The Manhattan Project

Hans Bethe's Interview (1993)

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Hans Bethe was a German-American physicist who was head of the Theoretical Division at Los Alamos. He played an important role in the development of the hydrogen fusion bomb, working alongside Edward Teller. In this interview, Bethe discusses espionage and Soviet spying during the Manhattan Project, explaining the impact Soviet spies including Harry Gold and Klaus Fuchs had on the USSR's nuclear program. He and Rhodes discuss FBI security concerns of anyone with a European background, including Bethe and Teller. He also discusses the Soviet hydrogen bomb project, and explains his role in the post-war development of the hydrogen bomb in America.
Manhattan Project Location(s): 
Date of Interview: 
1993
Location of the Interview: 
Ithaca
Collections: 
Transcript: 

Richard Rhodes: Did David Holloway show you the documents that the Russians published?

Hans Bethe: Not the documents, but I got recent documents like [Yulii] Khariton.

Rhodes: Ah. They also published what [Klaus] Fuchs gave them. And, I have some of it here. I wanted to show you. You may not be able to comment. I think it is probably classified material in the United States.

Bethe: I do not know.

Rhodes: Well, I will show you and you can say.

Bethe: Let’s leave that for my—

Rhodes: It is all right.

Bethe: No, but I got many chapters of David Holloway’s book.

Rhodes: Good.

Bethe: Have you got that?

Rhodes: No, I have not. I had understood that he was nearly finished and then with all the new information, but still he needed to go back and do more work.

Bethe: Back to Russia? Well, good for him, tough for him you might say. Well, I have the initial chapters until ’45. It is most amazing how much Fuchs gave them. They were entirely on the wrong track before Fuchs.

Rhodes: In that they were going to uranium?

Bethe: Yes.

Bethe: Do you know?

Rhodes: I have their documents, yes.

Bethe: They did not know why they doubted that one could make chain reaction with any moderator, including heavy water. So, they were even more stupid than the Germans. But once they got Fuchs’s information, they were just fabulous. How could they put up so many industrial plants in such a short time, so that in ’49 they could have a test?

Rhodes: I spoke to a soldier, who was a guard at Chelyabinsk. He described the sheer terror that even the generals there felt about [Lavrentiy] Beria. When Beria would come, he said, “Even the generals were hiding like school children.”

Bethe: Yes, I am sure the generals would be most exposed.

Rhodes: It was such a sacrifice in a country where people were literally starving at that time.

Bethe: Yes.

Rhodes: And, living in holes in the ground.

Bethe: Did they really?

Rhodes: Yeah. So much had been destroyed; so much had been bombed out.

Bethe: And, it is not a climate where that is a pleasant thing to do. It is not like New Mexico where the Indians did that.

Rhodes: I was curious about whether Fuchs would have known much about the high implosion lenses.

Bethe: Fuchs knew all the implosion lenses that we had by the end of the war, and I read that the Russian bomb of ’49 was an exact copy of our Trinity. 

Rhodes: I should show you: this is the document that Fuchs passed in September of ’45. What is surprising to me is the detailed description of the initiator, which I had never seen before.

Bethe: I see. That is exactly what we did, yes. And, it is marvelous. Thirty-two explosive lenses, so there you have it. Yes, well, the initiator was a very important part. And, I am very proud of it, because I think Jack [Charles] Critchfield and I were the inventors, although I am not given credit for it. One of the few things I did for which I have not been given credit.

Rhodes: Well, maybe we can correct that.

Bethe: I couldn’t care less.

Rhodes: I know, I understand. I am confused, though, by one thing. You know the American soldier, David Greenglass, who was with the [Julius and Ethel] Rosenbergs, described in his court testimony an initiator that had, he said, cone-shaped Monroe-effect devices on it. This one has grooves.

Bethe: The grooves, yes.

Rhodes: Would he have seen an earlier design, or just simply been confused?

Bethe: It is possible. I do not know. He is a mystery to me.

Rhodes: How so?

Bethe: Well, his information was just subsidiary to Fuchs and the Rosenbergs just transmitted it and Greenglass, I think, was not punished, was he?

Rhodes: He went to prison for a relatively short time.

Bethe: I see.

Rhodes: Not so short, it was a portion of fifteen years, but his wife was not charged, and since she was implicated, it was really important to him that she not be. So, he exchanged his testimony against his sister, of course, who was then executed so that his wife would be kept from prison. I asked Khariton a few weeks ago, we are corresponding by fax.

Bethe: Oh, you do?

Rhodes: Yes.

Bethe: Good for you.

Rhodes: I asked him a few weeks ago when they decided to go with this design, rather than their design. And, he said not until 1948 when they were certain, because they had done the work that this was not disinformation. So, I think Greenglass fits in as someone who helped corroborate Fuchs’ information.

Bethe: I see.

Rhodes: Beria was such a paranoid, I think, that even at the time of the test, he had the people from Russia who had been at the Bikini shot come and watch and say, “Yes, that really was an atomic bomb. The physicists didn’t cheat you.”

Hans: Otherwise, heads off! [Laughs]

Rhodes: Which, of course, was the reason Khariton says they decided to use this design, because they knew it worked. Isn’t it an extraordinary story?

Bethe: It is extraordinary and very believable.

Rhodes: Oh yes. Now, the other thing that has come from this discussion with the Russians is that there was another physicist, Perseus, so-called—that was his code name—who was an American, who is still alive, who had joined the project in ’42 and who was also passing high-level information.

Bethe: Really?

Rhodes: There was a second courier, besides the man Harry Gold—it was a woman. She went to Los Alamos in April, or to Albuquerque in April of 1945, and was almost caught with a bunch of documents.

Bethe: Really?

Rhodes: She was about to get on the train in Albuquerque and she saw security people checking people’s luggage. And, she put the documents in a box of tissue, and she came up to the security man. She handed him the box and said, “Here, would you hold this? I’ve got to find my ticket.”  He held the box and gave it back to her. [Laughs] And, she got on the train.

Bethe: Very clever.

Rhodes: But, that information, which I also have here, was almost as detailed as what Fuchs passed.

Bethe: Really?

Rhodes: But, who could this person have been? He is supposed to be still alive.

Bethe: Well, this is most alarming, really. So, any day, somebody might get arrested.

Rhodes: I do not know if the statute of limitations applies to this or not. Well, the Russian who told the story died recently. Natskoff died about two months. And he did not pass the information, but there are others in the KGB who presumably know. So, I do not know. 

Could you have speculated about who this person could be?

Bethe: No.

Rhodes: It is hardly of interest at this point.

Bethe: Yeah.

Rhodes: Another name they have used for him is Fielding, and I presume that is also a code name, so.

Bethe: Yes.

Rhodes: I do not know. It is a curious part of the story and suggests just how much information they were gathering from all over the place.

Bethe: I think it is rather nasty that they published that.

Rhodes: Well, they were nasty people. The KGB people, especially.

Bethe: Yes. 

Rhodes: The other information—

Bethe: This person was at Los Alamos?

Rhodes: Yes, from ’42 on. Now, he could not have been there in ’42, he must have been with the project in ’42. But, then was at Los Alamos, was a physicist. The woman with the tissue box, specifically said it was a physicist. But, no one has been able to work out more than that. It is just not enough information.

Bethe: And, supposedly he gave almost as good information as Fuchs?

Rhodes: He just sent a document, defined reliable figures for the critical mass, discussed implosion, described arranging of detonators in the use of explosive lenses. And, maybe most important, the information on spontaneous fission of PU-239, which was new in April and had not been, well, it came the previous summer, so he passed that information, too.

Bethe: I see.

Rhodes: Cross-sections of fission f or U-235 and PU-239, quite a lot.

Bethe: He is obviously a knowledgeable person.

Rhodes: Yeah. Someone you worked with.

Bethe: Very likely, very likely.

Rhodes: I thought perhaps [Edward] Teller. [laughs]

Bethe: Unlikely.

Rhodes: The other person I think you knew, whom has turned up in all this Russian, was Alfred Sarant.

Bethe: Yes.

Rhodes: Wasn’t that someone who was here at Cornell for a while?

Bethe: Yes.

Rhodes: You may know that he turned up as the head of a design bureau in Leningrad.

Bethe: Right.

Rhodes: Yes.

Bethe: I know that and he was a minor technician here and before that he had been at Bell Labs, and  he was one of the few people whom Robert Wilson, the lab director, fired for non-performance.

Rhodes: Well, he had much more success over there.

Bethe: Yes. He did know something about electronics and presumably far more than was known generally in Russia.

Rhodes: Although, you know it is interesting, my Russian associate said to me that in the early ‘50s, a very promising line of Soviet development in computers was suddenly aborted and replaced by what would seem to have been a Western line. I do not have the details, but it sounds as if they might have in fact delayed Soviet development of computer technology, if they brought over what we had and—

Bethe: I would look at that with caution, because it is not just an idea that is needed, you need solid industrial development. And, all right, maybe he had a good idea. I know that presently, the Russians are very good at software, and at programming, and I am told that, well, even by some Russians, that they had to be inventive, because their machines were deficient and therefore they had to be more inventive on how to arrange a calculation. And, so in that respect, they might have had good ideas already in the ‘50s. But, in the ‘50s, what was lacking was just hardware development.

Rhodes: I asked one of their senior scientists from Arzamas how they handled the difficult thermodynamics calculations for their hydrogen bomb since they did not have a MANIAC [Mathematical Analyzer, Numerical Integrator, and Computer] or an ENIAC [Electronic Numerical Integrator And Computer] at that time. He said, “We just used theoretical physicists.”

Bethe: Yes, well that is the way to do it. Yes, did we need the computer for our thermonuclear nuclear weapons? It certainly helped, but whether it was necessary, I do not know.

Rhodes: Well, when [Stanislaw] Ulam and [Enrico] Fermi did those calculations, they came pretty close to what the computer turned up, didn’t they?

Bethe: Yes, but, they were not so sure about it.

Rhodes: What I am trying to do now is write a book that will cover the period from ’45, where my last book stops, to the mid ‘50s. It will deal primarily with the development of the Soviet atomic and their first hydrogen bomb, or their Joe-4, and the development of our hydrogen bomb. But, more perhaps than the last book, will tell the larger story of the post-war political situation.

But, I do want to tell the usual things about participation, your participation and others, in the development of the hydrogen bomb, getting up to the Oppenheimer security hearing, where you all sort of come back on stage, one by one. And, then stopping in the mid-50s, I think, because then everything was in place.

Bethe: Yes. I thought you had come here about nuclear power.

Rhodes: Ah, no. That is, we are still working toward that, but this was to talk to you about the post-war time.

Bethe: I see. So, I am a totally false— [laughing]

Rhodes: The Public Broadcasting Service will not take four hours on that subject, but that they would be interested in a one-hour or ninety-minute program. So, we scaled back a little bit the proposal that we sent you and are in the process of beginning to look for funding.

Bethe: Yes. So, you do not want to hear about it, because I have assembled here some literature.

Rhodes: Can we do both?

Bethe: Well, my intention was first to warn you whether the American public is ready to receive the message in favor of nuclear power. I get information mostly from people who are for nuclear power and telling me that the public support is substantially more than half, which may be true, maybe not. But then I hear and read the skepticism in the newspaper and I hear the president and vice president, who are not very friendly to nuclear power.

Rhodes: It is certainly clear that the journalists are very anti-nuclear. I rarely encounter a fellow journalist who has even heard the arguments for nuclear power. They are often stunned to hear that there is a lot less waste than a coal factory, or that the French have had great success.

So, because we have been working on this together, we have really thought about this program as being something to educate journalists, perhaps even more than the general public.

Bethe: I see, yes. And, you will assemble them forcibly.

Rhodes: [Laughs] No, but they are people who watch public television. So, perhaps this can be a chink in their armor.

Bethe: So, this is really not an immediate problem. However, since I have assembled all that, I would like to talk to you about it.

Rhodes: Yes, do, that is fine, let’s do.

Bethe: But, you have more, let’s postpone, and you have more about the bomb history.

Rhodes: To stay for a moment with this Russian business and with the espionage, I gather from the documents I have seen that you were under suspicion at some point, before Fuchs was identified.

Bethe: Isn’t that interesting?

Rhodes: You, Rudy [Rudolph] Peierls, anyone I think with a European background is, even Teller was under suspicion by the FBI.

Bethe: Yes.

Rhodes: Were you aware of that?

Bethe: No. There was only one incident that was just very vaguely in that direction. I was on not good terms with an FBI man, somewhat higher level—I think he worked out of Syracuse—who came to visit me from time to time. When the Rosenbergs were arrested he came to Seattle, where I was spending the month of July, I think, teaching summer school. And, he gave me a rather detailed searching quiz in one of the rooms. It was unpleasant. He did not arrest me. But, did I know anything about the Rosenbergs and I said, “No.” 

Then Sarant came in and I told him what I knew about Sarant. And, Sarant had by that time already disappeared to Mexico, which he told me. Sarant was somewhat put under my wings by his father-in-law, Victor Ross, who was a very innocent lawyer, who somehow was involved in selling our present house to us and who was an acquaintance of our very good friends. 

So, Ross said, “Well, there is this son-in-law of mine. He is coming here to study physics, but would you supervise him?” 

He was not ready to be a graduate student and so I gave him some things to read. Whether he did, I do not know. But, mostly he became a technician in the nuclear lab. At the beginning, he apparently was a perfectly reasonable technician. But, then he had found out that he could not find out anything from me, so he was no longer interested. 

So, he stopped working, so he got fired. But, he had much more success with the wife of a very nice graduate student by the name of Dayton, he ran away with her. And, then he became a great man in Russia.

I think we should not underestimate the difference in sophistication between the United States and Russia at that time.

Rhodes: Scientifically?

Bethe: Technically.

Rhodes: Technically, yes.

Bethe: Electronics really in this country was years ahead of Europe—except England—which in turn was years ahead of Russia. Electronics, where my good friend, Bob Bacher, who was atomic energy commissioner at one time, said several times the Germans could never have put together an implosion bomb, because their electronics were not fast enough to observe the assembly. Even if they had had the idea, even if they had been able to shape the explosive, they could not have found out whether it was symmetrical. And, the Russians probably were even worse off. So, much the more credit goes to the Russians for imitating the Trinity bomb.

Rhodes: I asked Lev Altshuler—you remember I sent you a letter of Altshuler’s? I asked him if they had any idea of implosion before the Fuchs information and he seems to want to say that they did, that implosion as an idea had been around. Does that make sense to you? I mean, I understand that shaped charges had been around, the Monroe effect had been around.

Bethe: Yeah, shaped charges had been around, but a shaped charge does not an implosion make. It took a lot of further ideas to make it symmetrical. But, I remember the experiments by [Seth] Nedermeyer, the early days of Los Alamos, which gave absolute hash. The jets went all over the place and you could not possibly assemble anything that way.

Rhodes: This is one of the mysteries that I have been puzzling about with what David Greenglass passed along. I am sure you have seen the drawings he did for the FBI of the experiment that he worked with, which is clearly a thin sheet of explosives imploding a cylindrical tube—a two-dimensional, one of those many, I guess, early experiments.

Bethe: Yes, correct.

Rhodes: It is hard to see how this would have been of any great use to the Russians.

Bethe: Not much.

Rhodes: I would not think so.

Bethe: But, he did give them a drawing of the thirty-two lenses, also, didn’t he?

Rhodes: This is the other drawing that the FBI made public, which is, again, not of any great use. Fuchs, however, passed hundreds of pages of material, so it seems likely that he included in that more detailed description of the lenses.

Bethe: But, I thought Greenglass was a technician who was working on lenses.

Rhodes: Well, he was, but this is what he told the FBI, at least this is what they made public.

Who knows?

Bethe: Maybe they kept within the regulations of the AEC [Atomic Energy Commission].

Rhodes: He talked about thirty-two lenses. He clearly had some sense.

Bethe: Yes, right. He was important to the Russians because he was confirmed.

Rhodes: Fuchs and Perseus, because there were two high-level sources of good physics; he had very little sense of physics, but he was physically working on the objects, so he extrapolated from that. By the way, I do not know if you have seen this photograph of their 58-megaton device.

Bethe: No, I have never.

Rhodes: It was a very large object. This is the one where they said they had 97% fusion yield.

Bethe: Yes, that is probably correct. Fifty-eight [megatons], they say?

Rhodes: That was the big one that they tested in the early ‘60s, yes.

Bethe: We said 62%, we were pretty good.

Rhodes: And, they have also released a few photographs of what I take to be some of the early implosion devices, but I do not know what year that thing dates from.

Bethe: Oh, it does not give a date?

Rhodes: At least, I cannot read the Russian, so.

Bethe: You can’t?

Rhodes: No.

Bethe: You should have a—

Rhodes: I have a translator, he is coming from Moscow next week, yes.

Bethe: But, translators are abundant at MIT and Harvard.

Rhodes: Yes, yes.

Bethe: You do not need to import one.

Rhodes: Ah, but he is so inexpensive. And, he is on the scene in Moscow, so he finds things for me.

Bethe: Well, this is obviously Fat Man and this is Little Boy, if anything. This is a gun assembly and this is—

Rhodes: That was one of the questions that I asked Khariton recently, how their original design that they claimed they had—as well as the Fuchs design—differed from the one that Fuchs gave them? And their answer was the Soviet atomic device tested in 1951, which as I understand it was a uranium bomb, in addition to other advantages, had much lesser diameter than the Fat Man. It was achieved through original engineering decision on creating implosion. 

One of the things that they learned from Fuchs was about levitating the core. And, that was also something Greenglass knew a little bit about. Would that have reduced the diameter of the weapon?

Bethe: Levitating is very useful for that. Los Alamos reduced the diameter step-by-step from ’45 on. The solid core clearly was very hard to compress, and we knew that very well by ’45. Originally, we had wanted a hollow shell, but we did not trust the symmetry. Then we decided we could after all have a hollow shell and if we had a hollow shell, it was useful to have the very center solid so that the hollow shell was pasted on the explosive, so to speak, and the core had to be levitated.

And, so the question was could you make thin enough wires, which were strong enough so that they could survive transportation by plane and falling down and be possible where you do not need to have it impact on the ground? But they had to be strong enough and yet thin enough so they would not disturb the spherical symmetry. Because, the spherical symmetry is all-important; only then do you get the increase in density, which you bank on.

In addition to that, with the hollow construction, you can put a little more material in. You can put in more than a critical mass, which again increased the yield. And, then already in the last month of Los Alamos, we invented the composite, which is a great increase in yield, to have plutonium in the center and then uranium outside. Plutonium was much more expensive than uranium—the separated uranium—three times maybe. And, therefore, we would get a much better arsenal by having the mixture.

So in many tests series in Nevada and also occasionally in the Pacific, Los Alamos went to smaller and smaller diameter high explosive. I think the Fat Man was fifty-four inches diameter, and we soon got it down to thirty and then below thirty to a twenty, and they all worked. In fact, Fermi told [Norris] Bradbury, the director of Los Alamos, “You are very bad as an experimental physicist, because all your experiments worked!”

And, so this was going on constantly, and they were all composites. Now, the Russians obviously needed to establish isotope separation. 

Rhodes: And, their first bomb, of their own design, came on just as quickly, I think, as they could get the U-235.

Bethe: Right.

Rhodes: Yes.

Bethe: That makes sense.

Rhodes: They were apparently having trouble making plutonium for a while. They only had one production reactor, and then they built a second one.

Bethe: Do you know where?

Rhodes: Chelyabinsk.

Bethe: In Chelyabinsk.

Rhodes: Yes. They buried it 240 feet under a lake. They were afraid we were going to bomb it. They dug this huge hole. They used the technology they had used to build the Moscow subway, and they put it under ground, and the only thing that showed from the air was the smokestack.

Bethe: I see. Did they poison the lake?

Rhodes: I do not know. There is, of course, the lake there that is terribly, terribly radioactive—a swamp really that they dumped their fission by-products into directly. You know about that, I am sure.

Bethe: I know that.

Rhodes: 600 R [roentgens] on the shoreline today. But, you know, the old engineer who started that place told a physicist friend of mine, “Every morning, we listened for the B-29s coming over the Urals. We couldn’t believe you’d let us get the bomb.” They were anticipating the sort of thing the Israelis did to the Iraqis.

Bethe: Really? Yes. Well, two things I want to say in this connection. One is I listened to a group of high-level people from Chelyabinsk, who were invited by that organization at the University of Maryland, East-West investigation into the changes in the Soviet Union, Susan Eisenhower and Roald Sagdeev.

And, the Chelyabinsk people were very sensible and completely set upon conversion of the land to peaceful purposes. And, they thought about such things as optical fibers for telephone and for TV, and they had lots of good ideas. So, I was very, very impressed by them. The Arzamas people, I have not talked to, but they were here at one time. Their ideas still run to applications of nuclear explosions—digging a deep hole and destroying, let’s say, chemical weapons thereby.

Rhodes: Yes, that is right.

Bethe: I do not know, maybe that is a possible idea. It is, and I think it should be given enough thought to find out whether that is feasible. My physical chemist brother-in-law says, “I’d rather take them apart and then expose them to a very, very high temperature.” He has thought about these things, and he had, I think he is in agreement with the American plan, namely, to bring the temperature up to a 1,000 degrees Celsius. 

He says if you do it at any lower temperature, then you may form some new compounds, which may be equally poisonous as what you are destroying. You just do not know. Only is you go to 1,000 degrees, you will decompose the material into CO2, H2O and nitrogen, and they are all very easy to live with.

Rhodes: Arzamas maybe having some of the problems that Los Alamos and Livermore are having, trying to do think what to do next, and the tendency to stay with the past.

Bethe: Los Alamos and Livermore are having terrible problems. I am very worried, because I am fond of Los Alamos.

Rhodes: I was there at the beginning of April, at that conference they had.

Bethe: Ah, yes. Was it good?

Rhodes: Well, I was only there for the first part of the week. The security discussions, I did not stay for, so I do not know. What we talked about was the past. We discussed the history .

Bethe: Yes, but was it good?

Rhodes: Yes, yes, well, it was certainly valuable for me to go back. I have not been back in a long time.

Bethe: Yes, well, I think, I think their program was good. But, they do not have a charter to do civilian development, and I do not see how that will come about. I hope so. Certainly very, very intelligent people [at Los Alamos] and the same goes for Livermore. Well, that is not your subject.

Rhodes: I would like to talk with you about your personal decisions of working on the hydrogen bomb. You remember the paper that you did for Scientific American?

Bethe: I remember.

Rhodes: Yes. Where have I got that? Well, you remember it, you wrote it.

Bethe: Right, in which I was totally opposed.

Rhodes: Yes. Opposed in particular on grounds that you felt were ethical grounds at that time, right.

Bethe: Right.

Rhodes: How did you come to change?

Bethe: Well, I think the main point was the Teller-Ulam invention, and the Teller-Ulam invention made it very likely that it could be done. And, in fact, it was so good that it seemed that the Russians could also do it, which they did three years later. And, so I was perfectly right. Now, it was something that could be done by both countries, and the British did it three years after the Russians, which puts it in for ’58, and the Chinese did it remarkably quickly in ’63 or ’64, and it was only the French which took so long. They had entirely the wrong idea, but that is classified. I mean, anything beyond what I have said. 

So, I was convinced that the Russians could do it and I figured that if they could they probably would. And, reading [Andrei] Sakharov, I am more convinced than ever that they would.

Rhodes: They had started by ’48. Their proposal went to Stalin in ’46, a general proposal. They did discuss then this need to increase the density of deuterium, too, or of the hydrogen.

Bethe: Right.

Rhodes: It was a very theoretical little document.

Bethe: Yes. That is one I have not seen.

Rhodes: I did not bring it with me, but I could send it to you.

Bethe: Yes, that would be useful. So, in ’48, they started?

Rhodes: When Sakharov came, that was really part of the beginning of their working on the hydrogen [bomb].

Bethe: Sakharov came only in ’48?

Rhodes: Yes.

Bethe: I see.

Rhodes: I am fairly sure that is true.

Bethe: In that connection, by the way, the Joe-4—

Rhodes: Yes, I was going to ask you about this.

Bethe: Which I have publicly said was not a true hydrogen bomb, and I got some unhappy letter from Khariton on that. I do not know how they did it. I do not know whether we could do it.

Rhodes: Wasn’t it like our alarm clock design?

Bethe: That was the design, but somehow it was probably superior to it. It was compressed by He. It was alternating layers of uranium and lithium deuteride. All that we figured out just from seeing the debris. We also figured out that it was a single-stage device from the debris. But, Khariton has now said that its diameter was the same as the Fat Man—fifty-four inches or whatever. And, it gave 400 kilotons.

Rhodes: But, they say that they could have scaled it up to a megaton or better.

Bethe: In the same size?  

Rhodes: I gather they mean the same size. One of my recent correspondences with Khariton implies that. An H-bomb of a megaton yield, and they also point out that it was 15-20% fusion.

Bethe: Yes.

Rhodes: You and I in a sense have been corresponding with them, because I called you, you may recall, when I first heard from there. Khariton sent his best wishes, by the way, and said that he remembered you with great warmth and admiration.

Bethe: Isn’t that nice. Have I met him?

Rhodes: Yes, you met him in 1958 in England at one of those conferences, probably one of the nuclear power conferences. I think it was in England.

Bethe: Not in Geneva?

Rhodes: I think it was in England.

Bethe: Geneva is more likely, but possible.

Rhodes: I believe he said in England, after the Geneva conference of ’55, several years later.

Bethe: I see.

Rhodes: I seem to remember there was an appearance of the Russians, well, I do not remember exactly. In any case, he is responding to the question, were they a true H-bomb, in this fax. It seems to us that the term true is unconstructive as applied to a technical device. It is more interesting to speak about the design, what did it do. So, he is obviously very unhappy that no one takes this seriously, this hydrogen bomb, because they used our design for the first one, for the fission bomb, and he would like to feel that they did something independent and original.

Bethe: That is absolutely true, and I responded to him and said, “Well, as far as I can tell, their ’55 bomb, while it used the same principles as ours, was entirely independently designed.” There is every evidence on that and I have even said that publicly. The ’53, as I said, it is remarkable that they could do it. I have not asked anybody at Los Alamos or Livermore whether we could do it now. Certainly, we could not have done it at that time. 

Rhodes: What do you think was the difference? They had to deal with the instabilities, yes, between the two materials.

Bethe: No, we did not even think of that. I would love to see a blueprint of the interior of that bomb, or at least a drawing. But that is just curiosity. Well, you have to compress the uranium and the deuterium enough to make it go. When we, in ’51, were just considering the compression of a central ball of lithium deuteride, then that after escaped the booster, that was successful. But, we did not think of, we did not think there was enough compression of power to do the alarm clock.

Rhodes: Was the alarm clock intended at one time to be the primary for the two-stage device?

Bethe: No. No, it was to stand on its own, and it was indeed a layer cake, but we thought we would need much higher explosive power to assemble it than was available.

Rhodes: So, it probably was not so much that it was inefficient as whether it would go at all?

Bethe: That is right.

Rhodes: Did we actually test one, do you know?

Bethe: Did we test one, I do not know. But, probably your friends at Los Alamos or Livermore could tell you. I do not think it is a secret. I am not aware of it, and once we had Mike, we were no longer interested.

Rhodes: Yes, right.

Bethe: So, as I say, it was an achievement to get that much out of that design, without Ulam-Teller.

Rhodes: Good.

Bethe: But, to finish my story about my change of mind, the main reason was that after the Teller-Ulam invention, it was clear that either the United States or the Soviets could do it. I figured it was better if we did it first and did it better. That was really the argument.

Rhodes: You mentioned last time we talked also that the Korean War influenced your feelings.

Bethe: I was just going to mention it. Go ahead.

Rhodes: Because, your arguments in the Scientific American piece are essentially ethical arguments, moralizing.

Bethe: That is right, yes.

Rhodes: Not technical.

Bethe: Right.

Rhodes: So, I guess I am looking for that change of mind.

Bethe: It was just as bad after it was feasible as it had been when it was not feasible. And, I would have loved it if it had never been done. You know about the attempt by Vannevar Bush to postpone and possibly eliminate the tests.

Rhodes: Was [Lewis] Strauss in the middle of making sure that did not happen? He seems to have been in the middle of so many things that were happening at this time, Lewis Strauss.

Bethe: Strauss. I am sure he was involved in it, but I think it was squelched by [Dean] Atchison. See, there is a very good discussion of that by Barton Bernstein? Have you read that?

Rhodes: I think I have, yes.

Bethe: That gives me the impression of being very genuine, well-researched and it is the best I know. The right point in Bush was that he said, “Let’s not test it, but let’s complete the design and construction. And, then let us declare where we have that device and we can test it any day we want, but we won’t do it unless some other country does it.” So, I think he was very clever. Whether it would have succeeded, I do not know.

Rhodes: That initiative.

Bethe: Sakharov has declared that just an approach to the Soviet government that we both refrain from doing it would have failed. And, he may be right. I am not so sure whether he would have been right after Stalin’s death. But, just an approach, they would not have believed that we were doing it in good faith.

Rhodes: There was such an inferiority complex over there.

Bethe: Right.

Rhodes: And in addition, apparently after second World War, they felt so much that they had achieved a kind of security, because of the Red Army, and that we had wiped all that out in one blow with our bomb. I am sure you know.

Bethe: Right. I am sure that is right.

Rhodes: I talked to two or three of the people who worked on their bombs, this was not a question of communism, this was a question of the same sort of desperation that you felt about the Germans.

Bethe: Right.

Rhodes: Yes, understandably.

Bethe: Right. And, it must have been a terrible let down, and Stalin knew all about our development when Truman approached him in Potsdam, and that is very well-written by David Holloway. He gave Truman a non-committal answer and immediately went to his staff and said this has to be accelerated.

Rhodes: And, I have found documents that they received from their espionage from England as early as 1941.

Bethe: Yes.

Rhodes: They were getting the minutes of the uranium committee meetings and discussions of whether ICI would build a diffusion plant in Scotland.

Bethe: Yes.

Rhodes: I mean they were completely plugged in all along the way. It is remarkable how much they knew.

Bethe: It is remarkable how much they knew and how little the Germans knew.

Rhodes: We walked around their first nickel reactor at the Kurchatov Institute. It is still up and running, and it is apparently a copy of one of the test reactors at Hanford. It is a graphite pile, but it is apparently identical to one that was built there in ’44.

Bethe: Really?

Rhodes: No one has identified any spy who was working at Hanford, although I suppose it was probably designed in Chicago at the metallurgical laboratory. And, there were spies there. So, it is, it was completely transparent to them—our program was transparent to them. It is amazing.

Bethe: It is amazing. They only know how to do it.

Rhodes: But, you are right, when the implosion came in and the plutonium came in, [Igor] Kurchatov’s notes say, “This will change everything.”

Bethe: Right.

Rhodes: Yes. 

Bethe: And, Kurchatov noted that also when the first information came in about making a chain-reacting pile with graphite, not with heavy water, a very easily available material.

Rhodes: Yes, he was very surprised.

Bethe: Yes.

Rhodes: The number they had used had come from Khariton, who had done work in ’39 to calculate critical masses and so forth and their number were not good enough. They were not even sure they could do it, as you said, with heavy water. They were interested in doing it with heavy water.

Bethe: Right. So, I think you should have Holloway send you that manuscript, which is very interesting and I think very well researched.

Rhodes: I will ask him, if he will; there is some competition, we will see.

Bethe: I guess there is some competition. But he starts in 1900 with the development of research institutes in Russia.

Rhodes: And, those early sources of uranium, yeah. I am curious as to why our H-bomb program before the Teller-Ulam invention painted itself into the corner of the “Super,” the classical “Super.”

Bethe: Nobody had the idea. People had the idea that higher density would be useful, and that was the basis of the alarm clock. The alarm clock then was followed particularly by [Lothar] Nordheim. I do not know whether he is still alive.

Rhodes: I do not know.

Bethe: He, for the last decades, has lived in San Diego and for a long time he was at General Atomic, and they would know his address. He is a very nice man, but he is one of the last survivors of the last century, if he is still alive. Now, so Nordheim worked on this, but nobody could see a way to compress the alarm clock sufficiently to get the desired high densities. 

Why did we still follow the classical “Super?” Well, for one thing, it had not been proved that it was dead. For another thing, nobody had an alternative and better idea. That was very simple. I did not want to have anything to do with it and neither did most of the people at Los Alamos. Los Alamos had a very demanding and important program, namely to make the fission device smaller and smaller, more yield and less weight. And, this was before the days of intercontinental missiles. It was just a question of having less material and having easily transportable weapons.

Los Alamos was very, very busy from the day of Hiroshima until the H-bomb order came from Truman. And, after all, a lot was achieved in those five years. Without that, they have would not have been able to construct a good [Ivy] Mike. We had to have a small atomic bomb in order to let the radiation out, which was the key to Teller-Ulam.

Rhodes: Smaller, because otherwise all the material would get in the way of the release of the radiation from the core?

Bethe: The radiation would just not get out, because there is all that high explosive around first, the uranium and then the high explosive. So you needed a very small and highly efficient bomb. That existed by ’49.

Rhodes: To what extent was the fact that the Soviets did not have a bomb—wasn’t that an alleviation of a sense of pressure? I mean, Teller went off to Chicago and did some science.

Bethe: There was a lot of research on improving nuclear weapons. The best person always to talk to is Carson Mark, which you might—

Rhodes: I have not yet, but I will in June when they have the reunion.

Bethe: So, there was pressure both at Los Alamos and from Washington to improve nuclear weapons. There was a scarcity of material, and we did want to have a big arsenal, easily transportable. And, we could not see any reason for higher yields. We could do 100 kilotons with the greatest of ease, that small.

Rhodes: So the hydrogen bomb really was the result of the Soviets testing an atomic bomb.

Bethe: Right.

Rhodes: And, I wondered the extent to which, not thinking of the new invention, even that is partly related to that pressure. Teller went to Chicago for several years, yes, and worked as a physicist on his own science?

Bethe: Yes, but he also always went to Los Alamos and constantly agitated for a second lab.

Rhodes: Even that early, before ’49?

Bethe: Certainly before ’49. How long before ’49, I am not sure.

Rhodes: That is interesting.

Bethe: Did he talk while you were—?

Rhodes: No, but he has asked to meet with me and some other writers in June, which is a great surprise. He does not like me at all and he has not spoken with me for a long time. That he suddenly now is interested in discussing all this is curious. Whether, I do not know if he is fixing up his historical image or what he is doing.

Bethe: Well, he is writing his autobiography, and his memory is very much a Swiss cheese. 

Rhodes: Or, is it a very selective Swiss cheese?

Bethe: Very selective Swiss cheese.

Rhodes: Yes, he seems to have forgotten the name Ulam, for example.

Bethe: Has he?

Rhodes: Well.

Bethe: Well, he would love to.

Rhodes: I am very curious as to what he will have to say.

Bethe: You will get together in June in Los Alamos?

Rhodes: Yes.

Bethe: Yes, you are rightly curious. But, remember the Swiss cheese. 

Rhodes: I know.

Bethe: One example which struck me as particularly strange, in 1940, we both wanted to work for the allied war effort. And, he was related to Theodore von Kàrmàn.

Rhodes: Oh, was he?

Bethe: At least he called him uncle. And, so we both visited Von Kàrmàn at Cal Tech, had a very good talk and we asked him to give us a Ph.D. subject, so to speak, having to do with defense. So, Kàrmàn said, “Why don’t you investigate the approach to equilibrium behind the shock wave?”

Edward and I were great friends at the time, sat down and wrote a very good paper – which was never published, but was made available by the Aberdeen Proving Ground – about the approach to equilibrium in shock waves. He has forgotten it, because I was involved, I think. [Laughs] It is a very important paper, because it then was the basis for very intricate experiments, some of them done by Arthur Kantrowitz at Avco-Everett Laboratory [AERL] on the equilibrium behind shock waves.

And, you see very high temperatures are reached, much higher than directly at the shock front, and some way chemical reactions take place. For instance, you make a lot of nitrogen oxide, which Kantrowitz could observe in the shock tube. So, I think many aeronautical physicists live on our paper. I say that without exaggeration, but Edward Teller has forgotten it exists.

Rhodes: Well.

Bethe: Just one hole in the Swiss cheese.

Rhodes: Last time we spoke, you and Mrs. [Rose] Bethe talked about trying to dissuade Teller from testifying against Oppenheimer.

Bethe: Right.

Rhodes: And, you know Teller has said that was a last-minute decision on his part, that only minutes before he testified— 

Bethe: Swiss cheese.

Rhodes: I agree. I found a document where he was out at Berkeley a week before saying, “Oppenheimer has got to be stopped.” 

Bethe: Right.

Rhodes: But, I wonder if you could recall for me what happened with your and your wife and Teller?

Bethe: Well, I cannot tell you more than you just said. We got together.

Rhodes: Do you remember when in relation to his testimony?

Bethe: Maybe the night before, maybe several nights before.

Rhodes: You were in Washington to testify?

Bethe: We were in Washington for meeting of the American Physical Society, and at the same time testimony went on. And, I was going to testify in favor of Oppenheimer. We tried to persuade Teller to do the same, or otherwise just not testify. And, there was not a chance to do that. He said, “Oppenheimer has made so many mistakes.”

And, for instance he had, as the chairman of the General Advisory Committee, done something against certain experiments at Oak Ridge—I forgot just what it was. And, there was quite a litany of mistakes that Oppenheimer allegedly had made. There was no way to penetrate. And the arguments Teller gives now for changing his mind, I think, makes it worse. 

Rhodes: Well, it is certainly untrue that he had heard none of this before, or had not made up his mind earlier. Clearly, he had. 

Bethe: Yes.

Rhodes: It is less clear to me why he was so angry at Oppenheimer. That seems to have been a very old feud.

Bethe: It was an old feud going back to Los Alamos. It was an old feud relating to the second laboratory. It was most important. Teller wanted a very strong policy against Russia and Oppenheimer just wanted the policy of containment and no more. It was an old feud because Oppenheimer advised everybody in the government, especially Atchison. But, also, I think the Pentagon. Oppenheimer very deliberately tried to reduce strategic bombing.

Rhodes: Yes, which ran him afoul of the Air Force.

Bethe: Yes, right.

Rhodes: Could you talk a little bit about the work you did toward the H-bomb when you went back?

Bethe: I did very little. I think my main contribution was that I said in one of the meetings that one inch is 2.54 centimeters, not 2.5. Because the engineers had gotten themselves all tied up by using 2.5. And, so the centimeter dimensions and the inch dimensions just never would agree. So, I solved that problem.

I did watch the calculations on propagation of radiation through the channels surrounding the secondary. It was a difficult problem at that time, and I do not know what the details were, but I kept my eye on it. I worked some on the question of penetration of radiation into the outer container of the weapon. Of course, radiation goes everywhere.

Teller pointed out once he had left Los Alamos, even though they were working on his weapon, he found all sorts of reasons why it would not work. He hated the project director, Marshall Holloway, who was a very good experimental physicist, without the flair that Edward Teller has, spritely ideas. So, he tried to criticize it whenever possible. So, at one time he said, “Well, it may only work perfectly well, except that the radiation will go into the casing and then there will be Taylor instability.”

Now, I knew a lot about Taylor instability and I worked on this radiation penetration and then came out with the conclusion that there would not be Taylor instability, and then wrote it down and sent this to Teller. That is the main thing I remember. Yes, well, I did work some on the H-bomb, but I guess I worked at least as much on other things at Los Alamos. And, certainly my work was not critical to success.

Rhodes: The Russians make a good deal of the fact that the Mike shot was done with liquid DT. 

Bethe: Right, liquid D.

Rhodes: That was not because we were not aware of lithium deuteride?

Bethe: We were very much aware of lithium deuteride. We were not totally sure how well it would work. But, already while Mike was in preparation, we said the next test we want to make will be lithium deuteride. We were much aware that liquid hydrogen was difficult to transport, although not that difficult.

Rhodes: Made for big weapons.

Bethe: Right.

Rhodes: Yeah. Does that suggest that their using lithium in Joe-4 was rather a risk on their part?

Bethe: Well in Joe-4, the compression would work just about as well for lithium deuteride as for deuterium. I do not know how much they worked out beforehand.

Rhodes: Harold Agnew at Los Alamos in April mentioned the primary on Mike was changed just before the shot. 

Bethe: I did not know that. 

Rhodes: He said that Marshall Holloway—

Bethe: There is Marshall Holloway and Marshall Rosenbluth.

Rhodes: Rosenblum, he said Rosenbluth.

Bethe: Or was it –bluth.

Rhodes: -bluth?

Bethe: Yes.

Rhodes: That he saved the shot. He said he lay awake worrying about the particular primary we were going to use and convinced Carson Mark to change it. “Maybe it would have worked, maybe it would not,” he said. 

Bethe: Yes. Well, Rosenbluth may have been there.

Rhodes: I think he was. This happened out there. 

Bethe: He is a theorist, and a very good one, and was very important in the theoretical work toward Mike, and also afterwards. He may be the world’s leading expert on thermonuclear power.

Rhodes: Controlled.

Bethe: Controlled.

Rhodes: Did you attend any of these shots? Were you at the Mike shot? 

Bethe: No.

Rhodes: Did you ever go out to Bikini [Atoll] or Eniwetok [Atoll]? 

Bethe: The only shot I ever saw was Trinity.

Rhodes: Oh. Well, there was—

Bethe: But, you see it—

Rhodes: I gather people were taken aback by Mike, that it was so big. 

Bethe: Of course.

Rhodes: So hot.

Bethe: Of course. I could be taken aback just by knowing that it was ten megatons plus. But, no, of course, seeing the spectacle takes you aback some more. But, it is much too much trouble. I thought I had better things to do.