HARVARD CYCLOTRON LABORATORY - 50TH

A Symposium Celebrating 50 years of Proton Beams at the Harvard Cyclotron Laboratory (HCL)

Saturday, 5 June 1999 

This transcript is taken from a recording and corrected by R.Wilson.  It may be inaccurate but many of the interesting stories may be correct.

OPENING SESSION:

Chairman:  Dr S. James (JIM) ADELSTEIN:  The research goals of the cyclotron have been a  part of the noble tradition, following the discovery  of x-rays by Roentgen and of radio-activity by Bequerel more than a century ago -- that has seen the radiation sciences enrolled, both in the exploration of the natural world, and in the care of the sick and the suffering. Certainly, it epitomizes the importance of technology to modem medicine. And, for very parochial purposes, a happy collaboration of the Faculty of Arts & Sciences at this University, with its medical counterpart. And, 50 years are not the end of an era, but the beginning. For out of the phoenix of the Harvard Cyclotron, so to speak, here in Cambridge, is arising on the grounds of the Suffolk County jailhouse the next generation of protons in the service of patients. All of this makes for a joyful occasion. An opportunity to review history, and a chance to acknowledge the efforts of those who have made it happen. The staff of the Cyclotron, both past and present. Those who have worked with it are to be congratulated -- especially it's past Director, Andy Koehler, and its present one, Miles Wagner. It's also an occasion to recall the late members of the University, on both sides of the River who have gone before. And I know that Norman Ramsey, and Richard Wilson will recall their efforts and exploits. I should also like to acknowledge my fellow committee members  -- Michael Goitein, Richard Lahey, Jay Loeffler, Paul Martin, Costas Papalolious, Carl Stohlberg, Herman Suit, and Dick Wilson. Dick, cleverly stepped out of the Chairmanship when he went on sabbatical sixteen  years ago and  asked me to fill in for him. I'm still filling. But he has continued to be the Cyclotron committee's principal component and advocate. And, of course to Alice Coggeshall who kept us well organized. It's now our privilege to have the President of the University provide the official welcome. Neil Rudenstine has championed the cause of inter-faculty cooperation among his far-flung elements of his empire. And, I hope he finds in this one, a source of satisfaction. We, in turn, are grateful for his presence. Mr. President.

 PRESIDENT NEIL RUDENSTINE:    Good morning. There's hardly anything worse than introductions  --  except introductions by Presidents. And, except introductions by Presidents, early on Saturday morning. But I do say I'm very pleased to be here. Very few things in the world these days, last as long as 50 years. And, scientific machines, as you know, better than I -- are some of the shortest-lasting instruments anywhere. So, we human beings, on the whole, outlive virtually anything made by man any more. And it is something remarkable to be able to celebrate 50 years of a Cyclotron that's seen, essentially, three different lives. One, as you probably know, the first one was built in the last 1930's here. It just began operations, and then it was commandeered by the United States Government. A group of people arrived, stealthily, in the middle of a night -- disassembled it. Packed it. Re-assembled it at Los Alamos. And used it thereafter in atomic work during the War, leading to the Atomic Bomb. Los Alamos, at the end, refused to give it back. How you can not give back a Cyclotron, I don't know. But, it's not just some little piece of equipment that you mislay somewhere. Anyway, the United States Government was good enough to provide us with funds to build another one -- which happened, as you know, shortly after the War. That Cyclotron had two lives. That makes three altogether. The first ghost-like haunting one of the '30's.  The the second life was the present cyclotron first used in Physics. And then, as Jim Adelstein has just said so imaginatively, in this collaboration between the Medical School and the Physics Department. I don't need to tell you what important work was done in Physics here -- including, of course, the training of many graduate students who then went out and did well in other places -- as well as those of you who were here from the beginning. And others not here today. The medical work, I think, has been particularly exciting. It took extraordinary imagination and leadership, back in 1970, when it looked like all Cyclotrons were collapsing -- to be able to not simply revive it, and keep it going. But then, in fact, to build a remarkable program with the help of NIH -­focusing, as you know, mainly on things such as brain tumors, eye malignant problems and so on. I think it's now, Jim Adelstein assures me, established that at least one or two of these treatments are the preferred method of treatment. It never would have happened without the people here. And, others -- still in an exploratory stage -- having to do with molecular degeneration and so on, are promising. One never knows. But there's much, much work to be done. And that will take place at the MGH when the new machine comes on-line. So, all in all, we can celebrate three lives -- thanks to the imagination and skill and early intervention of lots of people. And, of course, when the original Cyclotron was built -- or the second one, I guess, after the War -- it was the third largest in the United States. So, in that sense, pioneers on all sides, and pioneers in the medical side, as well. So thank you. I promised everybody no more than five minutes, and 34 seconds -- and that's what you're getting. Thank you very much. Thank you for coming. And let me, particularly congratulate Dick Wilson, Professor Ramsey, Professor Adelstein, the various Directors of the lab. And all of those of you, from the Physics Department, to the Medical School, who've worked so well together on what was a truly remarkable insight into what use a Cyclotron might be made of in medical surgery, so to speak. Have a very good conference. I must now leave.  I wish you well, and congratulations on the 50th.

 [Applause]

 MORNING SESSION

Physics Rules! 1949-1967: Professor Richard Wilson, Chair

WILSON: That's one of the problems of having a Symposium, just before Harvard Commencement. The President, and Deans are busy with their real work -- which is, of course, raising money. (laughter) And we're going straight into the next session. I have just a couple of preparatory words. The first time I heard of the Harvard Cyclotron as a young, impecunious graduate student, I hitchhiked to my first conference in Cambridge, England. And among other people there, I met Professor Kenneth Bainbridge, who described the plans for the Harvard Cyclotron. And the thing I remember was the neutron beam was going to head straight for the Divinity School -- ­which, of course, it did. (laughter).  Unfortunately, Ken is not here to share this occasion -- he is no longer here with us. And then, the next person that we would have liked to have here with us is Robert Wilson. And, unfortunately, he's still alive, but unfortunately able to come, nor, is his wife, Jane. And Jane sends her regrets. And, Bob Wilson had a lot to do with the initial work of this cyclotron. The person who is here and was at the beginning was Norman Ramsey. I personally met Norman Ramsey at  the American Physical Society Meeting in the end of January 1951. And it was a violation of the usual rule at Conferences - when you're very crowded only short people meet short people, and tall people meet tall people. But, Norman Ramsey had a sufficiently loud voice, I met him anyway. (laughter) And he wanted me to come to Harvard a little while later, after he built the machine.   Norman, can you tell us all-- anything - you want to say about the Cyclotron?

 The Beginnings of HCL - Professor Emeritus Norman Ramsey

RAMSEY: I noted with pleasure when I got here on time -- on scheduled time – that there was a nice set-up with the overhead projector, which has momentarily been removed. And, I would like to get it back it.   OK. Well, let me say, it is actually a real honor and a pleasure for me to speak at this Celebration of the 50th Anniversary of this very successful accelerator. And that's a very rare thing. In fact, I don't think it's ever occurred before of somebody speaking to celebrate the 50th Anniversary of an accelerator. The half-life of an accelerator is usually about 20 years. And, in fact, that was almost the case here. They had a great party about 20, 25 years ago. To celebrate the close-down of the Harvard Cyclotron. It was supposed to close-down within a week. And, then suddenly, there was a reprieve. NIH had found some funds, and it was kept going a little bit for research purposes. The research was very fruitful for medical purposes, and it's been going ever since. And it's still going, very happily at the present time. And now, I am particularly happy to get the transparencies now - because what I was going to do at the beginning is to ­say something about the principal contributors.  There is a problem that any project of this size.  An unfortunate characteristic that they contributors a're too many.  But that is also a  fortunate characteristic.   Hopefully, there are many young people to contribute. But there's no way of being fair and being pressed, for time  I will do so with this first transparency.

TECHNICIAN: May I put the microphone on you, sir?

RAMSEY: Yes. Oh sure. Do I need to repeat for the people who couldn't hear in the back?

CALL FROM REAR:No.

RAMSEY: I thought -- usually I don't have to. Well, there really have been many contributors to the project. Although I'm not listing on this in the next transparency by any means all of them. But I am listing some of the principal contributors over the period of the first five years or so. One important name has already been mentioned, which is Richard Wilson.  The is also Robert Wilson -- Bob Wilson. R.R Wilson. Sometimes I distinguish in these -- R Bob, and R. Wilson -- that's Richard Wilson. And, RR Wilson, which is Robert Wilson. Or RR Wilson and our R Wilson who is Richard Wilson.  And, RR Wilson was the Director from 1946 to '47. Then Ken Bainbridge who  was here at Harvard for a long time. But he was particularly served as Director from '47 to '48. I was Director from '49 to '54. And then, the -- but the key thing, if you'll note at the beginning --  the Directors were only here for about one year. They  changed through the first three years .  In the first three years ­there were three successive Directors. Ordinarily, that is a total disaster for a project, I mean, to have that many changes. But, there was a key thing that made it quite feasible which was -- there was  a very excellent person -- originally called a coordinator, and then later Deputy (Associate) Director. Lee Davenport, who served through all this transition period. And he absolutely, I think, really functioned as Director during that time -- even though others of us had the official title. And, I am very happy to see that he is here today for this celebration. Because I think the success, the initial success of the Cyclotron was largely due to Lee Davenport. And then, there was the Nuclear Physics Committee which included Bainbridge. Again, Robert Wilson, for the year he was here,  Curry Street,  Ed. Purcell and others. And then, to just quickly go through the staff. Then, there was a large number of people on the staff. The Engineering Design was headed by Bob Grensback. The oscillator was headed by Al Pote.   I don't know whether we paid Al Pote, or he was just here as a volunteer.  These were the days before TV. He owned one of the larger radio stations in the area. Also, fortunately for us, he owned the largest yacht in Boston Harbor. So it was a great place for the laboratory to have its celebrations and picnics on his yacht. But, he did an excellent job doing and running and building the accelerator, and designing it. And then, the control system required lots of ingenuity. Well, actually, that work was directed by a graduate student  -- graduate students were interesting at that time. They had been  doing technical work during WorId War II, sometimes as a soldier and sometimes as a civilian. And then, were coming back for their degrees. And, this was true of Leo Lavatelli . So Leo arranged for the basic design of the electronics, and the control system, which turned out to be very successful. And then, particularly,  Art Hanson who was heading the machine shop. And then, there was also a lot of important organizational support.   One was the Manhattan District.  It is a little bit hard to say whether the Manhattan District  supported Harvard or not:  whether it was the villain or the help. It's the Manhattan District that took the first cyclotron to Los Alamos -- for the Federal Government. It provided $200,000 dollars for making up for its having stolen the first Cyclotron, which provided the building that was used. And then, also, very importantly, the Office of Naval Research, who agreed to really negotiate one of their first contracts with Harvard. It was an experimental organization that  we had. And people didn't know how big they the laboratories should be, or how they  should be run. But that worked out very well. And that (ONR) was actually the predecessor to the National Science Foundation. Well now, having given my names in this fashion, let me now go on to more of an anecdotal history of the sequence of events that led to the Cyclotron ,  this second Cyclotron. 

    The first really important sequence would start in 1943, when the Manhattan District stole the first Cyclotron from Harvard. It was one of the more reliably operating Cyclotrons. It was a small one. It was 11 million volts for deuterons which means even less for protons. It was primarily used for deuterons. Primarily used for studying nuclear reactions. And in those days, that was the new thing subject in physics. And, it went to Los Alamos. And the group that it went to at Los Alamos was headed by a young Princeton Ph.D., Robert Wilson. Robert Rathbun Wilson. Bob Wilson. And, he headed the group -- and this served as the one accelerator of that kind at Los Alamos during the War. But then, at the end of the War, he (Bob Wilson)  was recruited to come to Harvard. Presumably to spend the rest of his scientific career. And he and Ken Bainbridge got together particularly with Curry Street, to plan for a replacement for the First Harvard Cyclotron. And they did so. They persuaded the Manhattan District, to contribute -- to pay for what they'd already stolen. And pay a pretty good price. Harvard made a big bargain, because this money went to Harvard. And it probably cost them $50,000 dollars in the first place. And Harvard got  $200,000 back. But they also persuaded Harvard to in turn, spend the money on a replacement building. You couldn't get a big accelerator with that sum of money. But you could get a building. And so they agreed -- the University, with that money, agreed to pay for it. It didn't cost the University anything. But I mean, they even probably got a little overhead out of it. But, nevertheless, that did provide the basic building. And, with that, then Wilson and Bainbridge, in particular went to the Manhattan District, and to the Office of the Naval Research, which was a new office. And ONR had done very little. It was just at the end of World War II. The Navy realized that they had gotten a great deal of help from physicists during the War,  particularly on radar, and things of that kind. And they wanted to, in turn, keep physics alive in the country. And they agreed -- and they initially started a very small program for research support. It was not clear that they could support anything as large as a Cyclotron, but they did. And, agreed to give the construction support, and also the building of it. But the budget had to be pretty small. And that led to the selection of what the energy should be for the Cyclotron.

    Now, on the chart I state the energy.  The choice was that particularly of Wilson and Bainbridge, who probably had some bad luck, and some good luck. The bad luck was that at the time that they made the choice, pi mesons had not been discovered. And there was evidence from cosmic Rays that no Accelerator could ever produce neutrons, and therefore, there was no particularly obvious threshold of energy. And there was also no particularly obvious threshold of how much money the Office of Naval Research could put for a machine. So they chose a bit conservatively. And chose an energy of about 130 MeV. Unfortunately, after this design decision was made, the pion was discovered and it showed that had the energy had been more, you could have produced pions. On the other hand, it was still a very useful machine for studying nuclear forces -- which is what it had been originally designed for. And, so - that was the bad luck. If they had known about  pions earlier, they could have persuaded ONR to have gone a little bit higher in energy (and money). The second bit of the good luck that compensated -- it turned out that was just the right energy for proton therapy. Well now, proton therapy wasn't known at the time. So, that was not in their plans. But that was, I guess, in the long run, has been a fully compensating bit of good luck. A little worse for the physicist - but certainly better for the medical people.

Well then, Robert  Wilson was appointed Director of the Laboratory. And, he realized that most of the talent and knowledge about designing accelerators existed at Berkeley. So he really spent most of that first year, and, as it turned out  his only year at Harvard ,  in Berkeley. Designing , using their facilities and their advice on designing,  the Harvard Cyclotron, which designs he was then going to bring back to Harvard  and get it built. While he was there he was also is a pretty active physicist. He did a very important experiment, from the first experiments at comparable energies, on  proton -  proton scattering. And then,  he  wrote one very important paper -- which was the first paper suggesting proton therapy. And in the paper he noted that there is the thing known as a Bragg curve -- when a high energy proton goes through any material such as water or tissue. As it gets near the end of its track,  the proton is going slower and slower. And since, it's slower, it spends more time in the presence of each atom. Therefore, the electrical field acts a little longer, and gives a bigger impulse to the electron. And, therefore, the ionization is greater at the end of its track, than it was at the beginning. Well, since the main problem one has on using radiation therapy is trying to damage the cancerous tissue as much as you can with damaging the normal tissue as little as you can,  he recognized that if you could bombard a patient from different directions ,  but always try to make it such that the protons were near the end of their range, where they were in the cancerous region ,  this would significantly increase the damage done to normal tissue.  It would increase the damage done to the cancer, and diminish the damage done to other tissue. So he wrote this up in a paper in 1946. And, then came back to start his work on the building of it here, and finishing the design. But then, in 1947, one year later he was lured away to Cornell.

    And, then that same year, I was lured from Columbia to Harvard a fact which did not have anything to do with the cyclotron. I was supposed to be setting up molecular beam research. Study on radio frequency spectroscopy, which we had then been doing very well at Columbia. Ken Bainbridge  actually succeeded Bob Wilson as Director of the Lab and as Chairman of the Nuclear Physics Committee. And then, the following year -- after I was here a year -- I guess they felt that now I  had been caught properly at Harvard. And then, they advised very strongly that I should become Director of HCL. Bainbridge was anxious to get on with his mass spectrometry. So I agreed to be Director. This particularly became feasible because of the excellence of Lee Davenport who was the  so-called Coordinator of the project. And he provided continuity for the work that was done there. And I think that the two of us had a very happy time in running that laboratory, from that point on, for the next few years in the next phase of construction. The design period really gone from '46 to about '47, '48. But, some design changes continued on to '49. But on the other hand, construction began in some parts in '47. Some contracts were let out before I was involved  but the principal activities on construction occurred after I was Director. And one of my most valuable contributions was recognizing that the Cyclotron was a very well-designed machine. And therefore, I shouldn't make many changes. I should just see the design through. We didn't have a lot of changes to make. And, secondly, it was a very good design. I think for this, Bob Wilson, deserves much credit. I think we had the good luck -- it wasn't merely that he was so tall in that connection. I think he is probably the world's most talented accelerator designer. He, in fact, became the Director at Fermi Lab -- which is still the world's highest energy accelerator ever built. In fact, there at Fermilab he and I had our second collaboration. And in that case, I was President of URA. And I had to hire the Director, and work together. But he was also the Director, and his ingenuity and design worked out very well in that highly successful accelerator. But, in any case, his design here was clearly very good. So, we basically followed that. And as I say, I make a useful contribution of not making too many changes. Then, we did concentrate on trying to do our best for achieving reliability and the design was such that it could be easy maintenance. And, I think Alice Coggeshall  warned me that I had better be careful about that statement, because the maintenance people in the lab will say, "boy! it's not that easy to maintain!". Well, it's not easy to maintain. No accelerator is easy to maintain. But, compared to almost all other accelerators, this one is relatively easy. It does run quite well for accelerators of this energy.

    The first experiment was done during the construction phase -- before it was finished. It was sort of a joke almost. Namely Purcell had just invented NMR -- the two of us were closely working in that general field of resonance. And, we began speculating.  Could, by any chance, the proton's spin orientation be related to memory storage? Because you've got a tremendous amount of storage if you have every proton in your brain, determining that lots of bits can be stored that way. And we didn't think it was likely. But you know, it might be. So, we devised the following experiment. This was in the days before OSHA. And before you had to get approval for experiments involving humans. Ed made up a coil and an oscillator. He brought an oscillator over and  I turned up the magnet. I knew how to run the Cyclotron magnet then.  So, one Sunday evening afternoon -- when I turned up the magnet, we tossed a coin to see who went in first. Ed went in first. And put a coil around his head. And then I cranked it through the proton resonance. We weren't sure what was going to happen. Maybe he'd say "ouch". The worst would be maybe to wipe out his memory. (laughter) Then, he'd start all over. And, well-- nothing happened. (laughter) So, then, it was my turn. Nothing happened with me. So, we sheepishly folded up the apparatus.  Obviously we didn't publish this experiment. (laughter) But except somehow that schpiel got spread around. And there are several books on the history of MRI -- Magnetic Resonance Imaging. which quote this as the first Magnetic Resonance Experiment (laughter) on humans. Well, it's not our proudest experiment. But, nevertheless, we did do it.

    But to return to the construction.   Primarily the design was a really very good design. That doesn't mean there were no construction problems. I mean there were construction problems. This was still fairly shortly after World War H. And, there was a shortage of everything still. And, deliveries were badly delayed. But, somehow, we got around them. And went really surprisingly rapidly. And on that, Lee Davenport was an expert at expediting what we were doing. And we also had some problems. Although the design was excellent, there were some problems -- one of which pertained to leaks -- vacuum leaks. There, Berkeley accelerator experts -- the experts at Berkeley ---  just at the time that this accelerator was being designed persuaded us to buy a new stainless steel that was non-magnetic that had just been developed. They thought that this was going to be the greatest thing ever. They'd never used it, but they thought it would be good. So, they convinced Bob Wilson, and Bob Grensback, that's the material to use here. So we got that ordered and cut. And then it turned out it was a great material. For it had the magnetic properties desired. But nobody could weld it successfully. It was a real problem.  We had arranged for the welding of the vacuum tank to be done by the Navy Yard which had expert welders. I mean they'd been welding all sorts of ships during World War II  but  they couldn't weld this  very well. Neither could anybody else in Massachussets.  Nor could anybody in Berkeley. They never had used this. But, we'd finally forced it through - but, with lots of worries, and unfortunately, with a considerable effort spent on leak hunting. I remember, in fact, one time when we were having this misery tracking down the leaks, and getting it re-welded in places,  that in those days, the President of the University had a formal reception for the members of the faculty.  You know, black tie, tuxedo, and the women in long dresses. And while we were at the reception, Lee and I were talking about possible other places that could leak and  we had a good idea. So, we said we'll go back after this reception, and hunt for leaks, which we did. We were in our tuxedos, and leak­ hunting. And I really felt very badly as we were doing this, that there was, at that time, no camera in the laboratory. Because it would have been marvelous to have had a photograph of Lee, and myself, in tuxedo leak-hunting, and then we could show the transparencies -- and say, this is how we leak-hunt at Harvard. (laughter) But, unfortunately, that picture exists in my mind, but not otherwise. Well, another problem that we've had -- particularly on leak-hunting. It turned out -- one very -- one of the pumps was very inaccessible. Very hard to get to, to do the leak testing on. And, that had been tested by the manufacturer. Guaranteed to be absolutely tight. So, we sort of hoped.   But, we still kept having a rather persistent leak, which we thought was due to the vacuum chamber walls, but it seemed not to be there. And, well finally, it turned out that after the pump had been made by the manufacturer, and tested fully.  But  then wanted to put the label on, naming the manufacturer. And, in the process, they drilled a hole through the side. (laughter) And, although it got pretty well plugged by the screw, it leaked just a little  amount and a small leak was hard to find. But at the same time, it was critical. Well, then, one of our final things happened  after we got everything going Wee got the magnet going. Well, we got the oscillator oscillating well. We had the vacuum system going well. But we couldn't make it work together. When we turned on the magnetic field, the oscillator failed. Turned off the oscillator field, the oscillator was fine. And, we all stood around for a while. Well, it finally turned out that someone had left a screwdriver in there, on top of the magnet pole. And when the magnet was off, it laid flat on the bottom, and caused no problem. When the magnet was turned on, it rose up on end. (laughter) And shorted the osccilator out.(laughter) So we got that problem overcome.  So that is sort of typical of the problems that you have. But finally, we got our first beam on June 3rd of 1949. And, really got it operating.

    The two things that you had for an accelerator So, this really is, very accurately, the 50th anniversary. It always takes a big interval of time between the first beam, and the reliable operations. Sometimes it is a year or so. In this case, it was pretty short, but it was still a time. And I'd say that I noted one thing in one of our data books-- saying that we had a reliable operation, beginning September 30th, 1949. That' was a couple of months later. Now, of course, after the War, I'm sure some Presidents usually say there's still no reliable operation. No one ever considers an accelerator is totally reliable if he's a user. But, nevertheless, from the point of view of those who build it,  it was going really very reliable then. Well now, in conclusion, I just want to say  about what happened after the beginning of operatiion.  In the ­first place, we did  fairly early concentrate on this desire for higher energy than had been designed. We did manage to squeak the energy up from 130 to 160 Me V -- and maybe we could go up to 180 or 190 if we pushed very hard, but not very reliably there. So, we didn't.  160 was about the highest. Which was still below the pion production threshold. But was very good from the point of view of sundry and fundamental physics.

    Now, the subsequent speakers are scheduled to talk about the physics results of the experiments. So I will say nothing about them. And, I'll only make on this early operation, comments on about three different things, pertaining to the operation of the machine, or the things that didn't pertain to physics results. One of features - -that worked out very successfully -- was that the machine was signed to be capable of being operated by the students who did research there. We had a day-time crew to run the machine, and help train students. But then, if they wanted to run all night, as you usually had to do, they could run the machine themselves. This worked out very well. The machine, I think -- in that sense -- was relatively easy for them to learn, and operate. We had one incident that was close to a catastrophe. I think I almost lost a graduate student to a heart attack on that. And this was a very good student.    Uli Cruze. And he had gone through his training period with the professional crew. He was still in his first when he was in charge in the evening. And another graduate student was with him for safety reasons. But, other than that -- he was on his own. Finally, he sort of checked through his check list. And he was already to go. And he pressed the "On" button. And, immediately, all the lights went down in the building. The relays began to  clash and in and out -- in and out. Making a huge noise. And he didn't know what it was all about. He looked out the window. And the lights in the surrounding Cambridge were going up and down (laughter) Well, I was home in Belmont when I knew he was having his first run. And our lights were going up and down. (laughter) So, I rushed in. Drove down to the lab to see what was happening. Well, eventually, it turned -out that it had nothing to do with the cyclotron. It was pure coincidence. Had­ absolutely nothing to do with his pressing the "On" button. Somewhere in Western Massachusetts, they were doing some work on one of the main power plants, and with one of these air hammers, they were drilling through two places, and they short-circuited the main bus bars for this grid in New England. In fact, all of Massachusetts was off.   New England, I think, was off for about a day as they were rectifying this. But it was pretty panicking for years. And I was a little bit ill at ease too, I must admit. And I may also mention something else too, at this time. This was our contribution to Alan Cormack's Nobel Prize from our lab.  The first prize that anyone had done. And, namely, Alan Cormack was a post-Doctoral research fellow, or something, working with Dick Wilson and myself. We were paying him from our funds. And, we knew he was boondoggling some on the evenings. He was doing calculations on his own. But that's OK.  We were very nice. We let him do it. Well, it turned out that what he was doing was doing the theory for interpreting CAT-Scans. And for this, he received the Nobel prize. And I think -- and I'd like to say well, you know, we are partly responsible for that. If we had a well­ disciplined lab, we would have prevented it. And then, he couldn't have done it. (laughter) So it is sort of a negative contribution to his Nobel Prize. But I think he was delighted when he got it.

    On the whole we had good relations with the biologists who were worried whether our radiation was going to upset their instruments.  So we decided we are going to do a super careful check. We got one of the technicians with a cart with a very sensitive radiation detector. And, a walkie-talkie -- going around in different locations. And, the levels were down very low, because it was even further way than we usually looked. But then, suddenly, as he got to the entrance to the Biology labs, he got a great big signal. He got on his walkie ­talkie:  "shut down the Cyclotron right away! We've got to shut down."  So we shut down the Cyclotron. He still got high readings.   Well, then it turned out that the granite in the very attractive entry­way(between the herbarium and the museum) was quite radio-active, and produced radiation levels way above the tolerance that we would allow for our neighborhood. From that point, well we've had no subsequent complaints about radiation from the biologists. And they are all we got from anyone as a matter of fact. And now, I'd like to conclude with just a couple of quick pictures of how the Cyclotron looked in its earlier days.

   SLIDE:             Then the couple of interior views.

   SLIDE:             This is a view of the Cyclotron itself.

   SLIDE:             This is when we were just about ready to operate it. It wasn't running I think, at that time.

   SLIDE:             And this is -- the dark-haired one in here is myself. And the other is Lee Davenport, which is a very effective Deputy Director at the Lab. And, who did so much to help getting this started.

   SLIDE:             And then, finally, here is another one - a photograph of a view of the machine. This is -- Lee Davenport here. And, this is Leo Lavatelli. He was a graduate student. A pretty senior graduate student, because he had been doing technical work during World War II. And he had a job - and one of the useful things that the Cyclotron did in its early phases of being built -- was that at that time, there was no NSF. There were no NSF fellowships. And there was a problem of support for students. Some of them had support, some of them did not. But one of the key sources of support was actually came from the hiring graduate students to do much of the building of the Accelerator. They got experience out of it. And, in particular, they also got some financial report. And I think, this, I think I will close. It is time to move on to some of the results with it. I think it's been a very pleasantly successful operation. I know that Lee Davenport and I were talking just earlier. I mean it's had a much longer life than we expected. The normal life of an accelerator I would say is 20 years, or less. By that time, it's usually out of date. And no longer interesting. And in this case, well in a certain sense, that was true of this accelerator for its first career -- namely as a physics instrument. There isn't much with it. But, it then had this great new career in medical treatment -- particularly in proton therapy.  And I am just delighted to see the way that it is going. And, we know that about 30 years ago, I attended a marvelous party to celebrate the close-down of the Harvard Cyclotron, which was supposed to occur a week later. This was revived. And, it's still running. And it seems to be a cat of many lives. And so, I wish to express great pleasure to all. And, particularly, the people who supported it at that time. Thank you. 

An Overview of the Nuclear Physics Program: Professor Richard Wilson

WILSON: Thank you, Norman. And at the moment, I am going to talk about the upgrade of the Cyclotron. And that just synchronizes with the time I first came here - ­which was 44 years ago. And so, there are actually some physics reasons for the uipgrade. In 1955, why did we want to change the Cyclotron? It was working well. It was doing some nice experiments. Well, there were two reasons. Firstly, like all machines, you want to get the beam out - get a nice external beam.   To only have a beam  going round in circles inside the magnet was not a good idea. You want an external beam. And, secondly, we wanted to increase the energy. And the primary reason at that time, was to get a high polarization of the beam. And just to remind you -- it turned out, if you scatter protons off a spin-zero target, you can get nearly 100 percent polarization. And this is, by the way, the figure that we'll mention later which was taken here.  This particular spin-zero target was helium. If you have 150 MeV, you can polarization to a certain angle -- 95 percent. If you go down to 60 MeV, the polarization is only 15 percent. So, we wanted to get up to that higher energy with the high polarization. And it was clear already from experiments of Chuck Oxley at Rochester and other places that this was important. So when I came, This was just the proposal everyone was talking about. And so, the first thing we asked  was -- how do we increase the energy? When it turned out it had  been  running at 90 MeV wheareas it had been designed for 130, but wasn't actually running at 130. We have to improve the field at large radius. Karl Strauch  and I  particularly coped with that. We had to shim the magnet. And the thing that I remember was that Karl Strauch  and I were there  until 11 :00 p.m. on Christmas Eve with  tin shears, cutting shims. We were putting them  inside the magnet. And they are still sitting there, by the way. But for us the thing important thing was  that for some strange reason, our wives forgave us from being away from the family on Christmas Eve. But that happened.

    Then we had to modify the Oscillator to make sure it covered a wider frequency range. And the responsible people   there were Andy Koehler, who's still hereof course, and Paul Cooper who  unfortunately  died a few years ago. We always think of PAul as the last of the Fenimore Coopers. And he was a graduate student at the time. Andy Koehler came to the Cyclotron, I think, one year or so before I came. And so, this was one of the first things that he was involved with. So, then came the beam extraction. And what's the problem with beam extraction? Or course, you have to be able to get the beam out. The problem came that when you have the beam in the Cyclotrons in those days -- we used to have very large radial oscillations around an equilibrium orbit. But you couldn't have very larger vertical oscillations, or you'd hit the poles. And when you got a particular value of "n" which is a particular parameter of the magnet  field gradient.  When n is  equal to 0.2 there was a coupling of vertical and radial oscillations. And that inevitably happens in an accelerator. And so what happens is that as soon as the particles accelerate and get out to  radius where n  equals 0.2, all the energy in the radial oscillations goes into the vertical oscillations and you lose the beam because of the relatively small vertical gap.   The first solution was by two bright people, Jim Tuck, an Englishman who went to Los Alamos and Lee Teng, of Chicago. They thought of the idea of a regenerator and a peeler. They decided that  to have coherent oscillations, you must interact with the particles as they are going around   You first push them in, and then you pull them out and you repeat the process. For this you have a regenerator, and then the  peeler. The peeler to pull them out, and the regenerator to push them in. And, they tried that out in Chicago. And it was never used very much, because Le Couteur came up with a better idea. He said,  that you don't really have to peel at the one location. You can be pulling the protons out all the time ­because the field falls off anyway. All you have to do is be pushing them in coherently at one location. Effectively, that makes the average beam parameter "n" equal to 0 .  The average parameter to zero. And this was first tried at Liverpool, and then at Chicago. And then, we were the next people who used it.  In spring 1955, before I came here, I went up to Liverpool, especially to see that beam extraction and talk with Le Couteur, and we had a design. Well, we finished this work, and we wrote about it. Here is the xerox of the paper by  Gerry Calome et al.   (see reference list) One of the authors, Paul Cooper is not here unfortunately. He died of a heart attack in an island off Australia. I don't know where Engelsberg is is. George Gerstein apologizes for not being able to make it. He's in Europe at the moment. Andy, of course is here. Arthur Kuckes is here. I don't think Jim Meadows managed to get here. Karl Strauch is unwell and has  not been able to get here. And myself. So those were the people. I'll remind you of the procedure this picture. I tried to find some photographs of the whole regenerator.   The picture of what is now inside the Cyclotron. Well, naturally opening up the Cyclotron and taking the photographs is now hard work. We should have had them in the files.

    We did something, I think,   which was unique to this cyclotron. We thought of a number of ideas which we thought was unique. We decided that we'd have more than one place to get the beam out. The one which everybody now uses. We'd get the external beam out. And the other  was a partial extraction of the beam. To extract it to just hit a target. And this was unique for us, I think. But I'll explain why we did it from the physics point of view.   In this schematic (from the paper) we show what the regenerator actually is a couple of pieces of cobalt steel concentrating the field in this location, as the radius of about 42 inches. And then, in order compensate in order to make sure that the field is the right sort of shape, we put all sorts of shims out here. And, then we had to match Le Couteur’s careful calculation with what we can actually achieve. And we actually achieved pretty well what Le Couteur recommended. Then, of course, how do you measure the field? Again, it was a graduate student that designed the equipment -- Arthur Kuckes. One of the best experimenters that we've ever had. He introduced me to a DC amplifiers  called “flip-chips” I think they were called. Maybe they were Philbrick  units. And he found them, and bought them. They were to integrate the induced EMF.  Normally to measure a magnetic field you have a coil which is flipped over and the EMF is integrated.  We were laboriously measuring the field by taking the coil at each location on the orbit, flipping it over and integrating the EMF.   Arthur  said, let's not do this. Let's just get the core and let's rotate it around the center of the magnet along a particle orbit.. And this he did. And automatically as we rotated the coil, we measured measure exactly what we wanted to know – the line integral of the field.  So those were Arthur Kuckes' contributions. And I think he took only a very short time.  I think it was about 6:00 o'clock at night is when he and I were discussing this. And by the time I came in the next morning, Arthur Kuckes had made the devices. It was certainly one of the things which was positive was the speed of doing things was rather greater in those days than now. Then, we came to a day in April 1956, the first external beam. We put a little probe -- an ionization chamber on a  probe we pushed in on the machine. And the idea was that if the beam was coming out this far and the beam had jumped over the gap, where the wall of the ionization chamber was, we'd get some ionization. So, we accelerated  the beam in to a large radius, and we got to where the beam was supposed to be striking the edge here. We saw no ionization.  But then we think we did not completely understand it. And, it wasn't until we pulled the probe a little further out that the beam oscillated with a large enough amplitude that it was no longer striking the edge. We suddenly realized that we were extracting the beam. Although  we hadn't really quite expected it. It was about 1 am.  It was all written up in the lab notebook which I could not find again last week.  So, of course, we celebrated, and Paul Cooper went back home.  We called up Norman and we woke him up, and he came in to help celebrate. With a  bottle of 1837 Madeira, which Paul Cooper came back and provided. The actual label on that bottle was put in the notebook. But, the notebook seems to have vanished. Well, of course, the bottle of Madeira vanished much quicker. 

We realized that the distribution in time of the beam corresponds to the distribution in energy of the equilibrium orbit.    The t ime distribution of the beam -- without any beam extraction,  was like this. (SLIDE) But now you start getting the beam oscillating. You're picking out, not just particles of several equilibrium orbits, which are hitting the target -- because they happen to have large oscillations. But one equilibrium orbit only. And so, the width of the time distribution comes down, and so does the energy distribution.  If we were very careful we could install a “clipper” to try to reduce the oscillations,  the time distribution becomes  much tighter. And that  corresponded to an energy width of about an MeV. For some reason, I've never been able to figure out, we were never able to actually produce that energy distribution in experiment. Well, at least I wasn't. I think Bernie may have been able to.

 We then did some experiments. And I'll just share  just one of them, before getting onto introducing the other speakers. This is one of them that we did - this was presented at conferences by Allan Cormack. Norman  mentioned Allan Cormack. This is particularly scattering the protons by helium. In fact, that was the figure that I showed you earlier, of the polarization on a spin zero target. And there is a story about that experiment .  Of course, we were running around the clock. And one Saturday night Allan Cormack was on night shift. And I came in at 8:00 o'clock to relieve Allan, on Sunday morning -- and Norman Ramsey was coming in shortly afterwards - about 9, I think. But, Alan had lost the beam. And my contribution was to notice that  the magnet current had gone too high.   He  lost the beam because the magnet regulator had suddenly gone to pieces. We had a mechanical feedback system from a sensor to an electric (Selsyn) motor to drive the power supply. And that mechanical link was a chain link with some limit switches. And the drive had gone beyond this limit switch and broken the chain. And we all had to learn how to fix it. So my job was over when I figured out what was wrong. Then, came in Norman Ramsey who figured out what to do. And, what we did was you replace this chain link, by an O-ring, which goes over a pulley which slips when it gets to the end, rather than breaks anything. So then, how to make the pulley. Allan Cormack went to the machine shop, and made the pulley.  So by 10:00 o'clock in the morning, we were back in action. So, those were the three of us. And of course, you can see they did the work -- which is of course the reason why those are the people who got the Nobel prize. (laughter). 

We had a fairly simple way of coping with hydrogen targets in those days. We had no OSHA. And actually  I thought it was complicated. For when I first used a liquid hydrogen target at Oxford, I just went to the hydrogen liquefier, got some liquid and opened up the valve. I filled up a glass Dewar  with liquid hydrogen. Put it in the back of my car. Drove it 50 miles out to the Harwell cyclotron, ­poured it into the target, and we started running the experiment within a few minutes. I was a little careful driving the car out there. (laughter) I just went slowly over bumps, and put a little tube out of the open windows to make sure. (laughter) But, this (picture) was the complicated target. Instead of a metal can,  here was the target. We had a thin wall of mylar. And I'm not sure we were allowed to do that. Because we found out that mylar worked at low temperatures. If the target wall had been aluminum, it would break. And, we had a transfer tube putting liquid hydrogen into that location. Just transferred it from the Dewar flask. The Dewar had to come in from elsewhere.  The first liquid hydrogen we'd got came up from Brookhaven. And I can't remember whom, but  some graduate student brought it up from Brookhaven. And we rented a pick-up truck on this occasion. Not a car. And he had trouble when he crossed the bridge over Long Island Sound. We did have proper labels. Liquid Hydrogen, caution, flammable, etc., etc. And when he got to the toll house the tollkeeper said -- "you are not allowed to bring that stuff here -- but, go on quick." (laughter) So, those were the days  before OSHA rules.  I've just been trained as a target operator at CEBAF. And it takes about two days of training how to cope with the special  complicated refrigerator and target. Which has far less hydrogen in it than we had;  and it is cooled by liquid helium. And it has an enormous number of complications.  It has three computers working to keep the temperature constant and so on. Life has gotten a little more complicated. 

There was one other story we'll tell. And, just after we'd started operating again, George Gerstein who is not here -- was running the machine. And at night -- he just couldn't get the beam working. So, I came in at midnight to see if I could help him. And we struggled for  about 2 hours. And one change I had made in the Cyclotron was put a window on the edge of the vacuum tank so that I could look in, and have a look at the ion source. I always like seeing things with my eyes, or handling with my hands. And so, we switched the thing on. Sure the ion source was on. You could see the bright light of the ion discharge. The magnet was on. We had a little trouble keeping the oscillator on , but with a bit of effort we got it on, with a higher DC voltage than usual. But, we could get no beam at all. Everything seemed to be otherwise all right. So as we were looking at the ion source -- suddenly I realized that I had these magnetic keys in my pocket which I should have left outside. The keys, in my pocket were horizontal. And why?  They should follwo the field.  The field shouldn't be horizontal, it should be vertical. Someone  -- just that day -  had disconnected the coils and they had been misconnected .  The top coils were inverse to the bottom coils and the thing was connected as a  quadrupole, instead of an ordinary magnet. And so, the thing was, of course, not working. (laughter) This was found at 2:00 in the morning.

 So with that, we'll pass the thing over to Jacques Lefrancois who is a French Canadian living in Paris. And we have had two other Canadians, who were born in other English ­speaking parts of  Canada. So we have had a nice mixture here.

 [Applause]

Proton-Nucleon Scattering Program: Dr. Jaques Lefrancois

LEFRANCOIS:  Right away, I live in Paris, because Dick send me there (laughter) for two years. I retired 8 years ago. So, I prepared a few transparencies on the program of the Harvard Cyclotron. And, of course, I've only seen a short part. But I tried to collect either my memories, or articles on what happened. And I will tell you a bit about the motivation of that physics' program. The why, and the what of the program. And then, also I will say a few words, which are more personal- -on the life of a Ph.D. around 1960 which is how we did these experiments. Now, motivation. Now, I have the excerpts from the first team. So, these were very serious people. You've got two Nobel prizes in there, so you have to believe what they say. And, luckily they got the Nobel Prize not for the programs.   We only worked with the Cyclotron, so we didn't get invited to Sweden with them. So I read that, in the investigation of nuclear force, the nucleon- nucleon interaction bears a role of primary importance, they said. Its relative simplicity rendered it more susceptible to analysis than interaction involving heavier nuclei. And they went on to say that maybe there's a hope that by understanding the nucleon- nucleon interaction, you could calculate and predict what would happen on complex nuclei. And this turned out to be partly true - ­the second part. But, the first part not as well. Now, the other point is that this is what they said. But, my memory of a young -- I shouldn't say young Ph.D. -- young graduate student was much more hopeful. The idea is that we wanted to understand where the nuclear forces were. And what was clear to us was to understand, or to me was that we'd have to study elementary particles in interaction. Because if you want to understand something, you should put yourself in the most elementary situation to understand what happened. That was the understanding of protons and neutrons.  Now, in 1960, when I arrived there, they were very careful not to say that. But, of course, young graduate students says -- what can be more elementary than a nucleon? This just shows how naive we can be. Because we now know better. Now the proton, the neutron -- these are now known to be very complicated objects.   They are made of quarks, glueons and virtual core quantum type block pairs. And, in the 1950s  we understood a bit of the complication, because in the 1960 language, we knew that there was a pion cloud around the proton. Around the core of the proton. And, actually, we also knew that we could calculate part of that -- of the nuclear force -- by taking in account the fact that this pion cloud existed -- and was doing exchange between the two nucleon. But this was only a small part of the whole story. And, actually, the whole thing was much more complicated. And it was complicated because the proton is complicated. And there was no hope of getting any fundamental interaction by doing proton -- or proton scattering at low energy. It's like trying to understand the electric force by doing the scattering of two big neutral molecules -- you would have no chance. (laughter) So, that was it.

    Now, nevertheless, I think we all learned quite a bit from doing the physics there. And what I would say -- what I would think I've learned is that if something -- if a program -- if some measure is believed to be important, then it should be done well. And I will try to explain what "well" meant. Since nucleons have spin, scattering will depend on the spin­ orientation. There will be a spin-spin force. And, a spin-orbit force. And a complete interaction should measure those effects. Now, it was in 1956 -- a very nice article and review of nuclear science by Wolfenstein which characterized completely -- gave the formalism of this interaction. And scattering is characterized by five complex functions of energy of angle. And then you put in another condition, because the reactions can only be elastic, because we are below pion threshold. That was one good thing -- below the pion threshold. And then, you decide that you have five independent numbers at each angle of energy. And, if you have five unknowns, you need to have five measurements. So, we need at least five different experiments to obtain these five independent numbers. So, doing the program well meant doing five, or more than five experiments. And, these experiments are written here. Cross-section. Polarization. D, R, A-Prime. On proton­ proton. And, proton-neutron, or neutron-proton. And I'll explain a bit what these things are about. So, I have to say first -- the role of proton-carbon, and neutron-carbon scattering. Dick already showed it on helium. But you have the same thing with protons on protons. At this energy, when you send proton on a carbon target, and look at the right angle -- around 13 degrees or so, 14-degrees, you get the very high polarization. In other words, if you send a polarized beam, it will be scattered essentially in only one side. If the spin is up, scattered  to the left, if  the spin is down, scattered to the right. Then by using the carbon target as an analyzer of polarization by the left-right asymmetry, you understand what is the polarization of your proton. Conversely, if you send an unpolarized beam you get polarization.  Snce the one which are up are scattered to the left, and the ones which are down, are scattered to the right.  If you look at the beam which is scattered on one side, and one direction, you get a polarized beam. So, this is how the program was done. The proton beam was sent into a carbon target. Very close to the output of the cyclotron, actually. And, you extract the beam which was polarized. Send it onto a hydrogen target. And then, you measure a cross-section by looking at the number of scattered particles as a function of the scattering angle. And you measure the polarization ,which is how hydrogen scatters to the right or to the left to polarize the proton which comes in. So, hydrogen was used as an analyzer there to get the polarization function of hydrogen. Then you do the more complicated things. You get your polarized beam scattered on a hydrogen target. And look at how much polarization there is left after scattering.  By scattering again on carbon, and looking at right or left. This is called "D". And this was the first of the triple-scattering experiments.
    OK? You scatter first on carbon.secondly on hydrogen, then on carbon to analyze again. And then, the next one was to put a magnet with a field along the trajectory of the particles. The spin of the proton, , which was up,  is rotated by the field. When it rotates 90 degrees, then you scatter on hydrogen. You look at how much spin you have left, by doing your scattering on carbon up-down instead of left and right.  Then you measure "R". And then, there is another spin orientation. You do that by having a magnet with the field  perpendicular to the trajectory. The spin rotates again at this plane until now it goes along the direction of the particle. You then look at how much spin there is perpendicular to the particle afterwards. And to do this you scatter again  up and down to measure the parameter "A". And then you do a similar thing. But you put the magnet after the second scattering. So, you look at the spin which is longitudinal before the magnet. The magnet rotates it. So, it's then perpendicular to the particle trajectory. So, again, if you want to know the spin, you scatter up and down. This is "R' ". And the next one, which wasn't done, which is "A' " would be longitudinal, before the hydrogen target, and longitudinal after. So, you would need two magnets. So the need for two magnets is the reason why it wasn't done, and it was not needed, because the last one,  "A' " is a simple function of "R' " "A" and "R". So, it's not an independent number. So, in principle, one could also do other experiments. More complicated ones. Scattering a polarized beam on a polarized target. And, doing polarization correlation co-efficient, they're called. But, in principle again, this is not needed if we had done six measurements. And, you need five. That would be enough. Then, we had a complete set of experiments. And, what I've said is that you need these five experiments at all angles. Now, we dont really need  "all angles". Because we are great believers in the fact that reality is continuous. So, you don't need to take all points. The curves must be rather smoothly varying. And how smooth depends on how many partial waves you have in the amplitude. How you decomposed the amplitude into partial waves. And, at a certain energy, you find that you have a wave which is looking at this (SLIDE). The cross-section is constant.  Or it could vary as cos q as cos² q (SLIDE). And then, there could be  higher waves. And a way to formalize this, is to do a phase-shift analysis. And this was done by a team at Yale, which was making predictions. Actually analyzing other experiments, and doing predictions of what we would measure. And they were parameterizing our ignorance in phase-shift analyses which had several parameters at each energy. And, once you have these numbers, you can predict the angular variations. And you have the parameters as function of energy fitting some experimental numbers. They had predictions. But,  when you have a certain number of unknowns,  and, a certain number of experiments,  there are sometimes ambiguities. And, therefore, they have  various solutions. And this (SLIDE) ahows their predictions for the proton - neutron interaction, I believe. And for the solutions numbered YLE0, YLE3, YLE3M and so on. Now, this was a parameterization of about 15 different numbers at each energy.

    There was a hope of finding a potential. Now, a potential would have been very nice, because it would have been trying to understand the real force. Once, if you find the electric force, and you say that you have a potential lover R, the force is lover R-squared. And you really understand the electric force. So, if we could find a potential, that may be we were getting closer to understand really the nuclear force. But, we had no luck. I mean it was not possible for a complicated situation to have a simple potential. And we knew that the potential was attractive -- because, actually, nucleons stick together to make nuclei. So, it must be attractive. But, they don't coalesce. So it must be also slightly repulsive. So there's a repulsive core, plus pions which attract. So this meant that there was a rather complicated shape. The potential was different for every spin state. So, in all, theorists had  a potential -- but that  had 14 parameters, and it didn't fit the data very, very well. So, again, retrospectively, there was no hope of simple parameterization of complicated physics.

    Now, let me say a word on the problem of the neutron-proton experiments. You have two choices. If you want to do neutron-proton physics -- either you send neutron beam on a proton target, or a proton beam on a neutron target. Now, neutron beams are less intense, because you have to produce them with your proton beam, so that is decreasing the intensity of the beam. You cannot bend them, ionization them in energy. You can not force them with quadrupoles, so the beam is not very well defined. So, there were some experiments done, but they were very difficult experiments, because of this. Now, the other way would be much easier to send beams on neutron targets. But of course, pure neutron targets do not exist. And the idea was to pretend that the neutron in a deuteron  in a liquid targets is free.  This target  was  designed by Hoffman, for his Ph.D.thesis.  This deuterium target which was a bit more complicated than for the liquid hydrogen that Dick has shown you. And, you pretend that the deuteron is actually a free proton, and neutron. And you make some correction for the fact that the proton and neutron are bound, and the deuteron slightly bound. This means that they have a Fermi momentum going around. So there's a smearing of the kinetics. one particle hits at a target which is moving at random in various direction. But you can correct for that by doing some kinematics, actually. I wrote a program on the computer at Harvard, which was very, very slow computer - doing the kinematics of this. And, but one thing you can do -- when you hit a proton with your incoming proton beam, then there will be your proton which is scattered, and you will be a proton recoil. And, when you hit the neutron, there will be a neutron recoil. So, you can separate event by event, whether you've hit the proton, or neutron. And then, looking at the case where you have the proton report, and comparing it to the case of a pure hydrogen target, you can check whether your assumption was valid. And, so  both experiments were done, and P - NP experiments we're performed. And there were also some elastic PD.  This  may fall in-between what Bernie is going to talk about -- nuclear physics. And what I'm discussing -- proton, elastic scattering on deuteron -- I would say was really used to determine the phase-shift analysis, or things of that sort. Because the physics is a bit more complicated. But, it was a nice test of the first idea that you can calculate nuclear interaction if you know the proton-proton, and the proton-neutron interaction.

    Now, there were predecessors for that program. We were not the first to try to have a complete program like that. Owen Chamberlain, and his colleagues at Berkeley, at the Berkeley Cyclotron, at 310 MeV had done a series of experiments like those. But the energy was above the pion production threshold, and this complicated the analysis quite a bit. And, then we had competitors at Harwell, U.K., and Orsay in France. But they were doing only part of the program. They didn't get around to do the full set of measurements. And then, there was Rochester, which had done one experiment before us. But then, they had a more complete program after Ed Thorndike, who had started with Harvard Cyclotron, went over there. So I tried to make a list of everything that was done. And, pardon me for the over-sights. I may have forgotten some. So, we had first the cross-section, and polarization. That was the first paper by Palmieri, Cormack, Ramsey and Wilson, which you saw. And, this (SLIDE) is a picture from that program. This is the picture of the person we celebrate today. The Cyclotron, where you see the carbon target here, and you do the polarized beam, which is focused with the spare of quadrupoles. And, then there was this neutron beam, which could also -- which you don't see it well here but, you could have a target there, and see a scattered neutron beam, which was polarized also. Then, there was a measurement of "D" which was done by Hwang, Ophel, Thorndike and Wilson. They also reduced the beam energy by putting absorber -- they reduced the energy, and measured "D" at 90-80 MaV. That was done by Thorndike and Ophel.   "R" is the first experiment in which I worked, starting by helping Ed Thorndike to finish his thesis. And then, he helped us after, and stayed on as a post-Doc. And then "A" was measured a bit later by Thorndike, and Hee and "R' " by Hee and Wilson. So that was all the proton measurements. 

     We also studied the proton - deuteron interaction.  The cross-section and polarization were the series of experiments to test the fact that you measured the sum of proton proton and proton interactions- that the deuteron could be used as a neutron target. So, you had a series of experiments by Stairs, Wilson and Cooper. Kuckes, Kuckes and Wilson. Wilson and Postma, on cross-energy and polarization on the deuteron. And then, "R,N,A" were done by LeFrancois, Hoffman, Thorndike, and Wilson. And then, neutron-proton experiments were done. 

    Let me show perhaps a few of the details on the polarization measurements. This slide is  from the paper of the thesis of Thorndike on the measurement of D for protons on hydrogen.  The polarized proton beam is coming here, hitting the hydrogen target. And then, you have really a tiny carbon target. So, the number of particles was going down quite a bit.   The carbon target  was to scatter again, to the right or to the left. And, detecting the scattering with scintillators. And then, you see in the articles what was the formula for "D" .  Looking at the various symmetries, and normalizing with the polarization. This slide was one of the experiments on the deuteron to measure "A" on the neutron target. And you see that's   just the end of the solenoid the proton-beam is going like that (shown on the drawing) ­- the spin being rotated by the solenoid -- when in the magnet, the spin went like that (shown on the drawing). the proton hits the hydrogen target or the deuteron target. And you see that on the side, for the recoil, we were looking at either the proton, or the neutron. And then, on the side here, we had the carbon targets, and we were scattering up and down, because we were measuring "R" -- or "A" in this case.

    So this picture is rotated  by 90 degrees. And you see the scattering system here. And, I can show one of the results. I've shown the phase-shift analysis. And you see one of the two solutions, which was predicted by Bright who had produced  the YLM0 and YLM3 solutions.   We preferred YLM3 phase-shift analysis. So, I'm assuming that there were these measurements on neutron – proton scattering. And I will show some of those. Polarization was measured by Carroll, Patel,  Strauch and Miller. "D" by Carroll, Patel, Strauch, and Miller. "D" again, on a different angle by Collins and Miller. And I had forgotten were some cross section (sigma) experiments which were done by Palmieri and Cormack. And, actually  some of these cross-sections -- were not normalized correctly. So, that was important also. It was done afterwards. For the proton-neutron, you see the apparatus in this slide. You produce a neutron beam. You scatter it on the carbon target. And then you have this solenoid which has to be stronger tahn for protons, because neutrons have a smaller magnetic moment. So, to rotate the spin, it is a bit harder. And you had a longer solenoid, and then, you do your scattering on hydrogen. And then, you do your right-left, or an up-down symmetry. And, this was done by  Hobbie and Miller, I believe. And this is a measurement of polarization with a neutron. And, you see the result of Kuckes and Wilson of doing>the scattering of a proton and neutron. And the present work which was neutron and proton. And the points do seem to disagree a bit. But, you have to remember that one is at 145 MeV. And the other one is at 128, because the neutron beam, of course, can only be at a lower energy than the proton beam which has created it. So, actually, the results agree. And, one last results by Pattel, et al.  This  work that was measurement of "D". And you see that you were -- so these were the measurement of neutron on proton, and measuring "D". And you see that you prefer, again, the YLM3, and the YLM solution. So that was the program. And, it was completed. And to prove that it was completed so that nobody came back and tried to do it again. No one tried to do more experiments on nucleaon nucleaon scattering at these energies again. 

    Now a few words on the life and role of a Ph.D. around 1960. It was a fascinating time for graduate students. The Cyclotron Lab was our lab, and even sometime "our home". And this was not only because we spend a lot of time there (laughter).  The usual shifts were 13 hours, and that would go on for 10 days in a row. But,  it was our home.  Because in those times -- and this must not have changed - -the winter can be pretty horrible, and the summer in Cambridge-- hot and humid. What may have changed was that undergraduates and graduate students were pretty poor in those days, and could not afford air-conditioning. And the only place which was free and air-conditioned was the lab. So, you would see sometimes the spouse coming, and people playing cards, reading books, and coming.    Sometimes children in the coffee room, close to the Cyclotron machine. (laughter)  So, it was really a home. Now, the machine. We had really an excellent team to maintain and repair it. But, to get the Ph.D. we were expected to run it alone at night. Except that, for safety reasons, we had to have a baby sitter. So, we had undergraduate students which were sitting there with us, so that if we collapsed of a heart attack, because of a problem they could warn somebody. But we had to do also our ion source repair alone. And I think that I've taken more radiation in my Harvard years, than in all the time after. Because changing this ion source involved pulling out the probe, relacing the filament and the filament was pretty radioactive.

     Now, we were also allowed to suggest modifications to the machine and try to do it. So, I'll give a bit of my experience on that. Because my thesis was doing scattering on this proton and neutron, we had to do a coincidence on the side. And we were plagued by random rate. Actually, we were limited by the random rate -- random coincidence. And the fact that the Cyclotron was injecting the proton over a very, very short time -- you saw something like 50 micro-seconds - the dead time was a nuisance. And so, I've shown here the frequency of the single Cyclotron. And you extract over this short time here. Now, this I've shown here, I realize, the teeth of the rotating condenser. And so, I had the idea that if you shape  those teeth, maybe you can have a different frequency curve when they pass in front of each other. So, I took a bit of an aluminum piece, cut it -- and tried to machine it in the machine shop, and imitate the section of the rotating condenser. And then, pass it slowly - measuring the capacity. And, it turned out that by shaping it correctly, I could predict that the shape would be like that. And then, I went to Andy Koehler who -- I said, well how can we do something about this on the machine? And, he said, yes. We have a spare, rotating condenser, and we put it in the machine shop. We changed  the shape. I think it was the only spare. So, it was pretty brave of him. (laughter) So, we put it in. There was some bit of electronics to control it. But it was done, if I'm correct, in a few months time. And it gained a factor of 6 for the duty cycle of the Cyclotron. Now, Bernard Gottschalk did much better later for the bremsstrahlung experiements.  And he may talk about it. But it was a more difficult modification to obtain an even better duty cycle. But, you know, I'm trying to imagine the face of the certain engineers now -- if an undergraduate student would come and say, well-- I have an idea on how to modify the machine for my thesis. (laughter) So, we were really privileged at the time to have ideas like that.

    For the electronics -- it was the same thing. There was very little commercial electronics. Some scatterers. A pulse analyzer. And, most of the thing was home-made with vacuum tube. But the fast transistor has arrived in 1959. And, then we could design the coincidence circuit, gate and stretcher, fast-pre-skaters. And the help that we got, was of course discussing with the other graduate students who were there. And Dick Wilson generously paid some undergraduate student to help in the cabling. There was, actually -- I remember when I was saying they had the help of discussion with other graduate students -- there was a competition with Bernie Gottschalk on who could design the fastest coincidence circuit. I mean, I used the 2N-501 tansister. But, I got the 2N-1500 -- which had (laughter) just arrived on the market. So it was a very good time. The data analysis is not such a good story. There was no computer to do our data analysis. It was replaced by two undergraduate students, working on parallel, on mechanical machines. Now, for the younger people in this room, you may never have seen a mechanical adding , multiplying and dividing machine. I can tell you -- a division -- you write your two numbers, and it goes -- glock, glock, glock, glock, glock, glock -- (laughter) for a few seconds, until you get your results. So, this was not my greatest assets to do the physics in my future. But all in all, it was a wonderful atmosphere. We were, what is, I would say is very different from what is happening today is that we were allowed to learn by our mistakes. I made some, but Dick may think it was many. But, certainly, this is something we all regret. The students nowdon't have the chance to build something and to say, OK. Maybe we'll succeed, maybe we'll fail. You take your chance. You don't give them a chance to be wrong. We had Ophel from a small group of more senior physicists. Of course, I had Dick as my thesis supervisor. But, Ed Thorndike -- he was one of the first who exemplified  the idea that people could stay after their thesis, sometimes, as Post-Doc. And certainly a lot of the physics that I knew I learnt from Ed. Working with Ed was a privileged experience of learning how to do experimental physics. I think if I go back, I don't think I've learned a lot about nuclear forces by doing this thesis. But, I certainly learned, and we all learn, I think, on how to design an experiment, and how to perform an experiment. So they was great times. Thank you.

[Applause]

 WILSON: I think the next thing on the schedule is to have a break for coffee, and we'll be assembled at 11. And, then  Bernie Gottschalk. But, after that -- one or two former graduate students are going to give five minute-talks on their reminiscences. If you want to be one of them, please let me know, so that I can have a slight degree of order in that. So, meanwhile, have some good conversations in the next half hour.

WILSON: We might as well get started again. We would have liked to have had Karl Strauch talk at this moment. But he's unable to -- he's not well enough to come to the meeting, unfortunately. So, he can't. But, one of his best graduate students who's here -- and he's been with us for as long as I've been here . for 44 years, I think he's been around Harvard although not here all the time. And, he's still with the Cyclotron lab. And that's Bernie Gottschalk. And he's going to tell us about all the things that's he's done with the Cyclotron in the last umpteen years. Nuclear Physics; Proton-Proton Bremsstrahlung: Dr. Bernard Gottchalk

 GOTTSCHALK:  Thank you, Dick. Actually, I won't be talking  about­ my recent work - I have worked on medical work for quite a few years now.  But what I'll do now is just speak about the nuclear physics program during the physics part of the Cyclotron's activities. First of all, I'd like to thank Andy Koehler, for among many other things, ­keeping excellent records of Cyclotron activities. In the late '60's, there was a plan to write a final report for the Cyclotron. That never actually got finished, but some of the source materials are very useful. For instance, there's a list of about 280 publications connected with the Cyclotron. There are about 35 Ph.D. theses by Harvard students, and about 10 by outside students who used the Cyclotron. (That is, people from other universities.) And we have almost all of those theses. They are a lot of fun to read because, in a thesis, people tend to let their hair down. This, for instance, from George Gerstein's thesis. First of all, you see, it's actually a carbon copy. This is on flimsy paper, and it was one of three carbon copies. And it says "The adjustment of beam focusing conditions was carried out by placing a zinc sulphide screen at the desired target location, and observing the screen illumination with a 60-power telescope and two mirrors from a safe place." (laughter) So it's really -- amusing, to read these theses. Eventually though, after having fun reading the theses and some articles for a couple of days, I realized that I had really better start working on the talk. So, unlike what Jacques did, which was quite a systematic account of the nucleon-nucleon program, I'm really just going to give some highlights of stuff that appealed to me.

Here's the first one. In the early days, the Cyclotron didn't have an external beam at all. And yet, many excellent experiments were carried out. They all had to be done inside the machine, and some of them used a great deal of ingenuity, such as this experiment by Norton Hintz and Norman Ramsey. This experiment wanted to measure the excitation function - that is, the energy
dependence of making certain isotopes, if you bombard a target. The standard technique, which (already at this time) was an old technique, and is still used today -- is  the stacked-foil technique. You just take a stack of foils which is deep enough to stop the beam. So at each foil, you know the energy of the proton. In other words, if you know the incident energy, then by using the
stopping power relation, you know the energy of the protons hitting each foil. And then, after the exposure, you take the stack apart, and by various means -- radioactive analysis, and so on, you measure the radioactivity. Today, it would be by accelerator mass spectrometry. You analyze how many isotopes you've produced,  and that gives you the energy-dependence.

Unfortunately, the technique does not work unless the energy spread of the incident beam is very small. Because a large energy spread would translate into a huge uncertainty of the energy at the end of the stack. In those days, we didn't have an external beam, and the energy spread of the internal beam was very large, because of the radial oscillations. Well, this technique overcame those problems.  They put a small scatterer at one location. And that scattered a bit of the beam. And then 180 degrees away, they put their stack. It was outside the median plane, so that you wouldn't interfere with the protons that were en route to the scatterer. This way, they used the Cyclotron as its own analysis and focusing magnet. So it was really a very ingenious technique, which made the most of what they had. And, here, just for instance, are three excitation energies that they measured for daughters of Aluminum 27. So that was an example of an experiment done inside the Cyclotron.

A few years later, around 1953, there was, in fact, an external beam. It was fairly crude, and the beam wasn't very intense. But a few experiments were done with it. This is from Walter Titus' thesis. He was a student of Karl Strauch's, and I second Dick's real regrets that Karl couldn't be here today. So, here was the external beam. There was a magnetic channel which got some of the protons out, and then some slits for energy analysis, and a bending and focusing magnet. And the result was an external beam at about 95 MeV. It had rather poor intensity which was the main motivation for the upgrade a few years later that Dick described. And here was Titus' set-up: just to give you a feeling for the style. He used a range telescope. A range telescope is an arrangement where you basically determine the energy of the protons by how far they go in a stack of scintillators.

Remember in those days, electronics was fairly crude, and fairly expensive. So, just having enough coincidence circuits to implement this sort of arrangement was non-trivial. When you started taking data -- I remember one spent half a day, or a day, just verifying that all the coincidence circuits were working, which is something you almost take for granted, nowadays. Titus and Strauch were interested in looking at elastic and inelastic scattering from nuclei. So, this is an experiment where the proton really interacts with the nucleus as a whole. It sort of sees the nucleus as a cloudy crystal ball. And it can either just bounce off of it -- elastic-scattering -- or, it can interact with it somewhat, and leave it in an excited state, which subsequently decays. This experiment, though, only looked at what happened to the proton, after it was scattered. And you can see, in this case, for instance, where the target is carbon, the proton either comes out with the energy corresponding to elastic scattering, here, or it can leave the nucleus in one of a number of well-defined excited states. In those days, a major topic in physics was determining the excited states , and measuring how they were excited by incident protons, among other things. And, for instance, this is also from Titus' thesis.
"Elastic Scattering as a Function of Atomic Weight" . It increases rapidly, because you have here a coherent process which depends upon all of the nucleons. And therefore it increases more or less as the square of the number of nucleons.

Well, then there was the shutdown, after which the Cyclotron came back up with three beams. And, I should mention, by the way, that the shut-down took just about a year, and really involved a lot of work. That is the longest time the Harvard Cyclotron has ever been shut down in its entire career. So then, among other things, you had a high intensity proton beam, at 160 MeV. And Karl's program was continued by George Gerstein, who was actually the first graduate student that I worked for. And I was one of the folks that checked his coincidence circuits to make sure they were all working. And his technique was not very different from Titus'. Here you have a range telescope. Now, there's a vacuum chamber around the target to try to reduce the background from air. Because of energy resolution considerations, the target itself has to be rather thin, and that makes the air contribution appreciable. Therefore we used vacuum chambers to try to get rid of the background from air. Otherwise, the experiment was pretty much the same as before. George was interested in measuring the angular distribution of elastic scattering, and got results like this one. This measures the angular distribution of elastic scattering from lead over several decades. The fit is basically a phenomenological fit with a nuclear potential that has both real and imaginary parts.

By this time, computers were coming into use. The parameters of this fit were adjusted by using a Univac computer which was one of the first University-wide computers at Harvard. By the way, apropos of that, I want to tell everybody that the very first Harvard computer, or about half of it, is on display in the hall. Many of you have probably already seen it. It's the Mark I, and you should really take time to look at that machine. It was the world's first programmable computer. It did not use vacuum tubes. It's mechanical. But it had the feature that, rather than being built to solve a specific mathematical problem, it could solve a whole array of mathematical problems depending on a program tape that you fed in. So it was the world's first programmable computer. Have a look at it during one of the breaks. It was built towards the end of the War, and was used by the Navy for about three years. Mostly, I understand, to crank out Bessel functions. There's a very excellent set of descriptions and photographs under the computer. It's right behind where we were having coffee. So, actually, it's a little bit older than the Harvard Cyclotron. But, unlike the Cyclotron, it has not been in continuous use. (laughter)

WILSON: It was still working in 1955.

GOTTSCHALK: Is that right?

WILSON: We did some calculations on it.

GOTTSCHALK: I see. OK, I didn't know that. '55. That's amazing. By today's standards, it is a 50-hertz, I think,  2 kilobyte machine. (laughter) So now I am going to get to some experiments that I did with Karl Strauch. Now, the experiments I've talked about so far were experiments where the incoming proton interacts with the nucleus as a whole. But, already in the early '50's,
Chamberlain and Segre at Berkeley  had established the existence of an entirely different kind of reaction -- where the incoming proton would knock constituents out of the nucleus. The simplest thing is that it would knock another proton out, and at that time, the surprising thing is that the kinematics were such that it was almost as though this proton that was being knocked out was a free
proton. And these things came to be called quasi-elastic reactions. And, in fact, from a nuclear physics of view, as you go up in energy, that's where most of the action is. In other words, the more interesting things to study are where you are knocking out nuclear constituents. Of course, history repeats itself - 10 or 15 years later -- at SLAC, they were doing "deep inelastic reactions on protons" and all that really is, is knocking constituents out of protons. So everything seems to repeat itself, over and over again, on a smaller scale. Well, anyway -- in this case, we were smashing nuclei. And, I've never understood why these machines are called "atom-smashers". Anybody can smash an atom. What we were smashing was nuclei, and that's the harder thing to do.

Anyway, to come to the the apparatus.  In my experiment, we had two telescopes to detect the protons. The principle of this experiment is that you would determine the energy of the proton by how much light it produced in a sodium iodide scintillator. We had found by experimentation that sodium iodide gave you the best energy resolution, and also the most linear response with respect to proton energy. Here's a close-up view of the scintillation counter. Of course, all of the counters had to be encased in iron shields because, even 50 feet from the Cyclotron magnet, there is still an appreciable fringe field, which would otherwise prevent the phototube from working. If you look at the lower picture here, it's interesting, because it shows some of the data logging equipment we had in those days.

We're in the late '50's, early '60's and devices called "analog to digital converters" had just become available. There was a company in Cambridge that made them: they cost $5,000 dollars apiece. And they did use transistors, but those were very early transistors so you had lifetime problems. Occasionally, a transistor would actually fail which almost never happens nowadays. And then, you would have to go in and find out which one it was, and replace it. Well, anyway, we had two of these things to convert the two proton pulses into numbers. And the first thing we did was display the numbers on these neon read-out tubes, and record them on a movie film that was slowly moving. And then some poor soul, namely me, most of the time -- had to read these numbers, transcribe them, and do the calculations. I got tired of doing that. And, by that time, IBM cards and card punches had come along. So at about that stage in the experiment, I built a huge matrix of relays that would drive an IBM card punch. And, every time an event came along, which was a few per minute, as I remember, the card ­punch would burp, and punch 6 columns. And, at the end of the experiment, I would have 10 large boxes of cards. I would lug them over to the central computer which, at that time, was at the Smithsonian, and it would process them. It was an IBM computer and it was programmable in Fortran. I always feel that IBM has not gotten enough credit for inventing Fortran, which was the major thing that really made computation accessible to scientists. So, that was the style in the early '60's. So this is an experiment where we knock a proton out of the nucleus, and then measure the energy of both protons coming out. And, the neat thing about this experiment is that by doing the kinematics, you can find out what the momentum was of the target proton before you hit it. So, in a way, it is a very direct measurement of the wave function of the target protons in the nucleus. These results I'm showing here are for carbon. For each event I've just done a scatter plot of the energy of one proton versus the energy of the other proton. And you see that it has a very clear structure. If you go in this direction, that is, along the diagonal -- I don't have time to prove this to you -- but if you follow through the kinematics, the coordinate in this direction is just the binding energy of the proton that you knocked out. So you see that there's a very clear group here of protons with one binding energy. And then, further down, a much fuzzier group of protons with another binding energy. And then, if you further do the kinematics, you find that going at right angles to the diagonal, that coordinate is equivalent to the momentum of the proton that you knocked out. So this group of protons seems to have a peak momentum which is not zero. It's greater than zero. Whereas this fuzzy group of more strongly bound protons has a momentum which is very broad, but peaks at zero. So this diagram, if you know how to read it, ­was the most direct demonstration by far, that carbon consists of four P­-state protons which are weakly bound, and two S-state protons which are far more strongly bound. And these quasi-elastic experiments went on for quite a while. They were done by all our sister machines in other parts of the world:   Orsay, Uppsala and Harwell. And really improved our knowledge of the nuclear model.

Now, you don't just have to knock elementary particles out of nuclei. You can also knock clusters of particles out. And, a few years after the experiment that I've just shown, Sue Kannenberg, who is in the audience today, and who was at that time a graduate student at Northeastern University, did this experiment under my direction. In principle, it's very similar. We're knocking something out of the nucleus but in this case we're looking for the scattered proton in coincidence with an alpha cluster. So, this is called a (p,p alpha) experiment. I don't have time to tell you how we identified the alpha and all that sort of thing. But we see very clear evidence of an alpha cluster, with a very unique binding energy and a unique momentum distribution. The thing that makes the alpha experiment even more interesting is that unlike the proton-proton scattering cross-section which is almost uniform in the
center-of-mass system, the p,p alpha scattering cross-section has this enormous momentum dependence. You see here, it varies by almost a factor of 30 over the angles that we explored. And yet, that very same momentum dependence that's measured
for free protons and alphas seems to also apply when the alphas are bound inside a nucleus. So, actually, to an amazing degree, these quasi elastic reactions go on and behave almost like free interactions. And they give you a further insight into nuclear models. In other words, a nuclear model can now try to predict how often you will hit an alpha cluster and that sort of thing.

Well, for the remainder of my talk, I'd like to concentrate on what was one of the last experiments at the Cyclotron. It was actually a nucleon-nucleon experiment. But, because I was the principal investigator, and we used a lot of the techniques that had been developed for the nuclear physics, I was chosen to give this part of the talk. You may recognize this fellow in the slide. Still looking
pretty good. (laughter) Maybe not quite as bushy-tailed, but pretty good.  Somebody looks a lot better than I can over there (laughter). (BG showed a slide of Richard Wilson and Frank Pipkin at a Physics Department picnic. Richard is raising a can of beer.)

GOTTSCHALK:  I also have to mention the fellow without the beer.  This, by the way, was taken at a Physics picnic, I think some time in the late '50's or early '60's. This is Frank Pipkin, who died tragically young a number of years ago, and is sorely missed by all of us in the Physics Department. He was an active CEA experimenter, but actually never did experiments at the Cyclotron. So, the motivation of this bremsstrahlung experiment is the following. All of the experiments that Jacques described -- this lengthy program -- really, only measured cases where the protons scatter elastically off nucleons: where p,p or p,n reactions occur elastically. That is, energy is conserved. Now, if you want to use those results to interpret nuclear models, you have to cover cases where energy is not conserved in the two-nucleon system, because you're dealing with a many­-body problem. I mean the simplest complication is when nucleons scatter off each other in the nucleus, they're bound. So energy is not conserved in that reaction. The jargon for that is off-energy shell, or off-mass shell scattering. And people were interested in measuring that. You can't do it really very well by studying nuclear physics, because there's so much going on in the nucleus, that it is hard to separate out these effects. And the thought was that it would be easier to separate them out, if you used a simple process. And the simplest process people could think of, was the emission of a photon or a gamma ray. And because it's the same as bremsstrahlung, by which we make X-rays for diagnostic medicine, it's called proton-proton bremsstrahlung. The desirability of doing this experiment had been realized for a few years. It is, however, a very hard experiment, because the cross-section is more than 1,000 times
lower than elastic scattering. So the event rate is very small, and elastic scattering presents a huge background. So most of your ingenuity has to be devoted to trying to get rid of that background. The reason I showed a picture of Dick there is that around this time, Dick had written a book, which sort of summarized the experimental knowledge about nucleon ­nucleon scattering. and he was urging both me and Ed Thorndike, who had recently gone to Rochester, to try this proton-proton bremstrahlung experiment. The technique we finally settted on was really an outgrowth of the nuclear physics. How many people do you have volunteering, Dick? (BG meant, to give other talks!)

WILSON: Seven, I think.

GOTTSCHALK: Seven? Oh, OK. I'll make this fast then. As fast as I can. Again, if you do a scatter plot of the two proton energies, and what you had going on was a bremsstrahlung event, the two energies should lie on a ring-shaped structure. And the size of the ring depends on the angle at which the telescopes are placed. That arrangement subsequently became known as the Harvard geometry. In a preliminary run, we saw some signal. But the experiment wasn't nearly clean enough to say that we had seen proton-proton bremsstrahlung. We decided that we had to make a further improvement of the Cyclotron duty
cycle, which we did. But that took another year. During that year, we got a progress report from Ed Thorndike, who is also in the audience today. It said "Dear Bill" -- Bill Shlaer was the thesis student on this experiment -- "Enclosed is a progress report on our work. A crude comparison with Cromer and Sobel's cross-section (two theorists who had tried to estimate the results of this experiment) suggests that they are high by a factor of five or more. Which turned out to be almost exactly correct. This letter, of course, got us very worried, because it showed that Ed Thorndike was hot on our heels. Or, I guess, as he would say a little bit ahead of us. (laughter) But anyhow, we finally did the experiment in June '65. And, I'm really skipping ahead here. What you are seeing here is the results of over a month of data-taking. And you can see even here in the raw data, you can see the clear evidence of those rings that indicate that what is going on is proton-proton bremsstrahlung. The thing I forgot to emphasize is this is a way of detecting proton-proton bremsstrahlung without even looking at the gamma ray. Because large gamma ray detectors are difficult and expensive to build. So what we had invented, basically, was kind of a short-cut, whereby, just looking at the protons, we could identify the reaction. I'll just show a few more pictures. Here's me 35 years ago. The person on the left is Bill Shlaer who I've sort of lost track of. We invited him to this meeting, but the letter came back. And the other person is George Wang, who took care of the computer. By the way, this experiment was done on-line to a PDP-l computer, which had been set up and the software had been managed by Al Brenner. I should mention that because for its day it was very advanced. It was not only serving our experiment but, at the same time, two other experiments at CEA. The high-energy group was kind enough to let us use it as well. And it was what would nowadays be called a "real-time multi-tasking data collection operation" which, for those days, the mid '60's, was extremely advanced. It was certainly one of the first of its kind.

WILSON: It had a 10K memory.

GOTTSCHALK: Yes. And we were allowed to use 2K of that memory, one tape drive, one oscilloscope output and one input port. So those were the resources we had in those days. Here's a plan view of the apparatus for the bremsstrahlung experiment. And then, just one final note which is sort of tragi-comic. ­During our main data collection run, a tragedy occurred which was the CEA explosion. And, at the time there were just three of us to take data. So, we had hired this guy named Val Kirsis who was sort of a mercenary. He was actually a chemistry major. But he took data for a lot of Cyclotron experiments in those days. And was extremely conscientious. And, here -- very early in the morning on the 5th of July -- are his notes. It says "Beam off for a while. CEA explosion." At that point, he went out back. The explosion had blown in one of the doors, which set off an interlock, so that the Cyclotron turned off. So, he restored the door, and went on taking data. Then it says "Then stop run. Firemen on roof." (laughter) Because the roof was a fairy high radiation area, we weren't allowed to run the machine, if there were people on the roof. So, as soon as the firemen came in, he conscientiously turned the machine off. Of course, a few minutes later, the firemen turned off power in the entire area so they could fight the fire. So, anyway, this is sort of an extreme example of what you find, when you go back through old data books. The CEA explosion has assumed almost mythic proportions in Cambridge. And, usually, one way or another, the Cyclotron is implicated, even though we had absolutely nothing to do with it. Just a couple of weeks ago, a friend of one of the Cyclotron operators was being shown an apartment by a real estate agent, and he asked "Why is Oxford Street closed?" And the answer was "Because the Cyclotron blew up." (laughter) So I think what we have here is a very distant echo of that tragic accident at the CEA. Well, I've already run way over my time. So thank you.

 Thank you.  [Applause]

WILSON: Just before I call on people – I just wanted to mention a few people who have sent their regrets - David Bodansky, and Bob Birge.  I will mention Owen Chamberlain. He was here on leave for six months, and was starting an experiment at the Cyclotron, which got interrupted. But he was on shift. And, actually having lunch at the Faculty Club with us -- sneaking off and leaving the graduate student to run the machine -- when he got a phone call from Stockholm -- which made him the famous announcement. So, we went back to the Cyclotron and I arranged the first celebration of his Nobel Prize with champagne at the Harvard Cyclotron control room. At the control panel where he was sitting down, running the machine. But, he's unable to get here, because he also is not particularly well. Dave Measday is rushing off trying to sell his apartment at the present moment - otherwise, he could come. And we are not able to talk very much about his extremely fine work with a monochromatic neutron beam. I just want to mention three other people who have unfortunately passed away. Chester Hwang deserves a worthy  note.  He was a pilot in the Chinese Air Force. And went to Taiwan with Chang Kai Shek and then came to this country to get further training on jets. And then, his General absconded with $2 million dollars and went to South America -- leaving him -- leaving all the pilots without any salary. So, Chester Hwang came to graduate school. but the thing we should note, because it is in the news nowadays -- what happens to Chinese (or Taiwanese) in this sort of position. Chester later got married, and had four children. And, sent pictures of his children back to his father and mother in Beijing. And he was very careful not to tell them that he ever got a degree in Physics. Or that he'd ever done anything in physics. Only told them of what he children were doing. And perhaps that's a note of caution that one should look at when one's reading the Cox Report on the Los Alamos issues. Well, I think the first person that I'll call on is Lee Davenport, who is here and will tell us something. 

LEE DAVENPORT: Thank you. Well, after all of this long-haired commentary, concerning nuclear physics, and protons -- I've memorized all these words - -and a number of other things. I thought it might be well to look back a little bit, less formally, at what went on in the earliest days of this Cyclotron. I must say that I'm one of the very lucky people who's sitting in this room, for having had a chance to be associated with it at all. And my luck started way back, at a long time ago. It started at a meeting at MIT in October of 1940. A year before war was declared. That meeting was a meeting called "A Conference in Applied Nuclear Physics". There were some 600 key accelerator people who got together at the time. One of which was a man whom I'd never met before -- named Kenneth Bainbridge. I noticed -- I was a graduate student then. I noticed that a number of the upper-level people if I might call them  that -- disappeared from these meetings and weren't there for all of the sessions. And, of course, the reason for that was that nuclear physicists were being summoned to what was soon to become the radiation laboratory at MIT. And, Ken Bainbridge was a key member of that initial group. Ken became kind of a hero for me. When I joined the radiation lab a month or so later, I reported to Ken for a brief period -- but he moved onto other projects. I stayed there with the initial project that I was involved with called "The SCR-584 Radar Anti-Aircraft Fire Control". But the radiation laboratory brought to a number of us, what I would call a feeling or urgency. We were there to win a war. And we were there to get things done. And, Ken Bainbridge contributed a great deal to that feeling. And, I enjoyed the chance to work with him. Of course, he was siphoned off to go to Los Alamos, as you know. And, pretty soon, the Cyclotron here at Harvard was also siphoned over to Los Alamos. And, Ken didn't return until the end of the War. However, he and Curry Street got together and met me just as the radiation lab was closing and said  "you know, we've got an exciting program here starting up at Harvard. We're going to build a Cyclotron to replace the one that's gone. And would you consider coming up and being a member of the Physics Department? And joining the Faculty?" That meant that I got to go to the Faculty Club and eat horse steak, which we served in those days. And I considered this to be quite an honor at the time. And, to become a part of the team and it truly was a team effort that led to the construction of this machine. By the time I got here, which was in September of 1946, Ken and Curry Street, and Roger Hickman, Bob Wilson -- had pretty much put all of the specifications of the machine together. And my job, somewhat ill-defined -- it was a research officer on the staff, and the faculty.  I'm not surprised that the title of the exact job came through was "Coordinator" -- or, whatever it did come through as -- because we weren't all sure of what our titles were. Everybody just settled in to work, and get this machine going with a sense of real urgency. The first meeting I ever attended of this group was with the architectural firm of Coolidge, Shepley, Bullfinch, and Abbott -- who did all the architectural design for the buildings at Harvard University at the time. And I thought -- boy, this is really a strange situation. The old Cyclotron sat in a wooden, World War I building called Gordon McKay. And now we're talking about building a concrete monument with another building alongside of it -- with the world's leading architects. And that was my introduction to what this project was all about. We started by having to hire people. It was a stand-alone program. Had to have your own machine shop, your own engineering department. We couldn't depend on the rest of the facilities - the Physics Department. So, there you get the beginnings of what was called "The Nuclear Laboratory", not the Cyclotron laboratory, but the Nuclear Laboratory. The urgency was clear. Harvard was probably the only major U.S. institution offering graduate work in Physics. It did not have much of any equipment. The Cyclotron was gone. Much of the surrounding equipment was gone. And, the number of graduate students in Physics who wanted to study nuclear, or atomic work, had jumped from about 5 pre-War to about 100 Post-War. So there we sat with an increasingly large requirement for facilities and no machine. The urgency was clear, and we went to work on it in a great hurry. I never would have believed 53 years later, that I would be standing here, talking about a machine, which is just now ready to shut down. Now, at that time, Cyclotrons were growing pretty rapidly in size. The 184 inch was already under way. And unlike today's computers which become obsolete 3 weeks after you've bought it -- it's up to another 500 megahertz.   Like those, the Cyclotrons were moving pretty fast. But we knew that we had to get going on this. And so, most of the activity that went into the original building of this machine, was hurried, and rapid activity. We engineered as we went along -no question about it. Were we going to build the magnet out of 16 pieces or 4 or l7? And if we did, how were we going to get it machined? And who was going to cast the pieces? Obviously, the biggest problem of all was getting that magnet. And, between Bethlehem Steel, and Watertown Arsenal, which did the machining -- and a company that we hired from California to move the pieces of steel from Watertown Arsenal down here, and rig them together and make a Cyclotron magnet out of it -- were doing this job for the first time. In fact, they had to reinforce some of the culverts under the streets over which that equipment was brought -- to get it here without breaking through the pavement -- between Watertown Arsensal and Oxford Street. Well, you've heard a little about these unusual things. I'll give you a couple of more tid-bits, and then I'll get out of the way, and defer to people who have used the machine, rather than helped to construct it. The basic specs, as I said, were pretty well done. We had, however, a lot of what we considered to be very clever ideas worked into it. One, was a movable shielding. Movable shielding was quite a new concept. And the idea of how to move it, was another new concept. We put in a crane over the top that would pull cables, and it would move the shielding when you needed to do that. Hopefully, that was also going to lift the magnet pieces in place. Of course, when we found out how big they were, it was clear that no crane was going to lift them in that building. So the rigging people had to come and do that. So, not everything worked smoothly. The stainless steel problem, which Norman so clearly referred to.   We used more Glyptol  than GE -- General Electric -- could manufacture -- trying to get that thing leak-proof. And, finally, we heard about a company down in Long Island, and I remember their name was VECO -- Vacuum Engineering -- Leak Detectors. And we bought them. One of their first -- we pried it out of them -- to bring it up here to help us find leaks. Norman pointed out that probably the strangest of the leaks - -the one that was in the vacuum pump itself. But, we did funny things. And another one that I'll conclude with ­- Cooling Water. Cooling water was going to be a problem. You couldn't dump it in the sewers. The City of Cambridge wouldn't handle that. We had to get rid of it. And if we had to get it in, we decided to build a well -- dig a well -- and, we did. We dug a nice well on the site. And, dug another return well to put it back in the ground so. 

ARTHUR KUCKES: ..I will not talk about the cyclotron but about what I am doing now.   Using electromagnetic detection to find pipes and often put out oil fires. This (SLIDE) is a fire which started in the beginning of December in California. And, it's about 100 yards from the California Aqueduct -- which is right here - -which carries the water into Los Angeles, which is the dominant source of water, I guess. And, the flames which you see here -­they reported those to be close to 200 feet high. So, by scale, these tanks here they are about 35 feet. So this is quite a fire. And, it is a problem of great visibility, and we did not get involved with it right away. Indeed, the work which we do - is. pretty much of a last resort. Most of these oil field problems can be dealt with at the surface. And what we do is a last resort. However, that said, the capping and the surface intervention problems they went through eight failures on this project which -- at a million dollars each -- was getting to be another major problem. And nevertheless, the State of California did insist on that being taken care of. So anyway, what we do is to -- well, instead of doing things at the surface, we'll drill a second well, a relief well.