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Interview of Luis Alvarez by Charles Weiner and Barry Richman on 1967 February 14,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Early education in physics, University of Chicago 1930’s; high-energy particle counter; discovery of positron; discovery of neutrons; neutron experiments; reminiscences of Berkeley; Foundation support of research; 60-inch cyclotron building cloud chambers; neutron spectroscopy; neutron time-of-flight; magnetic moment of the neutron: transuraniun elements; announcement of fission; Tizard Mission; war research work; building of a betatron; effect of war techniques on post-war research; cyclotron work 1947; impressions of present day nuclear physics 1966.
We’ve had a chance to consult your Faculty Lecture which gives a very coherent account of your career and the things that you regard as most important. There are certain questions that we’d like to fill in, however, and in most cases we are not going to try to duplicate the things you’ve already said very effectively there. You mentioned that at the University of Chicago you soon became interested in physics. Was it after your second year?
There are a few things that aren’t clear. Did you ultimately take your degree in physics?
Yes, in 1932, I got a B.S. In ‘34 I got an M.S. and in ‘36 a Ph. D.
In other words you actually made the switch about half way through?
That’s right. I found out I wasn’t going to be a very good chemist. I had solid B’s for seven courses.
You initially chose chemistry because of some of the popular science reading you had done, which was all about chemists. Do you remember anything in particular that influenced you?
I remember reading a couple of books by Slossin. I think he was with Science Service. Actually people didn’t really know that there was such a thing as a physicist in those days. When I got my Ph.D. in physics and I would go to a cocktail party, somebody would say, “What do you do?” And I would say, “I am a chemist.” If I said I was a physicist, people would say, “What’s that?” And you’d have to go back to the first principles and explain what a physicist did. It’s hard for people nowadays to recall that physicists were just not known to the public.
In your chemistry work, did you go as far as physical chemistry?
No, I got out Just before physical chemistry; [I took] qualitative and quantitative analysis, organic chemistry.
The switch to physics took place about 1930?
Do you recall anything special about the courses you took? Were they standard physics courses, and if so, were electricity and magnetism included?
Yes, I had what we’d call freshman physics here. I had that when I was a sophomore concurrently with my chemistry. Then I got into the upper division courses, as we call them here--in Chicago they are the 200 series--and the thing that really got me interested was a course in optics, given by George Monk; I mention this in my Faculty Research Lecture. This was a course in which we used spectrometers, Interferometers, things of that sort that Michelson had brought into the University of Chicago Physics Department--he had trained all the professors. There was just a tradition for doing good optics, just like we have a tradition in high energy physics around here.
You didn’t mention the names of the people who worked with Michelson who were important to you, although you did say that they were very important.
There were two of them: one was Dr. Monk who taught this course, and the other was Dean Gale. Did I mention him in my Lecture?
I should have--Dean Henry Gordon Gale. Actually I started to build a 10-inch reflecting telescope and Dean Gale let me use a room down in the basement of Ryerson Laboratory, and one day he came down there and looked over my shoulder. I was pushing the glass back and forth, going slowly around, you know, the way you have to do for a couple of weeks.
Your father had previously arranged one summer to see that you got some experience in the machine shop?
I worked in the Mayo Clinic shop for two summers. My father was with the Mayo Clinic at the time.
What happened with this telescope?
Well, Dean Gale was just depressed by how slow it was because at that time he had charge of the optical shop upstairs, Michelson’s old shop, where if Michelson wanted a 10-inch telescope mirror, his assistants would put it on the rotating machines and grind it down in an afternoon, or maybe a day. So Dean Gale said, “Why don’t you come upstairs and use the real machines?” Naturally I was delighted, and so I went up there and his assistants--formerly Michelson’s assistants--helped me grind the mirror, and then I polished it later. Pardon my cold, that comes from being up most of the weekend; I had a couple of hours sleep one night and four the next.
In connection with the balloon?
Was Tom O’Donnell one of the assistants?
Tom O’Donnell was one of them, and Tom and have been good friends ever since. I got to know all of Michelson’s assistants: Fred Pearson, Tom O’Donnell, Fred Purdy and all those people.
I saw O’Donnell last year.
Tom’s a good guy. When I finished the telescope mirror, Dean Gale said, “What are you going to do for a mounting for this mirror?” And I said, “I don’t know how I’ll build it.” And he said, “Why don’t you use the student shop in Ryerson?” I was a junior in physics there, and the only people who had keys to the machine shop were seniors who were doing undergraduate research or the graduate students, so I was the youngest person with a key to the machine shop. Of course I knew how to use the tools, so I built the mounting in the student shop at Ryerson. Dean Gale and I got to be very good friends. He was sort of my sponsor and patron, and I was his protege, and he got me scholarships for the next two years and then four years of fellowships.
What was the source of the fellowships?
University of Chicago funds. They weren’t very much. The scholarships were $300 a year and the fellowships were $500 a year, and you had to pay $300 for tuition. You were left with $200 from the fellowship and nothing from a scholarship.
You didn’t have to do anything for it; it wasn’t the same as an assistantship?
Yes, I had to act as an assistant in the lab courses.
You mentioned an adviser suggesting that you build a Geiger-Mueller counter.
Yes, that was Professor J. Barton Hoag. He was my immediate superior, guess you would say, and he suggested that I build a Geiger counter. I had a room right next to his in Ryerson. I used to see him several times a day, and I learned a great deal from him.
He was very much interested in apparatus. I know he built some demonstration equipment for the oil-drop experiment.
Yes, he wrote the book called Electron and Nuclear Physics, and he designed the equipment that went with that.
He passed away about a year or so ago?
A little over a year ago.
I visited Mrs. Hoag in Gainesville.
She is a very nice person.
She preserved his papers. We have them now in our archives.
Oh, how nice. I am glad to know that.
I just thought of it, and I wish I had looked at it before we came. It includes some correspondence with you in later years.
I got Bart out to Berkeley on his Sabbatical, probably about 1938.
So it was his suggestion. What did you expect to use this counter for?
Nothing, nobody had ever seen a counter. I built the first counter that anybody in Chicago had ever seen.
Without any application in mind?
No, [the idea was] just to build a counter.
To count what? What did you count with it?
Radioactivity, cosmic rays.
I see. The cosmic ray [application] was apparent there because of Compton’s work.
Yes, but it was pretty rudimentary, since to measure cosmic rays you need more than one counter. You have to put them in coincidence because the normal radioactivity background in a room makes the thing count. Then, as I probably said in my Faculty Research Lecture, people who could build good Geiger counters with low backgrounds were thought to be wizards or sorcerers. Let me digress for a moment just to say that I have just completed a scientific memoir on Ernest Lawrence for the National Academy, and in that I specifically mention this business. I guess my secretary has another copy and I will give one to you. It tells a lot about the early days in the radiation laboratory and my interaction with Ernest Lawrence.
I want to ask about that too, maybe in a different way. How reliable were the counters in 1931?
Completely unreliable. If you ever made one that worked it was pretty surprising. I never made a good one in my life until--oh, probably I never made a really good one. I made some moderately good ones after I got to Berkeley. The ones that I used in cosmic rays by any modern standards would be just considered junk. You’d throw them away. They had very large backgrounds. We didn’t know anything about how to process the cathode or the anode; you didn’t know what you were supposed to do, what made a good counter. I remember that the counters I made I just put on a Cenco vacuum pump with a rubber tube and pulled them down from atmospheric pressure to 7 centimeters and sealed them off. Nowadays you put them on a high vacuum line and you bake them and you load them with various kinds of gases and treat the surface. We didn’t know what to do. Almost anything I did made them worse.
What did you go on? What was the standard information available?
There wasn’t any.
No published literature?
Well, the published literature just said that if you did these various things you’d have a Geiger counter, that was about all. It told you what voltage to run it at and what pressure of air; there was nothing about putting alcohol vapor in, there were no quenching circuits. One of my biggest problems was that I didn’t have an amplifier that I knew was any good. I had to build a high-voltage power supply and a Geiger counter and an amplifier, and I had no way of checking the amplifier because I didn’t know anything about electronics. I didn’t have any test gear. I spent the first two or three months with the high-voltage power supply hooked up backwards because it didn’t say “plus” and “minus” on it--I shouldn’t say this but it’s true. In a rectifier the part of the output terminal that is hooked to the plate of the tube is negative. It collects electrons, so it becomes negative, but I was brought up to believe that a vacuum tube had its anode positive, so I thought that was the positive terminal. So I had the high-voltage power hooked up backwards on the Geiger counter, and eventually I made it operate as a matter of fact. I found out later that some other people had done that too.
Did anyone there have any knowledge to help you or criticize you?
Nobody knew anything about vacuum tubes with the exception of Bart Hoag. In those days vacuum tubes were kind of spooky things, the way transistors were to the average electronics man ten years ago. He knew that there were some people who understood these things but he didn’t understand them himself.
What other detectors were available in that period?
The standard thing for cosmic rays was the ionization chamber, either running at atmospheric pressure or under higher pressure to get more ionization current. Compton used high-pressure ionization chambers.
Let me digress for a minute back to the general circumstances of your student work. Was there any particular student or group of students whom you were associated with and discussed physics?
Yes, we had one young chap who by general consensus was the smartest fellow in the graduate area. His name was Harold Plumley, and he was an exceedingly good experimentalist. He did his doctor’s thesis when he was a senior. He discovered the resonance spectrum of iodine which had eluded R. W. Wood. Wood had found it in bromine. I guess it was the other way around--Wood had seen it in iodine and missed in bromine. Plumley was also the local expert on quantum mechanics. Most of the graduate students didn’t understand any quantum mechanics, largely for the reason that the professors had just learned it themselves and were so bewildered by the mathematics that they thought quantum mechanics were recursion formulas for Hermite polynomials or something like that. They couldn’t see the forest for the trees. So when they tried to explain quantum mechanics to us, we were thoroughly confused too.
This was at the graduate level?
Yes, nobody taught quantum mechanics except at the graduate level. So Plumley was the smart boy and it’s strange that he is not known, nobody has ever heard of him. He went into the Navy research business during World War II and did very well and I guess he stayed as Director of the Navy Ordnance Laboratory someplace. It’s interesting that somebody who everyone agreed was the best physicist of the bunch was never heard of again.
Was Mullikan involved at all?
No, never had a course with Mullikan; Plumley was Mullikan’s disciple and we learned a great deal from him, I never learned a thing from Mullikan, largely because I didn’t take his courses and largely because I figured that if I did take his courses I wouldn’t understand anything.
How do we get you from undergraduate to graduate status? When was it that you decided that you were going on into graduate work in physics?
I think I decided that while I was taking Dr. Monk’s course in experimental spectroscopy. I just assumed from then on that I was going to be a physicist.
You mentioned in your Faculty Lecture that Arthur Compton took an interest in your counter and in you.
Yes. This was after I had finished my first counter and had given my first lecture. I think I probably mentioned that I gave half of a seminar on my counter and demonstrated it. I showed that it would go faster if I put my wristwatch up to it, and everybody was impressed. Then shortly after that Lemaitre, the Belgian priest, and Vallarta, the Mexican physicist then at MIT, developed their theory of the motion of high-energy charged particles in the earth’s magnetic field. It was an extension of Stormer,the Swedish or Norwegian aurora physicist. They showed how if the cosmic rays were charged particles as Compton’s verification of Clay’s latitude effect experiments showed Clay had shown that the cosmic rays dropped off as you went towards the equator, but nobody believed him because Millikan’s experiment showed that they were constant over the whole surface of the globe. The only persons apparently to believe Clay’s work were Clay himself and Compton, who had apparently known Clay and knew he was a reliable person. So Compton designed a series of cosmic-ray meters where there was a calibration possible by means of a standard radium source that was placed a meter away. So he had a good standard in his cosmic-ray measurements that the other people didn’t have. Everybody else measured the ionization current, and that can depend on changes in a number of variables that you don’t have any control over.
As Compton said, “If I put this standard source a meter away and see how the ionization rises, that change in ionization will always be the same regardless of the background.” So he built this and carried this thing around the world and indeed confirmed Clay’s result. From then on everybody believed it. That showed that the cosmic rays did contain a charged-particle component, because it was sensitive to the earth’s magnetic field. Then the problem came up, are these charged particles positively or negatively charged? Are they electrons or are they protons? Those were the only two possible things they could be of course in those days As Lemaitre and Vallarta pointed out at a Physical Society meeting held in Chicago, probably in 1933 at the time of the World’s Fair, if you went south to some point that was part-way down on the leg of the cosmic ray curve, there is a flat horizontal part and then the curve with respect to latitude drops down and flattens up at the equator and comes back up again. While the curve is falling down that means that some of the particles are being excluded; in other words, in order to go to that particular latitude some particles would have had to go inside the earth, so those are chopped off essentially by the earth’s shadow. And so in that region if you look up, say at 45° to the West and then look 45° to the East, that is at an elevation angle of 45°, at an azimuth either East or West you should see a difference in the counting rate. When you are up on the flat part, all of the rays are getting there from both directions, the earth is not shielding any; the same thing is true down at the flat part near the equator. So one had to go to a lower geomagnetic latitude than Chicago was
. Actually Bruno Rossi had had terribly bad luck. He had done this experiment before the theory was well known and before the results of Compton were in, and so he didn’t know that there was this relatively narrow region of geomagnetic latitude where one could look, and he’d gone down to Eritrea which was an Italian colony in Africa, had done the experiment that would have seen the East-West effect had he done it at a different longitude. Now, the earth’s dipole is tilted with respect to the geographic North-South axis, and so Eritrea was at the right latitude, think at about the same geographic latitude as Mexico City, but because of the inclination of the earth’s dipole Bruno didn’t see it. It was just bad luck. Let’s see ... Eritrea, I guess that would be Asmara, a latitude of 15 degrees which isn’t very far from Mexico City. There is Ethiopia [looking at an atlas]. Mexico City is like 19 degrees. So actually just by this quirk of fate Bruno Rossi missed discovering the East-West effect. He was there first with better apparatus than I had and Dr. Johnson--Tom Johnson of the Bartol Foundation--was in Mexico City as I probably mentioned in my article. We found the East-West effect simultaneously on the same day. Rossi had tried it some months earlier; he just had bad luck.
Was that the first real application of your counter?
Yes. Well, I had learned a little bit about making counters in the meantime; not very much, but I could make ones that worked.
This was an improved version of it?
Yes, and it was also in coincidence. I had to put the two in coincidence to get rid of the radioactivity background and the general high counting rate in the tubes because they weren’t well made.
You mentioned that people later began accepting Clay’s results. How about Millikan?
Well, let me revert now for a moment to my old status as a Compton student and I will tell you how at that time we interpreted what Millikan said in his book, Electrons, Positive and Negative. If you look at the chapter here on cosmic rays [leafing through book] you will find in detail all the places where Millikan went and carried his cosmic-ray equipment up and down the globe. As he says here, he went here and there and here and there and there was no change at all. Then all of a sudden without mentioning Compton--which was of course obvious to us at the time--he mentioned the fact that there is a change with latitude and he tells about his experiments showing that cosmic-ray intensity did change with latitude, and then finally he found out that Alvarez and Compton observed the East-West effect along with Johnson. As I remember, there is no mention at all of Compton and the latitude effect. What we said--and this may sound kind of catty but it’s interesting from an historical point of view--all of Compton’s students said that Millikan’s book said that: “In the first place I don’t believe that there is a latitude effect but if there is I discovered it.” That’s the way we interpreted him. Then he talks about how he went here, to Lake Titicaca, and Peru, and Panama and Churchill where he found the sea-level intensity is the same in the two localities with an error of not more than 1%. Now Clay comes in. Clay reported a l5% drop, you see. But then simultaneously with these results Millikan found out that there was no change at all.
Then you go along here [leafing through the book] and here we are at March Field and Riverside and Northern Canada, and the R.A.F, here we are and we keep on going. Here all of a sudden we have the high-altitude latitude effects. These are Millikan’s high-altitude latitude effects, right here. So far we haven’t heard of Compton. Here we are again, and we keep on going a long way. Ah, here we are. Here’s Compton, Compton and Stevenson, and this balloon flight. Then we go on some more and eventually we come to the East-West effect. Oh, here is Compton again. But anyway, it’s a kind of a strange way to write things up. Apparently, historically when you talk about your own work, and you show that Clay comes in and you show that Clay said there was l5 and you couldn’t find any change at all, and you go on and then suddenly your latitude effect is there with no explanation of how it got there. The way it got there was that Compton came and did the best work.
Wasn’t this part of a continuing dispute that the Compton-Millikan debate generally raised?
It was just because of this difference--Compton said there was a latitude effect and Millikan said there wasn’t; it was as simple as that. Eventually Millikan came around as you see from the book, and said there was latitude effect, but never admitted that Compton had anything to do with it. Being a Compton partisan, naturally I took offense at this.
It’s an interesting thing. We catalogued the Millikan papers in Caltech last summer, and going through them, it was evident that the two of them corresponded regularly.
I think they were quite good friends.
They were very polite and very proper, but there was great disagreement.
Oh, there was strong disagreement.
But it was a polite battle; a public battle too, some of it got in the papers at the time.
This is an extraordinary book too. You find out in the chapter on the neutron, you read all about how Charlie Lauritsen did this and that on the neutron. Here we are, you will go a long way through here before you find out that the neutron was discovered by Chadwick. You find out that Lauritsen and Bennett were building giant X-ray tubes and Lawrence was making the cyclotron, and Cockcroft-Walton did various things, and then you find out how Charlie made neutrons. Oh yes, here we are, Bothe and Becker, and we finally come to Chadwick. Right at the beginning you find Crane, Lauritsen and Soltan were making transformations yielding neutrons, and that’s two pages before you find Chadwick. I am sorry to carry these unpleasant memories of Millikan, because he was a real nice guy, but I think you should remember--and this is a good historical note--that when this book came out it was reviewed by Ed Condon. Did you ever hear of that famous review?
Ed Condon reviewed this book in the kind of vein that I am talking about and said, “The only thing that’s missing in this book is a subtitle, it should be called “Happy Days and Nights in the Norman Bridge Laboratory. The only things that are worth reporting in here are those that happened in Millikan’s own laboratory.”
Let me ask two questions. One is on the reaction to the discovery of the positron. Weren’t you in cosmic-ray work in Chicago at this time? How did you hear of it?
I read about it in the paper, I believe.
And what was the response at Chicago?
Everybody was terribly excited about it. I remember the very first day Sam Allison calculated where the wavelengths of the positronium lines would come--a positron revolving around an electron and vice versa--and went to the astronomical solar wavelength tables to see whether there was any positronium in the sun and then looked at the spectra of some stars. There was immediate excitement; everybody realized this was an important thing. They didn’t think about annihilation.
Did they connect it at all with the Dirac work?
Oh no, I don’t think that Carl Anderson connected it with the Dirac work. Dirac apparently had almost convinced himself really--maybe he hadn’t--but I believe that he had convinced himself that negative energy states were protons of negative mass and protons with holes in the sea.
Oppenheimer, I think, demonstrated that they couldn’t be protons, and so this put it up in the air.
I don’t agree at all with people who say that Anderson confirmed Dirac’s prediction that there would be a positron, because I lived through that period of time and I never heard the thing mentioned, and it took some while for people to realize that there was a connection. I am sure that this was not in Anderson’s or in Millikan’s mind. Somebody had to point out to them that it was connected, and maybe they also had to point it out to Dirac. Probably Dirac realized it was soon as he heard about it, since he’s a really smart fellow.
Do you remember the Physical Review paper in which the discovery of the positron was published?
It was a letter to the editor. It had a picture of a platinum plate and a positron coming up from below and circling around.
Do you remember whether they called it a positive electron?
I believe so.
What was their understanding at the time in the context of negative-energy state?
None at all. Nobody had thought of that concept, as far as I know. This was something that the theorists talked about but it hadn’t filtered down to the experimentalists. The theorists always have lots of things that they talk about among themselves and experimentalists don’t know about until there is some reason for them to know. We have lots of secrets we don’t talk to them about--about finding leaks in vacuum systems and all kinds of things that can go wrong in experimental apparatus. There is one thing that maybe Charlie Lauritsen didn’t tell you, maybe nobody has, that I found out from Carl Anderson in 1931, when I was there. When Carl found the positron, the first thing he thought was, “Those Cal Tech jokesters have reconnected wires to my magnet and have reversed its polarity.” And the reason that he thought that was that it hadn’t been so much earlier when the Caltech students had reconnected the wires on the wind tunnel motors that drove the big fans and they went backwards. They weren’t stressed for that, and one of them pulled off the wall, or had almost pulled off the wall, or something. Anyway, somebody had reconnected something, and the generators that Anderson used to power his magnet were the generators for the wind tunnel. In fact, that’s why he could only run at night. They had this one megawatt DC generator and this was hooked up during the night hours to Anderson’s magnet and then during the day it was hooked to the wind tunnel again. So Anderson had heard the stories about the boys hooking their wires up backwards, and apparently that was his first thought, that they had done that. But then they looked in pictures just prior to the positron picture and just after that and the electrons had the right sign, and it was clear that no one could have disconnected the thing when it was hot, and reconnect it; so the field must have been in the same sense all the time. But it’s interesting that I’ve never heard this story anywhere but from Carl Anderson himself in ‘34.
I did talk with him last spring. I know the wind tunnel equipment came out. I don’t think he mentioned this. Let me ask another question, in 1932 when the announcement was made of the discovery of the neutron, how did you hear about it and what was the reaction at Chicago?
I heard about it from Professor Harkins who came over and gave a speech on it. The main impact of the speech was that Professor Harkins had predicted the neutron back in 1915 or 1919 and it had finally been discovered by some young upstart named Chadwick.
How long after the discovery was this?
It was probably just a few days later that Harkins came over. In fact as graduate students, we always used to say, “Well, let’s harkin’ back to 1915.” Harkins was a chemist who had apparently written some articles on nuclear structure in which he predicted everything, and anytime anything new was found you could always go back and find it in Harkins’s articles. It was better for Harkins if you didn’t go back and look because you then also found that he predicted everything. It was bound to show up. He never got any recognition by any physicist and, until his dying days, he thought he should have been recognized for a number of discoveries in physics, in view of the fact that he predicted everything with a shotgun approach. Nobody gave him any credit and it really hurt him.
Where was he?
He was professor of chemistry at Chicago. He got to be pretty much of a bore. I saw him buttonholing people in the National Academy corridors, telling them how he discovered things and people tried to get away. This was a tragic sort of thing. He really thought he’d done something and he hadn’t done anything at all--in that area.
What did happen, though, other than the fact that he made the presentation of it? Did this lead to a lot of speculation, a lot of interest?
Oh yes, it was a very exciting thing. I went up to Michael Reese Hospital one time with ... what’s the name of the fellow who worked with Libby on the discovery of carbon 14 in the atmosphere?
No. He helped with the separation. This is a man who discovered element 9l. He was a chemist who liked to work in nuclear physics and what he used to do was borrow the radium needles at Michael Reese Hospital over the weekend when the doctors weren’t using them for treatment, and he mixed them with beryllium to make neutrons. (I’ll find his name for you.) But those were the first neutrons I ever “saw” if I can use that word in quotes.
How did he detect them?
He was detecting them with a hydrogen-recoil ionization chamber if I remember correctly. He was doing scattering experiments. The next time I saw neutrons was at Columbia where John Dunning was doing scattering of high—energy neutrons. Dunning had a better source and seemed to understand a little bit more about what he was doing; he had better equipment. I was in Dunning’s laboratory just after he had verified the slow-neutron production. In fact I didn’t even know what he was talking about because he was telling me how if he cooled his paraffin howitzer down to liquid-nitrogen temperature, he got more activity in something or other, and I couldn’t see how it made any difference, using one-million volt neutrons, whether you cooled them down to liquid-nitrogen [temperatures] or not. He apparently assumed that I had heard about slow neutrons, which I hadn’t. To me, neutrons were fast things. At that time I was working on optics. I wasn’t even in cosmic rays or nuclear physics, so it was not unnatural that I wouldn’t know about slow neutrons which had just been discovered, because he had just verified this thing a few days before and was all excited about it.
Why were you there?
I gave a paper at the American Physical Society meeting in New York.
When was this?
I would guess this was about 1934. I remember that I rode the bus to New York and back, and the bus went through the main streets of Cleveland and all the other towns; it was pretty grim. Naturally nobody paid my way.
You were still a graduate student?
Was the work using a radium needle as a source in the beginning of nuclear physics in Chicago?
It really had nothing to do with the University of Chicago as such. This was done by a chemist just working for his own pleasure. Maybe he published something, I don’t know. He had worked with Hahn and discovered element 91.
How did nuclear physics get started at Chicago?
It didn’t get started until Sam Allison went to Cambridge on his sabbatical, and returned to build a Cockcroft-Walton machine. But the thing that makes Chicago famous for nuclear physics was the fact that Arthur Compton brought the Columbia group to Chicago to make the first reactors.
Nothing before then?
It was pretty poor. They had a cyclotron but I don’t remember that they did very much with it. It was a pretty poor cyclotron.
Was the cyclotron built while you were there?
No, It was built, I would say, in ‘38 or ’39.
But while you were there, there were no seminars, no teaching on it?
There was no nuclear physics at all.
You never took a course, as late as 1936?
And it wasn’t because you were doing…
Nobody worked in nuclear physics; nobody.
I’m just exhausting all possibilities. Some institutions of course had started a lot earlier.
No, there was no nuclear physics there at all. No professor working on it. Oh, I should say Dempster was doing some mass spectroscopic work, and he found uranium 235 at that time, but that was just as a rare isotope. Rutherford had predicted that there should be--maybe it was Rutherford, maybe it was Hahn; some one of the fellows working on natural radioactivity knew that there had to be a parent for the actinium series. The thorium series had thorium-232 as a parent and the uranium series had uranium 238 as a parent, and there was a missing parent for the actinium series. They knew the atomic weight of the lead into which actinium decayed and so they knew what the formula was for all of the ones in the actinium series, and if the parent was a uranium isotope it had to be 235. So this was known, and Dempster just looked in a straight mass-spectroscopic way and found the line and announced the discovery of uranium-235. So probably the University of Chicago publicity department says they were doing nuclear physics in those days, but it’s a pretty narrow legal interpretation.
What was your awareness, though, you and other graduate students and faculty, of this field that was beginning to develop? Were you very much interested in it? And were you keeping up with it?
I was certainly not keeping up with it. I was interested in what Ernest Lawrence was doing because my sister was his secretary, as I said in my lecture. My father had been a director of one of the foundations that gave Lawrence some money, it was a medical foundation--the Markie Foundation. And so I had heard from both my father and my sister about what Lawrence was doing. Of course I had read his articles in The Physical Review, had read them casually though; I didn’t know anything about radioactivity.
The first thing you knew about the slow neutron was in Dunning’s lab?
And so you weren’t familiar with that sort of work.
No. The slow neutrons were found in ‘34. That ties in with my going to the Physical Society meeting.
You did some work on artificial radioactivity and cosmic rays in 1935, but it was strictly on another type of problem.
Oh, that; I was just criticizing an article that had been written by somebody in Australia who said that he had evidence for radioactivity induced by cosmic rays. I just pointed out that he hadn’t done his statistical analysis properly and the distribution he had was exactly what you’d get from a purely statistical distribution of pulses and there was no evidence of radioactivity induced by cosmic rays. I didn’t do any work. I just read this paper and said, “Look, this sounds like what I hear with my Geiger counter.” So I checked him out and he was wrong.
What about the Century of Progress Exposition? The theme was science. It’s interesting that the light from Arcturus is not 40 light years away, but something like 36.
I hadn’t heard that.
Since science was one of the main themes at the Century of Progress Exposition in 1933, was nuclear physics, nuclear energy, or any of these things mentioned?
Nuclear energy was certainly not mentioned because nobody had thought of it except from an astronomical point of view. People knew that the stars must run on nuclear energy although nobody knew what chain of reactions was involved.
What about atomic energy? Compton had written to Henry Ford in 1931; we found a letter of his, talking about the potential of atomic energy.
Atomic energy meaning nuclear energy?
It’s not clear what he meant?
I don’t know what he meant, but I would assume that by atomic energy he meant what we now call nuclear energy, or what makes atomic bombs run.
He was talking about the decay of uranium and so forth; not to Ford, but in his notebook on the same day you find this entry. But anyway this didn’t show up in a public way in the Fair?
No. Well, I shouldn’t say categorically no; I don’t remember seeing it.
The gimmicks that you mentioned, the cosmic ray balloon--it was not a gimmick but it was a dramatic thing; it had a dramatic effect.
And the Geiger counter telescope.
Well, the Geiger counter telescope was a way for General Motors getting one up on the Fair management.
They were part of the Fair though. This was their exhibit at the Fair?
The exhibit was at the Fair but they opened a few days before the Fair itself opened.
How was it decided to try cosmic rays?
I think somebody in the General Motors publicity department probably called Arthur Compton and said, “We’d like to be one up on the Fair. What could we use that would be bigger or better or something or other than what the Fair is using?” And Compton said, “Use cosmic rays.” They’ve been going around forever, probably. He had been influenced by Lemaitre and the big-bang theory. So he said, “Look, maybe they will be going around for ten billion years. That beats forty years.”
By 1936 you had done your doctoral work. You mentioned that the job situation wasn’t very hopeful.
It was terrible.
How many people got Ph.D.s along with you in physics?
I guess there must have been perhaps 5 or 6 a year.
Do you have any idea what happened to this group?
Yes, generally they went down into the oil fields and ran seismic prospecting gangs.
Is that what they had hoped to do, or was this the only thing available?
It was the only way you could get a job. But a few of them got jobs teaching in small colleges, or occasionally a high school.
What did Lawrence expect of you? What did he expect you could do for him?
I am sure he talked with Arthur Compton about me. As a matter of fact he told me that Arthur Compton had given me a very good recommendation. Arthur Compton was one of Ernest Lawrence’s heroes, so I am sure that probably did me as much good as my sister being there. At any rate, all he expected from me I think was lots and lots of hard work, unlimited hours, repairing the cyclotron and operating it, and getting in a little physics if there was any time left over.
But you hadn’t done anything in nuclear physics up until that time?
Well, hardly anybody in the country had because nuclear physics was done only in a few places. It was done at Charlie Lauritsen’s place; Merle Tuve and Ernest Lawrence, too, and that was about it.
Yes. Very, very few places were doing nuclear physics. So most of the people who came to work with Ernest had no previous experience, in fact many of them were independently wealthy. That’s how he helped to staff his laboratory, with people who didn’t require any salary. They turned out to be awfully hard-working, dedicated people. I wasn’t independently wealthy. My wife and I lived on our $100 per month--the original salary was supposed to be $1000 per year.
When did you start learning nuclear physics, and how?
Essentially the day I walked into the laboratory. I just learned it by total immersion. Everybody talked nuclear physics all the time--nuclear physics and cyclotrons and radio engineering.
Was there one particular thing you’d refer to, to sort of get the background? Some book or some articles?
Well, I was very fortunate in that Bethe’s first issue came out in April 1936 and I arrived in Berkeley in May 1936, so I was one of the very lucky ones who had a compendium of all existing knowledge in nuclear physics right up to date. Hans Bethe wrote it, as he later said, to educate himself. He had been in optical spectroscopy, and he realized that was running out of steam and nuclear physics was a coming thing, so, in his characteristic thorough-going German way, he learned everything that there was to know about nuclear physics and wrote it down. It was a tremendous service to everybody else. I guess the first one was Bethe and Bacher.
And the second one he did himself.
Yes, so that was a tremendous thing and not only was it a good summary of everything that was known but it also told of a lot of crucial experiments that could be done, in fact told of some that were important but were impossible to do, like measuring the half-life of the neutron and a few things like that that I spent a lot of time on later. That was the first time I heard of electron capture, the possibility of it. It was just wonderful. It had everything that was known and a lot of experiments that should be done, and I was in a position where with a little imagination one could do the experiments.
You were also in the place. What was the difference in your impression of Berkeley as compared to Chicago?
Oh, it was a completely different world, absolutely--almost unrelated. Berkeley was unrelated to Chicago in that Berkeley was alive, people were doing things, it was on the forefront of a new field. Chicago was sort of slowly dying and talking about the great days when Michelson and Millikan and Compton were the three American Nobel Prize winners and it was the best place in the world; like a Tennessee Williams play. I never thought of it that way before, but that was the atmosphere.
And Berkeley was younger in spirit.
Oh yes, and everybody was working hard, everybody was enthusiastic about what he was doing; people communicated their ideas back and forth. In Chicago everybody lived in a little separate cubbyhole down in the basement and you hardly saw the people that were in the next room. Everybody worked in his own little room, had his vacuum system and his equipment and generally the equipment was tied down to the table so that the guy next door wouldn’t come in and borrow it. It was a kind of an oppressive place. The graduate students had a good time, but the faculty was pretty dead.
But at Berkeley you did have ties with the rest of the physics department?
Yes, the Radiation Laboratory was a part of the Physics Department. It was called The Radiation Laboratory of the Department of Physics of the University of California.
How did you see these people, at seminars, socially, or did you live together?
I spent most of my time in the Radiation Laboratory, but when I worked on radioactive materials I took them over to Le Conte Hall where I had my electroscopes and magnets and things of that sort. And I went to the Journal Club every Monday night which was held in Le Conte Hall, and we just felt very close to the Physics Department. Ernest Lawrence’s office was in Le Conte Hall. The rest of us didn’t have offices or secretaries or telephones or anything, I am so surprised now when I find out the first thing that all my graduate students want is a desk. I was at Berkeley for two years before I had a desk, and then I only had one in Le Conte Hall to see students. I would hold office hours there.
In those days it was probably more appropriate to have a tool box.
I did have a tool box.
What were the first problems that you worked on?
I spent the first 9 months or so just repairing the cyclotron and operating it, not doing anything else; watching other people do physics. I think I signed up for my first bombardment about the end of 1936, I just felt that I ought to put some money in the bank before I started withdrawing it. Cyclotron time was very scarce in those days because most of the time the machine didn’t run. People would sign up for an hour of bombardment of copper or something, and generally the machine was off; the insulator had blown or something horrible had happened to the machine. So we’d take it apart and work all night putting it back together again.
Was there generally a long waiting list?
I wouldn’t say that. I think people were very accommodating to each other. There was no formal scheduling committee the way there is at all large accelerator laboratories now. People just knew what other people were doing and scheduled their work in such a way that there was something for everybody.
But the main point of focus of the laboratory was the cyclotron; this was the thing that dominated the whole schedule?
It would be interesting if you could estimate the ratio of time available in physics experiments as opposed to time not available. In other words, time used in maintenance, in perfecting and improving the machine--which is different than maintenance--and perhaps in medical therapy.
In 1936 for the first several months I was there, I would say the cyclotron probably ran about 15% of the time. The rest of the time was repairs, making basic changes, trying to bring the beam out--things of that sort.
Was this approximately 15% of the time used for physics experiments?
Mainly for making things radioactive. I think it’s safe to say that people at that time did all their physics on radioactivities. In that way you could sort of disconnect yourself from the machine. If you were doing an experiment on neutron scattering or scattering of the deuterons coming out of the machine, you’d have to have your experimental equipment running at the same time that the cyclotron was running. There were several difficulties with that: one is that the counting machinery--the electronics, ionization chambers, and what not--were so complicated that the chances of having them going at the same time as the cyclotron were kind of low. And the other thing was that there was an awful lot of radio interference from the cyclotron that would sneak in and paralyze the amplifiers. So by the time I got here in ‘36 essentially all of the physics was done on the radioactivities. People would bombard something and take it over to Le Conte or some place and do chemical separations, measure decay curves, absorption curves and things of that sort, to find out the properties of their materials, do cross bombardments to find out the identification of radioactive material. Nowadays one does this of course by getting separated isotopic samples, but we didn’t have those then, so we did what we called cross bombarding.
Then in that case they were very much like the Chicago group, because each one would work in his own room…
That was a small fraction of our time; most of the time we spent in the great big room together. It was nothing like the Chicago atmosphere at all.
What I meant was that each one was running his own experiments, not with any central equipment, and that the team research applied to the improvement of the cyclotron, but the detection and what you did afterwards was still the old-fashioned…
That was the old-fashioned way; except that people loaned each other equipment. I used McMillan’s electroscope when I discovered electron capture, and he’d built that with his own hands. He was doing other things and didn’t need his electroscope, so he let me have it.
That was the quartz fiber electroscope?
It’s sitting on his desk right now, on the top shelf back of his desk. He was very proud of that, he worked hard to make it, and it was quite a delicate thing to make.
When did the idea of team approach to detection techniques and to the whole operation begin to come into effect? Was that after the war?
I’d say probably during the war, when your job was not, so to speak, to write papers for The Physical Review with your own name on it, but to get a job done for the whole laboratory. Then people switched over to doing the detecting work in the team, whereas before, the only way you got any personal recognition or satisfaction out of your work was by publishing something that you’d done yourself. You couldn’t publish what you’d done in building the cyclotron and repairing it in the middle of the night, so you effectively advanced your scientific career by writing about what you did with the detecting equipment; somebody else wrote what he did.
How did you get involved in the problem of K-capture?
I just read in Bethe’s “Bible” that it was a process that should show up, and I think about the same time--maybe even earlier--I had read in Nature of a few attempts to find electron capture. They had been unsuccessful, people hadn’t looked in the right place or else they had used the wrong equipment, and so I looked in a better place and I built a special Geiger counter that had a thousandth of an inch cellophane wall to let the very long wavelength X-rays in. I found X-rays of the expected penetration in aluminum, when I looked at a titanium sample bombarded with deuterons. I published this as the discovery of electron capture. But it wasn’t sufficient merely to find X-rays, as I pointed out a bit later when I really discovered electron capture in gallium. I did it with the critical-absorption technique, which incidentally I introduced into this branch of physics. It was something that Paul H. Kirkpatrick had pioneered at Stanford, isolating spectral lines from an X-ray tube, but nobody had used it for identifying X-rays, as far as I know. So when I did that, I found out that my substance was emitting two different kinds of X—rays. That is I found things that were emitting X-rays both after electron capture and also after internal conversion. I realized that I hadn’t really discovered electron capture by just seeing some X-rays, because there is a hole left in the K-shell when you have an internal conversion, and X-rays are emitted when the hole is filled.
You couldn’t tell whether it was internal conversion?
Not unless I pinned down the wavelength and therefore the atomic number of the element emitting the X-rays, and the atomic number of the radioactive mother substance. So I determined the mother substance by chemistry, and I pinned down the wavelength of the X-rays by the critical absorption. And when I tied those two together there was no question but that it was electron capture and couldn’t be internal conversion. A radioactive form of gallium was emitting zinc K X-rays.
Did you do the chemistry yourself? Was your early chemical training helpful?
As a matter of fact I had a very good chemical assistant--his name was Glenn Seaborg.
What else was he doing at the time?
He and Jack Livingood were doing the same thing that everybody else was, finding new radioactive isotopes. Seaborg showed me the technique and after that I did it myself. He showed me how to separate gallium chloride from zinc chloride and most everything else. I guess I was bombarding zinc, but he showed me how to do the separation by a separation funnel using ether, how you shook it up and decanted it. I guess that was a pretty good system.
When did you have time to do this? Was it in bits and pieces?
In bits and pieces, yes.
Over how long a period of time?
Oh, I don’t know. I took a couple of weeks probably to pin the thing down.
But the primary responsibility that you felt was…
to the cyclotron.
What did you specialize in on the cyclotron? Were you a jack of all trades?
Everybody was a jack of all trades.
Was there any division of labor?
Yes, there were some people who were better at tuning oscillators and there were some people who were better at shimming the magnet. Ernest Lawrence was the best shimmer; he could always get more beam than anybody else. Van Voorhis was the best oscillator tuner. There were some people who were better at getting vacuum leaks than others--everybody was pretty good at that.
What was your specialty?
I think I was probably a jack of all trades the way most everybody else was. I don’t think I had any particular specialty. I think I could do anything as well as anybody with the exception of tuning the oscillators, where there were people who were better than I.
How much physics did it require?
Not very much.
And yet there was the feeling that this was important physics.
Well, it’s what professional accelerator operators do right now. Of course they don’t have as much work to do because the equipment is better built in the first place.
But in your mind, was there a subdivision: “Now I am doing physics, now I am working on the accelerator”?
Oh, there’s no question about it.
I don’t think this subdivision has come out in the past in public accounts of this. How large was the working staff involved full time at the Radiation Laboratory? First, on the basis of physicists with Ph.D.’s.
I would guess there were around ten or twelve, something like that.
And what about supporting personnel?
We had one W.P.A. draftsman and one W.P.A. machinist; that’s all, except for a night watchman. Ernest was afraid that the building might burn down in the middle of the night because it was soaked with transformer oil; the cyclotron tanks were always overflowing, and it was a wooden building.
What year did Brobeck come?
I’d say in ‘37.
You mentioned that one procedure that he introduced was systematic maintenance.
You might be interested in a word about Brobeck coming here because I was here the day he arrived. Brobeck knocked at the door and said he’d like to look around the laboratory, and I showed him around. I was impressed by the fact that he talked about preventive maintenance, a concept which I had never heard of before. We waited until things broke down and then we fixed them. He said: “Why don’t you oil motors and pumps every now and then, and inspect the level of oil in the oil tanks?”
Did you own a car at this time?
Yes. We were so busy fixing things that the idea of going around looking for things to fix just never occurred to anybody. Bill Brobeck told about himself. He said he had a degree in mechanical engineering--a graduate degree from Stanford--and he had been working with a company that made steam automobiles and this company had just gone broke. I felt that he had a lot to offer the laboratory and he said he’d like to come and work at the laboratory. So after I had shown him around for a couple of hours, Professor Lawrence came in and I told him the name of this chap who seemed to be potentially very useful to the laboratory and had lots of good ideas, and who said he’d like to work at the laboratory, and Professor Lawrence said to Bill: “I certainly would like to have you come and work in the laboratory but we just don’t have any money to hire you. I am terribly sorry.” And Bill said: “Who said anything about money to hire me? I just said I’d like to come work in the laboratory; I didn’t say I needed to be paid. You don’t have to worry about that,” or words to that effect. Bill, again, was one of these independently wealthy fellow that always seemed to turn up.
How many of the ten full-time people were in this position?
I can tell you what the scuttlebutt was at the time; I don’t know whether it was entirely true. We had one Italian count who once showed me a picture of his villa--Lorenzo Emo--I am sure he wasn’t getting paid. Malcolm Henderson I was told was independently wealthy as was Jack Livingood. Don Cooksey obviously was. Don was the associate director of the laboratory, Ernest’s closest friend. Don had a summer place up in the mountains where he used to take the young physicists for a few weeks and fatten them up and feed them good food and give them a rest. In fact Don used to talk about coming out to California as a small boy in his grandmother’s private railroad train. These were a few of them. There were also some very, very poor graduate students who lived in squalor practically, in basement rooms. Robert Oppenheimer, of course, came from a family of wealth; he didn’t actually work in the laboratory but he was in and out quite often.
Where did the support come from--whatever support there was?
The standard paper coming out of the laboratory in those days carried an acknowledgment, “We would like to thank the Research Corporation and the Chemical Foundation for financial support.”
Do you know the motives behind their giving the money?
I think in the case of the Research Corporation it was twofold: in the first place Dr. Cottrell, who was the founder of the Research Corporation, was an admirer of Ernest Lawrence. He recognized many of his own qualities in Ernest, they had lots of similarities. And the Research Corporation had the patents on the cyclotron assigned to it. You probably know how the Research Corporation is supposed to operate-it’s supposed to give money to people who then in turn invent things and assign the rights to the patents back to the patent pool at the Research Corporation, and then that generates more money which is supposed to keep the ball rolling. As far as I know, the cyclotron never produced any money. The Research Corporation gave everybody a license to build cyclotrons without any royalties. I don’t know anything about the Chemical Foundation. I have no idea what sort of an organization it was.
They had a role in founding the American Institute of Physics somehow. I came across that they contributed some money. What about the appeal on the basis of the use of the cyclotron for cancer therapy? How was this argument advanced?
I believe that the Markle Foundation gave some money on that basis.
This is the Foundation that your father was connected with?
Was the machine used very much for that purpose?
It was not used on humans until ‘38 or ‘39 or thereabouts. I think in the 1938-39 period the machine was covered up by white walls and patients were let in a side door which was cut for that purpose. So the patients walked into the side door of the cyclotron, and here it was, normally a great big ugly thing sitting in the middle of an oil-stained floor. And the patients came in through a little tunnel made out of plywood boards painted white, and they went around inside the water tanks of the cyclotron into a room again that was all brightly covered with white paint, electric light bulbs, and then the patient was put in position with his head about eight inches from the beryllium target being hit with a milliampere of deuterons and exposed. But the physics came to a halt during that time. I mean I was actually measuring, with Felix Bloch, the magnetic moment of the neutron during part of this time, and our neutron line was fixed exactly on the line where the patients went in, so we had to dismantle everything once a week and set it back up. We did this for two-thirds of the year; so it was a great inconvenience to me.
Whatever happened to this medical use? Was it profitable or was it disastrous?
I think all I can say is that there were some encouraging results; as far as I know it’s not used clinically at all at the moment. I may be wrong, but I haven’t heard of it for a long time. The basic idea was that the biological ratio for neutrons is greater than it is for gamma rays. The neutrons did damage to healthy tissues but did relatively more damage to the cancerous tissues than they did to the healthy tissues. It’s the so called biological ratio; are you familiar with that? In other words, the whole basis of radiation therapy of cancers is the fact that for a given amount of ionization dose to the body, you get relatively more killing of fast-growing tissues of cancers, than you do of normal healthy tissues. What you do is bombard right up to the point where you have just about knocked out the healthy tissues and you have given the cancerous tissue an overdose that knocks it out. The margin there is very, very thin for gamma rays, for X-rays, and what John Lawrence found out was that this biological ratio was bigger for neutrons, presumably due to the fact that the ionization density along the recoil proton track is greater than it is along the Compton electron [track]. That’s the obvious difference in the ionization procedure. But as I say, as far as I know it’s not used clinically at the moment.
The concentrated activity on this was in a particular year, ‘38 or ‘39?
Yes. Before that time John Lawrence and Paul Abersold, who is now with the A.E.C., had irradiated mice. They would inject tumor cultures into the abdomen of mice and let them grow. There was a strain of carcinoma that would grow in mice with a 100% take, so to speak, and then they would expose the mice in little tiny capsules and get them close to the neutron target, so it didn’t take very long to expose the mice and to see how their cancer regressed and how the mice population lived. That was where they found this biological factor great; they could give a mouse a larger number of units of radiation and still have the cancer being given much more and the cancer would disappear. So after this had been going on for for some while, I guess they tried it on some larger animals too for a while, and then they went on to the humans. It took two or three years to find out the biological effectiveness on the smaller animals; then they went to human beings. They were all terminal cancer patients, of course, patients who didn’t have a chance, all they could do was try it. They also did a lot of work on leukemia but that was again largely with radioactive phosphorus. And again they made the phosphorus when the machine was running and put it in the ice box and the patients were treated with it when they came in.
You said this period of putting a box around the cyclotron was for about two-thirds of the year?
No, I said it affected my work for two-thirds of the year. If you were going the radioactive route, which I had up to that time, then it made no difference. It was only because I was using the neutron beam out of the cyclotron, so I could only operate when the cyclotron was running.
How did it affect the work of other people?
Well, people who were working in radioactivity never knew the difference. It just meant you couldn’t “buy” any radioactivity, (“buy” in quotes), that day but you could use the radioactivity which you had made yesterday or last week or whatever, depending on lifetime.
Were there many other people doing the sort of work that you were which relied directly on the operation of the cyclotron?
No, as a matter of fact for that period of time I practically had the cyclotron to myself. The 60-inch cyclotron had just come in, so the people wanting radioactive samples all moved across the street to the Crocker Laboratory.
Oh, I see, there were two.
The 60-inch had come in, I can’t remember exactly when, ‘38 or ‘39.
What was the first use of the cyclotron for the in-operation experimental use of it? In other wards, was the thing you described something that depended on the running of the cyclotron?
All of the original work did, because the cyclotron was going before the discovery of artificial radioactivity. So all the original work was looking for alpha particles, protons and what-not coming off from the targets. In that work they used the shallow ionization chamber hooked to a linear amplifier. But as soon as the radioactivity was discovered that work disappeared; there was none of it going on when I got to the Laboratory in ‘36, although it had been all that anyone was doing in ‘34.
Could you describe the circumstances of the collaboration between you and Brobeck, using the cloud chamber in the cyclotron’s magnetic field? Was this when the cyclotron was down in 1938?
No, this was an experiment that had to take place when the cyclotron was running. I designed and built the cloud chamber and Bill Brobeck came in…and helped me use it. The chamber had been designed and built by the time Bill got here, and as far as I know that was the only physics experiment where he was a direct participant. He was sort of finding out what he wanted to do around the laboratory. He found out that nuclear physics was not as exciting to him as designing and building machines.
Was that the only cloud chamber at the laboratory?
Yes. There had been one a year or two earlier but it wasn’t operating then, so this was the only one. It wasn’t planned for a particularly good reason: Professor Lawrence always thought that there might be negative protons around some place, so he said why didn’t I look for them. So I built this cloud chamber and looked for them. Nobody had ever looked at the products from the cyclotron in this energy range with a magnetic field.
What was the energy range?
It was running at 6.3 million volt deuterons. And so Professor Lawrence said: “Why don’t you build a cloud chamber and have a look.” So I built it. The main difficulty was that the cloud chamber had to fit in between the pole pieces of the magnet to use the magnetic field, the fringing field of the cyclotron. So there was no space to put the normal push rods and all the rest of the stuff connected with a cloud chamber, so I built a very, very narrow cloud chamber with all the adjustments on the side, and a 45 degree mirror looked at by a camera that was in the magnetic field. The camera was driven by a spring motor, and the spring motor was outside the magnetic field, and there was a long brass rod connecting them. But the thing that people won’t believe now and it even seems incredible to me, was that we had no way in that period of turning the cyclotron beam on and off. We didn’t have a switch any place in the ion source; all it would have taken was a switch. So we sat there with our heads close to the target, looking right into the cloud chamber waiting for the thing to pop, and there were maybe ten or twenty seconds between pops.
There we were, right in there, that far away from the full beam of neutrons in the cyclotron. And we never turned the thing off. We’d sit there and look in that mirror at the beam of high—energy particles coming out, and the cyclotron would be kept going, waiting for the next pulse of the cloud chamber. Of course we knew about radiation and everything. I am very pleased that I had my eyes looked at just about three days ago, and I didn’t have any cataracts. In view of the fact that so many people got them in those days, they must really have worked very hard to get them, because we got terrible exposure.
How conscious were people at that point of the radiation hazards?
At that point the first shielding tanks had not gone up yet, and this story again you’ll find hard to believe, but it’s true: The Chemistry Department bought either a quarter or a half a curie of radium-beryllium to make things radioactive, to get some neutrons. G. N. Lewis was interested in this, and Bill Libby of carbon-l4 fame was also interested. He was a chemist at that time and didn’t come over to the laboratory. When he wanted some radioactive materials, he used to put them in shells around a radium-beryllium source and get a feeble radioactivity, the same way Fermi and his collaborators did in Rome. Then Bill found out that if he put samples up in the window of the chemistry building across the courtyard from the Radiation Laboratory, he could get stronger samples than he could from his radium-beryllium source, so they turned the radium—beryllium source back in. It’s hard to believe, but it must have been about 15 feet from the cyclotron target over to the wall and another 15 feet across the corridor and then they were up on the next floor. So it was probably 30 or 40 feet from the cyclotron target. And he was getting more neutrons there than he was getting right around the radium-beryllium source. Of course we were living closer than that and in a direct line to the neutron beam at the control table. The control table was closer to the cyclotron than Bill Libby’s window was, and the beam was pointing right at us. It was after that that the water tanks went up.
When was this?
And that marked a change in the general attitude? In other words, this coincides with Brobeck’s coming and his ideas of preventive maintenance? This is an extension of the same thing.
Don Cooksey was the one who had the only electroscope dose-meter in the laboratory. He had bought it with his personal funds from somebody working in the Charlie Lauritsen shop. So he used to look at it occasionally, and then John Lawrence used to come around and caution us about it. I think probably the most salutary thing in that period was the fact that on the desk of the control table at the 37-inch cyclotron in those days, there was a book called American Martyrs to Science Through the X-ray, and it was the most gruesome book you ever read in your life--about arms coming off, horrible ulcers, sores all over the body. I remember one story about Edison’s assistant. Edison made the first zinc-sulphide screen. Up to that time all work with X-rays had been done with photographic plates following Roentgen. Everybody made X-rays the day after Roentgen announced it because everybody had a Geissler tube in his lecture-demonstration kit and so everybody was making X-rays. They had been making them but they didn’t know it. Edison had an exhibit at the World’s Fair at that time, whether it was Philadelphia or where I don’t know--St. Louis?
There was one in St. Louis in 1903 or 1904.
This was in 1896 or rather 1897. X-rays were discovered in December 1896, I think, so this was in 1897. Anyway, within weeks of the time of the discovery of X-rays, Edison had invented the fluorescent screen and so he had an exhibit of his equipment and his assistant sat there with an X-ray tube here and his hand wiggling his bones. People filed by and looked at the zinc-sulphide screen, in not quite normal room brightness, probably darkened a little bit. And this guy’s arm came off; his hand essentially wasn’t there a day or two later. It just puffed up and they had to amputate, and his arm came off later and he died within a few weeks. The first martyr. So as I say, when the cyclotron was running well--which wasn’t very often--we read this book. I knew everyone of these fellows and what happened to them. We were very aware that we were dealing with a dangerous toy, and to the best of my knowledge nobody had any radiation damage and no one got cataracts. Bob Cornog once got his hand in an alpha particle beam and got a little burn, about so big; it didn’t last very long. That’s the only radiation damage I know of, whereas there were dozens of cyclotron people who got cataracts from looking into the accelerator tank--getting too much neutrons. How they got too much neutrons I’ll never know after what had happened at Berkeley. When I think of what we did now--fantastic.
I want to ask you about another piece of work that you did and that is your collaboration with Bloch. You mentioned it as far as the difficulty of getting the machine. I have no specific questions on it frankly, just would like to know in general how this collaboration came about.
That is interesting. He was at Stanford and one day the telephone rang and it was Felix Bloch whom I had never heard of, and he said he wanted to speak with Ernest Lawrence. Ernest got on the line and Ernest later told me that Felix had said, “I have just thought of how to measure the magnetic moment of the neutron; can I come up and do it?” And Ernest said, “Fine, how long do you think it will take?” And he said, “Oh, I don’t think it’ll take more than a few days.” I think he had the feeling he could probably do it that afternoon. His idea was that neutrons would be polarized in going through magnetized iron, and he wanted to be able to see the difference in the scattering of neutrons on magnetized and unmagnetized iron. That was the basic idea, that neutrons would be polarized and they would scatter differently. And his original idea was that if you measured the scattering from a piece of iron that was in the magnetic field of the cyclotron and then you took the iron and heated it above the Curie point, then you should see a difference in the number of scattered neutrons, think this is what Felix thought he could do that afternoon. Maybe it wasn’t quite that extreme, but anyway it seemed like a very, very trivial experiment. He came up the next afternoon and enlisted the aid of L. Jackson Laslett who incidentally is here in Berkeley now, working on the 200 Bev accelerator study. And if you want to know more about that, Jackson is probably the only person who has that bit of history tucked away in his brain because he was a graduate student at the time and Felix Bloch interested him in this experiment.
He was a graduate student here?
He was a graduate student at Berkeley. He was on the cyclotron team. And Felix Bloch got him all fired up about this. It was a very exciting experiment. It looked very easy and Jackson worked on it for a long time and never was able to see any polarization or any change in scattering or transmission. He used nickel and iron, and I remember his blow torches which heated these things up. Then we didn’t see or hear anything of Felix for some months and then he came up and said he knew how to do the magnetic moment of the neutron by the Rabi technique. I immediately thought he meant running a beam of neutrons down between shaped magnetic pole pieces, lining them up. And I told him that there wasn’t nearly enough intensity, that he was doing us a great compliment by saying this, but we couldn’t possibly do it. Then he came up to Berkeley and told me that he planned to use big slabs of iron as polarizers and analyzers and he would use the Rabi technique for flipping them over. And that made sense. I was the only one who had a neutron beam and detecting equipment available, so I was the obvious candidate to implement his idea.
Did this depend very much on the ability to collimate neutrons?
Not terribly much. Since we were working with slow neutrons, you could collimate them with half a millimeter of cadmium, so it was no problem. But then the interesting thing was that three people had independently said they had observed Felix Bloch’s effect, namely that the transmission through magnetized iron depended upon the state of magnetization. There were three publications in the literature. Did I mention this in my Faculty Research Lecture? Probably not.
One of these was Dunning, one was Frisch, and the other Van Halban. Otto Frisch is well known. And the other one was by somebody at Cornell, I think it was one of Stan Livingston’s students. And they all had verified the prediction that when you magnetized the iron the transmission went up. All had one or two standard deviation effects and all of the right sign. Felix and I assumed when we were going to do our experiment that we would just use this well-known technique, and we spent several months looking for it. We couldn’t reproduce what anybody else had done, and then Felix said, “Maybe…” By that time we concluded they were all wrong, that they hadn’t seen it, because we had a much more powerful source of neutrons. We had much smaller statistical errors and by trying to copy what they had done, the effect just wasn’t there.
In fact one of these people had used the residual magnetism of an iron bar, magnetized it, and cut out the current and used the residual magnetic field. Everybody now knows that doesn’t work. In fact you have to magnetize the iron up to so close to saturation that you have to put it in a field of about 20,000 Gauss. So we finally in desperation got the strongest magnet we could and tried it and found our first effect. So it was one of those crazy things where the effect is in the literature--it’s been verified and verified again--and yet Felix and I know perfectly well we were the first ones to see the effect. In fact we always referred to it as the Dunning effect because we got in the habit of referring to it as the Dunning effect because Dunning was the first to publish. Even after we knew that Dunning had never seen it, we kept calling it the Dunning effect. I think we said in a very polite way in our paper--if you look hard you can see it--it says there that we didn’t believe anybody else had found it, but we didn’t make a federal case out of it. That’s one of those crazy things.
You said you got the strongest magnet you could get. Where did you get the strongest magnet you could get?
We got it from the spectroscopy lab over in Le Conte Hall. We just poured the coal to this thing ... First of all we tried all different kinds of iron; we formed the iron into toroids and we wound helical strips around it and put current into those things; the straps melted and we couldn’t see any effect at all. We had fantastic statistics compared to anybody else. We finally did find the effect and then we went out and measured the magnetic moment of the neutron.
We are resuming now after a pause of about a half-hour. At the time of our last question you had completed telling us about your work with Bloch and your collaboration with him. This leads to another question: what was the relationship among other physicists in the area, including Berkeley? You mentioned that you were in the the same department and that there was a Journal Club. I’d like to know a little bit more about the exchange of ideas between the theoretical people and the experimental people during this period--whether in fact it existed.
It not only existed, it was very strong. The interaction was strong. Robert Oppenheimer, Bob Serber, Bob Christy, people of that sort talked with the experimental people frequently on an almost day-to-day basis. Every one came to the Journal Club on Monday nights; that was something nobody missed. No wives would think of scheduling anything on Monday night. Monday night was free for Journal Club and the theorists and the experimentalists went to that.
Graduate students too?
Yes. This was the time when theory and experiment were fairly well separated. A person was either an experimentalist or a theorist. Nowadays the people who call themselves experimentalists are to a large extent theorists. I mean they worry about phenomenological theories and curve fitting and things of that sort. In those days the experimental 1st was somebody who worked with a soldering iron and a screwdriver and a lathe, and a theorist worked with equations. The division was quite sharp. Fermi was the one who broke this down. After being the world’s greatest theorist he became one of the very best experimentalists, which showed that it could be done.
How was this interaction effective on problems in nuclear physics?
As I say the magnetic moment of the neutron was done because a theoretical physicist--namely Felix Bloch--50 miles away suggested the idea and then he actually came up and worked long hours with me. I was the one who made the equipment run. Felix helped take the data and gave me encouragement and did a lot of hard manual labor, pushing magnets around and lining things up. Later on before the war I measured with Ken Pitzer, who is now President of Rice Institute; Ken and I measured the scattering of slow neutrons in ortho and parahydrogen. That was an experiment that had been suggested by theorists, and in the particular case of our experiment, Julian Schwinger, a young National Research post-doctoral fellow, was the one who encouraged us to do the experiment and was ready to interpret the data. Schwinger, of course, won the Nobel Prize last year for his contribution to quantum electro-dynamics. He was one of Oppenheimer’s graduate students.
How about Oppenheimer and Serber, did they interact in any way in the machine-building phase?
They didn’t interact at all in the machine-building phase--they couldn’t care less. I should add that Bob Serber later did the critical theoretical analysis that enabled Don Kerst to build the first Betatron. Robert Oppenheimer did interact rather strongly with the calutron isotope separation plant in 1941. Ernest Lawrence started to think about separating isotopes using the cyclotron magnet and the mass-spectroscopic technique. And there are, as you know, second-order aberrations in the focusing, in which 180° focussing only works to first order, and Robert Oppenheimer figured out the shims that permitted focusing to be good for first and second order. He got rid of the aberrations so that you could use better separation. If you don’t have those and you take a reasonable angular acceptance of the ions, then some of the U-238 slops over in the U-235 pocket. But by using the shims you can correct the trajectory so that the 235 all lands in the 235 hole, and the 238 lands in its hole, and there is no mixing. There was one other occasion when Robert Oppenheimer calculated something for me that involved a machine. I had the basic idea for what later became known as the microtron, an electronic accelerator in which the particles slip one cycle every time they go around. I dreamed this up shortly before the war and gave a talk on it at the Journal Club. I have never pushed a claim to this. I have my original notes for it, but it seemed like something that wasn’t worth trying to go out and grab credit for because people re-invented it; in fact Schwinger re-invented it and built it. The reason that I couldn’t do anything about it was that there was no source of high-power microwaves in those days, and that’s what it took. So it was just an idea that was okay if somebody ever did come up with a good source of microwaves.
How about Serber, was he closer to the machine?
No, he became so when he went to Illinois. I never saw Bob interested in anything having to do with hardware or machines. He went to Illinois and as you know he did the calculations for the betatron that led to its successful operation. When he came back to Berkeley after the war he helped with the design of the cyclotrons and other experiments but until that time he had been completely divorced from hardware thoughts.
Then where was this interaction?
Well, it was pretty much that the theorist would suggest problems that were worthwhile doing. Sometimes the experimentalists learned of a problem, the way I did by reading Bethe; sometimes they learned of it by listening to Bloch, a visitor, the way I did; sometimes they learned about it by talking with a physicist at Berkeley like Schwinger. People got their ideas from the literature or by talking with the theorists, and the theorists were very interested in what we were doing and would give us lots of help in interpretation.
During the work itself?
Did you ever attend the joint Berkeley-Stanford colloquia?
I don’t remember that there were any.
I don’t know if they were known as that. We’ve had references to Bloch and Oppenheimer in some sort of debate on electrodynamics…
Oh, that must have been the theoretical seminar. As I said there was a sharp division between theorists and experimentalists. The theorists and the experimentalists all came to Ernest Lawrence’s Journal Club, but the experimentalists didn’t go to the theoretical seminars.
You had no teaching responsibilities at the Radiation Laboratory?
Not for the first two years; then I became instructor in physics. I was appointed instructor in ‘38 and I became an assistant professor in ‘40, then I went away to MIT. I was advanced to associate professor while I was away and came back as professor.
What did you teach?
I taught freshman physics, always, and then I also taught a laboratory course in nuclear and electronic physics--the kind of thing that Bart Hoag had done in his course at Chicago. It took a fair amount of time actually.
Considering the description you gave us of your ordinary schedule, this on top of it would make it pretty tight.
It was. As I said in my thing on Ernest, those who did not work 80 hours a week were considered “not very interested in physics.” I mean guys like Lorenzo Emo, our Italian count. We all thought good old Lorenzo was just a dilettante but he worked awfully hard, though he didn’t work as hard as the rest of us. We heard he was out visiting the society ladies in San Francisco.
"Adventures in Nuclear Physics," The 1962 University of California Faculty Research Lecture (University of California Radiation Laboratory Report No. UCRL-10476, March 1962).
Stormer, Fredrik Carl Mulertz (Norwegian)
Aristid V. Grosse