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Interview of Maurice Shapiro by Laurie Brown on 1978 May 30, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4887
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The interview concerns ray research during the decade 1937-47, mainly and Shapiro's participation in it. It covers briefly his family background, Orthodox Jewish, and his studies at the University of Chicago, including his Ph.D. research using photographic emulsion, in which Shapiro is a pioneer. An attempt is made to discover motivation for Shapiro's research.
Maurice, since we've known each other for a long time, I’m going to be calling you Maurice throughout this interview, and you might as well call me Laurie. I see from your vita that you were born in 1915 in Jerusalem, How did you happen to be in Jerusalem when you were born? Were your parents American citizens at the time, or —?
It happens that my own father, grandfather and great-grandfather all had American citizenship at the time I was born. My father, however, never came to this country, so he lost his citizenship at the age of 21. This was, I guess, early in World War I; and he also lost his life, due perhaps in part to his inherited American citizenship, because the Turks mistook him for still being an American citizen after he had passed his majority, passed 21, and they took him as a prisoner of war to Damascus. He, escaped, but apparently had caught some bad disease and got as far as Tiberias where he died.
So your family has lived for several generations in Jerusalem?
On my father's side, in Jerusalem. On my mother's side, they were Hungarians. She was brought to Jerusalem at the age of two by her parents, and that’s how I came to be born there.
Well, do I gather from you — I'm sort of interested in this, because now we’ll talk for a little bit about your youth, and I'm interested in cultural background. As you know, I'm working on a project on Yukawa and I’m interested, for example, in the Japanese cultural influences on a physicist, on an important physicist. So if you don't mind, perhaps we could talk a little bit about that as well?
Did you come from a religious family?
It was an exceedingly orthodox background, and in fact, I was born meters away from the corner of Jerusalem known as Mea Shearim — the ultra-religious quarter, Had I stayed there, the chances are that I would have, spent most of my youth doing nothing but poring over the Talmud, etc. But instead, I came to this country at the age of six.
But your great-grandfather who originally went there was an American citizen?
He didn't come from America. He acquired American citizenship in the course of spending some years there. He came from Poland, with his son, my grandfather, and my grandfather likewise spent quite a number of years here, particularly around World War I.
Approximately when did they go to Jerusalem?
When did they first arrive, you mean? My great-grandfather came there in the late part of the 19th century.
Well, Maurice, where did you go to elementary school?
That was in Chicago, where my parents came directly when they moved from what was then Palestine.
What part of Chicago is that?
This was the West Side, It was an elementary school called Victor F. Lawson. Then into Crane Technical High School, where I first took some physics, and decided already then that I should like to become a physicist.
That was my next question... At what point and how did you become interested in physics? What was it that caused you to become interested in physics?
It was reading about modern discoveries, including the Compton Effect, which was being talked about, because it was about the time that I was, being graduated from grammar schoo1, I think, that Arthur H. Compton got his Nobel Prize. The third physics prize of three, all given to people at the University of Chicago. This, of course, also gave me the ideas — since it would have been impractical for me to go elsewhere anyway to school, my parents couldn’t afford to send me — that I ought to try to get into the University of Chicago.
So the preeminence of the University of Chicago, the talk about the Nobel Prizes awarded — let's see, Michelson got one of those Nobel Prizes.
Then Millikan, then Arthur Compton.
So it was during high school that you became interested in physics. Did you think at that time about possible career opportunities? Did you view it as a way of career advancement, or was it purely a sort of intellectual fascination?
It was almost purely an intellectual fascination. I wasn’t really practical enough at that time to be thinking about how to make a living. I sort of dimly knew that it might not be easy to make a living in physics, especially in those years.
Especially in those years? We had just about entered the Depression period, is that right?
That is true. There was the Depression, and the post-Depression, in which I grew up in high school and later the university.
Did your Jewishness have anything to do — do you think — with?
It must have had a good deal to do, in the following sense: that simultaneously with my secular education, my parents, who as I said were very fundamentalist, sent me to a rabbinical academy, a Talmudic academy where one studied Talmud year after year. And of course, there I suppose I absorbed, as I might have even just at home, but there I certain1y absorbed a lot of learning, as it were, for its own sake, and a certain amount of intellectual stimulus. I can’t say that other than that, the study of the Talmud itself was particularly helpful later in my physics, because although the Talmud is certainly a fascinating sort of encyclopedic literature, the style of reasoning in the Talmud –- in the legalistic portions of rigorous thinking that we think of in the physical and mathematical sciences.
Like to think of, anyhow.
Yes. We would like to associate some degree of rigor... So, I don't see a very direct carryover of that kind…
What about Einstein? Did Einstein figure as a role model, or was he considered by your fundamentalist family to be an atheist? Was he respected?
He was, I would say, universally highly respected, by Jews of whatever religious belief. But in any event, what my immediate family might have thought of him, any reservations they might have had about the fact that he was, not a religious-person in the conventional sense, would not have influenced me very much anyway. I had to make my way into the Western culture, as distinct from old style Judaic culture, and so I would not have been unduly influenced that way.
OK, so you then attended the University of Chicago, You say that from the economic point of view, that was the only possibility?
Oh yes. I had to commute all the way from the West Side, about an hour and a half each day on the public streetcars of Chicago.
You entered as a physics major?
Yes, which was a bit unusual, I think. Most of my class in physics were pre-med students.
Do you recall any particular influences or teachers who were especially important to you as an undergraduate?
Yes, I would say that the man responsible more than any other for encouraging me to go ahead in physics was Carl Eckart, whom I had the good fortune to have already in my freshman year in physics. Now, I can't say that I regarded him as an inspiring teacher, because he really had a depth that was beyond me at the time, that I was unable to appreciate as a freshman college student. Nevertheless, I did come to him once for an important piece of advice. I told him that I evidently was finding it easier to excel in the humanities than I was in physics and math, particularly in math, for which I don't believe I have exceptional gifts at all, and asked him whether I was doing the right thing in pursuing physics. And Carl Eckart’s answer made a permanent impression on me. He answered me partly with a question, asking me, well, was I really interested? Was I deeply interested in physics? I told him I was. And he said “That’s the important thing. You mustn’t expect to learn everything in your college or even graduate years. You’ll keep at it all your life, and I believe that your degree of interest will go a long way.”
Yes. Eckart himself was almost a mathematical physicist, I would say, he was later on — I knew him at the Institute of Advanced Study, where we were both visiting in 1952-53, and at that time, he was at Scripps and was doing work on waves.
He was an extraordinary man. I believe he deserves to be considered one of the founders of the quantum mechanics, in the sense of being at least one of those who demonstrated the equivalence of wave mechanics and quantum mechanics, of the Heisenberg and Schrodinger types. Nevertheless, he was quite an individualist in not pursuing fads in physics. He followed his own path, his own interests, and some of those were quite classical.
Well, that was the general undergraduate atmosphere? Was that what people look back upon as the golden age of the University of Chicago? Some people have mentioned it. This was not the Hutchins era?
It was during the Hutchins era, and the Hutchins era must not be confused with the golden days of physics at Chicago. It was rather the humanities, the 100 Great Books and so forth, names like Mortimer Adler, which could be associated with that period. Nevertheless, I found the overall atmosphere exceedingly stimulating.
For a young physics undergraduate, it was a stimulating environment?
I must say that.
Were there other contemporaries of yours who made an impression on you?
There was a young man who died prematurely, later in his thirties, by the name of Leonard Miller, who was a close friend of mine. We had entered the University of Chicago together. And his strong interest certainly interacted with mine, and helped sustain it. I must say, I think as an undergraduate, I found other disciplines just as interesting as physics, and was really very grateful for a good general education that I got in the three years I spent getting my bachelor’s degree at Chicago.
Well, then you got you’re A.B. in 1936, and you got a Master’s Degree? Was that a normal thing to do, during, before the war?
It was not at all normal. It was rather my fear that for financial reasons I might not be able to finish all the way through to a doctorate. But I might say that there was a very short real digression, after getting my Bachelor’s degree in which, goaded on partly by my parents, I applied for and was admitted as a student at the Jewish Theological Seminary in New York. They still hoped that I might become a rabbi, since I had studied at the rabbinical seminary in Chicago, on a part time basis, for many years. And although I found the scholarly atmosphere in New York a lot more favorable than I had in Chicago, which was an old line orthodox institution, and I found some aspects of my student life at the seminary pleasant, I realized soon enough that I’d made a very serious error in not pursuing physics directly, and I withdrew from the seminary, went back to the university. I had a very tough time making ends meet initially, but I was re-admitted as a graduate student. I supported myself mainly in those difficult days by getting a job in the evening colleges, junior colleges of Chicago… I taught among other things a survey course in physical sciences, and widened a little bit thereby my knowledge of the physical sciences, because of course there's no better way than by teaching. I learned some astronomy, some geology, etc.
Yes. Was there ever any question in your mind about whether you would become a theoretical or experimental physicist?
Not really, I felt that I was not sufficiently gifted mathematically to consider seriously theory. In later years, on a number of occasions I pursued what I like to call the poor man’s theory, by which I mean really a straightforward application of theory to the solution of problems that seemed obviously in need of solving, but I would not elevate those efforts to the level of real research in theoretical physics in the usual sense.
What was your first research thing? What was the first project you were involved in?
I persuaded the late Arthur Compton to let me try my hand at using what appeared to be a brand new technique, the photographic emulsion technique, later called nuclear emulsions, to the study of cosmic rays. It came about partly this way, that Anderson and Neddermeyer, I think in 1936, took a cloud chamber up to the top of Pike's Peak, and spent a summer, as I recall, trying to study nuclear interactions in a slab of lead mostly in the middle of this cloud chamber.
That’s the work which led to the muon discovery, was it not?
It was parallel work, certainly, yes. In any event, they did study nuclear interactions, and got a total of some 200 examples of so called stars, the kind of star-like effect you get when a nucleus is disintegrated by an incident cosmic ray.
Excuse me, would those be tracks emerging from a thin lead plate, and some of the stars were made in the walls of the chamber. Very occasionally, very occasionally, there would be a star that started off in the gas of the chamber.
So that would generally be clusters of tracks, but you wouldn’t normally see the interaction?
There wou1d be clusters of tracks but you were sure to miss — you were sure to miss a lot of them this way. Moreover, the total number seen in the course of a whole summer of expansions of; this cloud chamber was rather limited. And I became aware, I think on the advice of the late-Marcel Schein, who was a research associate of Arthur Compton’s, of some work that had been done, just a few years' before by a couple of Viennese women, Wambacher and Blau. Blau should be mentioned first — she was the senior of the two —
I do want to go into that a little bit.
Fine, so we can postpone that discussion if you like.
When we come to discuss your review paper and so forth.
Right. Sure. In any event, I became aware that this technique had been used with some success in collecting quite impressive amounts of data statistically on the “stars,” and that this photographic emulsion technique had the marvelous attribute of being a completely visual technique, in that the starts would have their vertex and would be generate somewhere in the middle of this emulsion; then when the particles emerged, they were all visible.
So you think it was Marcel Schein who suggested this to you?
He told me about the literature.
Told you about it, and then you suggested to Compton that this might be a possible thesis topic for you to write?
Was it a Master’s thesis that you had in mind, at that time?
Not really, Not really.
I had a Ph.D. thesis in mind. This would have been about '39, I think.
And he agreed?
He agreed reluctantly. Right. There was a —
How did you go about that, then? Where did you get the emulsion?
l think, by the way, that the reason he disagreed, the reason he agreed only reluctantly after some persuasion, was that he probably felt that this could not be a very quantitative technique.
Yes, OK. So you, how did you get your emulsion and where did you make, your exposures?
Well, I scrounged. There were no research funds to speak of. Certainly I wasn’t given any, as I recall, I got samples of photographic plates, as they were then known, because the emulsion was always coated on glass and they were standard microscopic slides, size 1 x3 inches, and I got them from places like Eastman Kodak, Ilford in England and Agfa in Germany. And I began to teach myself, as it were, with the help of photographic literature, how to go about developing these emulsions.
According to your publication list, your first published article is a review article, “Tracks of Nuclear Particles in Photographic Emulsions,” published in THE REVIEW OF MODERN PHYSICS, in January, 1941. I’ve just been looking at that article, and I have of course noticed that Marietta Blau has an important work in this field. She has, according to your bibliography, 19 papers involving photographic emulsions and nuclear particles between 1925 and 1938. Now, you also mentioned that she was, her original impulse to begin this work in 1925 had something to do with the observations of Kirsch and Pettersson in Vienna.
No, they were using scintillation methods. They were trying to repeat some of the experiments of, that were carried out especially by Rutherford and Chadwick, using the scintillation technique, and although you merely mention that in this review article, I happen to have looked at their papers, and I know that that gave rise to a sort of scandal. They had claimed that they could distinguish scintillations caused by some of these experiments which involved bombardment of light elements in alpha particles, they claimed they couldn’t do. Therefore, they looked at 90 degrees, and saw many fewer events. So this group, which involved Kirsch, Pettersson and quite a number of other young people, found that they might find 10 to 100 times more nuclear disintegration than Chadwick and Rutherford. They also found, claimed, that they could disintegrate much heavier elements than Rutherford and Chadwick, who said they couldn’t disintegrate anything heavier than, I forget, something rather light (chlorine perhaps). They also said Rutherford and Chadwick couldn’t do what they were doing because they hadn’t properly analyzed the optics and the general experimental conditions. The response to that by Chadwick was to publish a long paper, in which he discussed, as far as I know for the first time anywhere, many experiments carried out in Rutherford’s laboratory and calculations, involving precisely microscope optics, optimal field of view, as well as tests on the psychology of observing scintillations, and all — they had done a fantastically fabulous job, which they never bothered to mention anywhere in any of their papers. And later on, of course, (I seem to be making a whole speech on this myself) — but later on, when the electrical techniques, counter techniques were used, it turned out that Rutherford and Chadwick were absolutely correct, and that this other group was completely wrong. That’s a very long introduction to ask this question; did Blau, in the paper of Blau, did she ever mention the work of Kirsch and Pettersson? Did she ever correct it? Because she could only have in principle have obtained quantitative results, which would have checked on some of their more outrageous claims.
It’s been far too long ago, and I just don’t remember whether Blau did in fact do so. I suspect she may have referred to some of their work, and if she was in any way stimulated or egged on by what they did to pursue her own, it wouldn’t be the only time in the history of physics, of course, where something quite spurious, something quite erroneous, nevertheless by good luck leads to something solid and worthwhile. In the history of cosmic rays, the important example of that, in a theoretical way, that comes to my mind is Millikan’s hypothesis about how cosmic rays are born out in space, which turned out to be quite erroneous, nevertheless by good luck leads to something solid and worthwhile.
Yes. OK. Well, as long as you've introduced that subject, I was really going to ask you next, your second paper that you published involves the study of these cosmic ray stars in special photographic plates that left on Mt. Evans, for nearly eight months, according to the abstract. I want to ask you about that paper, what that contributed to the knowledge of cosmic rays, but as an introduction to that, perhaps it would be interesting if you could tell us what was the problem situation in cosmic rays at that time? What were the prevailing ideas about cosmic rays? What were the problems, as you saw it, that needed to be solved, and so forth? These debates, this view of Millikan that you're talking about, which led to very well… publicized debates between Millikan and Compton in the early thirties, they were all over I suppose by that time?
They were all over.
You were talking about an earlier period when, after the latitude effect had been —
They were not quite over —
(crosstalk) — not quite over, because —
— because I attended practically —
— could you please, why don’t you say something about that?
Well, in response to that, r remember my first Physical Society meeting in Washington, where Millikan was still present. The meeting was being held on the grounds of the Bureau of Standards which was a favorite place. in those days for the annual Washington meeting, and he was still maintaining that his ideas about cosmic rays being the death cries of atoms were —
— birth cries, is what he —
— he may have called them birth cries, but I really think that the appropriate term must be death cries, because he was speaking of the annihilation of whole nucleons of matter. What he noticed is that they characteristic energy of cosmic rays, in what we call today the GEV region, (they called it billions of electron volts, BEV, in those days) — corresponded closely to the rest mass energy of nucleons.
OK, now we’re recording again, You were talking about the birth cries, or death cries rather, of nucleii. Basically his idea was that the primary cosmic rays were photons, rather than charged particles, whereas Compton was arguing for charged particles, and the matter was to be settled, as I understand, by whether or not there was a latitude effect, and the first indications seemed to be, there was not; and then afterwards it was confirmed, largely by the efforts of Compton himself, organizing a worldwide effort, that there was significant latitude effect, which indicated then that the primary cosmic rays were at least primarily, no pun intended, charged particles.
Yes, indeed. This was Compton's first major contribution to cosmic ray physics.
But at the time when you were working with him, was that his exclusive interest?
I think it would be an exaggeration to say I was working with him. The truth of the matter is that although he had graciously agreed to be my thesis adviser, I saw him in general only during the weekly seminars on cosmic rays. He was a terribly busy person, as you might imagine not only in physics. He of course was a Nobelist, a distinguished man, but he was so much in demand with the general public, I think that he was a great exponent of science to the public. He also had strong interests, as you may know, in the connection between religion and science, and this further extended his busy schedule.
And then later he became chancellor at St. Louis, is that right?
During my period at Chicago, he turned down many offers of university presidencies elsewhere. But after World War II, or perhaps during it, he agreed to serve as chancellor at his old university, where he had done the original work that got him his Nobel Prize.
Would you happen to know which year he came to Chicago?
No. I do not know that, I assume it would have been somewhere in the twenties.
I see. So let’s come back to this question, then — what at that time was the main interest and what you conceived to be the main problems in cosmic rays?
The 1930’s, as I recall, were a period in which a great deal was learned, and largely on the theoretical side, about what happens to cosmic rays in the atmosphere. Mainly the development of electromagnetic cascades, and this whole business of shower theory was simultaneously, as I recall, developed by such celebrated people as Oppenheimer and his students, Bethe and Heitler, Bhabha — quite a number of the really distinguished theoretical physicists of the time, and it's no wonder —
Rossi was on the experimental side mainly.
They wrote an important review article.
They did indeed — Rossi and Greisen.
Same year that you wrote your review, 1941.
Yes. The two don't deserve comparison, because theirs was really a monumental work, which summarized what was known then about showers. So the matter of an important component of the cosmic rays, as it developed in the atmosphere, was being beautifully developed on the theoretical side, in those years. Simultaneously, the predictions of Yukawa of a particle that would serve as nuclear glue, and the experimental work using cloud chambers by Anderson and Neddermeyer, leading to the discovery of the "mu-meson," as it was then called; we call it muon today, of course — sort of took care of another important component of the cosmic, of the secondary cosmic radiation that gets down to sea level — and as you know, most of the arriving cosmic rays at sea-level are these penetrating muons, And people talked in those days a great deal about the soft component, namely the electrons and photons, on the one hand, and the muon component, which was penetrating, and it was Rossi who made this nice practical distinction between the two by showing that at first, as you allowed incident cosmic rays at sea level or at mountain altitudes to impinge on a solid slab of material like lead, you had a growth of the number of particles as a function of the thickness of lead, namely a multiplication, leading to the famous Rossi transition curve, which applied to the soft component, and then as you went through a few centimeters of lead, you reached the situation where the number of particles that could penetrate more and more thicknesses of lead got to be quasi- level.
Right. Right. So that was by definition, a penetrating component.
This was a way to separate the soft and hard components. (crosstalk)
Hard components that consisted mainly of muons, studied by Pancini and Piccioni and Conversi —,
— oh, this came actually a good deal later, late in the war, even somewhat after World War II; I think, it happened in about '46, ‘47, when they demonstrated that those couldn’t possibly be the Yukawa particles, because, they just didn’t interact at all,
It might conceivably have been guessed, by people analyzing the Anderson Neddermeyer results, that in view of their great penetration — one could see particles in their cloud chamber that went straight through, and hardly did anything, and yet showed up on the other side, with only a modest amount of energy loss due to ionization, as we now know — that this was a component that evidently was not interacting very strongly. It certainly wasn't being absorbed out very readily.
Yes. Well, let’s go back to this second paper, actually your first research paper, then, — was this the work on which your Ph.D. thesis is based?
It was indeed, and I really do not consider it intrinsically an important work at all. If I had the opportunity of going back, being a student once more, I think I would have tried to do something really more solid in the way of a contribution to cosmic-ray physics or anything else, But what it was' useful for was as a concrete demonstration that, by the use of a really negligible amount of detector material, a little stack of small plates, that one could in a few months amass a great wealth of data about cosmic ray stars, Now the reason that I denigrate this initial research work of mine is mainly that I had no way of knowing really how very inadequate the, nuclear emulsions of that time were — the fact that there was so much that was not being seen because their threshold, their ionization threshold for giving tracks was so extremely —
— not sensitive to relativistic particles — (crosstalk)
— far from adequate sensitivity to relativistic particles,
— especially electrons.
Not only didn’t they show electrons, but of course, they only showed really slow alpha particles and protons. But I think the work, as I say, was useful, along with the earlier review paper, mainly in calling the attention of people to the fact that here was' a technique that had some potential, and I think in fact that mine was the first Ph.D. thesis using this emulsion technique for learning something about cosmic rays — at least in the U.S, this was the case, if not in Europe.
Yes. Let me ask you this question, in that connection. I noticed in this 1942 PHYS REV paper, that you did find that — you were in a way going beyond the study of the soft component, certainly —
Oh, indeed —
— in penetrating particles —
— indeed —
— 90 percent of the tracks, you say, were produced by protons, and most of the remaining were probably due to alpha particles of less than 9 MEV. And the equipment you used, you described, involved a binocular microscope, with a mechanical stage, with an eyepiece scale, and that was borrowed from the biology department.
Is this the first, to your knowledge, use of that type of quantitative measuring equipment?
No, I suspect not.
Or did Marietta Blau and her group use this, or did they just count — because you see, there are different ways of doing things. You can just count tracks and measure angles, and then there is the matter of more active measuring of — ranges, and so forth.
Well, I certainly endeavored to — right, I endeavored to be quantitative in this early work. But I doubt very much that whatever pioneering it represented was due to the quantitative aspect, I would credit some of the pioneers that proceeded me with trying to be similarly quantitative.
Well, that could well be, but it did seem to me, from the little I know about it that you were already using the whole, essentially the technique which was later used in the Bristol group and —
Yes, I doubt that I should be given too much credit for that, because the late Cecil F. Powell, who later discovered the pi-meson and the phenomenon of pi-mu electron decay, was certainly using quantitative means in low energy nuclear physics. The only difference really between what he was doing and what I was doing, the major difference, is that he was applying this new technique to problems in nuclear structure physics, whereas I was using it for cosmic rays.
Well, Maurice, I think it’s clear that we can probably go on for another hour or more, if I start asking you what you were doing at Los Alamos, and what you did at Oak Ridge, ask you how you got back into the cosmic rays, and about the development of emulsion techniques after the war and so on. You spent some time at Bristol, is that?
I only visited; this was after I got back into cosmic ray work.
Yes, And also of course the work later on that you’ve been doing, the very interesting work you’ve been doing lately in cosmic rays, particularly in relation to astrophysics. So I think we can go on for hours and hours, but perhaps it will be better if we just try to confine ourselves to the period before 1950, but rather than ask you — you did mention to me that you had had some contact with Yukawa. I would be especially interested if you could say something about your contacts with various people who are concerned particularly with the meson. So let’s say Yukawa, Powell, Occhialini, and who else?
Well, Carl Anderson notably.
Carl Anderson. Yes. Did you know Carl Anderson?
Yes. I was privileged, just by being a student at the University of Chicago, which was and I think still is a sort of crossroads for physicists — partly its geographic location and partly the reputation in physics of the University of Chicago — I was quite lucky to be there as a student, and to get to meet automatically, as it were, the wonderful people who passed through. One of them was Yukawa, who came and gave us a seminar. It was very difficult to understand anything of what he said.
When was that?
I would guess that this would have been in about '38.
Oh, I see. That’s very interesting. That would be the first time he ever left Japan, actually.
He had been, I know, it was '39, I believe, he had been invited to a conference, to attend the Solvay Conference which was actually cancelled because shortly after he arrived in Germany, the war broke out, and of course they cancelled the conference, and in his autobiography (which I’m having translated), he says that he was caught in Germany at the outbreak of the war, he made his way back to Japan through the United States.
Ah. Well, if it was after the outbreak of the war, then my recollection would be off by at least a year, because it would have been '39. You remember the war started in September of ’39.
Right. Exactly, yes.
So he would presumably —
Well, he had not yet left Japan in ’38. I know that.
I see. So he presumably would have visited in late ‘39 or even early '40 and addressed one of the weekly seminars that Arthur Compton conducted. Of course, Compton himself was a magnet for the visits of ever so many people. He knew physicists from around the world, and they would make it a point, if they, possibly could, to come and stop. Yukawa was not at all easy to understand — not so much the language difficulty as the fact that he tended to mumble as he spoke, sort of talked into his non- existent beard, as it were. But it was very inspiring to us who knew what he had done, to have a chance even to meet him. By this time, there already, I think, were lots of puzzlements among physicists, as to how the penetrating particles discovered by Anderson and Neddermeyer could quite fit the bill of Yukawa’s particle, which was later realized to be the pion. Well, Anderson also passed through, and he was a youngish man and a very modest informal man who simply insisted on everyone calling him Carl. The graduate students like myself had to call him Carl as well. It really made us feel close to the fount of active physics, to have a chance to talk with the man, to interchange with him. Now, you talk about the later work of Powell, which of course came almost a decade later. It was ‘47. At that time, I found myself, in my early postwar years, at Oak Ridge, where I had been eager to go and study neutron physics, with the new intense beams of neutrons that were available. My job at Oak Ridge was arranged for by an interesting threesome — as I recall, Edward Teller and the late John von Neumann, with whom I had the privilege of collaborating at Los Alamos on totally different work — these two men persuaded Lothar Nordheim, who was head of physics at Oak Ridge, to offer me a job. Well, Lothar invited me to come there, and I was easily persuaded. I wanted anyway to work with neutron beams. So while at Oak Ridge, I worked on such things as the phenomenal cross section of xenon-135,the famous pile poison, and measured it as a function of energy, along with a large group of physicists and chemists. The main other physicist was Seymour Bernstein. However, in late ‘47, if I remember, there came electrifying news, which if I recall, must have appeared in NATURE, of the discovery of new particles in the cosmic rays that were apparently of lower mass than the proton. They scattered, they multiply scattered very much when seen in nuclear emulsions, and moreover they were interactive with matter, with nuclei, in that the first two reports of this work, which were respectively by Don Perkins, a very young graduate student, and C.F. Powell, — these apparently were independent works — showed clearly the capture of what later turned out to be negative pi-mesons stopping particles with stars at the vertex. Very soon thereafter, there came the —
— unlike the muons which —
— Right — which only very rarely if ever did this kind of thing, and then the little burst, the star was not as impressive a thing as the few slow, particles that came out leaving rather black tracks. Now, those-topping tracks like this, they’re called sigma tracks, sigma for stopping, But then there was another kind of track, besides the one that caused stars yes, in the same plates which had been exposed at Chacaltaya in South America at an altitude of about 5 kilometers, the world’s highest altitude station,
In Bolivia. The nuclear emulsions that had been left there for awhile also revealed upon development another startling phenomenon The appearance of a meson track, which gave every indication of belonging to a particle that decayed from rest into a second particle, which in turn decayed into still another visible particle, and that was the first evidence obtained by Powell and his collaborators of the pi-mu-e event.
Now, something must have happened in between, because did they, in the very first of these observations, as you recall, did they actually see electrons? Or was it just the pi and mu?
I think your memory serves you better, and initially it was pi-mu, and it takes a little more luck, in getting the three tracks to be, almost co-planar, in the three dimensional emulsion, to have a good chance to see the electron.
And then one does need the electron-sensitive. I think —
— right —
— the first emulsion —
— had not quite been electron-sensitive?
I think it was only perhaps some six months later that —
— ah yes —
— they had electron-sensitive emulsions, this was —
— you're absolutely right —
— this was Berriman –-
That's right, Berriman out at Eastman Kodak in England was the first, as I recall, to achieve this ultimate sensitivity. But as it turned out, the most reliable steady source of emulsions soon got to be the Ilford Company, under the famous C. Waller, who for many years supplied the world with excellent research emulsions.
Yes. Well now, let’s come back to your own experience, which I think you were about to say, you had been working at Oak Ridge?
You were working on neutron physics, and then how did you happen to come back into cosmic rays? Was it related to this?
Oh very much so... This discovery of pi-mesons, especially when there, came along very soon thereafter another major discovery in cosmic rays, namely the discovery that the primaries incident on top of the atmosphere include besides protons, also alpha particles , and even heavier nuclei all of which collectively came to be called the heavies, the heavy primary nuclei; those were discovered by two groups, one in Minnesota, the other in Rochester. The Minnesota group made the initial discovery of the heavies, if X remember correctly, with photographic emulsions which were, being examined under the microscope by a graduate student named Phyllis Freier, who worked under Ed Ney, currently doing other astronomy, and others in the group were Frank Oppenheimer and Ed Lofgren. Now simultaneously there was a group at Rochester, smaller group of two, namely, Bradt and Bernard Peters, who were working on the same thing. I would say that the Minnesota group really deserves a lot of credit, for having realized that to pin down the character of these heavy primaries as being relativistic nuclei, relativistic heavy ions, to demonstrate this conclusively, they also sent up a little cloud chamber with a thick enough lead plate, through which these nuclei managed to penetrate — and from their specific ionization and the tracks above and below the lead plate, the thickness of the lead plate, it was clear that these had to be —
— these exposures were made with airplanes, is that correct? Or balloons?
This was, done with high flying balloons, just about the time that the technique of the so called skyhook balloons, the large plastic constant volume balloons had really transformed the business of exploring the upper reaches of the atmosphere.
I somehow remember that some of the original work was done by airplanes.
Of course, this was very limiting, because an awful lot happens above the altitudes that then were reached by airplanes, That wasn't high at all. Even the balloon' altitudes reached with the rubber balloons were limited to somewhere in the vicinity of 70,000 feet, It took a big cluster of balloons and lots of trouble to send those things up.
So about this time, you decided that you really were more interested in cosmic rays?
Oh, these two discoveries convinced me that I ought to get back as fast as I could. By happy coincidence, I was offered a position at the Naval Research Lab by the late Franz Kurie, famous for the Kurie plot in beta decay, and I lost no time in accepting.
Was that partly because you were conscious that you had been a pioneer in the use of emulsions?
Well, certainly, the fact that I had already made a modest contribution in this area was responsible for my following the whole thing With interest, and I felt that this field was really beginning to blossom in a very significant way.
Which aspect do you feel attracted you more — the elementary particle aspect? The fact that one was looking at new types of particles, new types of interactions? Or was it the possibility of learning more about the cosmology?
Well, it would be difficult to assign, in my mind or in my recollection; a priority. They both fascinated me because from the start, those of us who were, working in cosmic rays, even when it was the sole source of very high energy particles, for doing high energy physics, elementary particle physics, — nevertheless were well aware that here was a cosmic phenomenon that had many fascinating problems connected with it. Where did they come from and how did they get their high energies and so forth? So it’s hard for me to say which it was. I think certainly the combination of the two was irresistible.
Yes, and just at this time, with the discovery of the pion, that was of course a very attractive and fascinating feature, but you had no idea really, the real possible richness of the cosmic ray beam?
That’s a fair statement. No one could have anticipated that so soon thereafter, there would come all these strange particles, including the K-mesons, the hyperons, etc. So for a while, for maybe less than a decade, the cosmic rays certainly continued their role as “nature's accelerator; giving us both the tools and some of the results of elementary particle physics in that time.
Let me ask you another question. I remember when I was a graduate student and since, it always seemed to me that one of the outstanding characteristics of people who did experimental work in cosmic rays was the adventurous nature of the subject. I mean, looking at high altitudes and low latitudes and so forth. Did this aspect of it appeal to you? Are you an adventurer?
I don’t think this was so much a major factor in my case. I had been brought up as a city boy without really very much access to nature in the raw.
This is the second cassette in which Laurie Brown is interviewing Maurice Shapiro on May 30th, 1978. Maurice, you didn’t get a chance to finish what you were saying on the last tape, so could you?
Well, in response to your question about the extent to which I was intrigued by the adventure, all the travel that “cosmic rayers" have a chance to do, I would say that that was not a major factor in my own interest in the subject. In fact, I must confess that more often than not, when it came to balloon flights, I would be content to send some associates out into the field, rather than take the time myself. I was conscious always of there being so much literature to keep up with, and the greater pleasure. for me of just working with the observations, with the materials when they became available.
I was thinking about somebody like Occhialini, who’s a cave Explorer, spelunker and all out mountain climber.
He is certainly more o£ a universal man than I am.
He used to like to carry his plates to the tops of mountains in a knapsack and expose them and so on.
Right. I’m glad, Laurie, that you brought up his name, because certainly he deserves a great deal of credit, along with Powell and along with Giulio Lattes, also called Cesar Lattes, the Brazilian, for the discovery of the pi-mu-e decay, and it's well known of course that for Occhialini, participation in this enterprise was the second time that he participated in a Nobel Prize discovery, the first one having been with Blackett.
I’m happy to say, by the way, that I just heard that he was elected foreign member of the National Academy of Sciences in this country.
I see. I am very glad to hear that, too, because that is — do you know anything about — well, you said you visited Bristol, you know these people, but you have not actually worked at Bristol?
I have not worked at Bristol. It’s remarkable you should ask me this question, because on my first visit to Bristol in 1950, I was asked — well it wasn’t just to Bristol. It was to the British Isles, and I was attending an international nuclear conference, which included cosmic rays as only one component, and I was asked at that occasion at lunch time by Lise Meitner, who already was living in Sweden at the time, whether I felt that Occhialini would deserve a lot of credit, along with Powell, for this discovery. And since I had not actually been in the lab, I could only give my honest answer, that I knew he must have contributed significantly to almost anything that he participated in, but as to the relative strength of contribution, it was not possible for me to say. And just shortly thereafter, Powell did get the Nobel Prize. within a month that was announced. I was able to foreshadow it a little bit for Powell. It was very clear that he was a prime candidate.
Powell died rather young?
In his early sixties, I think,
What sort of person was he? I know that he was probably an adventurous type. In the thirties he had spent some time as a seismologist, on a trip to — I believe it was Mexico. Then he came back, and he did work, he was one of the earliest people to use nuclear emulsions.
In connection with nuclear physics, however, not with cosmic rays.
And his cosmic ray work began I think really after the war?
It did, after the development of these super-duper emulsions of higher sensitivity — which, by the way, he helped to encourage through some panel that had been set up. I think the panel was energized in part by Chadwick himself, as a matter of fact.
So he was not really a cosmic ray person, whereas Occhialini had already had already worked with the cloud chambers and the cosmic rays. Occhialini also is a great optical expert, expert in optical instruments. He has invented optical instruments. His father was professor of optics at University of Pisa.
An extraordinary physicist all around, bubbling with ideas, no question about it. One of the remarkable things, however, that sticks out in my mind is having visited Occhialini for the first time in Milan, where his main laboratory was located, in 1953. Occhialini is a lover of music, and yet he had never been to La Scala until I took him there! I had met his wife, Connie Dilworth Occhialini, three years earlier, in a brief visit to Brussels. At that time Occhialini was shuttling back and forth between Milan and Brussels, carrying on photographic emulsion work at both places, and your reference to the optics reminds me that among the many things he did, one was to work with Max Cosyns, a Belgian physicist, on developing a remarkable microscope particularly suitable for measuring multiple Coulomb scattering in photographic emulsions, a microscope with a stage that worked on a completely different principle from the ordinary sliding stages.
Most of his instruments he developed had the names of — taken from Winnie-the-Pooh. Was this the Poohstralina?
Yes, and Poohnicastro was — Poohnicastro was another gadget, the name of another gadget, and even his daughter was called Connie-Pooh. I think for the mother, I guess.
They were both called Connie but the daughter was Connie-Pooh to Distinguish her from the other. Now, you said there were two remarkable discoveries in the cosmic rays, one around 1947-48. One was the discovery of the pion.
Excuse me, Laurie, they were both in that time frame.
Yes, almost at the same time. One was perhaps of major interest to particle physics. The other was of major interest to astrophysics, the origin of cosmic rays — the theories of cosmology, the discovery of the heavy primaries, of the primary cosmic rays, You had been telling me previously that Marcel Schein had some important role to play in this.
Yes indeed. Marcel Schein, who was then a research associate at University of Chicago, along with two other research associates —
— at what time was this?
— connected with Arthur Compton. This was about 1941.
So you're going back now.
I'm going back, yes. Marcel Schein and Wollan and Jesse did a really landmark experiment, sending up, suspended from a balloon, an apparatus which was capable of distinguishing between incident high energy electrons and incident high energy heavier particles like protons, and they demonstrated quite conclusively that the primary particles coming in near the top of the atmosphere, which we call today galactic cosmic rays, could not be predominantly electrons. They even could be only to a minor extent electrons, because the apparatus in which they were making these observations had a set of Geiger counters strung along vertically on both sides of a deep lead absorber, and particles that succeeded in penetrating the lead, particles incident from above, were not setting off these guard counters. They would have been expected to set them off in large numbers, if showers, electromagnetic showers, had been produced, because there would have been high multiplicity, many electrons ending up registering in these counters. This did not happen.
— the horizontal spread of the shower?
— could be well calculated from theory?
Right, plenty of multiplication in the lead and so forth. And the fact that these so called guard counters, anti-coincidence counters, we're not being set off made it clear that the particles, were going straight through, doing very little in this chunk of lead that could not be identified with the soft component, with electrons, in other words. So it became clear that the particles must be protons. Of course, later on, when the Rochester and Minnesota groups showed that even heavier nucleii existed in the cosmic rays, it led to the famous bon mot of Karl Darrow —
— long time secretary of the American Physical Society, who kept up with these modern developments, and who commented rather interestingly that Millikan used to say or used to think that cosmic rays are the birth cries of atoms, and now it was clear that they were the atoms themselves which was a rather clever statement.
Yes. And you also have mentioned that this sort of physics, which is very pure in a sense, very difficult to see applications, nevertheless has led to some important —
— well, yes, as a matter of fact, it’s rather remarkable that the two things happening at once, essentially, in cosmic ray chronology, around 1947-48, namely the discovery of pi-mesons and the discovery that the primary cosmic rays include a whole range of heavy elements all the way up to iron at least, these two developments which brought me back in a rush to cosmic ray work, and took me from Oak Ridge to Washington, at NRL where I'd have a chance to work on these things — as I think back now, in the light of what has happened in pi-meson physics and in the physics of relativistic heavy ions, I am fascinated by the following thought: If anyone back in the late forties had told me that these esoteric things in the cosmic rays, these highly unstable pi-mesons, or for that matter, the heavy nuclei in the cosmic rays, would someday both be used by medical researchers in the exploratory treatment of cancer I think I would have been incredulous. And yet, within the space of some quarter century, this has come to take place. You have the meson factory in Los Alamos, which has an associated clinic for cancer treatment. And in Berkeley, where they're now accelerating, where they have been the last few years accelerating heavy ions to relativistic energies, some of those heavy ions are being simultaneously used in medical research as well as in biophysical research.
Yes. And of course the cosmic rays, then as now, always have provided the highest energy beam probably no matter how big accelerators are produced, there will always be events of still higher energy, which of course in physics means exploring still smaller distances, which can only be done to the cosmic rays.
That is certainly true. And therefore a certain number of elementary particle physicists continue to have an interest in what we might learn from the ultra-high energy cosmic rays, which simply cannot be learned in the early foreseeable future from accelerators. At the same time, there is a special fascination about the cosmological, the astrophysical aspects of the higher energy cosmic rays. We cannot yet be sure, for example, whether they are generated within our galaxy, as most of us believe the bulk of the cosmic rays are accelerated, or, instead, come from, come at the highest energies from other galaxies.
Yes. Well, as I say, I really have been talking with you almost entirely about events that took place more than 25 years ago, and strain your memory, and I thank you very much for that. I hope that another time, we can talk about all the fascinating things you’ve been doing since that time.
Thank you very much. I’ve enjoyed talking with you.