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Maurice, since we've known each other for a long time, Iím 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 thatís how I came to be born there.
Well, do I gather from you -- I'm sort of interested in this,
because now weíll 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 Iím 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
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
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
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 couldnít 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 wasnít 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 canít 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 Ė- 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 kindÖ
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 Eckartís 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 ďThatís the important thing. You mustnít expect to learn everything in your college or even graduate years. Youíll keep at it all your life, and I believe that your degree of interest will go a long way.Ē
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 bachelorís degree at Chicago.
Well, then you got youíre A.B. in 1936, and you got a Masterís 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 Bachelorís 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 Iíd 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 ChicagoÖ 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 manís 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
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.
Thatís 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 wouldnít 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 Comptonís, 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 ďstars,Ē 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 Masterís 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
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 wasnít 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, ďTracks of Nuclear Particles in Photographic Emulsions,Ē published in THE REVIEW OF MODERN PHYSICS, in January, 1941. Iíve 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 couldnít 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 couldnít disintegrate anything heavier than, I forget, something rather light (chlorine perhaps).
They also said Rutherford and Chadwick couldnít do what they were doing because they hadnít 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 Rutherfordís 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.
Thatís 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.
Itís been far too long ago, and I just donít 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 wouldnít 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 Millikanís 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
These debates, this view of Millikan that you're talking about,
which led to very wellÖ 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 donít 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 weíre 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
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 letís 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 1930ís, 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
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-
Right. Right. So that was by definition, a penetrating component.
This was a way to separate the soft and hard components.
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, Ď47,
when they demonstrated that those couldnít possibly be the Yukawa particles,
because, they just didnít 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, letís go back to this second paper, actually your
first research paper, then, -- was this the work on which your Ph.D. thesis
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 didnít 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
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
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 itís 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 youíve been doing,
the very interesting work youíve 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 letís 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
When was that?
I would guess that this would have been in about '38.
Oh, I see. Thatís 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
Iím 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 í39.
Right. Exactly, yes.
So he would presumably --
Well, he had not yet left Japan in í38. I know that.
I see. So he presumably would have visited in late Ď39 or
even early '40 and addressed one of the weekly seminars that Arthur Compton
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 Yukawaís 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 Ď47. 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
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 Ď47, 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, theyíre 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
worldís 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 Ė-
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, letís 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?
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
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 itís 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?
Thatís 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 ďnature'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 donít 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 didnít 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 ďcosmic 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, whoís 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. Iím 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
Iím 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. Itís remarkable you should ask
me this question, because on my first visit to Bristol in 1950, I was
asked -- well it wasnít 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, itís 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
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 youíve been doing since that time.
Thank you very much. Iíve enjoyed talking with you.