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National Museum of Nuclear Science & History

George Cowan’s Interview (1993)

George Cowan was a physical chemist who joined the Manhattan Project in 1942. In this interview, Cowan discusses the Soviet atomic program and their effort to build a nuclear bomb. In 1949, he helped convince U.S. government officials that the radiochemistry of air samples taken from the atmosphere proved that the Soviets had detonated their own atomic bomb, rather than what many assumed was just a peaceful nuclear reactor problem. Cowan also discusses Operation Crossroads, where he helped take air samples during atomic tests at Eniwetok Atoll in 1946.

Date of Interview:
June 8, 1993
Location of the Interview:


George Cowan: What you’ve learned from the Russians, for example?

Richard Rhodes: The main thing I have learned is that their first bomb was a carbon copy of Fat Man.

Cowan Cowan: Well of course. I knew that in 1949, about the middle of September of ’49 because we analyzed the debris from that and it was clear that it was a carbon copy.

Rhodes: Down to the fine measurements.

Cowan: It wasn’t surprising.

Rhodes: I have seen one of the major documents that Fuchs passed to them and there is a detailed description of the initiator, for example—exactly the dimensions and the pieces and so forth—and an equally detailed description of the various components of the shells of the Fat Man. It is a remarkable story. I think I have assembled as much as I am going to get from them and that is one component of the book. The Las Alamos component is also a very important part of the book.

Cowan: I used to talk to some of those Russians too and that was a time when nobody talked very much.

Rhodes: I talked to Victor Adamsky, who was a bomb designer. I talked directly by fax to Yuli Khariton, who ran their program and who is now 89 and just retired from their lab, and three or four other people affiliated at one level or another. [I also spoke with] Lev Altshuler, who was one of their implosion experts.

Cowan: Well you got much closer to the source than I ever did. One of the people that I talked to was a physicist who was doing ballistic calculations on the front with the Germans about the time that they got into this crash program, which came immediately after the reactor went critical at Stagg Field. That was when Stalin and the Russians were fighting for their life and decided they had better darned well get into this business. He feels it saved his life because his life expectancy where he was at the moment was apparently a week or two weeks and so he was called back to Moscow. They started their first laboratory at that time. It was in early ’43.

Rhodes: Yes. [Igor] Kurchatov and his group. What was his name? Do you recall?

Cowan: Yes, let’s see. He was the spontaneous fission guy. My memory is getting bad. It starts with an “F.” I will think about it. When I start deliberately searching for it.

Rhodes: I remember talking one time with Stan[islaw] Ulam just before he died. He had just come back from a conference on computers and the brain, and he was thinking about memory. He said, “You know, memory is a kind of a hound dog that you send out and it sniffs around and finally comes back with the word. [Laughter] Except the dog gets slower as you get older.”

Cowan:  He was quite interested in the brain. I remember he used to go to New York and talk to—who is the guy who won the Nobel Prize? 

Rhodes: What I would like to ask you is to talk a bit about your work here. I am very interested in trying to retell the story of the Crossroads test.

Cowan: Crossroads. Okay.

Rhodes: And the development of the weapons technology after the war.

Cowan: Yes. Crossroads was ’46, right? 

Rhodes: You were out there weren’t you?

Cowan: Yes. Right.

Rhodes: You are a radio chemist?

Cowan: Yes.

Rhodes: What did that involve? You were here during the wartime?

Cowan: I came here immediately after the war, actually. I had been at the Met Lab during the war and had traveled a great deal. I was single and they sent me across what they call the compartments. I was a troubleshooter or something, I don’t know. I went to Oak Ridge and MIT and St. Louis Washington University and various places where things had to be speeded up. I don’t know why but it usually speeded them up. One of the magic formulas was, you could call the White House and get them to talk to people or somebody in Washington and rather than be faced with that they usually speeded things up, so it gave me a feeling of immense power. I was about twenty-two or twenty-three years old. [Laughter] I could badger these executives. That was what bird-dogging amounted to— having an over-riding priority for everything.

Rhodes: Who were you under at the Met Lab?

Cowan: Actually, I went to work for Herb Anderson and started machining graphite for the Stagg Field reactor. I said I wanted to do something else and he thought I didn’t have any sense of history and that I should have stayed with the team. He was the guy that said, “Well, go on out and make sure everything gets here on time.” So that was when I went to St. Louis, when they were starting some uranium production at Mallinckrodt and also bombarding uranium to make plutonium at Washington University.

Then there was a big thing about getting uranium metal, which was going to the center of the reactor out of MIT. It was coming down from metal hydrides where they made this powder, which highly pyrophoric and caught fire the moment you opened the can and poured it into an induction furnace. I learned how to do that with CO2 but in the course of doing that they condensed water in the humid atmosphere at MIT and they would shoot the temperature up past the vaporization of water so fast with this high power induction furnace that it would explode and they thought the uranium metal was exploding and they were just exploding water. Anyway, that is the sort of thing they would do; they would bring in a new guy and he would say, “Well, this is obvious.” But that was all that was needed, and they would settle that problem.

I had a series of, on the surface they looked like striking successes but it was all very, very simple. [Laughter] Anyway, that was what I did. Then I became a plutonium chemist and went down to Oak Ridge because they couldn’t figure out how much plutonium they had and I had to vote with two guys that had different answers and I got a different answer than they did [laughter].

Rhodes: This was plutonium coming out of the big air-cooled reactor down there?

Cowan: Yes. They had the first small reactor, so when they first started getting macroscopic amounts of plutonium it was very difficult actually to decide how much there was and so we had a big conference down there and I spent several weeks down there. I have to look in my calendar or diary to see where I was half the time [laughter]. 

Then I came here because I met a young lady chemist that came to Los Alamos before I did. I went to Columbia to work with John Dunning. That was on another compartment completely, which was uranium-235 separation. They normally didn’t let people travel between them, but anyway I went with John and worked with really first-class people. That is the sort of thing I liked. I was working with a team that included Madame [Chien-Shiung] Wu and Jim Rainwater and people like that and learned a lot about time of flight neutron spectroscopy, which I used the rest of my life. I did research with bombs using it. The interesting thing was a bomb was a prompt burst of neutrons and then you could do time of flight neutron energy separation because the fast ones arrive first and the slow ones arrive later, so we just spun a wheel with targets on it past a slip and you could get reactions around the wheel as a function of time, so I did that.

Anyway, I married the young lady in Santa Fe and took her back East with me, but she liked New Mexico so she brought me back here in ’49. I still refer to her as my present wife so that she won’t get too comfortable [laughter]. Gosh, we’ve been married forty-seven years. She is drifting around. I will get her in here. She likes gardening and that sort of thing so she is probably out in the garden.

Rhodes: We saw the nice garden out in front. What did you study here? You came here when?

Cowan: Well, I first came in December of ’46 and shortly after I came I was asked to go on Operation Crossroads and join that team, which is what you say you are interested in. I think I left early in June or thereabouts of ’46, and I came back in September or late August or something with a king’s ransom of money. They paid us triple-time or something; that is why I went. I had already decided I was going to get married and go back to graduate school and finish my degree. So as soon as I got back we were married and I went back to graduate school.

Rhodes: Where did you go?

Cowan: Carnegie Tech, which is now Carnegie Mellon. I met Jake Warner during the war and he had gone back as dean of the graduate school and he offered to make me an instructor, which was a little better than the usual pay and hire. My wife was his personal assistant. I had been planning to go back to either the University of Chicago or Princeton, but neither one of them particularly wanted me so I went back to Carnegie.

Rhodes: So while you were going around during the Second World War threatening the White House you didn’t have your doctorate yet? [Laughter]

Cowan: No. I had hardly started. I graduated in June ’41 and went to Princeton in September ’41. I had been planning actually to go to graduate schools in economics at MIT and probably would have ended up with Paul Samuelson or somebody, but my draft board was taking a lot of interest in me at that time and they had just started to draft and my physics professor said he thought I would make a good physicist. I don’t know why because I flunked—I didn’t really flunk—I got a B or something in physics. But he had a friend at Princeton who needed somebody and he thought I would be a good guy because I knew chemistry and physics, and so I went down there. His friend was Eugene Wigner.

Eugene Wigner hired me. In fact, Eugene Wigner said he didn’t know whether he wanted me or not but he asked me a question. I said I didn’t have the slightest idea what the answer was, but if they had a good library around there I would come back in an hour and tell him what I learned [laughter].

So I did that and I told him what I had learned and he said, “Do you want to come and work for me?”

And I said, “Fine.”

So I got $75 a month and graduate courses, that sort of thing. Anyway, the war started right after that and then it was a seven-day per week job. I was the only guy in chemistry and there were a bunch of physicists and they worked three shifts and I worked two shifts.

Rhodes: Putting together CP-1?

Cowan: No. We were using the cyclotron at Princeton.

Rhodes: Oh earlier, I see. 

Cowan: This was at Princeton before we went to Chicago. Herb Anderson was at Columbia at that time. He went to Chicago from Columbia. I was with Eugene Wigner and Ed Creutz. In fact, the two people I originally worked with were Wigner but then Ed Creutz and Bob Wilson, who went to Cornell after the war. You know Bob. Then Bob Wilson went off with—the other way to separate uranium-235, which was electromagnetic separation. So Ed Creutz and his team, which included me—Wigner of course was the director of that—were measuring the resonance capture cross section of neutrons on uranium in the epithermal region because the reactor would not be kept at room temperature and the capture cross section uranium-238 seems abnormally low at room temperature. They were afraid that if they elevated the temperature in the reactor that it would be very much higher. 

In fact, it was. The resonance integral in epithermal neutrons is very much higher than the thermal capture cross section in uranium-238. It turned out the structure was such that it wasn’t catastrophic and nature in that respect was neither kind nor unkind because it could have easily been catastrophic in which case there would have been no graphite reactor unless they kept it cold. It was very difficult to keep the graphite reactor cold at any reasonable production level. It turned out that the resonance capture cross section was still not high enough at a practical, working temperature to poison the chain reaction. That was a critical question, which most of the histories do not cover but it was a very critical thing and needed to be known before they could feel confident that they could design a production reactor.

We got the answer to that pretty much working around the clock by around March or April of 1942. It turned out that it was okay. The thing you had to do was to heat the uranium in a furnace and run neutrons through it at 1000 degrees Centigrade, and they insulated this furnace with carbon. [They] failed to keep the carbon from producing high levels of carbon monoxide, so when I passed out they had to figure out why that happened. 

I was working on the furnace and Ed Creutz brought in a canary, and he read that you used canaries to find out whether the atmosphere was poisonous or not. But he had to calibrate it, so we covered him and the canary (which was in a cage) with a blanket and ran a tube with a gas line in there and an electric light so we could see what was happening to the canary. Then we heard this cry of triumph, whipped off the blanket and the canary was lying flat in the cage at the time [laughter] and Ed was still conscious so that calibrated the canary [laughter]. So we put the canary next to the furnace and the canary promptly passed out, proving we had to do something about that.  We just got more air in there with fans blowing. So much for the stories.

Rhodes: Back to Crossroads.

Cowan: Yes, Crossroads. 

Rhodes: [Klaus] Fuchs was involved?

Cowan: No, he wasn’t involved in Crossroads.

Rhodes: He was asked to stay on for a while to do some work that had to do with Crossroads.

Cowan: That may well be. He certainly didn’t go overseas.

Rhodes: No, he went back to England.

Cowan: He may have been doing some design work. On the other hand, I am not sure what the devil they were designing because they were using the standard design.

Rhodes: What was the point at Crossroads? Was there a serious point to Crossroads other than to blow up some Navy ships?

Cowan: I don’t think so. I think they wanted to get rid of some ships. The Navy was concerned about their own vulnerability and they particularly wanted, I think, to stake out their role, and so they ran the first military exercise but it was a joint exercise because it involved the Air Force. I think it just involved the Navy and the Air Force. I still have some stuff that I brought back from that operation; if you want to look at it I can bring it out for you.

Rhodes: Yes, I would. I think Lewis Strauss proposed Crossroads, from what I have seen so far.

Cowan: I see. I never was senior enough to find out.

Rhodes: He was an Admiral.

Cowan: I see. He proposed it, okay. 

Rhodes: I think you’re right—to get the Navy involved in the bomb. 

Cowan: I think that they felt left out. It was an Air Force exercise or something.

Rhodes: From the Russian point of view, it was a disaster. It was a deliberate waving of the bomb. They were much threatened by it.

Cowan: They would have felt very threatened by anything at that time because we had the decisive weapon and they didn’t have anything. I don’t think they trusted us, particularly remembering the history of the history of the First World War when we tried to wipe out the Russian Revolution. They probably figured that now that we had a decisive advantage, we would be landing in continental Russia at any time and trying to wipe out Moscow. I am sure they felt very much threatened.

Rhodes: They did. They felt as if they put together a huge Army for the war and had a great victory and there were ashes in their mouth.

Cowan: Well, that is totally understandable.

Rhodes: Yes, it is understandable.

Cowan: In fact, it was even realistic. There was a war party, as you know, in Washington at that time which said, “Well, we should take advantage of things and just roll over these people.”

Rhodes: We really didn’t have the arsenal to do that yet though really, did we?

Cowan: We didn’t. Also I think we should give credit to some of the people around at that time. They were not a power-hungry lot. Things have gone a little bit beyond that. The Cold War didn’t really start, I guess, until when? ’48 or so? When was the real confrontation in Greece and Turkey and thereabouts? At least I was back in graduate school and out of touch. When I went into graduate school, which was ’46, it was still possible to think of the Russians as friends and allies. When I came out in ’49, things were highly polarized. The environment had changed entirely. My feeling is that it [the relationship between the United States and the Soviet Union] had deteriorated very rapidly somewhere around in ’47.

Rhodes: Yes. I think that is true.

Cowan: The confrontation really had to do with whether or not the Russians were going to move into Greece. The line had been drawn and they were trying to move past it.

Rhodes: Although I think you could make a good case that the really decisive, defining event in the Cold War was their test of the nuclear weapon. 

Cowan: In ’49?

Rhodes: Yes. After that we were much more deeply threatened by them. If Edward Teller’s wonderings are a kind of barometer for the Cold War, that is when he decided to come back to the lab.

Cowan: Well Edward, of course, had constructed—I don’t know whether that memorandum is still around—but he had constructed an argument, which was wrong, but Edward was always a genius in the sense that he felt they never would have done a graphite reactor. They would have gone to a heavy water reactor, which in a country with a lot of electricity could be done. It was not the easiest way to go. The Canadians thought of that as a way to go, and of course the French were working on that. When they were invaded, they were trying to accumulate all the heavy water and then there was a lot of counterintelligence, which told the Germans that was the only way to go. 

Anyway, he [Edward Teller] said they probably went to a heavy water reactor, which has a characteristic of excess neutrons, which means that you can make tritium by putting lithium in it. Therefore, they had tritium and therefore they were further along the line to a thermonuclear weapon than we were and so forth and we had better get cracking. I think that is what his memorandum said.

Rhodes: That turned out to be, by the way, terribly wrong across the board [laughter]. I have got [Igor] Kurchatov’s notes on the espionage that he received from our side, and he did indeed go for a heavy water reactor as a secondary program.

Cowan: They had been told the graphite reactor was the way to go—the fast way to go.

Rhodes: Their first reactor apparently was a copy of one of ours.

Cowan: Sure. Right it was.

Rhodes: When you went to hydrogen weapons or hydrogen-like weapons their first one, Joe-4, was lithium deuteride. They didn’t go with tritium and I don’t think they got into boosting at first, for example.

Cowan: You say they didn’t have tritium—now you are telling me something I don’t know and I’m prepared to argue about that. You say they didn’t have tritium in their Joe-4?

Rhodes: They say they didn’t have tritium in their Joe-4. They say that it was made with lithium-6 deuteride and uranium—concentric spheres of some sort of arrangement.

Cowan: Yes. I am sure I understand that part of it.

Rhodes: I am not sure when and at what schedule they developed boosting. Presumably they did develop boosting but they have never talked about it.

Cowan: Did they have a heavy water reactor prior to Joe-4?

Rhodes: I don’t know.

Cowan: Because I would have guessed they put tritium in it.

Rhodes: You would think so.

Cowan: I think—that was a long time ago.

Rhodes: I know this—in’46 Khariton and some others put together a paper that they presented to at least Kurchatov and maybe to Beria and Stalin arguing for the research into a thermonuclear. It specifically mentioned various D-T reactions. They were aware of tritium. They would like to brag that their weapon was a deliverable weapon, that Joe-4 could have been dropped from a plane.

Cowan: It was what I would call a table thumper. I think that they were told—this is my own notion, I cannot guarantee it—but I would have thought when the November ’52 thing was successful and publically obviously successful, they had to produce something that would make this country stop and think and they had to do it as soon as possible.

Rhodes: That is my theory too.

Cowan: They couldn’t have engineered it. It may have been in principle deliverable, but it certainly wasn’t a military weapon. It was something that—we got this.

Rhodes: Khariton said in a talk recently that the Joe-4 was a size comparable to Fat Man.

Cowan: Yes, it probably would have been.

Rhodes: But of course, Sakharov jointed the program in ’48 specifically as that was their first thermonuclear group. He didn’t join the program to help them develop fission weapons, as far as his memoirs say. He signed on to the beginnings of a thermonuclear group, so there was work going on at some level.

Cowan: I really would like to know, because my impression was that there wasn’t much lithium-6 around this thing. I am trying to remember now how sophisticated we were at that time, but it would have been a necessary product of lithium-6 if it had been there and if it had been at all successful. All we saw, I don’t know how far I can go even now with these things, but I was as much using radiochemical data, I was as much involved in reconstructing what that thing was like as possibly more than most people because I had been in charge of coming up with measures of thermonuclear performance for our first thermonuclear device.

Actually, we had done other things as you know in May of 1952, and I had been in charge of putting things on that and coming up with things for the Ivy [tests]. The problem with thermonuclear devices is that from a radiochemical diagnostic point of view, the products of the reaction itself are neutrons and helium, and nothing that shows up very well as a diagnostic product. So you have to look at secondary things and what do the fast neutrons make, and if you get more sophisticated what do deuterons make, and so forth.

I personally was convinced, although as I recall that data were not all that complete at that time and the analyses were not all that sophisticated—they got better later on—I was personally convinced that it was a cryogenic thing, that it didn’t have lithium-6 in it. I can’t remember whether I could be talked out of that. I would have to go back and look at the data now.

Rhodes: They are very adamant about that design.

Cowan: They had some lithium. How did they get enriched lithium-6? When was Joe-2? Was it in ’53? They would have had time to do some lithium-6 enrichment, that’s right. That was a pretty sophisticated idea. It was being explored by the United States but after all, the first notion was to do cryogeny. That was the simplest and easiest thing to do, and to use liquid deuterium and liquid tritium. That was not readily deliverable, because although the size of the thing would have been Fat Man, the cryogeny that was associated with it was outside of that, and it is bigger and heavier, although it doesn’t have to be. But certainly the thing they tested, I suspect, was a pretty cumbersome thing, which was the first thing they could put together that looked thermonuclear.

Rhodes: They are so adamant about this design because now they have admitted that their first design wasn’t their design. So it is terribly important to Khariton and the other guys I have spoken with that this was indeed something that they did and that it was something that, in some sense, was “better than” what we did.

Cowan: Have you looked at the first things the French did? The first things the British did? I think you would get a sense of a history of this too. They followed on too. They were looking at what they thought the Russians did. Of course they had lithium-6 available at that time and of course they were He[lium] initiated. In a sense they were all failures. The first thing the Russians did, the first thing the British did and the first the French did were all quite similar, and they were the way that people thought at that time.

Rhodes: Joe-4, by the way, they claim was 400 kilotons, a larger yield than I think we thought. [Hans] Bethe, at least, was surprised at that number.

Cowan: Bethe was surprised at 400?

Rhodes: And was surprised that they could do an alarm clock at 400 kilotons. He said we couldn’t get the squeeze.

Cowan: I am surprised too and I still would like to see the evidence for it. I have to go back and look to see the data now again and review it, but I am quite sure we looked for something that would have said lithium-6 and I don’t recall seeing it. What we did see in abundance was lead-203. That was my suggestion, and we looked for it and I know what that said.

Rhodes: What does that say?

Cowan: Well, that it was similar. No wait a minute—I am sorry, I am getting mixed up. That was Joe, which was their real thermonuclear device. I’m sorry. The first one had lead-203, the other one didn’t—I am sorry, I am confused. No, to my mind Joe-4 was a table thumper.

Rhodes: So you didn’t find lead-203 in Joe-4? They claim about a 15% to 20% fusion yield for Joe-4, which is a respectful yield.

Cowan: Again, this is a long time ago. Okay, look. If in fact they say 400 kilotons and that kind of a fusion yield and they had no tritium, then it was a very respectable device.

Rhodes: I don’t know the tritium but I will do this: I am in touch with Khariton. We send faxes back and forth and I ask him questions, and I will ask him. They seem to be willing to answer.

Cowan: If it was loaded with tritium, then it was quite understandable, everything you say. But it then means they didn’t have enough tritium to make these things. I mean, they took all the tritium they had and put it in there. To me, that is not a military device. It is a table thumper. If it was lithium-6D, then it was a thermonuclear device. I am just talking in hard, stockpile terms. They couldn’t have stockpiled Joe-4.

Rhodes: The truth is they didn’t follow up, once they came across the Teller-Ulam two-stage design.

Cowan: They dropped it because they were buying time is what they were doing, and then they could conduct a reasonable research program to produce something that was a weapon, while the mystery persisted in the West as to what the hell they actually had. As long as that mystery persists, that sort of pools the ardor of the war party, unless they can assure the President that these guys have no thermonuclear retaliatory weapons, which they would have a tough time doing because they had already done Joe-4. But I don’t think Joe-4 could have been long-term. I don’t know. Again, I am just talking from convictions more or less that hardened over the years about what they actually did.

Rhodes: Were you involved in tracking their tests? Is that part of the work that you did here?

Cowan: Well I was a member of the Bethe panel, so if you were talking with Bethe our sources of information are the same, except that when we did the radiochemistry, which the Bethe panel paid so much attention to, I was closer to those numbers than Bethe was. So far as he was concerned, they were things that we told him and he had to interpret them.

Rhodes: Did you work on weapons development here at all?

Cowan: I worked on weapons testing, which was the diagnostic aspect of weapons development.

Rhodes: Oh sure. Of course. 

Cowan: Theoretical design, fabrication, testing, diagnostics. I was on the far end of the diagnostics part.

Rhodes: So you went to the Greenhouse series? One of the points of this book will be to try to talk about our development of hydrogen weapons.

Cowan: Yes, I was at the Greenhouse series. I had to sit with the weapons designers in order to figure out what the diagnostic tests that would measure thermonuclear performance would be. There was really only radioactive debris tests that would measure secondary products that would give any detail other than the total yield. The total yield came out of the measurements the physicist made generally, but we could also deduce the total yield from radiochemical debris. But the first measurements were always the fireball tests, which you may or may not be familiar with, for total yield. 

For the fireball, they take fast photography of the fireball, and the gamma radiation produces fluorescence around the bomb immediately. It escapes very quickly and then a shockwave escapes. When the shockwave catches up with the gamma-induced light and passes it, the initial brilliance, which is blinding, dims because now you are looking at a shockwave that is coming towards you, which is more or less opaque, and the time in which that dimming occurs is a function of the total yield. I won’t go through the mathematics because it is hydrodynamics and radiation transfer and propagation and so forth, but there is a theory that was developed. Gosh, I don’t even know who developed all the fireball theory.

Rhodes: Bethe did a lot of it. 

Cowan: I think Bethe did a lot of fireball theory, right. That was the way to measure the total yield.

Rhodes: Then the light comes up again with the second flash, right? So you get the double flash?

Cowan: Then the shock wave dissipates and you look back into the flowing material, but when that opaque thing comes out it dims the glow, then it dissipates, and you are seeing that and so it comes up. That hydrodynamics contained in it is a variable yield.

Rhodes: That is interesting.

Cowan: There was always a so-called fast action photography, which took successive frames fast enough so that you could unravel the hydrodynamics and get a yield out of it.

Rhodes: But then you had to go to your specialty to get more information?

Cowan: Yes. All the rest of the information, particularly with respect to thermonuclear performance because as I said, the information you could get from physics about the thermonuclear performance was quite limited. The detailed information on how things worked came out of radiochemistry. There were mistakes made initially but it gradually got more sophisticated. The detector business that you had to surround the device with and bury in it certain elements, which were activated by fast neutrons.

Rhodes: So some of the diagnostics were actually built into the devices that you were doing.

Cowan: They were always fighting between fear that you would screw things up by putting detectors in and desire for more information. We discovered very early that if we only got a very minimal amount of information, it didn’t do any good because they would prefer to believe that if we disagreed with them that we were doing something wrong, and so you had to be redundant and you couldn’t get minimal information. We were always arguing for redundancy, they were always arguing for minimal, and so you had to make your case and there was a lot of that going on.

Rhodes: Is it straightforward to distinguish between the fission component and the fusion component of a test?

Cowan: Well you can measure the fission component in a very straightforward way, and you can take the total yield and subtract the fission component from that. That will tell you what the thermonuclear component was, if you do the fireball measurement and then do the fission component. There are two fission components and distinguishing between those is important but that is not straightforward. You can get the total fission yield in a reasonably straightforward way and, as I say, subtract that from the total, but it is not clear that you get the right answer by doing that. In fact, it turns out that there are some subtleties about that which you need to take into consideration. 

Rhodes: During the Bikini test, for example, the Crossroads test, what kind of instrumentation did you have out there? Where did you set it up?

Cowan: For radiochemistry?

Rhodes: What you were doing.

Cowan: What I was doing? We set up a radiochemistry laboratory out there in Eniwetok and we had an Air Force team of B-17s, which were drones. They were sampling aircraft and they were operated from a mother aircraft. Each drone had a mother B-17 and they just toggled switches to vector the drone into the cloud to sample. They had sampling tanks and then they would bring it back to another airstrip. Eniwetok was too far away from Bikini. [They brought the samples to] an adjacent island and landed it and those were the air samples. 

There were two tests at Crossroads. You could take air samples in both of them, but one of them was the underwater shot and it was believed that the only trustworthy samples there had to be collected from the lagoon. So there was also a drone ship that went in and scooped water samples from near the bomb site and brought back large samples of greasy, debris-filled seawater. Those were the primary underwater samples. The primary air samples were collected by the B-17s. The fast chemistry that needed to be done was done there. There were also samples shipped back here and there was another rig of chemistry laboratory with the stateside group waiting to repeat our measurements and to do the longer life stuff. Then, of course, we were comparing notes as to what we were getting and what they were getting. 

The Navy put on quite a show because they had quite a press corps out there and it was a public relations thing. It was a disaster for the Air Force because they had practiced their airdrops day after day and week after week. You would talk to the guys when they came back from their exercises and they would say, “Dropped it right down the old pickle barrel.” And then come the actual drop they missed by miles—it was horrible [laughter].

Rhodes: Tibbets has bitter things to say about all of that. 

Cowan: I still don’t know how that happened. I never trusted the Air Force to tell the truth about anything [laughter].

Rhodes: I think Tibbets blames it on someone else being allowed to fly the mission, if I remember right.

Cowan: Well, that was not the first time I saw the Air Force come up with egg in its face. As a matter of fact, I always expected it after that and they very rarely disappointed [laughter]. They talk a great game. Somebody else was flying, you say? That is interesting.

Rhodes: Actually I am sorry, I’m confused. It is Curtis LeMay who complains bitterly.

Cowan: Okay, LeMay. Yes, I would understand that.

Rhodes: He was overruled by someone about who was going to fly the mission because LeMay was in charge of this mission.

Cowan: Right. LeMay was in charge. I remember him very well. Boy, it has been a long time. Let me see if I can find some of this stuff.

Cowan: This is the radiochemistry group that was overseas in front of their laboratory.

Rhodes: Which one are you? You’ve got a moustache.

Cowan: Yes. That came off as soon as I came home and my wife started laughing. 

Unidentified Female: Moustaches are rough.

Cowan: May 28, 1946—I guess that is when I went traveling.

Rhodes: Are these your orders?

Cowan: My orders, my military orders, travel orders. Dick Metcalf, Joe Kim, and myself.

Rhodes: How did you get out there? Did you fly out?

Cowan: We went out with military aircraft, with so-called Green Hornets. They are the C-54s. They flew their own MATs. It was Military Air Transportation system. 

Rhodes: So military orders?

Cowan: This is the B-17 drones. This is pulling a sampling bag out of one of the B-17s. I am the little skinny guy standing more or less in the background.

Rhodes: Was it in fact a bag like this?

Cowan: Yes. There were also filter papers.

Rhodes: Is that a rubberized bag of some kind?

Cowan: It is a rubberized bag, yes, but there were also some other things. Filter papers hung from the wings. I even have this. It has my picture on it.

Unidentified Female: The stripes on the rudder indicate that it is a drone?

Cowan: Yes, the stripes I think were indicative of that.

Rhodes: The airfield is made with pieces of metal that are laid over coral.

Unidentified Female: Bumpity bump. 

Cowan: This came out about the time I was getting ready to leave, I guess. That was on the island.   Eventually I got something signed by Lyndon Johnson.

Rhodes: The Florence Award?

Cowan: That was largely actually for my serving on the Bethe panel with Hans Bethe and a lot of what we call euphemistically foreign technology. This was apparently nominally signed by Curtis LeMay.

Unidentified Female: Interesting—the copy on this photo calls the cloud formation “the donut cloud.”

Rhodes: I am not sure. Maybe it hadn’t been fixed yet.

Unidentified Female: It hadn’t evolved yet.

Cowan: There are a lot of other pictures around somewhere. I thought they might have been in here. I don’t know where they are apparently—in a folder somewhere. There were a lot of photographs taken at that time. I don’t know what I did with the rest of them. I guess they are in my folders somewhere. If you are interested I will find them later, but not now. 

Rhodes: Did you watch the Mike Shot?

Cowan: Yes.

Rhodes: You had seen quite a few tests by them, right?

Cowan: Yes.

Rhodes: Can you describe your reactions?

Cowan: To the Mike Shot?

Rhodes: Yes.

Cowan: Well, I was stunned. It was big. I had been trying to visualize what it was going to be like, and in fact we had little ways to try to calibrate the initial fireball. I guess I would calibrate it by holding a quarter and if that would cover the fireball, it would be less than something. If the fireball were bigger than that, it would be more than something. This again was using fireball and I was using my dark glasses and the question was could I, looking through dark glasses, still cover the fireball with a quarter? And I couldn’t, so I knew it was big. As soon as we could whip off our dark glasses, this was that enormous thing that was bigger than I ever imagined; it would be that blotted out the whole horizon.

Unidentified Female: Where were you?

Cowan: I was standing on the deck of the USS Estes which is where all the scientific personnel were. We had been evacuated off the island. Everybody had been evacuated and we were all at sea patrolling. Then I was taken off that with a helicopter just a few hours after the shot and transferred to an aircraft carrier. I forget what the name of it was. From there I was catapulted off the aircraft carrier back to Eniwetok and from Eniwetok transported back to the United States. I was one of the first two people that were back in the States from that shot. After the shot we came back within twenty-four hours and I was couriering the first samples and the first report of the fireball measurements and a few other things. I had forgotten to change clothes. I got off in a snowstorm in Albuquerque in skivvies. They found me a blanket [laughter].

Rhodes: So you brought that material here to Los Alamos?

Cowan: Yes, the first bomb samples for rapid diagnosis.

Rhodes: By then had people here heard about the yield?

Cowan: Oh yes.

Rhodes: It was evidently a success, right?

Cowan: Teller was getting his first measurements of the yield from the seismic shocks that were being registered everywhere. He calibrated what that ought to be and so he knew it was big. I got the first fireball readings and they were also wired back here so they knew them before, but they got all the data and the measurements and checked for them back in the lab. I took back the tape and measurements with me. Herb Greer was my partner because he was the guy in charge of the fireball measurements, as a matter of fact, so the two of us were in the same torpedo bomber or something, sitting in a two-seater. There was supposed to be one person sitting there and we shared a seat in this thing and learned what it was like to be catapulted.

Rhodes: When you said “catapulted,” you meant literally you were steam catapulted off the aircraft carrier?

Cowan: That’s right. They fling those things off the deck.

Rhodes: I thought that was a metaphor, but you are talking about the real thing.

Cowan: It was a steam catapult.

Rhodes: How did you collect samples on the Mike Shot? The same way? With drones?

Cowan: No, by then they had given up drones. They were using manned aircraft with a special allotment of radiation for the crazy pilots who flew through the cloud.

Rhodes: Similarly with filters?

Cowan: They had gone to manned aircraft. They had been doing exercises and they figured if they did it right, nipped in and out they would take no more than 2R. So they had a whole bunch of pilots, more pilots than airplanes, and each guy would take his 2R. They wore their radiation badges. Some of them would take 15R because they were superheroes or something. They had to get their samples. The worst you could do was ground them. But nominally they took 2R.

I never heard a complaint out of any one of those guys. I have heard all the complaints about cancer and disease from ground troops who were stationed in trenches miles away from any bomb blasts, but the fellows who really took the radiation, I don’t think I have ever heard from any of them, but they took a lot. So did I, by the way. I’m going on seventy-four years old and I told my wife if I ever died of cancer to sue the government and she would have a sure thing, but unfortunately for her I never did [laughter].

Rhodes: Yes, Bob Serber once quietly pointed out to me that the average fallout from the Nagasaki bomb I think was 5R per reader or something. He said, “I don’t think cancer is induced.” In the Japanese, anyone who was there that day is counted as a casualty when he or she dies. We got their numbers up to a half million from Hiroshima now. Bob takes that a little personally.

Cowan: Is that right? It wasn’t that high, you mean, because they counted all the cancers as casualties? Well the fact is, as you know, there is no standard man, so some people do probably get cancers from relatively low radiation and other people just don’t. Fortunately for me, I am one of the people that if I had been on the other side of the distribution probably wouldn’t.

Rhodes: Did you pick up some of the turmoil that was going on around the decision to push they hydrogen bomb program here?

Cowan: Oh yes. That was something everybody more or less participated in at the time.

Rhodes: I have heard that Los Alamos in fact, and it doesn’t surprise me, was in favor of developing the hydrogen bomb.

Cowan: Well there was a lot of debate about it, the notion that it had to be done or it didn’t have to be done. There were a lot of debates about the technical feasibility. That certainly wasn’t clear and in fact, at the time that as you probably know, we went on a forty-eight hour workweek as a crash program. It was more than forty-eight hours. It was like a wartime thing. But at the time that happened, it wasn’t at all clear it was going to happen, and in fact if we continued the way we were going, it wouldn’t have happened. Not at that time anyway.

Rhodes: You mean with the Runaway Super?

Cowan: The Runaway Super, right. Edward understood that clearly, that you have got to get a lot of good people thinking about it before you really understand what you are doing, and then you can come up with a good idea. But at the time it got started, the good ideas were pretty scarce. There was that kind of discussion, a lot of that. And then there were discussions as to whether it was a good idea anyway. I would say that people were fairly much divided about that.

Rhodes: Here as well as elsewhere. What settled the issue? Was it the Teller-Ulam breakthrough?

Cowan: Knowing that it was going to work sure encourages people to go ahead and do it particularly because now whether you believed that it was a good idea or not, the fact that the power was available—I mean, anybody who has a realistic view about the way power gets used by governments knew that you had to do it. That was no longer an option.

Rhodes: Had to do it because Soviets would presumably do it?

Cowan: Despite all of the debates you see, no responsible government would ever voluntarily forego developing a very powerful new weapon if they knew how to do it. That is something that you can talk about if you are not in the government, but if you are in the government it is not an option.

Rhodes: Despite all the historians’ agonies over the decision, I think it is pretty clear that Truman listened to the Joint Chiefs when they said, “We had better do it.” It didn’t sound to me that Truman had much difficulty making up his mind once he talked to the military.

Cowan: Well, you can agonize about it, but in the end if you are the President—you can imagine saying, “Well, let’s not do it.” The man has the reins of power in his hands and to say “Let’s not use that power” means that he has a belief in the altruistic nature of other governments, and that is not realistic. I think that anybody who says that we should set a good example in that respect simply doesn’t understand the situation.

Rhodes: This is one of the mysteries. Talking with everyone over the years from Luis Alvarez, Edward Teller, Bob Serber and others, I have never been able to figure out about what Oppenheimer really meant. Could it be that he really did mean that he thought we should set a good example? He seems to be a more intelligent and realistic human being than that.

Cowan: He didn’t know it would work. He thought if we started doing it, it would simply heat up the Cold War, and he really didn’t think it was going to work. The moment he knew it was going to work he had no doubts at all. It was that feeling that if we get going on one of Teller’s crazy ideas—I am just trying to reconstruct his thinking. He didn’t like Teller’s crazy ideas. He had been bothered with them all during the war, and Teller was a fanatic about H-bombs, and he didn’t think it was going to work. Teller believed in the Runaway Super and Oppie felt it would never work, and that is what he was judging. That is what he was passing judgment on.

Rhodes: And he was right.

Cowan: Well, it might work. It is marginal. If we worked on it for twenty years we might have gotten something to work, especially if we had made a lot of tritium, sure it would have worked. But he [Oppenheimer] had a pretty realistic idea of where things stood at the time and he said, “Let’s not do it. We’ll just heat up the war and get the Russians more concerned about the fact that we want to fight with them and probably precipitate a real war. There won’t be any thermonuclear weapons—there will just be atomic weapons.” I suspect that is what he is thinking about. I can reconstruct that in my own mind. In fact, that is what we were arguing about at the time.

Rhodes: And it is also clear, I think, from the GAC’s [General Advisory Committee to the Atomic Energy Commission] discussions that there really was a tradeoff. If you are going to make a lot of tritium, you are not going to make a lot of plutonium for a while and we wanted to build more fission weapons.

Cowan: Yes, and D+T works easily enough, so you were fairly confident it would work. That is what they demonstrated in May 1952 with Greenhouse. I was there too and that worked fine. I was working at that time with Dick Garwin and Herb York on diagnostics. They were both young people and I guess we were all out there at the time.

Rhodes: Greenhouse George has been described as a very large fission device that was used to set off a very small amount of hydrogen.

Cowan: Which is somewhat like what I think the Russians did in Joe-4. I think it is very much like Greenhouse George. That is what I think. It seems more logical to me then that they would have separated lithium-6 and come up with something that worked that well without putting a hell of a lot of tritium in it. They could have done that too, but in that case they didn’t need the lithium-6. They needed lithium DT, which would be the normal lithium. It would have been a solid. It wouldn’t have been separated lithium. The details are important.

If I was still in that business, I would have been back in Russia finding out what it was all about, but I purposely gave it up several years ago in order to do something else. I make a virtue of my ignorance on a lot of things now rather than my expertise of things I used to do. 

Rhodes: It is hysterically interesting to me to know what they did do.

Cowan: It is interesting to me too, but not interesting enough so that I would have pursued it past the point I did.

Rhodes: Yes. I am getting paid to write a book about it. [Laughter].

Cowan: And I assure you that I will buy the book just as “The Making of The Atomic Bomb.” By the way, that is probably the best piece of scientific journalism I ever read.

Rhodes: Thank you very much.

Cowan: I have read plenty of bad pieces of scientific journalism.

Rhodes: It is disappointing how much journalists don’t try to understand the technology. It is, of course, always crucial. Emilio Segre said to me one time, “You know, all these policies and all these big high-level meetings wouldn’t have meant anything if the cross-section of uranium had been slightly different from what it was.”

Cowan: If capture cross-section of U-238 had been bigger than three barns—and all of those heavy elements were up around 1000 barns, just to give you a sense—it is as though Mother Nature conspired [it]. In fact, when I first learned that the French were talking a natural reactor, I just knew that was impossible because I knew too much. When they found a natural reactor in Africa, I really agonized about what the hell they were up to. That is, one of the things I got into was demonstrating they were wrong, and then very quickly demonstrating they were correct. It turned out that that uranium deposit had been formed two billion years ago and went critical shortly thereafter, and two billion years ago U-235 was 3.5%. It means that if we were around two billion years ago, we would have just scooped up that uranium and made bombs with it, or reactors, because that is what you make reactors with. Now it is only 0.7%, and it was impossible.

Rhodes: You know, the reasons that the Russians didn’t think you could make a heavy water reaction—they didn’t until we were, because they had miscalculated some of these numbers.

Cowan: The capture cross-section of uranium-238—it should poison it. Any sensible person would have told you immediately that it was impossible. It was just this crazy fact that you are sitting between two big resonance peaks of thermal in uranium-238. So you are down in a well, and the capture cross-section is so small that it didn’t poison it.

Rhodes: It was only when Fuchs sent them information about what Hans Halban and [Lew] Kowarski were doing in England in ’42 that Kurchatov realized you could indeed do heavy water reactors.

Cowan: Actually they were doing it even in ’41. They left France in ’40. I met Hans Halban in ’42 and he told me about escaping with all that heavy water in the back of the open touring car with his kids sitting on top of a blanket spread over it.

Rhodes: The Russians had that information then too from England from Fuchs. The first documents they got were the October meetings of a British uranium committee in 1941. They really were plugged in early. It’s amazing.

Cowan: I am quite sure the British, once they understood the importance of graphite, freely let the heavy water stuff leak because they wanted everybody to believe that was the way to go. It was too easy to do it with graphite and it was sort of a red herring, I think. You had to have a good electrochemical industry and a big project for separating the material and that sort of thing, whereas making pure graphite was a nice straightforward industrial thing. 

Rhodes: You know, the Russians—we talked to the engineer who runs their F-1 reactor, their first reactor, which is still in use as a diagnostic tool. He said that their real problem was they didn’t know how to make uranium metal in quantity until after the war, until the Germans helped them. Does that make sense to you?

Cowan: Yes, that makes sense to me because it was really [Frank] Spedding at Ames, Iowa who came up with a pretty good way to make uranium metal. It wasn’t all that bad, but there were things in literature—in fact, that was one of the problems I had to solve for Wigner. I found that the first people who made pure uranium metal were Westinghouse in Bloomfield, New Jersey making lamp filaments. They made lamp filaments of anything they thought might make a good lamp filament,t so they made some pure uranium metal. 

Then we got them to make the first pure uranium metal we needed at Princeton on a crash basis. I can still remember the names of the investors that held that patent, [John Wesley] Marden and [Harvey Clayton] Rentschler, and they were still around and knew how to make it. That was public property.

Rhodes: It was not?

Cowan: It was.

Rhodes: It was?

Cowan: Yes, and if they had access to good enough library they would have found it. That was an expensive way to make it. Spedding at Ames was put in charge of finding better ways of making it and it took him a year but it wasn’t all that big a deal. They just improved on it.

Rhodes: Their first uranium metal came out of one of their metallurgical institutes pretty late in ’44.

Cowan: Is that right?

Rhodes: The first sample. It wasn’t until after the war that they really got going.

Cowan: I am really surprised, and I’ll tell you why. The Russians have always been wonderful metallurgists. Over the centuries they have been just great metallurgists, and I would have thought they would have gone straight to a nice efficient way.

Rhodes: He might have been inaccurate because their real pacing problem was getting enough uranium ore. The first real batch of ore they got was some that was in Germany. We ran over and grabbed some from the Russians, and the Soviets got some from Germany. They ran over and grabbed some that they found in our side. We were going back and forth and Kurchatov told Khariton that 130 tons of high-grade Belgian ore was the first significant component of their production reactor.

Cowan: The first available uranium that should have been available to them—I am trying to figure when. The Germans turned to Joachimsthal in Czechoslovakia. That would have been available to the Russians as soon as they got there.

Rhodes: The Russians signed a deal with the Czech’s in the autumn of ’45-spring of ’46, very quickly, right after the war.

Cowan: Well, they had also invaded Vienna and there was a big stockpile of that Joachimsthal uranium in Vienna because they were doing measurements with it then. A year and a half ago, I talked with a guy who is eighty-four years old who was one of the chemists doing those measurements, and they took me down to this place where they had uranium stored in big ceramic jugs. They were wine jugs actually. They had a big stockpile of it under the University of Vienna campus and they wanted me to take it off their hands. They didn’t know what to do with it.

I was interested in it because it was pre-war uranium, and the last science I did was double beta decay of uranium-238 to make plutonium-238. I got involved in that because I knew how to separate plutonium since 1941 from large amounts of uranium. So we had to separate a few atoms of plutonium-238 from a large amount of uranium in order to measure the double beta decay of uranium-238, and that is what I did at the University of Chicago and just finished that two years ago. In the course of doing that, I was interested in finding some real old uranium that had been around before there was any plutonium anywhere and that had been stored somewhere. I found this stockpile in Vienna. Some of it hadn’t been opened since 1913. It had been sealed. It was being used for separating uranium. Uranium was the big cure for cancer and they were doing it by the old Madame Curie method.

Rhodes: I am surprised the Russians didn’t grab that.

Cowan: They should have. They didn’t know it was there.

Rhodes: They took some 300 kilograms of uranium, whether metal or something, I don’t know because it wasn’t said. This was an Army document that I saw. They liberated 300 kilos of uranium and some of heavy water from an institute in Vienna in ’45.

Cowan: Yes, a lot of it was in Vienna. Why didn’t they take this along with them? It hadn’t been touched. It was down in the bowels of this—

Rhodes: They must not have known.

Cowan: They didn’t find it.

Rhodes: They certainly would have taken it otherwise. That is interesting.

Cowan: I brought back some of it from Vienna, as a matter of fact, and even asked the DOE to bring the rest of it over here. But by then you had to unroll so much red tape to ship uranium anywhere that they just didn’t bother. They said, “Let’s leave it there.” It is kind of interesting because it had never been exposed to fallout. It had no plutonium in it. The only plutonium would have been double beta decay of uranium. 

Plutonium has been around. It was always thought to be a synthetic material, but it has been around in uranium as a result of this natural radioactive double beta decay, which gives you plutonium-238 since forever. In addition to rich deposits of uranium, as you probably know, it gives off neutrons—spontaneous fission makes plutonium-239. Both 238 and 239 existed before they were man-made, but the techniques for measuring them had to be developed.

Rhodes: They spontaneously decay pretty quickly, right?

Cowan: Well 238 is ninety years, yes, so it is short lived. And 239 is 25,000 years. They have to be in equilibrium with something that is making them, otherwise they wouldn’t exist in nature. Plutonium-244, on the other hand, was another thing that I worked on but I took my name off it because I wanted to do it twice. Darleane Hoffman worked for me and announced the discovery of plutonium-244. It didn’t meet my standards for discovery so although I had started the experiment, she found plutonium-244 in nature and that was done here, too. We chased down all the plutonium isotopes.

Rhodes: I’ve seen a kind of poetic description of thermonuclear fireball as momentarily having in it all the elements. Is that fanciful?

Cowan: A thermonuclear fireball? Well the Mike explosion, as you know, made new elements. I will always be ashamed of the fact that I hadn’t predicted that, because I was in charge of predicting everything that Mike thought was going to happen and I didn’t predict it. I’d love to tell you why but if you understand statistics, and I am sure you do, the Mike explosion produced measurable quantities of past californium-252 and probably produced everything that existed that would have existed even for fractions of a second, on up to mass-265 or something. Nature produces these things in the R-process and supernovae. It wouldn’t produce anything much beyond what was produced in Mike. 

At least with respect to Mike, momentarily, the fireball must have included every element. It never occurred to me but it is probably true. It probably included every element that has ever been made by nature, although many of them would have decayed very quickly and so you wouldn’t have proved that they were there, but you can extrapolate what happened in Mike to make that statement, I think. 

The reason why I didn’t calculate—neither did Dick Garwin and Herb York, who are much smarter than I am—that Mike would produce what it did was that—if you know what a Poisson distribution is and what the characteristics of a Poisson distribution are, very simply, a Poisson distribution says—let’s put it this way: if there are 200 million people in the United States and I mail a million letters addressed randomly and I don’t try to eliminate the name of any post office address after I have used it once so that the probability of using it again remains the same, what would be the distribution of letters that would be received at any mailbox? Everybody has the same chance of getting one letter. That is a Poisson distribution and you can solve the problem that way. It is a very simple problem to solve. 

The question is almost never asked this way: if you say there are 200 million citizens and I am going to mail a billion letters, what is the distribution? It has an entirely different shape. The Poisson distribution for small probabilities has a nice, interesting shape. The problem almost never comes up that you are going to have probabilities more than one. There is no such thing as having a probability more than one, but in terms of how many letters you are going to get, there is a probability you are going to get five or ten. In fact, it turns out for that kind of Poisson distribution there is a peak around a multiple number, that you are going to get five or you are going to get six or you are going to get seven, and that will be the peak probability in the distribution. I never saw that Poisson distribution ever come up. 

In the case of Mike, it turned out that there were ten neutrons for every uranium atom because it was enormously—every uranium atom that was ever in there. It was like asking that question, what is the probability that a uranium atom is going to get hit ten times? It never even occurred to me to ask that question. I was calculating what it was going to do on the average and the probability was less than one. But if you mix a little bit of uranium into this big soup, which is just really a neutron soup because it was so efficient and the neutrons themselves can’t get out for a while, then you have to ask this question about “What if there are ten neutrons per uranium atom? What then?” If we had solved that problem we would have said, “Gee, we are going to make a bunch of new elements because we are going to move straight on up the periodic table way past plutonium.” We just weren’t smart enough to do that.

Rhodes: It was a brand new gadget, a brand new situation. 

Cowan: Well you think about these things on the average and then you think about the first order past that and the second order past that, and once you reach the second order you think, “Well, I’ve covered all the probabilities.” This was the tenth order. Proving that you never think of everything. So they found all these new elements in Mike and they did it just by observing how much plutonium had been made and going to the next thing, and it never stopped. One thing after another kept popping out.

Rhodes: It really isn’t too fanciful to say it was a small star, is it?

Cowan: Yes, it was. It was a little different. It is different than a supernova because there the neutron population persists for seconds maybe, which is still a very short time. In the case of thermonuclear explosion, it persists for a microsecond so it needs to be differentiated from a supernovae explosion. A star doesn’t produce neutrons; it produces thermonuclear reactions. Neutron reactions only occur in nature really in supernovae in the R-process and that has a history of maybe a couple seconds. It is meaningful. Neutron capture can occur in times. Once you are going over a period of a second or so, it means that the neutron density can be a million times lower in a supernova than in a Mike explosion. In the Mike explosion actually, neutron density is probably ten million times higher than a supernovae, so in that respect it is more impressive than a star. I don’t know. Is there anything else I can tell you about?

Rhodes: No, this seems like a nice cosmic place to stop here. It is wonderful.

Cowan: You say you have talked with Bethe? You talked with Carson Mark?

Rhodes: That is to come.

Cowan: Carson is also a member of the Bethe Panel. Rod Spence was another member. Rod was another radiochemist. I worked for Rod in the Joe-4 test. I had come back in ’49, back here, a month before the Joe-4 test and just moved into a new laboratory, and Rod was my boss. He was the guy who received the first debris from Joe-1 in August ’49. He moved into my laboratory because I had never opened a bottle or done anything there, so in the end he had to tell me what he was doing otherwise I wouldn’t have found out at that time, so I was let in on it.

I don’t think [Norris] Bradbury knew that debris had arrived here. It was very, very covert—the fact that debris was being collected. I think they had only started routinely sampling for radioactive debris just prior to Joe-1 and that was one of the arguments that Teller I think used; it was unlikely it was their first shot because no sooner do we start collecting debris then we pick up some radioactivity. 

Rhodes: Lewis Strauss used that argument too and, in fact, that was all they had. Well, maybe that was all they had. They may have had one more pit available when they tested that one.

Cowan: It was the very first thing they could do and as you say, it was a carbon copy. Again, I think that was a table thumper. They were just so afraid that we were going to wage a pre-emptive war.

Rhodes: That is quite true. It really was internal politics in a way. Beria and Stalin were impatient, and you didn’t let Beria be impatient very long. He was a very dangerous man. He had other physicists in the background that he trusted. Whether they could have done the job is another question. 

Cowan: They had a thing going on.

Rhodes: They were already working a bomb, probably a levitated core, which they had already heard about from Los Alamos, although they claim it was all an original design. Their next bomb, since it was considerably smaller than Fat Man and it was 40 kilotons, I would guess it was levitated.

Cowan: But they did say to you that Joe-4 was original?

Rhodes: They are very adamant about that.

Cowan: It was an original design. It wasn’t based on any leaks. That is very interesting to me. I was persuaded there were no leaks at that time, and I felt, “Gee, this is a test about whether or not they still have a guy around because they did this stupid thing.” I thought it was stupid, frankly. I thought, “Gosh, if they have any further leaks they wouldn’t have done it,” but I never really pursued that argument with anybody. It was just my own conviction.

Rhodes: Well you know, the KGB claims that there was an American physicist who is still alive who was an additional spy for them.

Copyright 1993 Richard Rhodes. This transcript may not be quoted, reproduced, or redistributed in whole or in part by any means except with the written permission of Richard Rhodes. Exclusive rights granted to Atomic Heritage Foundation.