weeks of intense work, a good collaboration with no great clashes of personality — did people feel you really had something when you announced your results?

McMillan:

Yes, there was a fair amount of excitement. I would say there was not as much excitement then as there might be now. It’s a little surprising to me that the national interest was not enormous. The local papers made a big story of it.

Weiner:

Do you have that in a scrapbook?

McMillan:

Yes, I have the stories from the local papers. But it wasn’t a big national story, as I remember. Of course, the public would not be aware of the military implications of a thing like this. Phil Abelson and I were aware of that but apparently didn’t consider that as any part of publication. We published it as a normal piece of scientific work, and later on, we were criticized for having published it. Secrecy in the uranium field was beginning although I don’t believe we knew about it at that time.

Weiner:

It wasn’t official and there was no policy yet in the journals.

McMillan:

They clamped down just after that, but there were some people who told me we should not have published it.

Weiner:

Columbia was holding press conferences. There is an interesting letter that I found from Bethe to Pegram regarding that, and saying that perhaps there was too much publicity.

McMillan:

Speaking of publicity, I don’t think that Abelson and I felt any lack in that sense. We were not doing this for publicity. We were doing it as a piece of scientific work.

Weiner:

Was there a public announcement made at the time the letter went off?

McMillan:

I don’t remember, but we will check the date of the story.

Weiner:

It seems to me that it is an important event because it is a new element. Kids are taught in school how many elements there are and all of a sudden everything is out of date as of that moment.

McMillan:

I object to that kind of statement. That’s just like saying that all of a map is out of date because somebody started a new town somewhere. It’s a strong statement when people say that any new discovery has destroyed all previous theories. It’s rarely true. Relativity, for instance, did not destroy Newtonian theory in any sense at all. Newtonian theory is still quite valid as a limiting case for special relativity. The table of the elements was still perfectly good. We added a number. The table of the elements even had some gaps in it still. When people said that there were 92 elements, and then number 93 was discovered, there weren’t 92 elements. 92 was the highest one known but there were still some holes in the distribution. I don’t mean to make a tirade about this, but science builds on itself. Very rarely does the whole structure get changed so that you have to say that everything before is obsolete.

Weiner:

It’s a good point, but I think there would be some public response to a new element, a natural thing that wasn’t known about before. We can look at the newspaper clippings and get the flavor of it. And it seems to me that it might have been received very well within the laboratory too as a great success of the laboratory.

McMillan:

It was indeed.

Weiner:

It had just missed out on fission as so many other places did, and so here was one of the first follow-ups and a very positive one.

McMillan:

Right.

Weiner:

You say there was less excitement than there was now. Was there any specific discussion of it? Did someone buy someone a drink to celebrate? Just how did people react?

McMillan:

No, we didn’t have any parties. We didn’t have any champagne. We just did the job and Abelson was preparing to go, as I recall. During the last part of the experiment we were making a very strong attempt to find the next element, as the decay product of neptunium would be the next element. We prepared a large sample, using a big platinum dish about a foot in diameter that we borrowed from the chemistry department to make the chemical separation. And we got rather inconclusive results, I think now that our technique wasn’t terribly good. That was rather a laborious operation working with the big sample and trying to work fast so as not to allow things to decay, and doing this at the last minute. So that when the thing was done and finally written for publication, I don’t think we were terribly interested in having a party about it.

Weiner:

From May 27th when the letter was submitted until November when you left for Cambridge, you continued on this.

McMillan:

I continued this, right. I was then working alone. I was trying to get some other people interested in helping me with it, but it turned out I was really working alone and trying to identify the decay product of neptunium, which had to be there. Something which emits a beta particle has to go to the next element up. And I had done some chemistry and pretty well convinced myself that this was a new element since the properties didn’t fit anything else. While I was doing that, I was also working pretty hard to try to identify the long-lived beryllium I mentioned. It was then that Lawrence asked me and Alvarez to go to help start the new laboratory at MIT, which they had decided to call the Radiation Laboratory. It ended up being a source of a great deal of confusion so that now people will say they were at the Radiation Laboratory, meaning MIT. And one has to think of some special way of saying it like the MIT Radar Laboratory or the Radiation Laboratory at MIT or something like that. I think that that name was cooked up between Lawrence and Loomis, partly as a cover.

Weiner:

Yes, to make it parallel to this one. The Harvard Laboratory was called the Radio Research Laboratory. I remember sorting those things out.

McMillan:

The Harvard Laboratory was set up to work on counter measures for radar. It was organized entirely separately and there was no communication between them. This was deliberate, because if somebody is going to work on the counter-measures they have to work in some ignorance of what they are trying to counter, or else it is not a realistic situation.

Weiner:

Although they were within a few miles of one another.

McMillan:

That’s right, but I don’t remember knowing very much about the Harvard Radio Research Laboratory at the time beyond the fact that it existed.

Weiner:

Let me get back, before we get into that period, to the in-between period and the work with Abelson. How did the idea of the stack of cigarette papers come about? You explained why it was useful, but I wonder if that was reasoning after the fact, or did you deliberately turn to those kinds of materials?

McMillan:

It was a simple way to get something very thin and uniform which was not itself made radioactive. Thin metal foils are even better, in the sense that they come more uniform and thinner. The best experiments in that series were actually done with aluminum foil, but the initial experiments were done with paper in order to have something which the neutrons do not make active. If anybody wants to buy some thin paper, that’s the best way to get it.

Weiner:

You used just the paper that you rolled a cigarette on?

McMillan:

Right. I wasn’t rolling cigarettes then but I went out and bought some.

Weiner:

You mean it wasn’t an off-the-shelf laboratory item.

McMillan:

No, I went out and bought some.

Weiner:

But you just thought of it in that particular context? There was no precedent in this?

McMillan:

It was a natural thing. I think almost anyone, if you asked them how to get something very thin made of organic matter would say “Cigarette papers, of course.”

Weiner:

Maybe.

McMillan:

I suppose one could say that some kinds of tissue paper are thinner but tissue paper is excessively porous. There are spaces between the fibers, and for an experiment you need something that is compact and uniform.

Weiner:

I asked because it was an unusual thing. Another aspect of it is the choice of the name. The logic of neptunium is clear enough but what was the process of reasoning? How did you come to that? Had you considered other names first?

McMillan:

No, I believe that was after Abelson had gone. I don’t remember making any special effort to make a name, but at some point the thought occurred to me that neptunium would be a great name for this thing. Uranium had been named after the planet Uranus, and then the next element should be named after the planet Neptune. I believe the thought of how apt this would be occurred to me, rather than a search for the name ending up with this one. Also I had gone on to the next one which would be plutonium, and suggested that the next one should be called that, but Glenn Seaborg apparently independently thought of that name later. The name neptunium got into the papers. It is in that first press account. Plutonium did not. I was not talking about the next one. We didn’t have it, although I certainly had that thought. The two came together more or less.

Weiner:

So there was no baby-naming contest or anything like that. In the past, there had been quite a lot of discussion about whether the term deuton or deuteron should be used.

McMillan:

No, there was no contest. Now it seems strange that when new elements are found there is almost an international competition sometimes as to who should name it, or what the name should be. But there didn’t seem to be such an issue then, and my suggestion neptunium got into the newspapers but I don’t believe it got into the scientific literature until much later.

Weiner:

It would be interesting to track that down.

McMillan:

Somehow this issue did not seem that important then. Thinking back at it, it is hard to see why. I would think that having found a new element, one would be extremely eager to propose a name and be sure it got into the literature, but it didn’t happen that way. Fortunately, it did get picked up and it did get in. I would have ended up being extremely disappointed if some other name had been adopted. Another thing which may be the key to this situation is the fact that secrecy was coming in then, and rather soon after the publication I was made to believe that this should not have been done publicly, and all talk about these matters dried up very fast. That’s probably the real reason. You can’t make a big public issue of naming something when you can’t even discuss the thing that you are going to name.

Weiner:

What was Lawrence’s response to this? By that time he was really involved in planning for the war work. When you said some criticism came regarding the publication.

McMillan:

Not from Lawrence. Of course Lawrence was aware of the publication.

Weiner:

Where did the criticisms come from?

McMillan:

I can’t remember who — other people not at Berkeley. I think people connected with the national planning. There was a Uranium Committee then. I think it was the Uranium Committee.

Weiner:

That would have been in a letter to Lawrence perhaps.

McMillan:

Something like that.

Weiner:

In this five-month period from June to October, we have just discussed what you had been doing then. What about your other work that occupied you so much prior to this collaboration with Abelson? Were you concerned with the cyclotron?

McMillan:

I was certainly still concerned with the cyclotron.

Weiner:

Both the existing and the proposed ones? That kept up and didn’t change?

McMillan:

That did not change. The design work on the 184-inch was going very strong in there, and I was planning the electrical power system for the oscillator. I even made some trips to electrical manufacturers to look at equipment in connection with that planning. One of those trips I can date fairly easily, because when I was out at the Allis-Chalmers Company in Milwaukee I remember talking to someone who had extremely strong political opinions then that it was important that we all vote for Willkie, so this must have been not too long before the presidential election.

Weiner:

Did you have to come up with pretty exact estimates of the power needs for the cyclotron? This had been a problem in the past, and the estimates had affected the rest of the university in the kind of rates you could get from Pacific Gas and Electric, etc.

McMillan:

I wasn’t involved in that. I was involved in the equipment which would bring the power into the oscillator, the power equipment, and of course the ratings of those things had to be specified. Those were very definite, but the financial aspects of power rates, I wasn’t in on that.

Weiner:

In my study of the administrative files it loomed as a major issue.

McMillan:

I’m sure it did, but that wasn’t my part of it.

Weiner:

While we’re on that, the letter that I mentioned before from Warren Weaver to Ernest Lawrence on February 13, 1940 was written while the negotiations on the grant were going on. Obviously, as you know, Weaver was sympathetic and was trying to get this proposal through and trying to help Lawrence answer the kinds of questions that he thought would be necessary. One of the things that came up was this statement that he makes about the estimate of the energy that would probably be required to produce mesotrons: “Would one be subject to criticism for designing a cyclotron to produce particles of energy less than this amount, that is to say soon after such a cyclotron is built, is someone going to come along and say that now a new instrument obviously must be built large enough to produce mesotrons?” And then he says, “This question collapses of course if mesotrons could be produced by the instrument as you now have it planned, but I have had a rather wide range of estimates as to what voltage might be required for this purpose.” Do you recall that kind of discussion here? It implies some questions to me: First of all what is the purpose of the new machine, and secondly, if producing mesons or mesotrons is the purpose, was it the main purpose, or the only purpose? Whatever it is, how do you achieve it?

McMillan:

I do remember such discussions, I know that Ernest Lawrence himself was never very impressed with this kind of argument. He felt that in a frontier field you go ahead as fast as you can; there certainly are great unknown things out there, and you don’t allow yourself to be bound by any preconceived theoretical notions. And so Ernest did not give very much importance to this kind of argument. Of course, if we had gone ahead and built it as planned originally we would not have been able to make mesons, which would have been most unfortunate. But Lawrence did not think that way.

Weiner:

I’m not sure what you mean when you say that. Apparently one of the aims of the machine was to make mesons.

McMillan:

Yes, but it wasn’t really designed for that purpose. It was one of the things that you list as one of the possible things that you might do. But I think I was perhaps a little more impressed by this kind of argument than Ernest was.

Weiner:

Some of the things that we have mentioned are reflected in Lawrence’s correspondence. The letter I have in front of me is Weaver’s reply, talking about the “radium equivalent” of the proposed cyclotron. This is Weaver’s term because he knows it has dramatic interest. “It might be interesting to have some indication of the cost of radioactive chemicals as a function of the size of the cyclotron which produces them,” so that is one other point.

McMillan:

Yes, it would be used for producing radioactive materials.

Weiner:

It would do better than the 60-inch. And then he talks about the differences between the extension of the cyclotron voltage and the extension of x-ray voltages. He wants analogies to be drawn, in particular regarding application…I’m referring to the letter from Weaver to Lawrence, February 13, 1940, where he lists certain discoveries, “the positron, the neutron, induced radioactivity, mesotron identified from cosmic ray studies, and discovery of fission, none of them involving the cyclotron although some could perfectly well have used it,” and I’m wondering what Lawrence’s answer was on that. My point is: Was that the kind of criticism that was being expressed by other scientists and other people who were doing active work in the field?

McMillan:

I’ve heard things like that during that period.

Weiner:

Do you want to expand on that some, as to what form it took and from what source and what the response was?

McMillan:

No, I can’t be specific. I don’t mean I am being cagey. I mean that there were statements like that made, mostly from eastern physicists, as I remember, and I probably even got involved in some arguments myself on matters like that since I knew many people in the east. But I would say it was more of a school of thought or an atmosphere rather than certain individuals making this kind of statement. It certainly existed and to be honest, there was some embarrassment in the laboratory that some of these things had not been done.

Weiner:

Embarrassment because the potential was here to do them.

McMillan:

Yes, it certainly was. I said something about that in the first session of this, that if we had had something as simple as an electroscope in the laboratory and used it properly we could have found artificial radioactivity. And in 1932 the cyclotron could have discovered the disintegration of lithium. Finding the neutron is a little bit more subtle a matter. That, of course, could have been done too, but it is not quite so easy to say that it would have been if the right instruments were here, because that was a fairly subtle matter in distinguishing the neutron radiation from the gamma rays. But the fact that you could disintegrate a light element and the fact that things were made radioactive could easily have been done. And the positron. The best way to identify the positron would have been to induce radioactivity, where you can get a substance which emits nothing but positrons. You don’t have to search for them in a haystack but you can find a sample which gives nothing but.

Weiner:

Of course, it wasn’t discovered because someone was searching for it. It was discovered because there was an anomaly in the normal cosmic ray work.

McMillan:

No one was looking for a positron, certainly not in cosmic rays, but in the laboratory once you had made a radioactive material which emits positrons, then it stares you right in the face. These are positive particles coming out. And you find that they behave in a lot of ways like normal beta particles, so it would have been very easy.

Weiner:

So you are saying that there was a feeling like that even within the laboratory.

McMillan:

There was always a little feeling that some things should have been done, but nobody was downhearted about this. Ernest was certainly not in the least. There were enough successes without that.

Weiner:

Did the fission work, and the fo1low-up here in your own work, get brought in to the negotiations that Lawrence was doing for the new cyclotron?

McMillan:

I don’t believe so. I don’t remember that at all.

Weiner:

Because, after all, using the cyclotron to discover a new element is a very strong argument. Certainly, when hafnium was discovered in 1922 at the Bohr Institute, it was used as an argument to the Rockefeller Foundation in the proposal that Bohr made in 1923 to get additional support for his institute.

McMillan:

I’ll tell you a little story about hafnium, by the way. In 1922 — I would have been in high school then the local press in Pasadena had a story about it. It apparently did get a lot of publicity the discovery of a new element. And then the story went on to talk about possible practical uses for this discovery. Someone had pointed out that among the hafnium compounds, the oxide is a very refractory material. This writer said that hafnium compounds were indestructible and might be a good material for surfacing roads. I remember at that time thinking that it is such obvious nonsense that anyone would say this about what was a very rare element — the story said it was a very rare element — and this kind of suggested use made me very skeptical of the claims that one reads about scientific discoveries. I remember at that time having this skepticism and ever since then always being a little skeptical about what I read in the newspapers about scientific discoveries. For some reason that has stuck in my mind.

Weiner:

It certainly was well publicized.

McMillan:

It got a lot of publicity and whoever wrote this story was trying to think of a use for it, and said maybe you could use it for roads because it was indestructible. Even as a high school student I knew better than that.

Weiner:

I can look at some of the letters. I think I remember that there was some mention of fission as an example of recent work done in the laboratory.

McMillan:

It was probably referred to, but the cyclotron was not aimed at that purpose. After all, fission is caused by neutrons and you don’t need that high an energy to make neutrons.

Weiner:

Getting back to papers, you had a letter to Phys. Rev. on June 28, l940, “The Seven-Day Uranium Activity.” Actually, that’s your last paper before you got involved in war work and it was the only paper that followed the one with Abelson, so it is about a month later. In that paper you comment on Japanese work of Nishina and his group. How were you aware of this work from the literature, or correspondence, or what?

McMillan:

I was certainly not in correspondence. I believe that appeared in publication at the time. Is there a reference to it? [There is.]

Weiner:

I didn’t bring a copy because it is only a letter.

McMillan:

I think that was a publication that came out just about the time I was finishing that work. By the time I came to publish it I came to realize that I had not been first on that one.

Weiner:

My interest on that was primarily whether you had been in touch with them individually.

McMillan:

Mr. Nishina had visited here, but I wasn’t in touch with him.

Weiner:

Now, I would like to get to your correspondence with Seaborg.

McMillan:

You had better scratch that about Nishina. I am not sure he was here. I may have confused him with someone else.

Weiner:

Sagane was here.

McMillan:

And Yasaki was here.

Weiner:

I think there is a pretty good list of foreign visitors that can be checked.

McMillan:

Nishina was one of the older generation of the Japanese physicists and it was mostly the younger ones who came here.

Weiner:

I don’t have the names of the others but the Japanese paper had about three names on it. It may have been one of the other names. [Yasaki] But to get you in November to MIT in Cambridge, once you were there you corresponded with Seaborg. I gather that Seaborg initiated the correspondence to ask your permission, essentially to pick up the work that you had started, and that you were obviously not going to do anything with, at least for a while, although you expected to go there for only a few months.

McMillan:

That’s what Lawrence said, but I never really believed that. I had this very strong feeling that I was going to be there a long while. I think I said something about that in the previous session, that once war is on and you get into war work, you don’t drop it that easily.

Weiner:

So when Seaborg wrote, your feeling was that this was a question that you ware not going to be able to get back to for a while?

McMillan:

That’s right.

Weiner:

You said in our last time that you kept the correspondence.

McMillan:

I have it.

Weiner:

I think that would be very important to preserve to check in regard to what we are saying about it, to get the day to day discussions. How long did that correspondence continue, do you recall?

McMillan:

A period on the order of a month, I believe. There was a little difficulty in locating some of my notes which I had left here, which had to be searched for, so it went on in the order of a month. When this work became obviously secret, the correspondence stopped. By that time, I became fully involved in the radar work.

Weiner:

Let us talk about that a little bit. Nowhere do I see any specific mention of your duties except that you were doing some field testing. You were there from November ‘40 until what time in ‘41?

McMillan:

It was in August some time. Then I went directly to San Diego. [I left on August 5 by car, and arrived in San Diego on August 18.]

Weiner:

And from there directly to Los Alamos or did you come back here?

McMillan:

There was a transition period between San Diego and Los Alamos when I was in Berkeley. However, what I was doing here was planning for Los Alamos.

Weiner:

And that was at the stage when Los Alamos had not been set up yet?

McMillan:

No, the site had not been selected yet. It was a very interesting period.

Weiner:

Let’s go back then to MIT. When you got there did you find yourself assigned to a group? You went with Alvarez?

McMillan:

We went together, right. Of course, since it was a young laboratory, there wasn’t a great deal of organization. Lee DuBridge was director. There were a number of people there. Alvarez and I were not the very first, but I would be hard put to remember exactly who was there before us. You are better able to find that out than I am. You have the records.

Weiner:

The book by Baxter gives some of the history.

McMillan:

I haven’t read the book by Baxter.

Weiner:

I think it is called Scientists Against Time, and it covers the general work.

McMillan:

I have seen that in the library here. I’ll have to read it some time.

Weiner:

There is a manuscript by Henry Guerlac, which is a specific history of the MIT Laboratory and which is unpublished.

McMillan:

Now, you ask me what did I do there. At the beginning, I wasn’t working in any large group I remember, I was trying to be an inventor. I was trying to invent vacuum tubes for generating high frequency oscillations. They had the magnetron there, of course, but there were a number of people trying to think of better ways to do that. I tried to be an inventor, but I didn’t invent anything terribly useful. I also worked on a TR switch (that means transmit-receive switch), which allows one to use the same antenna for both transmitting at high power and then receiving at very low power, so there has to be some kind of a switch so that the high transmitted power doesn’t go into the very sensitive detector and burn it out. And since the time intervals involved are very short, one cannot use any mechanical kind of switch. It had to be electronic. The TR switches used then depended on sparks.

They were designed in such a way that when you are transmitting, a spark would jump across a gap which would then remove the voltage from the detector. They were designed so that the spark was not soaking up so much power that it was using up all the transmitted power. I tried to devise a TR box I called it — depending on a resonant cavity coupling between two loops, both in the same resonant cavity, where the response in the cavity could be altered by an electron stream inside the cavity. I spent some time working on this, but it never got developed into anything. In connection with that, I recall I spent some time at the Raytheon Company, which was near Boston, and that I got to know the head of their development department, a guy named Percy Spencer, who was really a very remarkable man. I got to know him very well.

Weiner:

Who was your supervisor, or did you have one at the lab?

McMillan:

I certainly had a supervisor but I can’t remember who it was.

Weiner:

But your work was pretty much individual?

McMillan:

For that initial period, it was individual.

Weiner:

Did you work with Alvarez, or was he doing something different?

McMillan:

He was doing something different. You have his tape. You must know what he did. Maybe he will tell you what I was doing. I’ll bet he has a better memory than I have.

Weiner:

I don’t recall all the details of his work. I know how it ended up and all the missions that he had to go on.

McMillan:

Anyhow, at some fairly early period, I became associated with the field work. This involved an old airplane, a B-l8, which was the military version of the DC-2. The one we had wasn’t much of an airplane. It was fairly decrepit, and we had a string of wild men for pilots, which led to some minor adventures in the air. But what I was doing was taking equipment aloft and testing it over targets on the ground. One of the relics I have, which can find, is the log of those flights — the days we went up and so on — I can find that. What would be done was that the equipment would be built in the laboratory. This was laboratory-style equipment. It wasn’t built in the way that one would normally build a prototype for a test. It was strictly laboratory equipment, which meant that it wasn’t really suited for flying in an airplane, but was frequently a little too fragile for that. And we had a good many failures in flight.

We’d spend a lot of time getting ready and fly out over the ocean, looking at things, and then something would break. A wire would break or something would fall apart, and we would have to come back down again. This led to an incident which I like to say is the beginning of what is now known as environmental testing. I don’t believe it really was the beginning, but for that laboratory it was. One of the important components of the system is a pulser that delivers the little pulses that modulate the transmitted beam. A pulsar was also called a modulator. When we were ready to go on one flight, this piece of equipment, which was a box about a couple of feet long, was all ready to go, and we had just had trouble with a broken wire in some equipment. I was looking at this thing and I picked it up a couple of inches and let it fall on the table. I said, “Now see if it still works,” and the people who built this nearly killed me, but it did work, and I think it got a point across. Another interesting thing about these B—18 flights was that the equipment used needed to have current at two different frequencies for some reason, and it needed more power than you could pull off of the generator for the plane itself.

So we had two little gasoline-driven generators out in the bomb bay of the airplane, delivering these two different frequencies, and I think we lost as much time by failure of these little gasoline engines as by anything else. I remember giving a talk once about this and saying that one of the things we were learning how to do was how to generate power in the air, that was one of our experimental tasks. I can date one of these flights precisely because I have it down. It was the first observation of submarines from the air. I remember Alvarez came along on this flight. There was a submarine base at New London, Connecticut. We also had along with us a visitor from Great Britain, a man named Dowding, and he was called “Stuffy” Dowding for some reason. He was Air Vice-Marshal, an important man in the RAF, and we went down to fly over New Haven, and they had some submarines and we saw them on the radar screen — the first observation, at least with microwave airborne radar, of submarines. So the conning tower was sufficient to pick it up — I don’t think periscopes were, but the conning tower was enough. [The date was April 29, 1941.]

Weiner:

It must have been a practical kind of experiment.

McMillan:

Field work is by definition practical experimentation. You don’t build anything in the field. You take it along and try to make it work and see what it will do. Then, on another occasion, I went out to Wright Field in Dayton, Ohio, with some equipment which they wanted to test out there. I carried this stuff out and set it up and they ran a test. I believe that was air to air.

Weiner:

Were you concerned, in most cases, with the conditions of the failure as well?

McMillan:

Failure can be of two kinds, at least. One kind is simple failure of components something breaks — and that is rather inexcusable. But the excusable kind of failure is when something just simply doesn’t have the capability of working. For instance, it may not have sufficient power to give you a strong enough signal to see, or the resolution may not be good enough. That is excusable and you learn something from that. You don’t learn anything from the failures which are simply breaking of a component, except to make the components better, but people already knew how to make components better. It was just the fact that these were done in the laboratory, where people were used to wiring things in a way which was all right in a stationary system but not all right aboard an airplane.

Weiner:

Did you find this style of work, and the assignments that you had, similar to what you had been doing, or far different?

McMillan:

Far different from anything I had done before.

Weiner:

What was your reaction?

McMillan:

I liked field work.

Weiner:

What aspects of it were especially appealing to you?

McMillan:

I don’t quite know how to answer a question like that. It is very interesting. If you are doing field testing of new equipment you are right at the interface — to use a modern word — between what the lab was doing and what the equipment is supposed to accomplish. It is a very great opportunity to try to understand the difficulties and transmit back what things are supposed to be done about them. I suppose I also liked the outdoor aspects of it. I told you I have always enjoyed being outside, and this was somewhat different from working entirely in a laboratory. I must say getting to the airport wasn’t any great fun. Between MIT and the Logan Airport where we worked, one has to drive right through the middle of Boston. I think Boston has the most impolite drivers in the whole world, as far as I know. One of the first things I noticed was the high incidence of bent fenders, and struggling through the narrow streets in the rather slow confused traffic twice a day, I don’t remember being any great fun.

Weiner:

Where did you live?

McMillan:

I lived in Cambridge at the Commander Hotel.

Weiner:

When you went out there you couldn’t know how long you were going to be there.

McMillan:

No, I didn’t know how long I was going to be there. Also, I got married there. We will come to that later. I got there in November and was married there in June of the next year. The Commander Hotel was an apartment hotel. In addition to single rooms, it had apartments, so all I had to do was to move from a room to an apartment when I got married.

Weiner:

How did that come about? Had you planned this beforehand or did all this occur on the spot?

McMillan:

It all occurred on the spot. I had met Elsie — Mrs. Ernest (Mollie) Lawrence’s sister — in Berkeley a couple of times. I had met her but I certainly had no intention of marriage. In fact, I always told my friends I didn’t mean to marry. I was not unhappy in a bachelor existence. But when I was out there, I went down a few times to visit Mollie Lawrence’s parents, whom I already knew, of course. They had visited Berkeley, I went down a few times. I remember having one Christmas there. It was during that time that Elsie and I decided to get married.

Weiner:

I was wondering if she was in Cambridge for some reason.

McMillan:

No, she wasn’t in Cambridge. I would go down to New Haven.

Weiner:

You got married, even with the uncertainties of the war and where you’d be and so forth?

McMillan:

That didn’t make any difference.

Weiner:

When was it that you knew you’d be leaving there? You got married in June, you say, and then you left in August. Had you known at that time where you were going?

McMillan:

It was not long before the departure, and again it was the influence of Ernest Lawrence, who told me that they were starting a new laboratory on underwater sound at San Diego. The submarine problem was a very serious one. The radar lab was going well. He wanted me to go to San Diego and help in establishing this new laboratory. I don’t think the interval was terribly long between when Lawrence told me and when we went.

Weiner:

Your position in the MIT Laboratory was in research. You didn’t have a large section of responsibility.

McMillan:

No, I didn’t have any large administrative responsibilities there. I was the head of the field work, but it was just a small number of people.

Weiner:

How would you compare the working atmosphere there, of course compensating for wartime differences, with the style and the working atmosphere at the Berkeley Laboratory that you had been used to?

McMillan:

It had the same kind of high spirits. The people were very excited about what they were doing.

Weiner:

Was there any noticeable effect of bureaucracy which hindered?

McMillan:

Not to me, but I understand that this did become a problem later. But certainly not in these first nine months – I was not aware of any problem there. I could get what I needed. The only real problem was making the equipment work.

Weiner:

Yes, but that was why you were there.

McMillan:

There was one story I meant to tell you back there. I think you might like a few anecdotes in this. In the very early days at MIT, we were just working with stationary equipment set up on the roof of the building, and the targets we had to look at were buildings and structures around town. Up at the northern edge of Boston was a big concrete water tank which made a beautiful target. That one always gave a strong signal. We calibrated things on that as being the strongest signal at a reasonable distance. So I remember saying one time that this equipment would be very good for desert warfare since it could be used for locating water tanks.

Weiner:

So you picked up and you went directly to San Diego. Vern Knudsen was the head of the laboratory there, and Lawrence was on the subcommittee, not only for the MIT Radiation Laboratory but also for the Underwater Sound Laboratory at San Diego. Was the structure there similar or different to what you had found at MIT?

McMillan:

The structure at San Diego was very different from any other place I have worked. First, it was attached to the Navy. Actually it was run by a contract by the University of California so that we were civilian employees. We operated under the personnel rules of the University. But it was on a Navy installation and there was an existing Naval Electronics Laboratory on the same site, so there was a very strong Navy influence. That, of course, means that there was more obvious bureaucracy there from the beginning than other places I have been used to.

Weiner:

They also had a relationship with the Scripps Institution. They got some personnel from there.

McMillan:

There was some understanding between them, so that one of the Scripps experimental ships was used in the work, but there was no administrative connection to my knowledge. There was some agreement whereby the ship was used and some people from Scripps were certainly members of the Lab staff. I got to know some of them quite well.

Weiner:

I have some background on it. It seems that some of the people in charge there were not only Vern Knudsen who was director of the lab, but Gaylord P. Harnwell and Carl Eckart.

McMillan:

Carl Eckart was there. Knudsen was the first director they had several changes of directorship - then there was a man who came out from Bell Labs, whose name I cannot think of now. It was an Armenian name, I believe. [L. J. Sivian] He was director for a while, and then Harnwell was the last director while I was there.

Weiner:

Lyman Spitzer came, but it may have been after your time.

McMillan:

I don’t remember Spitzer being there, might try to think quickly of people I knew that were there — Franz Kurie.

Weiner:

That was a nice obituary you wrote of him in Physics Today.

McMillan:

I was very fond of that guy, I tried to get into that - the sadness of the circumstances by which he became rather useless to himself and the world some twelve years before he died. Several of his friends have told me that they liked that obituary. He was there then. He and his wife and I and my wife were very good friends. We did a lot of things together. Professor Jenkins from Berkeley was down. He was a spectroscopist from the Berkeley Physics Department, not in the Radiation Lab, and was working on optical methods. There was a rather large contingent of electrical engineers from Hollywood, a number of the movie people were in on that. There were a number of people from Texas. Some of these people have gone on and become manufacturers of electronic equipment and have become well known in their fields now. I don’t want to try to think of all those names now.

Weiner:

I was curious about the overall structure but I am really more interested in your own role. You say the structure was more bureaucratic because it was involved with the Navy. What assignment did you first have when you came there?

McMillan:

The thing that I was working on first was an idea which had come from Ernest Lawrence. The idea was to have a set, a multiplicity, of sound-ranging devices, all pointing in slightly different directions so that one gets a picture. In the traditional use of underwater sound for detecting a submarine you send out a ping, a sound into the water, and it travels out and reflects back and you receive an echo. The time of return according to the velocity of sound gives you the distance, and if the submarine is moving it comes back with an altered frequency; with the Doppler effect you can tell how fast it is moving, and whether it is towards you or away from you.

This new device which we called a polyscope was to consist of a number of these things pointing in slightly different directions so that one could get a multiplicity of signals that would combine to make a picture of it. I spent a whole lot of time developing that and making experimental models, and so on, but it was not really a success. It certainly never got into service. The problem in underwater sound is that the ocean water is a very poor medium. It’s a murky medium. You don’t have the nice clarity of a radar beam travelling through air, but you’ve got suspended matter in the water and fish swimming. Worst of all, you have the temperature variation, because the velocity of sound depends on temperature, and whenever you have a gradient of temperature you get refraction which bends the beam. Putting all these things together, I was never able to get a really acceptable picture. Of course other means were being worked on, and some of the other things being developed there did go into use.

But the polyscope, in particular, never got into use. The one thing I did there which was my own idea was a target on which sound operators can practice. The use of old existing sonar equipment, as well as new equipment, was always tricky enough that people had to be trained to use it. With radar you can look the first time and see what is happening, but these things were not quite that simple. You had to point this device in the desired direction, orient it, and you had to listen and interpret what the sound means.

When you make the “ping” you get a large amount of sound that comes back, called reverberation, a long ringing shimmering kind of sound, and then in the middle of that is a tiny little peak which is the echo. You have to train yourself to pick this up. If there is any Doppler on it you can hear it easier because it is at a little higher or lower frequency. I might point out for the technical listeners here that the frequency of transmitting is not the frequency of hearing. There is a frequency converter in between. So there was a problem training these operators. The traditional method was to send a submarine out and train on that. I went out once on one of these submarines that was serving as a target, spent a day out there while some destroyers were practicing on us, and got a little chance to see what life on a submarine was like. It was not unpleasant actually. There was a very good spirit aboard a submarine. It is not uncomfortable at all. In wartime operation it could be very uncomfortable but out there it was not bad. I was also going out with crews on destroyers doing this practice, and they were trying to find some way of improving it.

My friend Firth Pierce that I mentioned earlier was working with developing training devices which would work by simulating the situation, so that you could do it all inside a building. But we were more interested in doing it in the field, which is where you have got to get your real final experience anyhow. I had the idea that if we could make some small target which would repeat the signal which strikes it, that would be just as good as a big target which was a real submarine. If small it could be towed behind a ship and you wouldn’t need a submarine. So this was what I called the echo repeater, and I worked on this quite hard. Mother fellow, Bill Myers, worked with me and we even have a patent together on this thing. He was a practical man, a great guy.

Weiner:

Was he from a university also?

McMillan:

No, he was not a university man. He was on the staff of the laboratory; he was not a Navy man, I believe. But he had had Navy experience. He was a real sea-going type. I want to tell you a little bit more about this device. We first checked it out on the side of a small boat. You have to have a receiver and then a transmitter, which have to be fairly close to each other, and also you can’t use a transmit-receive switch because it has to be receiving and transmitting at exactly the same time. You can’t introduce any time delay into this. So one had to design them so that there was no acoustic coupling between them — that was the real trick of it — to have a powerful transmitter and a sensitive receiver sitting right beside each other, and the receiver is not hearing the transmitter. This is possible, and we did it. In the actual working model we used a float — the kind of float that was used in connection with mine sweeping. It was a big metal float about six feet long, sort of a fish-shaped object. We called it the fish, and we fixed it up with equipment inside, and then a transmitter and receiver, one above and one below, and to tow this thing we had a cable with a conductor down the middle to supply power. The float had fins that could be set to make it dive to the desired depth when towed. This worked, and as I learned later, it was used in actual training.

Weiner:

Did you take the patent out during that time?

McMillan:

We can look it up and get the date. [patent no. 2,694,868, filed August 3, 1943, issued November 23, 1954]

Weiner:

It doesn’t show on your list and I don’t know anything about your patents.

McMillan:

It was classified at the time, it is not classified now.

Weiner:

Did you assign it to the Navy?

McMillan:

It was assigned to the U.S. Government. I have a number of patents. They are all assigned. I don’t have any patents that I have a financial interest in, but I have several patents. I made several at San Diego; made several here.

Weiner:

In this work that you mentioned, did you function in pretty much the same way, that is, with a specific project in mind, without much administrative responsibility?

McMillan:

I had administrative responsibility for the group doing these things. It was a small group of a few people, plus all the various services that are used, shops and so on. The people I had immediate charge of was a small number. I had Bill Myers, and there was another fellow, by the name of Reed, I believe, who was a real grizzled Navy type. Then there were several others.

Weiner:

Was that pretty much the way it went for the whole period you were there, or were there other projects you were involved in?

McMillan:

Following after the echo repeater, I was trying to use that same principle of the transmitter and receiver next to each other as a mine detector, using the fact that if you have a transmitter and a receiver which are uncoupled, they won’t oscillate, but once you introduce any coupling between them, they will oscillate, just as a loudspeaker will make a loud noise if the microphone can hear the loudspeaker, the system will oscillate, and you get a squeal. The idea was that if these two things are aiming out in some direction and there’s an object there, then the reflection will introduce a coupling between them, and if you come close to something like a mine floating in the water, the thing would squeal. I did some work on that and the work was still going on when I left, but I don’t know if it came to a practical device. Again the problem is the scattering by random suspended matter in the water. As soon as you put the gain up high enough to do what you really want to do, it squeals on account of some fish swimming by or suspended things in the water.

Weiner:

I notice that one piece of work that you did there didn’t appear as a technical report, then shows up as a paper in 1946 — that’s the reciprocity theorem.

McMillan:

That came as the result of my attempts to understand the operation of the types of transducers that we were using. The transducer in this usage was the thing that converts the electrical signal into sound either way, either going in or coming out, you use the same kind of thing. And one of the kinds they used had a piezoelectric crystal, a material which when you apply an electric potential to it undergoes a mechanical deformation. It couples the electrical to the mechanical. They used Rochelle salt crystals in the older transmitters.

Weiner:

Walter Cady did that actually.

McMillan:

Cady was there. I knew Cady very well. In trying to understand how one calculates such a system, in which one has electrical and mechanical elements coupled together in the same system, one tries to do this by the traditional methods of the electrical engineer, by writing suitable equations for them. And, in doing this, you have to make a correlation between a mechanical quantity and an electrical quantity. You want to treat them both as quantities in an equation, and it turned out that there were two systems used traditionally for how you relate mechanical to electrical quantities. The most obvious way of doing it would be to say that force correlates with voltage, and motion with current. But there also is another system in which those things are switched around. You could do it either way. You just write these equations a little differently. I got very puzzled by this, and trying to understand this whole thing, I ran across the phenomenon which is described in this paper. It was a very interesting thing to me, the fact that this is perhaps a little too technical for this kind of an account.

Weiner:

I don’t know why you say that, I think it should be.

McMillan:

Well, the reciprocity law essentially says something like this, that if you have a black box with two handles sticking out, and if you push one handle and the other one does something, then if you move the second one, the first one moves in a related way. In other words, it’s an action-reaction, but applied to the generality of an electric circuit, or mechanical system, whatever is in there. The reciprocity law is common to all the ordinary treatment of electrical circuits, unless you have something like an amplifier tube in there when you have an internal source of power, then all rules are off. I am talking about what you call a passive network with no source of power.

In a circuit of this kind you have four quantities to relate voltage and current at one end to voltage and current at the other end. You could say, with handles, it is force and motion. That’s a fairly good parallel. The reciprocity law says, if you write it all down in the simplest way, that you have a pair of equations relating the four quantities, and two of the coefficients of those equations are supposed to be equal. Whatever is in that black box, those two numbers have to be the same. After looking at this, it was clear to me that with electrical-mechanical components you could devise systems where those coefficients had opposite signs — one was plus and one was minus.

Then by combining a pair of these systems you can have it so that if you push on one end of each of these two systems, then the two motions that come out the other end will cancel each other because they have opposite signs, but on the other hand, if you push at that end it comes out this end with the same sign. In other words, you can make a circuit which is a one-way circuit, using only what we call passive linear components. So I wrote that up as a report. People were quite interested in it. Nobody had done that before, as far as I know, though it is implicit in the equations they were using. Then, much later after I got back here, I dug that thing out and got permission to publish it. It was originally classified. Everything was automatically classified.

Weiner:

I notice that Foldy and Primakoff, whom you mention here, had referred to it.

McMillan:

That is what brought it back to my attention. I hadn’t really thought of publishing it.

Weiner:

The technical report was one thing. By the way, those reports were published in this series, Summary Technical Reports of NDRC. I’m not sure that all of them were published, but they were summary reports. For this one on The Physics of Sound in the Sea, I have the Table of Contents. I don’t know if your paper was in there.

McMillan:

No, not in there.

Weiner:

Apparently this caused some further discussion. I saw several responses.

McMillan:

Right, there was a response, and a response back.

Weiner:

So the origins of this interest was the war sound work.

McMillan:

It was because I was just trying to get myself educated in how to handle certain types of problems, and found this anomaly.

Weiner:

You spent from August ‘41 there to sometime in ’42.

McMillan:

It was around November.

Weiner:

So it was more than a year then. When were you approached regarding what was to be the Manhattan Project?

McMillan:

That was around September of ’42. I was approached from several angles. Lawrence was trying to get me to come back here. Compton wanted me to come to Chicago. I have some of the papers on that so I can establish some of those things — letters and a telegram — it is not in that pile. These piles are all early stuff. The next time you come there will be a new, more recent pile. I’ll know by then which ones to try to find. [The telegram from Compton inviting me to a meeting in Chicago was dated September 14.]

Weiner:

Were you aware of the work going on at the various places or ware they just speaking in vague generalities?

McMillan:

Rather vaguely. I knew there was something going on. It was supposed to be secret.

Weiner:

Did you know what kind of a project it was — a fission project?

McMillan:

Well, I knew it had to do with atomic energy and with fission, certainly, but I can’t be specific now as to how much I knew, or how I knew. I will say that when Lawrence and Compton approached me it wasn’t a huge surprise to me. Of course, I had contacts back in Berkeley. San Diego is not very far from Berkeley. I certainly knew what was going on there to some extent. Lawrence wanted me to come here and work on his electromagnetic process. Compton was starting what they called the Metallurgical Laboratory, and asked me to come there. And I was talking to both of these people when the Project started a new laboratory for the final development. This was very appealing to me and this was what I ended up doing, but during that period of the late fall of 1942, I certainly had correspondence, I certainly visited in Berkeley.

Weiner:

We are now at the point of making the switch from the San Diego project to the projects which were taking shape at Berkeley and Chicago and other places, just at the point when it was being established as a centralized thing. Let me just ask this one question: Did you visit Berkeley during the San Diego period? Were you back and forth? You said that you knew what was going on here, but was that as a result of trips up the coast?

McMillan:

I’m not sure whether I came up the coast. There may have been no reason why I should have come up, but certainly there were Berkeley people coming down. Lawrence came down to visit the laboratory on several occasions, and he would tell me what was going on. [BREAK]

Weiner:

We have just had our lunch break plus. When we left off we were talking about how you got involved in the Los Alamos efforts and the nuclear energy efforts in the war. You said you had had inquiries from people wanting to get you involved, Compton on one hand, and Lawrence on the other.

McMillan:

Right, and I have some correspondence on that which can settle the exact dates.

Weiner:

And you were aware of the Berkeley work. You made the decision to come up, you were saying, in the fall of ‘42.

McMillan:

That is right, and there was a period in November sometime when I and my wife left San Diego. She settled in with her parents in San Marino, near Pasadena, and I commuted between there and Berkeley. I spent a great deal of the next few months up here living in a hotel and making the plans for the new laboratory, with the other people who were planning — of course, Oppenheimer primarily, by this time he had been chosen as director. Tolman was helping a lot. He came up from Pasadena and was there. We were using my old office on the top floor of LeConte Hall. It was set up as the first office for the project. Hugh Bradner was around and had a lot to do with that. Also the military was involved. There was a Col. Dudley who had been chosen to find a site and do initial site planning.

The initial scope of the laboratory, something of a layout, was started there. Equipment was ordered. I was responsible for ordering the machine tools for the shop, for example, so I signed many orders for lathes, drill presses, and things like that. We got an initial complement of electronics equipment. That was all going on in this office, and somewhere along there, the office next to it was also taken over, so the Project had two adjacent offices. Then there is the story of the trip which Oppenheimer and I made along with Dudley to inspect the site they had chosen. That’s a little story in itself. I have had some correspondence with Dudley recently — within the last year — and it’s a story that might be good to come back to with those papers in hand, rather than trying to do it right here. Perhaps we can splice that in. How would you like to do it?

Weiner:

If you could give an outline of it, that in itself would serve as a reminder.

McMillan:

All right, I will give an outline of it. I think in the course of the correspondence I did get some dates but I haven’t looked this session — it must have been in November. Colonel Dudley has chosen a site at a place called Jemez Springs. There was a certain prescription for what the site should be like. It should be isolated; it should be capable of being secured; and it must have the necessary things for life, such as water, access, and so on. A number of sites were proposed, mostly in the Southwest, and Col. Dudley has hit upon this as being the best site. So we went out – Oppenheimer and I and Col. Dudley went to Albuquerque and drove up to Jemez Springs. As will appear in a moment, this place was not too far from Los Alamos. We drove up Jemez Canyon and we came to some point and rented horses, because we were supposed to ride the boundaries to see where to put the boundary fence.

The three of us set off on our horses and started riding around this place. We never did ride around it because it would have been utterly impossible. The site is in the bottom of a deep canyon and the fence is supposed to be up on the top wall of the canyon which was pretty difficult and inaccessible. Also those walls would not have been any defense for a good climber who really wanted to get in, but just hard for anybody else. I was saying that I didn’t think this site was good. It was too small, too narrow, claustrophobic, and the sun didn’t get down in there; it was dismal, and this was not a suitable place. Oppenheimer was loyally defending the choice of Dudley. About this stage of the argument, Gen. Groves came in. He came in separately. He drove in and we met him at a prearranged spot. He had just flown out from the East, and one thing I remember was that one of his arms had fallen asleep. He had slept on the plane with his arm folded under him and it was asleep. It never did wake up the whole time he was there. Groves said almost immediately, this is not right, this is no good. By this point, of course, everybody had to agree. Dudley was very reluctant to agree.

He had put a lot of work on this thing, and he brought forth many attractions of it. But Groves, I suppose for about the same reasons I did, considered this site unsuitable for a laboratory. If we had started it there we would have had to move because it would not nearly have accommodated the amount of space that was eventually needed. At this point, Oppenheimer said, “Well, farther up the road, there is a boys’ school, The Los Alamos Ranch School. It is up on the top of the mesa and we might look there.” So we got in the car, the Jemez Canyon road goes on upstream, then you cut across the Valle Grande, an enormous extinct crater, cross that, go down the other side, and you come to Los Alamos. We got there. It was a boys’ school and some of the boys were out playing soccer in their shorts and there was a light snow falling. The boys and their masters were out there in their shorts with the snow falling — it was a scene I will never forget. We all liked it very much. Groves said essentially, “This is the place.” So that is how it was chosen. That would be, I think, in November. I tried to get this date settled once. Someone had brought it up and various books written in the period mention how this happened. I found out finally that Col. Dudley [now Gen. Dudley] had retired and was living in Texas. I got his address and wrote to him, and he was very cooperative. I have a correspondence of several exchanges. I was asking if he had travel records and so on, but he didn’t keep records either. Between us, I think we got this thing pretty well sorted out as to how and when that happened. [The date of the trip was Nov. 16, 1942.] The second time I was there was with Lawrence and Oppenheimer. I had been east to the Academy to talk to some people there about setting up the project, and on the way back stopped at Santa Fe and met Lawrence and Oppenheimer and we went up again.

Weiner:

The second trip was after the construction had started?

McMillan:

No, that was not long after the first. [Nov. 20] It was just another inspection, and this time they were arranging what to do about taking over the place.

Weiner:

Where did the story come from, and how much truth is there in it, as reported by Nuel Pharr Davis — someone who has generally been unreliable in terms of his historical accuracy — that you had been considered as director of the project.

McMillan:

There is this much truth in it — when I was in Chicago at an organizing meeting, discussing the project with Ernest Lawrence, he had said to me, “Well, we will have you for director.” There is that much truth in it. I don’t recall that I really took it so seriously that when it didn’t work out that way I had any sense of disappointment. Nuel Pharr Davis has it that Groves thought I was too young. I have no idea what process went on there. I don’t believe I ever discussed it with Groves. But the whole basis of this was that Lawrence had said to me, “Well, we will have you for director.” A remark like that is not something one bases one’s life on. Nuel Pharr Davis also has the story that Panofsky was approached to be director. Panofsky told me that that was ridiculous, as he was a graduate student at that time. Davis has made up or distorted large numbers of things in that book.

Weiner:

I have a copy of the letter you sent to Seeger outlining some of these things.

McMillan:

Yes, I did give you that.

Weiner:

At the stage of coming up to Berkeley and your office and the adjoining office being used as discussion rooms, by that time certain fundamental decisions had been reached. You weren’t in on those earlier decisions when the Project had been established, but it already had been working at several sites. The decision was made to find this out-of-the-way site, and it was at that time that you came in. Is that right?

McMillan:

Right. I was certainly in on that inspection of the site. It was rather close to the beginning.

Weiner:

And then the other work that you were involved in was getting materials set up. Was any scientific thinking and discussion done at that primary stage?

McMillan:

There was a great deal of scientific discussion.

Weiner:

Of course, you can’t order things without knowing what you are doing, but I mean specifically about the processes involved, the kinds of scientific investigations one would have to have.

McMillan:

We were trying to think of what kind of investigations would be needed and what kind of equipment would be needed to do these, and of course, the big problem which occupied a lot of the discussion was the matter of the assembly of the bomb. If you have fissionable material all together it will undergo a chain reaction and will then blow itself apart. So, if you assemble it slowly it will start blowing itself apart before it is completely assembled, and you get a small explosion. The bomb will fizzle. So one had to find a method of assembling components more rapidly than the time of the build-up of the fission reaction. There was a lot of discussion of that, as well as of the simple nuclear physics involved.

Weiner:

Much of that simple nuclear physics was known and published by that time.

McMillan:

Some was known but a lot of it was not because secrecy was clamped down fairly early.

Weiner:

That’s right and the British work was included. Did you have contact with British people at that stage?

McMillan:

I didn’t but others may have.

Weiner:

They weren’t involved in these discussions.

McMillan:

No.

Weiner:

How long after your return here did you leave for Los Alamos?

McMillan:

I tried to make a list of all the residences I have had, putting in the best guesses of the times. I have down here for moving there, March 1943. It can’t be too far off.

Weiner:

So the period here of four months, let’s say, was occupied in preparing the site.

McMillan:

Right, planning buildings. Even though Col. Dudley had been frustrated in his first choice, he was still with the project designing building layouts. We had maps of the area by then and were deciding where to put buildings, what kind of buildings, and so on. I think you can find when construction started — they keep good records of construction. By the time I came out, which I think was in March 1943, there was already construction well underway. There were technical area buildings. Buildings for housing for people were still being made, and there was an interim period when people were stationed in various little ranches throughout the valley. Down below the mesa there are Indian villages and various settlements, along the Rio Grande and its tributaries.

My wife and I and our infant daughter by that time stayed at the Ancon Ranch, a very charming group of adobe structures. Just recently I was at Los Alamos for the dedication of the new meson physics facility, and while there I did some touring around and found the old Ancon Ranch. It was still there and I walked in and looked at the place where we stayed. People are still living there and it is still a guest ranch. We were there for a period of a month or so before we actually moved on to the hill. Then when housing was ready, there was a sort of a movement from down the valley, taking residence on top of the hill. The house that my wife and had was one of the headmaster’s houses attached to the old school. We were one of the few fortunate ones. By virtue of being early in the game, we had staked some claims. When we arrived we found that a bunch of soldiers had been billeted there and hadn’t cleaned up very well, so that the place was a real mess. We didn’t even have a stove to cook on and for the first week or so we were doing our cooking over the fireplace. But we got settled in there rather quickly and it turned out to be a very nice place.

Weiner:

You came in very early were you given any title when you came in?

McMillan:

No, I don’t recall having a title. I was the head of a group. From the beginning was with a group whose general problem was the bomb assembly. There was a Capt. Parsons from the Navy that worked with. In fact, was under Parsons, if you want to get the organization right. Parsons was in general charge, and I was his deputy in charge of the test work for what was called the gun method. There was a ranch toward the southwest part of the Los Alamos mesa, known as Anchor Ranch, which was used as a site for the test range. Since it was a gun method we did have guns there, cannons which were firing test projectiles into other things. Since that was a fairly hazardous occupation it had to be done in an area remote from inhabited areas, and that was the Anchor Ranch station, which I more or less designed and supervised, and where I ran the test program for a considerable period.

Weiner:

How did you find it, once it got going?

McMillan:

As I told you before, I always end up doing field work. At San Diego I was out on ships testing things in the ocean. At Los Alamos I was out on Anchor Ranch.

Weiner:

Did that keep you, during the course of the Project, somewhat away from the day-to-day interactions with the other groups?

McMillan:

No, we had seminars, and our people got together. Gen. Groves initially had the notion of compartmentalization but among the scientists it never worked.

Weiner:

So, for example, the theoretical group and the experimental groups and the other people would still manage to have pretty regular consultations?

McMillan:

Not just manage to, we did. It was known that we did. There was nothing furtive about this.

Weiner:

How would you characterize the atmosphere there compared to the other places that you had been?

McMillan:

The atmosphere at Los Alamos was not like anything else that has ever happened that I know of. Scientifically, it was more like the MIT Radar Laboratory, a great deal of ferment and excitement, a great deal of freedom. There was much tighter security. Mail was censored. You knew that any mail that you sent or received was going to be opened and looked at. And there was an enormous air of urgency. But it was an exciting place to be, more so than San Diego, probably because of the existence of the older Navy Laboratory there and the more bureaucratic way of operation. Los Alamos retained a lot of the MIT feeling, plus isolation, plus secrecy.

Weiner:

You were living together as well. You were the community. It was quite different from a hotel room in Cambridge.

McMillan:

Right.

Weiner:

It seems to me that these wartime experiences were the first time that you came into wide contact on a working basis with so many people from other institutions.

McMillan:

Not so, at MIT there were people from all over the United States.

Weiner:

I meant all of them. It was true that Berkeley had visitors from all over, but it was still Berkeley and still a particular thing. This was a new enterprise, and this is not a question but just a comment that the experience seems to have been a very rich one for people, getting into contact with styles different from their own. You got to Los Alamos in March 1943 and I imagine began right away, but the work got more intensive as time went on. How was your schedule? Was your team working around the clock on these things or were there long periods when you had the opportunity to concentrate on other things?

McMillan:

Most people worked on a somewhat normal regular work schedule. We got up reasonably early, worked through the day and came home at night. I don’t mean there was no night work. There certainly was night work, but the regular routine was more that of a normal working schedule.

Weiner:

And then there was the additional problem of taking up the time to find a life in a new community questions that you didn’t have to worry about at home everything from laundry to law and order and water. Did you get involved in town affairs, politics?

McMillan:

The women got deeply involved in town affairs. Some men did, I don’t remember being very involved in it, but some people became very excited about town matters. My wife has written a book about that period from the women’s angle a manuscript I should say she hasn’t found a publisher yet. I don’t know if that is something you want to add to the archives or not.

Weiner:

If she would be willing.

McMillan:

If she adds it to the archives, would it then be impossible for her to publish it outside?

Weiner:

Of course she could publish it.

McMillan:

She still, I think, hopes to publish it.

Weiner:

It would be interesting to have that special point of view. Did you find time, if you worked a regular schedule, for many physics discussions within the working day, that is, not strictly technical things, but seminars on some related fields?

McMillan:

There were regular seminars. There were theoretical seminars and various group discussions. I know our group under Parsons had its own discussions. No single person would go to all the seminars they had at Los Alamos.

Weiner:

Would they be on the technical problems you were facing or on some aspect of physics?

McMillan:

They were pretty oriented toward what we were trying to do — those parts of physics which connected with it — but there weren’t, in my knowledge, general seminars on other topics in physics. It was not an academic atmosphere. The series that you are thinking of was intended for training new people, people who came in who knew little or not very much physics, and so they would start from the very beginning. By the way, you were talking about getting a copy of that — I’m sure we have copies of that around here. [Copy attached. I gave 7 lectures in the period September 14 - October 5, 1943.]

Weiner:

I would like to have one for our library. I don’t know why we don’t have one but if they are out of print, it would be good to get one from you. Were those lectures given as a sort of course?

McMillan:

They were given as a sort of course. They were regularly scheduled and they were attended by the younger people in the Project. We had a lot of SEDs (Special Engineer Detachment). They were mostly young people beginning scientific training who, when drafted into the Army, were put into this detachment in order to use their scientific ability. There were quite a large number of SEDs and they attended this course. It was quite elementary.

Weiner:

What about being abreast of other things going on, not only in that field but in general in physics, in other words, the current journal literature?

McMillan:

Of course, the library subscribed to all the journals. We knew what was going on in the journals. We didn’t keep up scientific contacts with our colleagues outside that would have been forbidden it was a one-way flow. We knew what was going on.

Weiner:

Did anyone who was at Los Alamos ever publish a paper from there by that mean, did they complete something they had started earlier?

McMillan:

To submit a paper from there during the Project, no.

Weiner:

Not date-marked there, it would be from their university, but do you know if for instance anyone published something in the Physical Review in ‘43 or ‘44 that originated in Los Alamos. Your synchrotron paper was ’45. That originated from Los Alamos, didn’t it?

McMillan:

It was written at Los Alamos but published out of Berkeley.

Weiner:

That is what I mean. Was there much of this going on?

McMillan:

I don’t know.

Weiner:

We could look at the Physical Review articles published during that period and then one could analyze who among the authors were at Los Alamos. I just thought you might have a personal impression.

McMillan:

No, I don’t.

Weiner:

But then you still were keeping in touch with world physics. Did you have much time for that — if you were teaching this elementary course?

McMillan:

Teaching the course didn’t take very much time because each individual only gave a few lectures. So apart from preparing it, that would mean a total of a couple of hours. The work of the Laboratory took a lot of time.

Weiner:

Is there anything more to say about your specific duties in the test branch?

McMillan:

First was to plan what we needed there, which I did jointly with Parsons. Capt. Parsons was raised to Admiral later. I was there almost every day to carry out the operations.

Weiner:

In your day-to-day routine how much of it was setting up a series of experiments which would give you little bits of information which you needed for something larger? And how much of it was similar to the work which you had done in San Diego, and in other places, where you had really worked on a more practical level?

McMillan:

It was more planning and setting up, because the operation was a rather specialized one and was mostly carried out by people who had special training. For example, the loading and firing of guns was done by experts who had to know how to handle powder and igniters, etc. There were ordnance experts who did that. I did a lot of the planning and evaluated the results afterwards.

Weiner:

These would be set up and tested with very specific runs, and then you would evaluate the results.

McMillan:

That’s right.

Weiner:

How closely was your work phased in with the other divisions? Were you working on a schedule determined by them? How dependent were you on their timetable and how dependent were they on yours?

McMillan:

I would think we meshed together pretty well. We had fairly close contact with some people in theory. I remember Charles Critchfield particularly was doing theoretical work in connection with this part of the work. He was helping to figure out what things we ought to try. I might say that the work we were doing at that time did not involve nuclear materials. It was the mechanics of the assembly, what happens when you have an impact of a projectile going at a high velocity into a cavity. It was the mechanics of it — there were no nuclear materials involved.

Weiner:

It was possible that that kind of work could have been done in some ordnance laboratory.

McMillan:

It could have been but it might have been hard to maintain secrecy, and there would have been a serious time lag. Having the Anchor Ranch stationed right there meant that if anybody had an idea that he wanted to try — and it was largely a matter of bright ideas at that time, there were no general principles — we could set it up and try it in a few days. We could get the parts made and fire it off and see what happened.

Weiner:

It was an ordnance problem, not a nuclear physics problem. I guess many things at Los Alamos were non-nuclear physics problems.

McMillan:

I never did any nuclear physics as such at Los Alamos, or during my whole wartime career as a researcher.

Weiner:

I am trying to establish the general setting there, to lead into the point of the development of your ideas which were to lead to the synchrotron.

McMillan:

Before we go to that, do you want to know what else happened at Los Alamos, just to get the time sequence a little straighter?

Weiner:

Certainly.

McMillan:

After I had been for some time at Anchor Ranch, and when Seth Neddermeyer had his idea of assembly by implosion — the fact of that is no longer classified — I worked over into that branch of the work. Neddermeyer had proposed the idea of imploding or compressing, assembly by implosion or compression, very early in the game. I remember him giving a seminar on this quite early, and I remember also it being received with considerable skepticism. But Seth was very persistent, and on his own started some experimental work along this line. He went out to the Bureau of Mines Explosives Test Station at a place called Bruceton, Pennsylvania, and I went with him because I was interested in that. While there, we met George Kistiakowsky who later joined the project, and whom I had known already when I was a graduate student. We visited this station, and Seth ran off a few experiments there to see how these things could be done.

Of course, in a bomb the implosion has to be spherical — one has to assemble it from all directions — but for test purposes one could do it in a cylindrical form, where one can observe optically through the hole and see what is happening. That is what he started doing there at Bruceton. We fired some shots there and then he came back to Los Alamos and set up a small sort of rustic test station out in a place called South Mesa, between Anchor Ranch and the main technical area. I helped him there — this means physical help, there was not much intellectual help — it was all his idea. But I was enjoying doing this. We had powdered TNT which was a little hard to manipulate, and then a plastic explosive which you could wrap around, and these rather primitive methods. We were starting to find out how to make good observations of these phenomena, and the general acceptance of the idea was growing in the laboratory.

Somewhere along the line it became an official branch and eventually Kistiakowsky was brought in to run this, and Seth Neddermeyer went off into something else. But Seth was the real originator of that method of assembly, and I was getting into it as a matter of interest because I like doing this kind of thing. So when the implosion program was well-established, there was a method for observing the motion of metal surfaces which was called the magnetic method, and which had been proposed by Joe Fowler. The administration wanted to set up this as a project so I moved in — or was moved in — sort of mutually on that. For the last part of my stay there I was in charge of this magnetic method. Ed Creutz came in at that point, Joe Fowler I mentioned, Louis Rosen was in that. He worked with me. He is now the head of the meson facility at Los Alamos.

Weiner:

Did you give up your other responsibilities?

McMillan:

I gave up the Anchor Ranch responsibilities at that time completely. From then on I was mostly in the laboratory. The other people were doing the field work. Creutz and Fowler and Rosen were doing the field work. I became a laboratory man for my last months. Then came the test at Trinity. I was there as an observer. I was not involved in the test. I was down there as an observer and saw this thing. Then pretty soon the war was over and I left.

Weiner:

Before that, what was your feeling about what you had witnessed? First of all, did you have any speculations as to its relative success and if so, did you have any feeling of foreboding?

McMillan:

I had some speculations as I remember. They had a poll on this and I believe I put in a rather low estimate, but not because I thought I was really capable of making a good estimate. There had been some problems with the magnetic method. The last big test with the magnetic method, which was done on a full scale model, showed some rather anomalous results, and it was shortly before the test was to be fired, and it got everybody very scared as to whether the implosion was going to be uniform enough. This observation was properly interpreted, I believe, by Bethe. He was the one who finally figured out why it was giving these peculiar results, which were that you would get certain signals at the beginning of motion, and these signals were a little bit fuzzier than they should have been. That was practically the last minute before the shot was to be fired, and there was a certain amount of apprehension about this result. But my estimate in the pool, which I don’t remember exactly, was on the low side.

Weiner:

How close were you to the blast?

McMillan:

I believe I was 20 miles. I was there as a visitor, not as a participant, and there was a site set up for all the VIPs, and I was out there with the VIPs. I was in fact with Ernest Lawrence who came out, and a number of others. You ask what were my feelings. I wrote up a little account of that which I can get for you. All observers were asked to write down what they saw, and I did. It was submitted and got into some classified report, but now it has been declassified and I’ve been able to get it back. It’s a slightly journalistic account.

Weiner:

It would be quite interesting.

McMillan:

I’ll give you that.^[1]

Weiner:

Was that written up at the moment, within the day?

McMillan:

Yes, we were asked to write it up right afterwards. You asked the question: What were my reactions? Did I have any feeling of foreboding or what? I don’t think so. I’m trying to reconstruct my feelings. Once the thing went as it was supposed to and I saw what it did, I was not really surprised that it worked. My low estimate was not based on a carefully reasoned thing — it was just the possibility or the general rule that if something deviates from the way it is supposed to be it usually deviates in such a way as not to be as good as it is supposed to be. Rarely does it deviate in the way of being better than it is supposed to be. So I estimated it wrong. When it went, I was not terribly surprised. I don’t think any feeling of foreboding for the future really set in until perhaps later. The chief emotion was that something you had worked on so long and so hard had been a success.

Weiner:

But you had no way of visualizing in advance the physical appearance?

McMillan:

No, I had no way of visualizing the physical appearance. It had been predicted there would be what they called a ball of fire, which would rise because it was very hot, like a hot-air balloon. This had been predicted. The long column that trails up behind it — I’m not sure that was predicted. And the mushroom cloud and the stem of the mushroom cloud — at least that was a surprise to me. The rising ball of fire was not. The color effects were somewhat of a surprise. It is all described in the account.

Weiner:

I really would like to see that.

McMillan:

I will get it for you.

Weiner:

You weren’t with the press people — were they somewhere else?

McMillan:

There was only one press man who was allowed at the site, and that was Bill Laurence of the New York Times. I was either with him or right next to him — he was with that party. I got to know him quite well and I certainly did talk to Bill Laurence on or about that time.

Weiner:

His account was published in a book.

McMillan:

Right, I have the book.

Weiner:

You said that later on some forebodings developed. Do you mean later on at Los Alamos?

McMillan:

No, I’m not trying to be too specific about this. Certainly the thoughts about what it was going to mean to the world to have available such a powerful explosive must have invaded my mind somewhere. You can’t help that. Certainly everybody else was talking about it. Among the scientists there was, of course, a great deal of discussion following this, and attempts to sway the course of events, and so on.

Weiner:

Do you remember those? There were various petitions circulating, at least in Chicago.

McMillan:

That’s right, there was the Chicago petition. There was a movement at Los Alamos which I did not take part in.

Weiner:

What was your response to that? You were working on the development of a weapon.

McMillan:

I assumed it was going to be used, of course. That’s why you develop it. I don’t recall in any way trying to prevent the use of this bomb in the Japanese war. That’s what it was for. To end the war, that was something worth doing. Anyway I was not in the chain of decision, so I didn’t have to force myself to take a position.

Weiner:

Do you recall any assumption that were made regarding other efforts, for example, the idea that the Germans might have been working on this?

McMillan:

There was a lot of speculation about that, of course.

Weiner:

Was there any new information that came in while you were there?

McMillan:

Not while I was there, no. The ALSOS project came considerably later.

Weiner:

I was just wondering whether this was a live issue or whether the original assumption was the same one that carried through.

McMillan:

There was a lot of speculation about what the Germans were doing, but no information.

Weiner:

That is one of the things that you wanted to fill in — how you switched from the Anchor Ranch project. Then you talked about Trinity and more general issues. Is there anything more?

McMillan:

I don’t think I can get any more information on that, because obviously I was not writing letters home and I don’t have any personal papers giving that date, unless you can find it in the records of the organization. I can’t get that date any better. Maybe you can get it from Seth Neddermeyer, or Ed Creutz — the magnetic method — or Louis Rosen. There are several people.

Weiner:

It could be included in the Hewlett and Anderson book. I’ll have to check that and see, or in the Stefan Groeuff books. [no dates are given]

McMillan:

Yes, the Groeuff book is very journalistic. He writes what I call a “Gee Whizz” style.

Weiner:

I’m sure it is mentioned in histories or in general accounts. It is not crucial anyway. The point is that those were your two major jobs.

McMillan:

Those were my only two jobs at Los Alamos. The synchrotron was private — it wasn’t part of my official duties.

Weiner:

Before we get into that — did you come into contact with people like Feynman there?

McMillan:

Very much so. In the beginning days of the project—it would have to be during the Berkeley period—I went on at least two recruiting trips. In one case it was to recruit people, that was the group at Princeton working under Bob Wilson in a method of separating isotopes which they called the Isotron. I made a trip to Princeton essentially to sign these people up for the project. The whole group moved en masse to Los Alamos. Feynman was among that group. I believe I met him on that visit or at least shortly after that. I got to know Feynman quite well. He is a very articulate person, a very interesting person. One thing I remember is when the first computers arrived at Los Alamos.

They were the old IBM computers, card programmed computers. They were largely mechanical rather than electronic, and therefore looked mush more complicated than the present computer does. These arrived without the service people who were supposed to set them up and get them running. Dick Feynman moved in and got these things running before the IBM people had come along to do it. He figured out how they worked and got them hooked up and was doing computations. That’s the kind of person he was. The other recruiting expedition was to recruit a piece of equipment, namely a cyclotron. The Laboratory wanted to acquire essentially one of each of the major types of nuclear physics equipment. I went out, I think with Oppenheimer and maybe with John Manley, on a trip around the country looking at various things. I know we looked at Van de Graaff machines, Cockcroft-Walton machines, and cyclotrons.

Then I made a special trip searching for a cyclotron suitable for moving to Los Alamos. In the course of that I visited something like five different cyclotron laboratories, including Harvard, and the Harvard cyclotron seemed to be the most suitable for this purpose. We had to have one that had sufficient power to do the job, and also of sufficiently good construction so that it could be moved without falling apart. The Harvard cyclotron filled that bill, and so it was then arranged at higher levels that the Harvard cyclotron would go to Los Alamos. I know that for years afterwards Harvard people called me “the man who stole their cyclotron.”

Weiner:

What other places did you visit?

McMillan:

A man was in this office just a few days ago who was with the Harvard cyclotron at that time, a guy by the name of Hickman (Roger W. Hickman, now retired) — he was here October 13. He reminded me of this how I’d come out there and stolen their cyclotron. He said they really weren’t very bitter about it, but they had put an awful lot of work into it and to have it taken away was something of a blow. The cyclotron was moved to Los Alamos and Bob Wilson was put in charge of the setting up and operation of that cyclotron — so my two recruiting efforts ended up in the same building.

Weiner:

What other places did you go to in search of a cyclotron?

McMillan:

That’s a little hard to remember.

Weiner:

Illinois, Purdue, MIT, Columbia, Cornell? By that time there were at least a dozen.

McMillan:

There were a dozen or so. The choice was on the basis of energy chiefly. Princeton, I think, was one. There was one at the Biochemical Research Foundation.

Weiner:

Bartol?

McMillan:

Not Bartol, the Biochemical Research Foundation was a different place.

Weiner:

In Philadelphia.

McMillan:

In that general area.

Weiner:

I have a list of all the cyclotrons in the post-war period, but it doesn’t list the one in Philadelphia.

McMillan:

Bartol had a 60-inch cyclotron. That is too big to move. Let me see your list. Dover, Delaware, the DuPont Company, could it be that one?

Weiner:

I don’t know whether the name Biochemical would be appropriate.

McMillan:

They could have acquired it. This is post-war. You ought to get pre-war.

Weiner:

I have that in some of Lawrence’s letters; Cooksey had a pre-war list which I will dig up. When did the recruiting trip for the cyclotron take place? Wilson must have been in the latter part of ’42 or the early part of ’43. Was the cyclotron after the Wilson trip?

McMillan:

It would be early in ‘43. I have to use very slight clues. I’m basing this on the fact that when I was out in Minnesota, which was on the previous trip looking over equipment in general, I remember it was winter because it was pretty cold. And so if the other one is later, it has to be early in ‘43. Ask Bob Wilson. I don’t know how far afield you want to go on this kind of research, but you can find out from the person who was moved as it is a key point in his life.

Weiner:

I have it from Feynman specifically. I realize I have another “Biochemical Research Foundation, Newark, Delaware.”

McMillan:

That is probably the one listed as DuPont.

Weiner:

It looks like 30-inch, maybe it is 36-inch, 12MeV deuterons.

McMillan:

That’s the one.

Weiner:

Bartol, as a matter of fact, is listed here as a Van de Graaff machine.

McMillan:

They had a 60-inch cyclotron that was probably built later.

Weiner:

OK, we solved that problem.

McMillan:

I’m glad my memory didn’t do me dirt on that one.

Weiner:

Getting back to Feynman, your contact with him at Los Alamos was in the same way as with loads of other people who weren’t working directly with you but you were aware of them. I know quite a bit about his role there. It would be interesting to characterize a few of the people you met for the first time there, and how you saw them at that stage of their development. You mentioned only a little bit about Feynman.

McMillan:

He struck me as one of the brightest people I had ever met. He was tremendously quick mentally. He did some very impressive things, like assembling a thing as complicated as one of those old IBM computers without even an instruction book, just by looking at the thing. And he was that way in doing his work too — his theory and his mathematics — very quick, very original.

Weiner:

Was it you who mentioned to me about the quadralogue?

McMillan:

He did that, yes. He liked to imitate voices, and I’ve often said that Feynman is one of the few physicists I’ve known who could have made a living in show business. He had a tremendous sense of rhythm. He was a good mimic. And the quadralogues which I heard him do once or twice would consist of an imaginary conversation between four people carrying on an argument and all using different voices.

Weiner:

Quadralogues instead of dialogues.

McMillan:

That’s right.

Weiner:

This was done there for entertainment of anyone?

McMillan:

Just for entertainment, yes. I don’t think he did this very often. I heard him on a couple of occasions. But the time I remember, we were riding in a car somewhere, and this was a small group of people. Feynman was sitting in the back seat just carrying this on. Everybody was having a great time listening to him. He wouldn’t do it if you asked him. He wouldn’t do it on request. He just had to feel right.

Weiner:

This was a very difficult period for him personally because of his wife’s illness.

McMillan:

He had a wife in a sanatorium in Albuquerque who was dying of tuberculosis.

Weiner:

And then there are all the stories about the games with censorship.

McMillan:

Oh yes, I think everybody has heard those stories.

Weiner:

What about other individuals there who impressed you in terms of their personalities or their physics?

McMillan:

Teller was there. Of course, Teller I had known before.

Weiner:

How had you known him? He was in Washington at the time.

McMillan:

I don’t remember when I first met him.

Weiner:

Did you ever go to the George Washington University conferences?

McMillan:

I never did. I have never been to any conference there.

Weiner:

I guess they were small theoretical conferences.

McMillan:

I have been to a meeting of The American Physical Washington Society held in George Washington University, but not to any special conferences. I am sure I met Teller before. Gamow I know I met before. Gamow had visited Berkeley. Bethe I got to know quite will there. I’m trying to think of theorists. Stan Ulam I saw recently, and still see occasionally.

Weiner:

Weisskopf, for example.

McMillan:

Weisskopf by all means. Anybody who was there in any reasonably prominent position I would have known because it was a small enough group so that everybody knew everybody.

Weiner:

What kind of contact did you maintain with Ernest Lawrence during the period that you were there and he was here?

McMillan:

Not very much. He visited the laboratory perhaps two or three times while I was there.

Weiner:

Now that we have done a lot of background, would like to trace, from the earliest possible moment that you can remember, your work on phase stability and all the ideas connected with that. You mentioned earlier, but guess it was off the tape, that the correspondence with Hans Bethe regarding the energy limits of the cyclotron.

McMillan:

Oh, that was in 37.

Weiner:

Anyway, along that period, but you were grateful for this because it made you think about these kinds of problems. I don’t know whether there is any kind of thread of continuity between that and the work that was done later.

McMillan:

No, that was just background. All that meant was that when I did come back to it I had some background and it did not seem like a strange subject to me. I think the beginning of that would have to be in June or July. Do you have any dates on that?

Weiner:

The paper is in September.

McMillan:

I think the earliest date I can establish is in July.

Weiner:

“Since my first thoughts on the subject occurred near the beginning of July 1945...” This is your little note on the origin of the synchrotron which is 1946. I trust that recollection, as you are saying, a year later, that you think, it was July. How did it come about?

McMillan:

Things were coming on toward a conclusion; I was on leave from the University of California and I was already starting to think about what I might do when I came back. I was thinking along the lines of getting higher energies than we had gotten with the cyclotron. Of course the 184-inch cyclotron wasn’t a cyclotron then. It was still being used as an isotope separator. I was trying to think of how one might go to the next level of energy. The 184-inch cyclotron as planned at that time would have reached something like 60 million volts, possibly stretchable to 100 million volts which was Lawrence’s goal. But by the methods we had then it was extremely difficult to go any farther, because the cyclotron depended upon the phase relation between the circulating beam particles and the high frequency field which was doing the accelerating. If the particle crosses the gap at the right time the field is urging it forward and accelerating it, but the time shifts around so it’s on the other half cycle when it will be pushing it backwards, the phase of the particle with respect to the RF changing during acceleration because the angular velocity is not strictly constant.

This is all following the old theory first put forth by Bethe, and I was trying to think of some way to overcome that. One way would be to use an induction accelerator, a betatron type of accelerator, in which there is no phase relation — the force is continuous. In order to get very high magnetic fields one would then go to an air core machine. As it happened there was a man at Los Alamos who had come out to help with the magnetic method of observing implosion. He was an expert at calculating magnetic fields from the Bureau of Standards. I got some help from him in methods of calculating the fields from arrangements of conductors.

Weiner:

Who was that?

McMillan:

I cannot now think of his name. I may be able to get it later. He was an older man, one of the old-time experts from the Bureau of Standards, but cannot remember his name. [Chester Snow] And so I was working out a conceptual design of an air core betatron, and fairly early had set on a figure something like 300 million electron volts energy for electrons, which was based in a very loose way on the production of mesons. As soon as got into this design a little way discovered that a machine like this had some very great practical difficulties on account of the large stored energy, that you store energy in the magnetic field which goes like the square of the field strength, and if you are going to high fields you end up with storing enormous amounts of energy. Energy has to go in and out of the machine every cycle of acceleration.

This began to look like a very impractical kind of thing. Somewhere along the line and the date of this is probably early in July (it could have been late June) I remember I was lying awake in bed one night and thinking about this problem of how to make an accelerator using the cyclotron principle of successive accelerations and maintaining the phase relation. So I started figuring out what happens when a particle does get out of phase, how does that change the amount of acceleration, and when I thought this through in my head, I realized that there was going to be a stability. This was all in one night and if I had had the true historical sense, as soon as I woke up in the morning I would have written down in a notebook: “I made a big invention last night.” I never did this, although I told people about it.

Once having the idea, then the next step was to work out the equations to see if the intuition I had was really going to work that way. The phase tends to lock in, that is the particle tends to stay in step with the field, but it can oscillate around that condition, it can move forward and back in an oscillatory way. If this oscillation about the proper phase gets too far then you pass into the region of instability and the particle stops being accelerated. So I had to convince myself and others that the amplitude of the oscillations would decrease as you accelerate rather than increasing. I had to get that part of the thing cleared up. That comes out of the full equations. Then another difficulty got thrown at me — this publication by a couple of Russians, Pomeranchuk and Ivanenko. It’s mentioned in my second letter.

Weiner:

In your second letter [to Phys. Rev.] you mention Veksler all the time.

McMillan:

No, there’s one you left out.

Weiner:

There’s a publication on your list, which I don’t have a copy of with me. (“Radiation from a Group of Electrons Moving in a Circular Orbit,” Phys. Rev. 68, 144-145, 1945.)

McMillan:

I’ll find it...I don’t cite them. They’re the ones who pointed it out. I don’t know why I didn’t refer to them. Probably the reason I didn’t cite them is that that formula comes directly out of electrodynamics and Pomeranchuk & Co. just pointed out the effect of this on betatron operation. Anyhow, I probably should have cited them. The other name was Ivanenko, whom I know. I have met him and had correspondence with him.

Weiner:

Let’s get back to the story. You said that this came out.

McMillan:

Some time around then it was pointed out to me that this radiation, which I think was well known — I don’t think it came out just then — if you look at the formula it contains the square of the electronic charge. Someone said that if you have a bunch of electrons going together then you would have to use the charge of the whole bunch, which would introduce the square of the number of particles in the bunch going around in the synchrotron. If you do that the rate of radiation is so colossal that the whole idea of it might as well be forgotten. That was the difficulty which was brought up to me — probably by Oppenheimer. I think it was Oppenheimer who pointed out to me this difficulty. So then I had to find out how to calculate the radiation from a bunch of electrons, which, of course, was a problem of another whole magnitude of difficulty than just calculating the radiation from a single electron. And I worked on that for some time.

It was a rather intractable problem if you’re not a real theorist which I’m not. Then Rabi came in one time visiting, and he knew about this problem, and he had a note from Schwinger with the formula which Schwinger had calculated for a bunch of electrons occupying a finite range in a segment of a circle. So all I had to do then was to go ahead and substitute in some numbers and show that with the actual dimensions that one would have this was not a serious problem. Then my friends said it was all right to go ahead and publish it. They had felt it would be a mistake to publish something which might turn out to be a thoroughly impractical device. It was all perfectly sound advice, but it did prevent me from publishing for a while. Then, when I finally got that cleared up and had the paper all written, I wanted to get it published right away. Lawrence knew about it, I had corresponded with him, I had talked to Lawrence about it, and we were hoping to build one in Berkeley.

In the paper I say it was planned, though of course we didn’t have any money, but we hoped to get support for it. I wanted to get it published and get on with it, but the patent department at Los Alamos began raising the issue that I hadn’t gotten it properly patented and I couldn’t publish it. So I said I would publish it from Berkeley — I was planning to leave then — and in order to get it into the next issues of the Physical Review I had it taken by Bob Wilson, who was leaving Los Alamos before I was, to be mailed outside. That is how it was published from Berkeley even though the work was done entirely at Los Alamos. After it was published I got some quite angry letters — not I personally, but some university officials, from Mr. Lavender who ran patents for the Manhattan District, saying that this should not have been done. I am very glad that it was done because it was only a month or so after that that I got the word of Veksler, again through Los Alamos, that this paper of Veksler’s had come into the Los Alamos Library. Charlotte Serber, who was then librarian, made a photostat and sent it to me and said, “This looks something like some of the work you’ve been doing.” And of course that was Veksler’s last paper in that series. Then later on managed to get hold of the two earlier ones there were three in that particular sequence which of course established his priority in date, but I’m in the clear for being independent because I didn’t even know about it. Then Veksler saw my publication in The Physical Review and wrote a somewhat snappy retort which you have, I presume.

Weiner:

I don’t have his.

McMillan:

Well, you have the reference to it. Then I wrote my little thing entitled “The Origin of the Synchrotron” (Phys. Rev. 69, 534, 1946) to clear up this matter. At the same time I sent a personal letter to Veksler. I thought that sending letters to the Soviet Union was probably a difficult and chancy thing, so I had it sent off through diplomatic channels. Quite a long time later my letter came back to me all creased up — it had obviously been handled a lot — with a note saying that since normal mail service is established with the Soviet Union, we suggest sending it through the normal mail channels. So then I had to re-do it and re-date it and send it to Veksler. Then I got a very nice reply from him in which he said that perhaps the English translation was somewhat more gruff than the Russian original. And later I got to know Veksler quite well.

Weiner:

Did you save that correspondence?

McMillan:

Yes, I have that. It was interesting — interesting is the wrong word — I can’t think of a proper word to explain the actions of a patent department that would try to stop the publication of a normal scientific paper because there might be some patent implications, and run the jeopardy of spoiling one’s whole chance of getting any credit for what one did. If I had gotten the Veksler thing before I published mine I could never say anything except just tell people, well, I thought of it too. One could have no stature as an independent discoverer. You can’t do that ex-post-facto; it has to be honest at the time of publication.

Weiner:

Of course the patent people would say that all they were doing was to try to protect your rights and give you credit al so.

McMillan:

No, they were interested in the commercial applications.

Weiner:

Let’s talk about the time scale from the time when you were lying in bed and the intuition comes to you, in July say, to the publication of the paper which was September — what was your activity? Did you immediately start calculations, and if so, was it on a steady basis? Did it occupy all of your time?

McMillan:

The initial part of the calculations — that which was in the first paper — was fairly straight-forward and that took, I think, a few days. Establishing the equations of motion for the system and investigating the question of damping or undamping of the phase oscillations which was pretty elementary, didn’t take very long. The second part of it, trying to attack this problem of the radiation from an extended bunch of electrons, I spent a lot of time on, over some period in disconnected pieces. I’d try to think of how to attack it, and go at it and throw it away. I can’t tell you how long that was. I know I didn’t save any of that work. It was all pretty fruitless attempts. But in principle, if one forgets about the radiation problems, the thing could have been published within a week after I had the idea.

Weiner:

When did you first communicate this to Lawrence?

McMillan:

I have the letter and we can look that up.

Weiner:

But it was first through a letter.

McMillan:

Yes, it was first a letter. [Dated July 4, 1945]

Weiner:

How soon was it apparent to you and to him that this statement could be made which you made in your September paper: “Construction of the 300 MeV electron accelerator using the above principle is now being planned at Berkeley.”? When did that idea of incorporating it take place?

McMillan:

Of building the machine – very early, practically from the beginning.

Weiner:

The machine that you had designed…

McMillan:

I didn’t have a design for a machine but a general lay-out of what it might look like. The principle was the main thing. Lawrence was enthusiastic. I don’t recall anyone I told about it who resisted the idea. This was one of these things that is so simple that once you get somebody to understand it, their first reaction is, “Now why didn’t I think of that.” At least one person said that — Don Kerst, who is the great betatron expert. I told him about it very soon after I thought of it, and he said, “I’m kicking myself I didn’t think of it.” His reaction was anger at himself that he had let that go by. I don’t remember anybody who said, “Aw, that will never work,” with the one exception of this possibility of massive radiation, which I must say most people didn’t worry about. My instinct was that it wasn’t a serious problem, simply because the size of the bunch was large compared to the wave length of the radiation you were talking about, but some people insisted you had to find out what it really was before you could be quite sure.

Weiner:

But the enthusiasm of Lawrence for it was translated into an idea for a machine, although the machine that was in progress before the war had not been completed.

McMillan:

Remember I am talking here about an electron synchrotron. The broader application to the cyclotron is covered in that paper, but the actual adaptation of the 184-inch to a design using this principle took a little time. Lawrence had always insisted on making things work on a model scale before he’d go on to major construction, so there was a program set up here using the old 37-inch cyclotron as a frequency modulated cyclotron with a rotary condenser. You see, in anything using the phase stability principle you have to vary something during the acceleration. You can’t do it with fixed magnetic field and frequency, so there was this preliminary work done with the 37-inch cyclotron in order to check the principle out. As soon as it was shown to work, then the 184-inch — all plans were stopped, and it was redesigned into a synchrocyclotron.

Weiner:

On the idea of the electron accelerator, the point I was trying to get at was that this had not been planned previously.

McMillan:

No, there was no previous plan to build an electron accelerator. That was a whole new effort.

Weiner:

So it came out of your idea, and the first announcement of it was in your September 1945 paper. Lawrence had not thought about it prior to that — had not tried to raise money.

McMillan:

No, you can’t raise money for something that doesn’t exist.

Weiner:

It seems to me very interesting that as the idea comes out — in the paper in which you announce the idea, at the same time you say you plan to carry it out.

McMillan:

Alvarez came back from Los Alamos with the idea of a linear accelerator for protons which he generated in about the same way I did at Los Alamos. We both came with ideas and started two projects when we came back.

Weiner:

It seems to me that you left Los Alamos just at the end of the project. A lot of people stayed on for six months or so.

McMillan:

Most people who were on leave had gone for the duration of the war.

Weiner:

In your case when did you return?

McMillan:

September something.

Weiner:

After the letters were submitted. One was submitted September 5th and one September 9th. You said you had mailed the letter ahead of you anyway. And just one biographical detail — I notice that you had become an Associate Professor in 1941.

McMillan:

I was promoted in absentia.

Weiner:

And then in 1946 the full professorship came. But you were back working in the Radiation Laboratory in your old position as of sometime in September. And you learned of the Veksler thing in October of ‘45.

McMillan:

Right.

Weiner:

So there is not much more to say about the phase stability work at Los Alamos.

McMillan:

The only thing that would be nice to add would be the exact date. I could pin it down to the minute if I had had the proper historical sense. I knew at the time I had hit something real good. At the time I had this feeling of discovery which one rarely gets full strength in a lifetime. I knew I had something great, and the first thing the next morning I started writing it down, getting equations, and telling people. I was telling people the next day, “Say, I’ve made an invention.”

Weiner:

And that was the first time you’d had that feeling in your work?

McMillan:

No, not the first time in my life, it was one of the rare times. I suppose the nearest to it would be the neptunium, although that was stretched out over a period of time. I have had it on other occasions. I have had some ideas I thought were great which turned out not to be, and I don’t even remember what they were. But this was one time when it really was.

Weiner:

Looking at my notes I find that you wrote Lawrence on July 4, 1945 — I’ll check my source a little later.

McMillan:

July 4th would be the earliest date then. July 4th is the date I remember as the earliest documentary evidence. That must have been very soon after the idea.

Weiner:

What happened on the betatron — the air core? There was the idea associated with it of using power from Boulder Dam.

McMillan:

I never said that. I may have said that. I may have said in a facetious way that this would need Boulder Dam to run it. I or somebody used this as a facetious reference, but certainly it was never planned to do that. Sometimes you have to be careful about making jokes or people will think you are being serious.

Weiner:

It is good to clarify that. You explained the reasons why one would need this tremendous source. I would like to return and discuss how you got down to work on the synchrotron idea, and then specifically, the atmosphere, the changes here, your duties.