The Manhattan Project

Philip Abelson's Interview (2002)

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Philip Abelson first became involved in uranium enrichment while a graduate student at the University of California-Berkeley, working with cyclotrons under Ernest O. Lawrence. He explains how he came up with the idea that liquid thermal diffusion could enrich uranium-238 to U-235, how this process was implemented first at a factory at the Philadelphia Navy Yard and later at the S-50 Plant in Oak Ridge, and the important role the S-50 Plant played in the uranium enrichment process. He recalls his encounters with Lawrence, J. Robert Oppenheimer, William “Deak” Parsons, Edwin McMillan, Luis Alvarez, and other Manhattan Project leaders.
Date of Interview: 
August 8, 2002
Location of the Interview: 

Philip Abelson: My name is Philip Abelson. I was the son of two Norwegian immigrants. My father was born north of the Arctic Circle, and my mother was born in middle Norway. I visited the birthplaces of both of them. They were very wonderful parents. I couldn’t have had better parents.

My father got his degree in civil engineering in 1909, at a time when not very many people completed college. My mother was with him the first two years, attending at Washington State in Pullman, Washington, and then my brother was born and that stopped her. It was interesting that they never spoke Norwegian in the home, except when some Norwegian visitors came. They never at any time had a disagreement in my presence.  They were always a partnership, and so it was a very happy home.

My father exposed me to elements of engineering early so that when I was only about fourteen, I had a summer job helping a local surveyor, who was surveying mining claims and also automobile accidents. He also took me to where construction was going on in a public utility hydroelectric project for the city of Takoma.

So I was immersed a bit in engineering early, and immersed in the attitude of, “If you have a problem, think about what is the most important aspect of it. What can you do about it? What should be your priority in making your plans and taking action?” That’s an approach that’s useful for many matters in life.

I was a rather relatively bright kid and so in grade school, I got double promotions and was actually ahead of other students in my class. When I went to high school, I went along with the others, but I got interested a bit in chemistry because there was a teacher who was really enthusiastic about her topic. I got interested in the high school newspaper because I had space and I wanted to do something for the high school before I left it. I learned the elements of journalism in high school and they are really very simple: who, what, when, where, why, and start out with an interesting first paragraph. That’s been useful throughout my whole career. 

I went to Washington State in chemistry. Since my father was interested in me becoming an engineer of some kind, I enrolled myself in chemical engineering. That caused me to take a first semester in machine shop. Learning about how to manipulate the various machines in the machine shop and being able to build something out of metal later was very helpful in my career. Ultimately, I changed to straight chemistry and I completed the Bachelor’s degree in chemistry in three years, taking some extra courses. 

Subsequently then, I got interested in physics because the professor that was heading the physics department was the most glamorous man on campus. He had his degree from Harvard and he had taught for two years in China. He knew how to give a lecture to interest the students. I took some of his upper division courses and ultimately was offered a teaching assistantship there. I got my Master’s degree in physics at Washington State.

It turned out a person who had been at Yale while Ernest Lawrence was at Yale came to Washington State, and he gave courses in elementary theoretical physics and in experimental nuclear physics. He assigned me to make a report on Ernest Lawrence and the cyclotron, and I knew once that I had made that report, that to Berkeley I wanted to go. That was their plan, of course, was to get me interested. So they got me the one out-of-state fellowship as a teaching assistant in Berkeley for that 1935. 

The moment I got down to Berkeley, I went to the cyclotron laboratory and there was Ernest Lawrence. He saw me and decided to put me to work right then and there, and so he asked me to paint the cyclotron. It had been a dirty black, and he wanted it a battleship gray. He had the paint there and the brush, so I started to paint. Pretty soon, all of a sudden, I had a companion in painting. Ernest Lawrence was painting too. Between the two of us, we painted the cyclotron. 

One of the problems as a graduate student: that year I was the one graduate student in the laboratory, and already the cyclotron laboratory was famous in this country. It was beginning to get write-ups in Time magazine and the like, so it attracted postdocs. The postdocs were of a different breed and different status than a miserable, starting-out graduate student, so I had to do much of the dirty work that was to be done around the place. At that time, the cyclotron was put together with beeswax and rosin, and whenever the magnetic field changed, that would move parts of the equipment around and spring a leak. Whenever there was a leak, I was expected to be on hand to help fix it. I was, in effect, consigned to leak-finding duty just virtually all the time.

Then I was forced to take these graduate courses and I was supposed to teach. One of the things I was supposed to also do was evaluate exam papers of another professor. This professor gave exams that were very complicated, and if he had graded them according to whether the guy got the right answer, only about 10% of his students would pass. So what he did was he fudged by asking that whoever was grading the papers give partial credit if the person seemed to know something about the subject, you know, knew a formula or made any kind of approach to getting an answer.

Well, when you have 150 students, you can see that they’re all trying to get something, so they all write something down. Whoever is correcting the thing will try to evaluate, but they’re all making little differences. Of course, when they find that they get their paper back and they got a certain grade, then they go snooping around to see what the other guys got. And pretty soon, if you aren’t awful careful in trying to remember what 150 students did, that takes some brainpower. I was fortunate in that there was a second guy grading the papers, and he was not as careful about how you did it. Being the better of the two bad examples, I got by with the matter.

At any rate, the first two years I had a miserable experience as a graduate student. I did manage to do some work for Ernest Lawrence, one of which was to repair some radioactive phosphorus-32 for tracer work, radioactive tracer work, and that was done in collaboration with some biologists in the biology department. Of course, Lawrence realized that if you could get some type of medical application with that cyclotron, or from what the cyclotron did, you could get money.  People wouldn’t give money to do a physical experiment, but if it had some connection with medicine, then there was all kinds of money to be had. He was all the time looking for that kind of application.

I won’t belabor further my problems, but it did turns out that ultimately after about two years, Lawrence subsequently went to bigger and bigger machines, and did expand the size of his cyclotron and vacuum chamber and got rid of the beeswax and rosin. The vacuum chamber, when it was delivered, had some tiny leaks in it, and I was assigned to find the leaks.

There were about thirty of them, and you could only find the biggest one first. Then you went in succession of thirty different-sized leaks, until you finally got the last one. I was able to find the leaks in about a day and a half, and that had the marvelous factor of meaning that postdocs who were using the cyclotron didn’t have to be hunting leaks, or have their work interrupted because the machine was leaking. My status in the place improved greatly, because I had been a hero who solved the damn vacuum problems.

Well, that was that one, but I’ll tell you the story about Lawrence and [J. Robert] Oppenheimer. I may have mentioned it to you, but I’ll repeat it. Turned out that in `36, `37, the Spanish Civil War was going on, and at that time the so-called Loyalists, or the Democratic Party, were fighting the Fascists in Spain who were trying to oust them. Oppenheimer was interested in supporting the Loyalists.

One Sunday morning I was operating the cyclotron. There was nobody in the place. They weren’t in church, you can be sure of that. Maybe they were recovering from a hangover from the last evening or something like that.

But at any rate, nobody was there but me who was running the cyclotron, making some radioactive tracers, and in comes Oppenheimer. He looks around, he eyeballs the place. He sees that I’m the only person there, and of course, being a poor graduate student with no theoretical background, I was a nonentity. So he didn’t waste any time on me, but he moved over to the backboard then and wrote on it something to the effect: “Cocktail party benefit of Loyalists,” and he gave the location and the time in the afternoon, that afternoon, and departed the place.

Well about a half an hour or an hour later, in comes Lawrence. The thing he was interested in was seeing whether the cyclotron was operating properly. He came over and saw that it was, and that I was doing what I was supposed to do. Then he kind of looked around to see what was going on, and his eyes fell on the blackboard. Lawrence had the habit that when something really agitated him, he would clench his jaws.

So I knew that this was bothering him, and he kind of stood there for a moment. Then he slowly walked over to the blackboard and he took and eraser and erased off what Oppenheimer had written. In my mind, that was the beginning of a division between them. That’s in my mind. I can’t be saying that I knew what was going on in his brain. But after all, the Radiation Laboratory was Ernest Lawrence’s domain and somebody had invaded his domain and was inciting his students should go to something that he wouldn’t exactly approve of. Lawrence was a very proud man. He was proud of his establishment and proud of what he had achieved. So as I say in my mind this was the beginning of a split that led to some later events. That’s all for that.

One other thing about Oppenheimer and me was that later on, I had to take some preliminary exam that Oppenheimer was on the committee. I had the misfortune that there was a young Chinese woman [Chien-Shiung Wu] who took the exam the morning that I was to be examined that afternoon, and she was a brilliant scholar and she just passed with flying colors. Here, that afternoon, by contrast, I was practically illiterate. But they didn’t flunk me because Lawrence was a big man on campus at that time and it wouldn’t have been diplomatically very feasible to flunk that guy. So I was passed, but it wasn’t because of any great sign of brilliance on my part. I didn’t have anything further to say about any connection with Oppenheimer.

It was true that after the news of fission came out, I did do some beautiful work because of my competence in chemistry. I was able to identify a large number of the fission products. Almost every week, there would be a seminar, a Monday seminar. Most of the time, Oppenheimer would sit in on it and I would be reporting some new results that I had obtained. All went well for me from then on, and I got my PhD May 8th of that year. It was one of the fastest—I’m sure one of the fastest PhD’s theses done in Berkeley in many a year.  

I think that’s enough on 1939 in Berkeley. I then proceeded back to Washington in September, but on the way back in September, the Germans had invaded Poland. At that time apparently, there had been an agreement between the Germans and the Russians about the Germans going after Poland. Nevertheless, this was not likely to stick, so when I got back here to Washington, I was here to help build a cyclotron to make isotopes, or make radioactive materials for the East Coast community to do tracer work. 

I decoded that I’d better start looking into the matter of isotope separation. But first I also, in `39, I also got to reading about what [Edwin] McMillan had done about irradiating uranium with neutrons. I figured out an experiment that needed to be done, and I tried it in Washington, but the radiation I had available was too skimpy. In May of 1940, I came back for a five-day visit, and was able to identify the chemical properties of neptunium and to show that neptunium, the material that McMillan was making, had chemical properties that were completely different from anything else in the periodic table.

Then, on my way back to Washington, at that time the Germans were invading France, and so I knew that we were in for it sooner or later. Then I began to really and carefully look into methods of isotope separation. 

One of the things that I remember with fondness was the mentoring that I obtained both from Luis Alvarez and Ed McMillan. Ed McMillan had been kind to me while I was a graduate student, and Luis Alvarez too. On the other hand, the other postdocs would say, “That’s a mere graduate student, you know, and he isn’t in our class.” That was kind of their attitude. So I remember those fellows fondly. Later on, I was able to do a partial reward to Luis Alvarez while I was editor of Science[Magazine].

This gets us to where I was getting to look into the matter of separating isotopes. I was working during the day on ordering parts for the cyclotron, but in the evening and on Saturdays and Sundays, I was looking into the matter of isotope separation. I would go to the Library of Congress and read their materials. I found that some Germans had done a liquid thermal diffusion separation of some zinc, but this was a zinc salt in water solution.

I didn’t have any way of doing zinc isotopes to confirm what they were doing, but there was someone at the Bureau of Standards that could measure potassium. I did the potassium salt, and I found that I could make a partial separation of the potassium isotope. Well, I tried a uranium soluble salt and that just made a dirty mess, so I knew I had to get a compound of uranium that was not going to react with water or anything else.

I looked in the various books and I found UF6, uranium hexaflouride. Then I looked into how this was made, and in the past, it had been made by reacting fluorine gas with metallic uranium, and metallic uranium was very expensive. I studied the matter further, and I found out I could make a UF4 from cheap chemicals and that it could be dried and then I could react the UF4 with fluorine. Fluorine is a very reactive gas, and so you need to be sure you can contain it. Whatever you’re going to heat up and put it in the equipment, you got to be sure that your equipment is going to be able to take it.

I found out that nickel would handle it. I found out that at lower temperatures, copper would work. Pretty soon, I began to assemble some columns with a hot wall of nickel and a cooler wall of copper. Turns out that uranium hexaflouride melts at 64 degrees Centigrade, so that had to be the cold wall. When people at the Department of Terrestrial Magnetism, where I was working found out that I was working with uranium, they didn’t want me around because they had been conducting precise experiments on proton, proton scattering, nuclear experiments in which they couldn’t stand to have much of a background. They didn’t want any help with particle background and they didn’t trust me. But they didn’t kick me out entirely. They just found a different place for me to work, namely the National Bureau of Standards, which was on Connecticut Avenue at the time. 

At that time, you couldn’t buy fluorine gas, you had to make it yourself. But I had the capability of machining and putting together the necessary equipment to make a Fluorine generator, and I did. I also determined that, while the ordinary metal tubing that you can get generally has some oil or grease on it, by treating it with fluorine—fluorine is more reactive than the UF6—you could clean the metal tubing. 

At any rate, I found that I could make equipment that could withstand the high temperature uranium hexaflouride with the nickel hot wall and the copper cold wall. Very simple equipment, just three concentric pipes. I was fortunate in that I knew Alfred Nier of the University of Minnesota, and I built a small column which I operated at the Bureau Standards. It was twelve feet long, and the degree of separation is sensitive to the dimensions of the column. By luck, I got a dimension that were not too far away from optimum. It was not nearly optimum, but it was close enough to optimum that I got an effect.

Once I got an effect, it turned out that Lyman J. Briggs, who was Director of the Bureau of Standards, was head of a federal committee. He had been appointed by President [Franklin] Roosevelt to head the Uranium Committee in the early days, and he had on his committee Ross Gunn of the Naval Research Laboratory.

Ross Gunn had decided that the future of submarines lay in getting nuclear propulsion for the submarine. He had decided that early, because when a typical submarine in those days had to come up, and radar was being developed to be so effective that it could be spotted. A submarine was vulnerable to attack when it surfaced. On the other hand, he could visualize a submarine which could stay underwater. You couldn’t find it, and it could stay underwater a long time.

When he heard that I had had a small separation, he was for having me go to the Naval Research Laboratory where he had better, bigger steam facilities. So I went. So in something like the first of June or the first of July, 1941, I went down to the Naval Research Laboratory. Then there followed the series where I built and found out the optimum spacing. I built longer columns. I built more of them.

That ultimately led to a decision by the Bureau of Ships to build a 300-column plant at Naval Boiler and Turbine Laboratory at the Philadelphia Navy Yard. That, in turn, ultimately led to the building of a 2,100-column plant at Oak Ridge, so called S-50 Plant.

I had been the first man advising Lyman J. Briggs about nuclear physics matters, but when I departed, he needed another advisor. Since he was the number one federal person at that time, he was able to ask Gregory Breit, quite a distinguished theoretical physics person, to come and be his advisor. Gregory Breit was, you know, they have these inner circles, and Gregory Breit knew what was going on in general. He knew Oppenheimer, and he knew what was going on at Los Alamos, and so he also knew what I was doing. It wasn’t too long after that, that he—I got to think about the sequence here.

But at any rate, at one time, the word was brought out to Oppenheimer that here was a method that was working. This was at a time when the other things weren’t working at all. I was in the lead at one time on this business, me myself practically, with my own hands. [Laughter] The result was that very early in the game, General [Leslie] Groves did come to the Naval Research Laboratory. For some reason or other—I guess maybe he didn’t like the looks of my boss, and there was of course a Navy/Army rivalry and so on—nothing came of it.

I think it was later on that I got the word—a year or two later—I got the word, things had progressed. We had got the plant moving in Philadelphia, and there had been more progress in the separation. In the meantime, those other people hadn’t achieved as much as they might. It was true that Lawrence had got his separation scheme going at Y-12 by then to a degree, but the gaseous diffusion plant still wasn’t working well.

I got word one day that I was to go to the Warner Theatre that evening, and at eight o’clock I was to go to the balcony. At eight o’clock I would be approached by a man who would identify himself. I was to have a summary of the status of the liquid thermal diffusion project and what it was doing. I went and I met [William] Deak Parsons. Deak Parsons went out to Los Alamos and very shortly thereafter, General Groves and some advisors appeared at the Naval Research Laboratory. Very shortly thereafter, the order of General Groves was, “Make a Chinese copy, 2100 columns. Make a Chinese copy, of what they have at the Philadelphia Navy Yard.”

In the end, what happened was that by then the Y-12 was beginning to be in production. The point was, if you could have the entry feed somewhat enhanced in the Uranium-235, that would increase the amount of product you could get. It would not only increase the amount of product, but it would increase the purity of the product. Because if you had a more enriched feed, then you could expect at the top a more enriched product. 

One of the problems, as I think about it now, one of the problems was the separation between the nickel and the copper was only .025 centimeters. .025. If you didn’t have tubing that was perfectly round, or that varied so that the diameter of the two tubes didn’t match properly, you wouldn’t get the optimum production.

In fact, what they did was they put that plant together in a remarkably fast time, and the so-called S-50 Plant was put in operation. It did make something of a difference. I think Congressional testimony ultimately said that it shortened the war by seven days. It was at a cost of twenty-five million dollars, and the cost per day of the war was approaching, I don’t know, something like a billion dollars, plus the number of lives lost and so on. It made a difference. Not an enormous difference, but it made a difference. 

Kelly: Do you remember how hard you worked?

Abelson: I wasn’t doing any forty-hour week, I can tell you that. I was at it more than twelve hours a day, seven days a week.

Kelly: One of the other veterans said you were known to sleep on the racks in your storm coat.                     

Abelson: I was up in Philadelphia Navy Yard. I wouldn’t go home or go to bed somewhere. I would just sleep right there.

Kelly: Did you much any contact with the people working on Y-12 or K-25?

Abelson: Practically no contact, very little. In part, that was a deliberate policy to avoid a lot of crosstalk. But in my case, I knew what I wanted to do. In general, that meant I didn’t have any time for a lot of chitchat.

Kelly: Looking back on the Manhattan Project, what’s your impression of the accomplishments during those twenty-seven months?

Abelson: In wartime, this was one of several major projects. You know, in peacetime, it would take ten times as long to do what was done, ten times or more, than was done during that war time period. When people know, “Here is the objective and this is what needs to be accomplished,” and they are putting their minds to it and their efforts and their thoughts, there’s almost a lesson to be learned. What happens when people are dedicated to achieving an end, and where there’s teamwork to do it.

Kelly: You probably worked closely with the Ferguson Company?

Abelson: H.K. Ferguson. Yes, yes.

Kelly: The stories are that Groves started out with six months [to build the S-50 Plant] and then cut it to four, and then cut it to ninety days. They still beat it. How did it happen, that they were able to do that?

Abelson: Well, at that time, the equipment for my thermal diffusion plant was very simple, so it was a matter of getting the priorities for the supplies. Groves could get them the absolute top priorities for the supplies. When you had that, then it was just a matter of getting the forces on hand and doing it.

Kelly: They were probably working the same kind of seven-day shifts?

Abelson: Oh, yes. Everyone was doing the best they knew how.

Kelly: Since you have spent your life in science and policy, how do you see how American science might have been changed during that period and over the next fifty years?

Abelson: One of the realities that soon emerged was the Cold War. The Cold War meant that we had to worry about the Russians and what they might do. This country responded accordingly by setting up certain laboratories and certain activities. We live in a changing world, and you have to adapt to whatever the boundary conditions are. You have to be responsive and do the best you know how. In part, of course, it depends on the attitude of the public. If the public is really concerned and worried, then that spreads to all the citizens, including the people who can do anything about it.

Now, at this time, there’s some concern about bio-terrorism, for instance. There are all kind of ways in which this country could be attacked. The public can’t very well evaluate it. It depends on, to a degree, what the communicators tell them, and sometimes communicators don’t get it straight. At any rate, that’s a complicated system with many points of interaction.

Kelly: To what extent do you credit the leadership of Robert Oppenheimer, General Groves, and some of the other people whose names have been in the limelight? Who were the forces behind the success?

Abelson: Well, I wasn’t at Los Alamos. I really don’t know. My impression is that there were assembled at Los Alamos a very talented group of individuals. For instance, they had Enrico Fermi there, and they had Hans Bethe, and [Edward] Teller. Then they had some younger people who were very, very bright. All I know is that they had first-class people. I’m not surprised that they did a first-class job. 

Kelly: At Oak Ridge, would you say they had the same caliber? 

Abelson: At Oak Ridge, in the separations work, there were some fairly good people at Oak Ridge, for instance in the Y-12. Of course, the big development of gaseous diffusion was done at Columbia University. I never really knew that crowd, so I can’t evaluate them, but in the end they delivered the goods a little slow.

Kelly: It seems that Groves’ strategy in trying to look at the four different processes. He had many different companies exploring different aspects.

Abelson: That was the sensible thing to do. You will do better in this world if you get a little competition going, and some alternatives.

Kelly: Well, I guess looking back on it, are there any other things that you think would be helpful for future generations to understand about what the experience was like? Or what you felt about it, or what lessons we might learn from it?

Abelson: I suppose if I were to make any recommendations, it would be that if this country wants to have its best chances of succeeding well in the future, it better see to it that its science and technology is top-notch, because if anything, there will be more developments.

For instance, in this matter of bio-terrorism, I’m not at all sure that we’re doing all that we should be doing about that at this time. It has a possibility that you can infect an awful lot of people and not really know what was happening until all of a sudden your hospitals were overloaded. And then when you didn’t know what was going on, all of a sudden, the published reports and so on would have everybody just in an absolute tizzy.

Kelly: Yes. Well I certainly think the stories of the Manhattan Project and how the scientists contributed so much not just in the Manhattan Project, but in radar and other developments and how they shaped the course of world history, is a dramatic one. Hopefully if we can get that out, there will be more students who might see how important science is, and technology.

Abelson: I was telling people that I had been around at the very early moment of the proximity fuse. The proximity fuse was very important in the naval war in the Pacific and then was important in Europe. What had happened there was that Merle Tuve, a distinguished nuclear physicist, had been looking at the TV or radio or whatever, and noted that the Germans were flying planes over England and dropping all kinds of bombs on London and Coventry. He was absolutely convinced that an anti-aircraft defense was absolutely essential.

If you wanted to have an anti-aircraft weapon at that time, you had to be able to shoot some kind of an electronic device out of the gun. The acceleration in the gun is 20,000 times gravity, g, 20,000 g. Any equipment that you were going to be firing out of the gun had to be specially designed to withstand that force. 

Merle Tuve was fortunate in that one of his associates and my associates was Richard Roberts. Dick Roberts had had ROTC training, and he had dealt with those weapons. He had dealt with artillery a bit, so he was at home with it. He molded a lead circular ball with a hole in it to put a radio tube in. He searched around the laboratory and he decided which was the most likely tube that they had there to withstand the shock. He put this tube in lead, dropped the lead from the top of a building down to the concrete below, and then measured the indentation of the lead. Then he could calculate what kind of acceleration that that tube underwent in order to withstand, and what it had withstood. It turned out that in that particular case, it was something like 2,000 g. 

We figured that if you could pick a tube that can withstand 2,000 g, you could use your brains and design a better tube that could stand 20,000 or more. In short order, they had permission from Vannevar Bush to seek to develop a proximity tube.

Kelly: And how long did it take?

Abelson: Actually, the first proximity fuses were tested about a year and a half later. What happened was that they took them out on a ship. They had some flying targets, and they were so successful in knocking down those flying targets, that they wouldn’t let them go back to port. Those sailors that were on that boat, they didn’t get a chance to communicate to anybody. The whole ship went off to the East Pacific or West Pacific. Shortly thereafter, one of my friends, also who had also been at DTM—[James] Van Allen, Van Allen of the Van Allen Belt, later—Van Allen went out and they used those things against the Japanese Kamikazes. But they didn’t use them in Europe right away, because they were afraid that the Germans would succeed in copying.

But later, nevertheless Tuve provided a sufficient number of fuses. When the Germans launched the buzz bombs toward the end of the war against London, the British were able to use those proximity fuses to knock down about 98% of the buzz bombs. The Germans gave up on that. Then at the time of that final offense—the Germans launched a big offense—they knew they had to use them for the ground war. The poor Germans didn’t know what was hitting them. They would be in concentrations, and they would shoot these proximity fuses just horizontally. Where there’s a concentration of tanks or metal, the thig would explode. It was very demoralizing. “In the middle of the night, how can those guys know where we are?” Etc, etc, etc. It was very demoralizing for the Germans, and it was crucial in bringing that war to an end.

Kelly: One last question, because it has to do with Carnegie. Were you around for that famous experiment with the Van De Graaff accelerator where Merle Tuve and others tried to create what Otto Hahn had done?

Abelson: No, I wasn’t there. Dick Roberts again was a key guy. I was at Berkeley at the time, it was in ‘39. In fact, another thing that Dick Roberts did that was very important, was very shortly thereafter, he found out that uranium fission was accompanied by delayed neutrons. It was the delayed neutrons that give you a reaction, a reactor, that can be controlled for making civilian nuclear power.