Martin Deutsch, “Physics on a Human Scale” - LNS46 Symposium: On the Matter of Particles
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MODERATOR: --speak of the early days. And I won't repeat again many of the things you've heard. I will say that he's justifiably recognized as one of the exceptional experimentalists in the field. Martin did seminal experiments with positronium as his trademark. He was a signal figure in the laboratory beyond his own researches. Director during the period of the J/psi excitement. So let me, without further ado, turn to Martin, an exceptional person as well.
DEUTSCH: It was really impossible to prepare make this talk. So obviously I can't give the talk, but I'll have to tell you why I can't give the talk. And that's what I'm going to spend my time on. Does somebody know the next line? Vicky, whom did you have in Latin in the sixth? You should know the-- no?
Clearly this is Virgil, I think. And it says the first age was the golden age. And so I think I'm supposed to speak about what I am supposed to perceive as the golden age. And I tried very hard to do that. And I said, well, it's obviously true that the days of tabletop physics, as it was first called in preparing this, was the age in which everything was wonderful.
You didn't have the bureaucracy, you didn't have to worry about money. You had lots of ideas, the experiments went quickly. And so I was trying to understand what the basis for this golden age really was. And of course, I made the model, I made the theory, and started working on it. And I concluded that the problem was not that-- at least I think the cause was not that experiments were smaller.
Because I think, compared with the gross national product, they are not that much more expensive or bigger now. Maybe one order of magnitude, but not three or four. So it had to be people. So it had to have to do with the interaction between people. And I will, at the end of this talk tell you the conclusion that I reached, and why I can't give the talk.
But I tried. I started out, and what you have here is a time scale. Because I didn't want to write that on each of these pieces of paper. So I started out by saying, well, what did I do in this time interval? This time interval goes from 1946 to-- it peters out somewhere around 1960. And I will tell you why I stop about then.
What I wrote on this first slide, which is not very important but to guide me on the time scale, was where I was at some of these times. And it turned out that I was away more of the time than I had realized. I had, starting 1946, which is the year of the big bang as far as we are concerned, I was away in '47, '48. Which seemed, in retrospect, incredible that I left here after a year.
In '52 I was busy in Washington. '53, '54 in Paris. The other things that happened that I have marked here is the following. The Laboratory of Nuclear Science started as a Laboratory for Nuclear Science and Engineering. And at this point, the engineering disappeared from the progress reports. So something happened here.
And the work I was doing was in a group called Radioactivity and Cyclotron Group. And at this point, the cyclotron was no longer mentioned. And here, in 1955, something interesting happened. My name appeared in the progress reports as somebody responsible for something. Until then, it was all Bob Evans. And that, I think, is a clue to what happened in those years.
I think Herman Feshbach and I are the only ones here that go back to before the big bang. I got my PhD here under Bob Evans in nuclear physics and then left, as soon as I got my citizenship and could do such things, for Los Alamos.
Unbeknownst to me, the department had decided not to continue my appointment here. If I had known that, I might have been a little worried. But when I came back, really in the way, I picked up where I left off. Something very important had changed in that time. And that was the status of nuclear physicists.
There had been Los Alamos, there had been the bomb. And we came back with a feeling of success. In a funny way, I think, we felt we could do anything. Certainly, the rest of the United States thought we could do anything. The description of what happened when Oppenheimer got off the plane is quite standard.
In fact, I remember going to a Washington meeting, in line at the hotel, and somebody said, oh, Oppenheimer, I'm sorry we must have lost your reservation, or something, we don't have a room. And I said to the man, this is Dr. Oppenheimer, you do have a room. And he goes oh, yes, sir. It went that way.
But the real feeling of having arrived came in 1952, quite late. At the meeting in Amsterdam, I-- you know, I tended not to have my hair cut as often as I should have. Now I never get it cut by a barber. I do it myself. But at that point, when I went to the barber to get my hair cut, they usually would say, what are you, a musician?
And what happened was, in Amsterdam, I got my hair cut, and the man looked at me and says, what are you, a nuclear physicist? And that showed that we had arrived. But seriously, I think that was probably the real element. At least I thought that was the big element.
The other element that gave me such an exhilarating period, of course, was the fact, at least I thought, that we didn't have to write proposals. We didn't have to persuade outsiders that what were doing was worthwhile. The relationship with the funding agencies, at least initially, was very interesting. They thought they knew much less than we did. I'm not so sure they were right. But that was certainly the relationship.
The idea, the way our activities were supported was, we want to support the good people to do what they want. Because that's the way we've been successful. There was a feeling the physicists did, in a certain sense, that decisive things in the war. Radar and the bomb.
And not because they had been working on communications or on bombs. That sank in. And we were treated with deference. What can we do to help you? And the relations between Washington and the universities was that. The idea was that we, as creative scientists, were a national asset. And that the purpose of the operation was to strengthen this national asset.
Today though, it seems to be that we are contractors. And the important thing is that we are assumed to cheat, like all other contractors. Therefore I have to be treated in the same way. Furthermore, we are apparently engaged in violations of anti-trust laws. Maybe we do, I don't know.
I think what happened later on was that, unfortunately, the people in Washington learned too much. They got too good. They knew too much physics. Today, our problem is not that they don't know physics, that they know too much physics.
Not only do they think they can make sensible decisions, but they can make sensible decisions, indeed. And sometimes they are right, and that cramps our style. But whatever it is, that was my thinking on the subject.
When I came back from Los Alamos, I had the program. The program was that I would work on two things. Again, I'm going to talk about myself. Not because I think it was the most important thing that happened, but because the experience was a personal one. And if I start talking, except in substantive context about experiences of others, I only dilute what is really, I think, you expect me to convey.
But I had two ideas. One thing was, I was going to study, what we today would say, nucleus structure through radioactive decay processes. I had done that before the war. The thing had gone on right into the war years. Even done a little bit of that in Los Alamos.
And the other thing that I was going to study was beta decay. Or today we would say weak interaction physics. And what I did not think of, although I should have stated it at the time, was, of course, electromagnetic interactions. in nuclear processes. The funny thing is those were the ones that turned out the most interesting.
But I went back over the progress reports of the lab, and I found no mention of electromagnetic interactions till quite a bit later. So I said, well-- I looked through the records what went on, what did we do, what did I do? I don't mean just I by myself, but what did the physics in my orbit consist of.
And the thing that is striking to me is how many things happened in any given year. So here we have one list. A list that has to do with nuclear structure and decay schemes. And the subjects, more or less, along the time line, written in green. And the black lines, the black ones are the names associated with it.
Well we did with decay schemes, energy levels, and things like that by the bushel. Sort of every three months there was a list of five or six things to fill the literature. I think that's stuff that today would properly be distributed only through computer disks.
But we developed an awful lot of techniques, ways of doing things. And some of them were fun. One was this business of studying nuclear angular momentum, essentially. Nuclear symmetry properties of states by angular correlation. The thing that happens when you get back and read those old papers, you say, my god, why did I even bother publishing this? Everybody knows that. And what one forgets is, that until I published it, not everybody knew it.
And I don't mean that I invented these things or that I created them all out of my brain. They were, of course, around, and other people were doing similar things. But it was awfully exciting, because look at the time scale. In this period pf two years, part of which I was away in Stockholm, we opened up correlations, gamma ray correlations, beta gamma correlations. And only a year or so later, we discovered that we could also measure the polarization of the gamma rays in these processes.
So all the things that today you do as a matter of course, were really quite new. Obviously, people had done that with optical radiations, but nobody had ever done this with nuclear radiations. It was really exciting.
And the other thing that is fun in looking back is the degree to which things that happened later were really already there seminally. The very first experiments we did on correlations between nuclear radiations, I had a chemist as a graduate student, because I said the problems may well be chemical.
You see, people had tried to do these experiments, but they didn't succeed. They didn't see any correlations. You must remember that the only radiation detectors one had at that time were Geiger counters. And Geiger counters are not very efficient detectors of gamma rays. Their circuits are slow, you can't use very strong sources, and people hadn't seen the effect.
So I said to myself, why could that be? The correlations must be there. I mean, that's just the geometry of radiations. And it's clear that they must be there. And I said maybe it has to do with the atomic fields perturbing the nuclei. And then I had the idea [INAUDIBLE] that, if we could get the stuff into gas, then you wouldn't have so many neighboring nuclei, and then maybe you could see the correlation.
So I got a chemist who said, yes, he could make a gaseous compound of cobalt so that we could study the radiations. Cobalt, for various-- well, cobalt-60 was a desirable nucleus to study. Now, as we now know that was moving the wrong direction. Because, in fact, you're more likely to have a overall symmetric situation, and therefore no perturbing field, in a solid-- although maybe not for cobalt-- but in general, than you have in the gas, where the neighboring atom clearly defines a direction in the molecule.
But the idea was there. And as I will show you in a few minutes, the fact that we did this turned out to be extremely useful at a later point. And that is one of my points, that if you get into physics of a particular area, everything's connected to everything else. How does that song go? The shin bone is connected to the thigh bone? If you learn physics, and it'll come in handy before long.
And the other thing that I thought was, maybe if the atoms disturb it, maybe if one puts on an external magnetic field, one can overcome this. Now, those of you who are in the field know that that is true. The important point about it is, I didn't understand it at all. I mean, I couldn't have sat down and calculated-- except, perhaps, just absolutely ghostly order of magnitudes-- what would happen when you did these things.
Did the experiment anyway. And that, I think, is a real difference. Because if I had had to build L3 to see whether it's true or not, I clearly wouldn't have, right? And I think that is one of the big differences.
You know, in a certain sense, I am in experiments the way Vicky says is, in theory, lazy. That is, I like an intuitive hand-waving argument. And if I do make an honest calculation, I won't let anybody know it, because I find it's demeaning. So I have started many experiments on what I persuaded myself was total ignorance.
Because you see, after a few years, after we had seen these initial things, indeed other people worked these phenomena out in detail. And the study of what happens to nuclear orientation, and therefore the correlations of the radiations that are emitted, in the presence of the atomic perturbation became a cottage industry in which we also participated.
And there were some very, very entertaining experiments that were done by studying the crystal symmetry, by seeing what happens to the correlations. And these experiments, of course later, were developed by people who are not ashamed of doing something carefully. And, combined with the Mossbauer experiments, and Lee Grodzins, who sort of took over from me at the bottom of this page, did some very outstanding work in this general area.
Now, there were a number of other amusing things, which I think I like to talk about, because they tell you how much fun one could have with some of this physics. One of the things I was trying to study was the transition probabilities. When you have cascade gamma rays, that is, the nucleus decays in a series of levels, what is the probability of the crossover gamma ray.
Because Vicky and others had developed what was at least an incipient theory of the transition probabilities. And I say incipient in the sense that one didn't have a detailed nuclear model to make very specific calculations. But one could make general estimates. Some had already been in the beta bible, but it was greatly refined in Blatt and Weisskopf.
And so there were definite predictions. And the idea was, maybe we could learn something about nuclear structure by seeing what the relative transition probabilities were. So what that involved was, perhaps, to look for transitions that were very rare. And a typical example might be, I don't know, cobalt-60, where you have two gamma rays of 1.1, 1.3 MeV in cascade. What is the probability of the crossover gamma ray?
Now, you would think that's easy, because you just look with some kind of a detector. It isn't that easy. I don't want to go into technical details, but there is a way of making a detector that will only detect the high energy gamma ray. And that is if you let it make a nuclear disintegration which has a threshold that is higher than the energy you have on the single gamma rays.
So what we said is, all right, you take cobalt and you put it, say, with heavy water. Then you should get photodisintegration of the deuteron, you'll get some neutrons. But how do we detect the neutrons? There will be very few. And what we did was something that is known as the Szilard-Chalmers Process.
We got a vat about this big and we filled it with a solution of potassium permanganate. You know, the thing you can gargle with. Now, we put the source in the center of that. The neutron will be captured by the manganese. When the manganese captures the neutron, its oxidation state is reduced, and it is precipitated as manganese dioxide.
Then we took this big vat and filtered it, and all the activity was on a little filter paper. And that way you could detect, oh, one part in 10 to the seventh of gamma rays. I thought that a fun experiment, because you didn't have to write a proposal, you did something new. So a lot of that happened, a lot of that kind of thing went on.
Now, in my confused way of not looking too hard, I had an idea. And I voiced that, and I'll tell you how I got slapped down properly. I said, look, electromagnetic interaction and beta decay have something in common. I don't know what it is. In retrospect, I know what it was I was talking about. At the time, I didn't.
When, I said it's, look, the selection rules are the same. You get the same kind of, what looks like a multiple expansion. And especially if you look at things like internal conversion, where the energy is not emitted as a gamma ray but as an electron from the shell, it really looks very much the same as phi-- what Vicky calls angular physics' concern. The only thing is the charge changes. In one case, an electron becomes a neutrino. In the other case, it stays an electron. Don't these things have something in common?
Well, I said, I don't know what it should be. I asked [INAUDIBLE] in Michigan, who was expert on beta decay. And he said to me, you don't understand Fermi Theory, this is nonsense. The electron neutrino is the field. That isn't the field in between, like the electromagnetic field, that induces the transition.
Well, the first part of the statement was correct. I did not understand Fermi Theory. The second part of the statement, of course, was wrong, because there is a W Z in between. So much for listening to the theorists. Maurice Goldhaber said something that was, I think, more constructive. He listened and said, well, I think that needs to be fleshed out a little.
But the idea persisted, and it sort of haunted me until the real answer came out. And then I had some real crazy ideas. For example, I said, look, in high energy beta decays, there is, among other processes, an electromagnetic process that creates electron pairs.
Now, that means you've got one more electron in there. I mean the transition in making the pair from negative to positive energy state. And if there really is something which electromagnetic and beta decay transitions have in common, maybe you get interference terms. It's wrong. Totally, totally silly idea now that we understand what happens.
But I said, let's try it. And I didn't have to write a proposal, and it didn't cost any money, it just cost a graduate student's life. I don't mean he died, I mean he just wasted his time. That was Jack Greenberg, who searched for positrons, an anomalous number of positrons. And, let's see, Dave Peaslee, I think, did the calculation for-- no, it was Kerson Huang who did the-- one of the two did the calculation for us. But in the process of looking for this thing, we found a lot of other interesting positrons coming from other processes.
So another case where misunderstanding the theory in the proper way was very productive. Well, I don't think there is much sense in telling you all the detail of things that happened. And it was then in 1956-- it must have been '56-- that one more new thing happened in this game. And that was, of course, when the parity violation was discovered.
And I remember being called up at an unusual hour by Chien-Shiung Wu, who told me what was happening, which I had heard already from [? Moirabe. ?] And she said, look, why don't you come down and have a look. We believe the experiment is right, but we'd like you to look at it. And I came down, I looked at the apparatus, and one of the big problems was in which direction was the magnetic field. You see, was the helicity positive or negative.
And I said, how did you check the field? She goes, well, with a compass needle. I said, be careful, because you can polarize a compass needle. No, no, we did it all right. And then she said we-- no, I said, are you sure it-- yes, the compass needle was all right. And I said, OK, now tell me one more thing. Did you think in Chinese, or did you think in English? Because in Chinese, you see, the compass points south. It's just as good, it's just the other end.
And she turned her head for a moment and thought. No, she said, it's all right. So you see how careful you have to be in physics. But one of the problems that was left over was the question whether the polarization in a pure Fermi transition, the helicity will be the same. And then now that we have a theory, this is all obvious. But that problem was left over, and we're going to look at the helicity of positrons in pure Fermi transitions.
And that was an interesting thing in a social sense. Maurice Goldhaber and Lee Grodzins had done this extremely pretty experiment on the helicity of the neutrino in orbital electron capture. It's a real gem. It's one of those experiments. It's a tease, isn't it cute.
You know, this is one of the troubles, why I hate retrospectives. I just hate them. And the reason is, anybody who's ever done an experiment-- probably theory have the same thing. You look back in an experiment, a couple of years later, and you know exactly what you should have done. And when you do that on a large scale, it can get quite painful.
But anyway, they had the same idea we had about how one does this detection of the helicity by determining the circular polarization of the annihilation radiation. And we both going to do it in chlorine-34. And [? Bernie ?] [? Gittel, ?] my new graduate student working on that.
And so I said, look, let's not do something silly. Because if we are running a competing experiment, that will make us publish prematurely and maybe we'll publish some nonsense. Let's keep each other informed, how we're doing. And then, you know, if one of us thinks he has enough data to publish, he'll tell the other one who can either-- we have to trust each other, we are honest people-- if he thinks he has good enough data, he will have a chance to publish it. If not, one publishes first. And we went on.
Now, I hope Lee will check whether my recollection is correct. Because, you know, all autobiographies are lies. Because you only remember what you like. And if there isn't anything to remember you like, you invent it. So let me tell you what I think happened. We both worked on it, and it was pretty miserable. It's a very difficult experiment, the way we were doing it. And I was quite dissatisfied.
On the other hand, probably by the way the statistics worked out, the bookkeeping people were a little more comfortable. And it went on, and we both were somewhat unhappy. But finally, I said, look, this isn't going to converge. I said to Bernie, let's do a different experiment. Let's do it differently, let's Use a spectrometer.
And I think, at the time, it was not an open and shut decision. That is, I think you guys thought you had an answer. But then we compared our data, we said that's no good. And I said, look, Lee, the thing to do is come up here, come to MIT. And we'll do the experiment together and do it right. And we did it, and we did it right, and it was an extremely successful experiment, because Lee stayed. And that's why this was an important experiment.
There was a whole series of other things. But now you say, well, OK, that's nice. You have a lab for nuclear spectroscopy. The problem is that something else went on in the same time. Now, when I put this on here, you will, of course, find that you can't read this anymore, because there is too much. Maybe you can. Some of it can be read.
This was we started working with positrons. As you can understand, I said, look, there's positron annihilation. And since I had the crazy idea that electromagnetic interactions might also involve some other interaction, I said maybe if we look at positron annihilation, we will discover some other interactions between electrons.
In retrospect, that's absolutely childish, because we know the mass of the W or the Z is much too high to see in phenomena of that low in energy. But it was fun. So I said let us-- I see no reason why these have to be-- you see, the reason I put these on top of each other was that they happened on top of each other. And that was the great fun that was going on. All these things went on in parallel.
So the first thing I said, well, let's see what happens when we don't really know how strong the-- the annihilation cross-section had never been measured. At least not in any meaningful way. So let's see what happens if one measures the annihilation of positrons in flight. A totally trivial thing you would say today.
So we started with it. I had a student, [? Shearer, ?] who did it first. And this thing continued and was finally done properly a couple of years later by Henry Kendall. It's interesting, you know, I just noticed something. You put these people together, here. These black lines all the people that worked with me. So let's see, we've got [INAUDIBLE], Kendall, and [INAUDIBLE]. So, three Nobel Prize winners. Not bad, is it?
So that was straightened out then. But then I said to Shearer, look, this wasn't a very good experiment. There is a way of measuring the cross section at low energies by doing it in a gas. Because you calculate the cross section and the density, how much material is it, to just be in the right range for these very nice things we have developed. Which were relatively good time resolution counters that would allow us to measure lifetimes in the order of 100 nanoseconds, which was very fast at the time. That should be just about the range and will tell us something about the interaction.
Which was, of course again, nonsense. Because you don't have free electrons. The annihilation occurs in a very complicated field. The available electron density is almost impossible to calculate. So again, it was rather nonsense. But the experiment was interesting.
And somewhere around here, reading in the progress reports, it says, well, we did the first experiments, but something's wrong. Because whatever the interaction is, after all if you put more gas in, the annihilation must go faster because there are more electrons, and it must go proportionately faster. And then of course then, the explanation was positronium.
And that then was a lot of fun, but I will not tell the positronium story again. You give this talk on positronium a certain number of times, and then you say, everybody must be so bored because they've head it so many time. So I'm not going to do it even if particular people have not seen it.
What I do want to show is how fast this stuff went. It branched into two areas. In one direction was the chemistry of positronium. And there we have a lot of fun. As I look back at the reports, that stuff was never really properly published. Because I couldn't get myself to believe that it was really interesting. Or maybe the reasons were different, maybe they were personal reasons. I don't really know. It was never properly published, but a whole industry has grown up around it.
I see occasionally in the literature, people do experiments to which we really had the answers at that time. But you know, at times, I have that contempt for chemistry of a typical physicist. At other times, I think the opposite, I'm a chemist at heart. But that's where this sort of didn't go quite as far as it should.
What we did instead was we studied, of course, the fine structure, which was very exciting stuff, and made a big splash. And as I say, I don't want to go over that again. Although in some ways it might be appropriate. Only, one thing that is not known, is that we also tried to look for the first optically excited state of positronium.
And that was Henry Kendall's thesis. It sort of failed. Probably. You can ask him. Maybe he saw it, maybe he didn't. It was an extremely ingenious thing. It was his idea. I was away that year. As I put this thing over it, I think it should show out that that I was in Paris at the time.
And I have referred to that several times, most recently when an Italian colleague said that I should really get a particular student to write a thesis on something we are doing. And I said, look, that's not good enough. And he says, oh, look, he will be very happy to get such straightforward thesis.
And I said, no, I had two students who-- at least two students who turned down a thesis, an offer that you could write a thesis on something they'd already done, because they thought the stuff wasn't good enough for their doctor's thesis. One was Henry Kendall and the other was Rae Stiening, whose name you saw before. Both of whom decided to do something more interesting. And I think when you get that student who does that, you know you've got a winner.
All right. I'm stopping at this point. Many things happened after that. But what happened, as far as my life is concerned, was, that among other things, that at that point, I became chairman of a directing committee of the lab. The story was the following. Jerrold Zacharias, who had created the lab, decided he had enough. And [? Pete ?] [? Dimas, ?] who had been designated in pectore-- as you know the expression-- some time before, was considered still a little bit too young.
And people ask me whether I would become director of the lab for a few years. And I said, no, I won't do that. But if we will create a directing committee, and I will serve as chairman of that committee, and I promise never to call a meeting of the committee.
And then they said, well, why do you want to be only chairman. I said, it's very simple. When I've had enough if I'm chairman, I just say, well, I guess the chairmanship should rotate, and that's the end of it. You just rotate and somebody else does it.
If you are chairman, you have to say, I'm going to resign as chairman, and you need a the search committee, and they keep you there for another year. So that was the reason. And at that point-- so I changed direction, and I decided I also should get out of the field and went on to do some high energy physics.
Now I only have to spend two minutes to tell you why. I mean, it's obvious to you now why I couldn't give this talk to you. Because it doesn't prove any of the things that I wanted to prove. And the reason it doesn't is because the things that I was saying were false. I said, we didn't have to write proposals. But we had to write a quarterly progress report. I said, we didn't have to struggle for money from Washington. I still don't struggle for money from Washington.
I mean, just like Vicky, I've never had the experience of not getting money for something I really thought needs doing. I don't think that's a difference. I know now-- last night, I suddenly realized what the difference really is, why it was so much more exhilarating, so much more fun.
I learned it from my mother when I was a very young man. She tried to tell me why life was so much better under the emperor than it was under the republic. And she said, you know, people were courteous, there wasn't that much crime, there was order, people were dressed better, and most important, one was so young. Thank you.