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German Goncharov on: What the Soviets Learned From Klaus Fuchs
Q: Let's go back in the history of the hydrogen bomb. You were telling me about some reports that came from America, from Klaus Fuchs in 1945 about the work in Los Alamos on the so-called superbomb. Tell me about that report.

GG: Yes. In fact, it is just now become clear in recent years, with some additional details being added even more recently, that we had gotten the first information about the work on the hydrogen bomb in the United States from Klaus Fuchs. And the interesting thing that I discovered not long ago was that already in his first report, delievered during his work at Los Alamos, at the first meeting during this period with Harry Gold -- I think it was on February 16, 1945, not far from Boston -- he passed on the report that was mostly dedicated to the works on the atomic bomb, but it also had a short segment on the super. There he brought to our attention the works conducted in the U.S. on the development of a bomb based on the principle of generating a nuclear blast through the reaction of light elements. But he emphasized that this work might be successful but was not a priority at the time, that is, it was not something which needed to be worked on immediately.

In the fall an additional report was received. Apparently, they were not coming from just one source. But the most significant one of them -- they were very short, that is, of a very general content, about a deuterium-base bomb was being developed. But the most remarkable document was the so-called Fermi lectures, which, according to all the data I had a chance to get acquainted with, were given to us by Klaus Fuchs during his last meeting with Harry Gold in Santa-Fe on September 19, 1945. It was theoretical material which contained various formulas, various physical processes, the course of reactions; in particular, the report quoted for the first time data still unknown in this country about the unique characteristics of the DT reaction, about its cross-section being 100 times larger than that of the reaction DD. It provided a basic diagram of the bomb, as it was conceived and it described several potential alternatives, but it was indicated that all the diagrams were quite preliminary. And, of course, this material did not contain any evidence of its feasibility. It was only of a scientific, informational quality, I would say. That is why, even before it was received, the technical council of the Special Committee gave an order, taking into consideration the information received by then about the superbomb.

The first order was given to [Igor] Kurchatov, [Iulii] Khariton, and [Abram] Alikhanov. The reason why Alikhanov was drawn in was unclear at first. But apparently, the reason had to do that his specialty was heavy-water reactors, connected to heavy-water deuterium. That is why it must have been decided that he might be somehow useful. But it was modified. Because two months later there was a report presented by Gurevich to the Technical Council. [The report was written] by Gurevich, Pamerunchuk, Khariton, and Zel'dovich; the report was presented by Zel'dovich. In this report the Soviet scientists outlined their first ideas regarding the hydrogen bomb. I must say that this report had been prepared undoubtedly without reading any of the Fermi's lectures. They had not been shown by then; they must have been still in the making, being translated.

The second impulse was Fuchs' information, which he passed along through Feklisov on March 13, 1948, when he was already in London. There he gave out a new design for the superbomb. This design again contained theoretical computations on the processes which were taking place. What was remarkable (about the report) was the new plan for triggering the superbomb. If earlier it had been considered that the current of neutrons of the nuclear bomb would simply ignite the tube at its primary section where tritium was located, it now proposed a new two-stage construction for the trigger. This two-stage construction was to initiate a powerful neutron current; it used the primary radiation of the nuclear bomb, and was the first version of radiation implosion. So, this draft contained a prototype of the future Teller-Ulam configuration, though the final decision and understanding of what was contained in it was not there yet.

Neither we nor Americans had gained the full understanding of it yet, though Americans must have had more access to this information than we did, because, judging by all the data, this report conformed to what had been discussed already at the April conference in Los Alamos in 1946, in which Fuchs participated. It is possible that it was noted that this draft corresponded in some way or was analogous to the Fuchs-von Neumann patent which, before Fuchs' departure from Los Alamos was submitted to the American patent agency on April 28, 1946, . It has not been published, that is, there is no exact information about it. But according to [author Richard] Rhodes, analyzing all of the published information, one can come to this conclusion. And under the influence of this information, it was decided to examine the data. It was for this purposed that the Tamm-Sakharov group was organized. This group at first worked at the FIAN [Physics Institute of the Academy of Science.] And there the "sloika" as an alternative was conceived.

But this work remained theoretical for a long time, throughout 1948-1949, until, after the test of the first Soviet atomic bomb, when the Americans started to discuss counter-measures [to the Soviet test] and the hydrogen bomb was proposed as the most effective measure. Before that the work on the hydrogen bomb did not encounter much active support, or even partially encountered opposition, as is well known. On January 31, 1950, President Truman announced his famous directive [to develop the H-bomb], and the response of the Soviet government was the decision to create the hydrogen bomb in two versions. On February 26, 1950, the Soviet of the Ministers' adopted the resolution to work on two versions of the H-bomb: the "sloika" and the classical Super, in which there was still some faith. That is, this work was continued, and as the result of this resolution, the Tamm-Sakharov group was moved to Arzamas for concrete work on the bomb...

Speaking of the classical super, the document of 1948 did not have any substantial information that had not already been elaborated in the document of 1945, you know. With the exception of the more detailed description of the usage of liquid deuterium. The materials of 1945 simply stated that deuterium is being examined with the density of liquid deuterium... and certain numbers were given. But the document of 1948 explained directly that it should be used in the form of liquid deuterium in this tube. And no new information regarding the tube was provided. All formulas of the physical processes were again quoted as in the document of 1945. Apparently, some of them were more accurate and maybe more detailed than the documents of 1945. But as far as I am familiar with the documents, I would not have noted any substantial innovations in that part. It was completely analogous to the one in 1945. The difference was only in the trigger, i. e., how it should be ignited. That is, there was a new draft for the ignition of the tube. The main idea was the same; that the tube should be ignited, detonation will start, and will yield great power. But the question was how to ignite.

Earlier it was considered that it could simply be ignited by the current of neutrons emerging from the regular nuclear bomb. That is, say, this "Little Boy", Uranium 235, (gun-type bomb) enclosed within the tamper; it explodes and discharges neutrons that transfer their energy and, especially if you add tritium to the initial segment, are capable to ignite... But here Fuchs... And no directions were provided; that is, there was no complete explanation; there was only an exposition of the project, just like data: it consists of this and that, one needs to do this, just like a prescription, you know, without any comparison with the previous one, without any explanation why it was better, you know. It was just a description of a concrete project. And the main idea consisted in the realization that in the materials of 1945 there had not been enough neutrons emitted by the regular bomb... One must create a powerful current of neutrons, of great energy. And this starter, this two-stage construction, was created specifically to produce this current of neutrons for the ignition...

But it had some very interesting characteristics that moved us closer to a very different solution of the whole problem. However, Fuchs did not understand that. And all the potential of this method was not seen in the United States. That is, there were many elements of the future Teller-Ulam configuration. That is, there was an opaque casing for radiation; a bomb was placed into this casing--a primary bomb, but of a cannon type, that's how it was drawn, however, it is inconsequential--so this bomb would emit radiation. And then there was this liquid composition that adjoined the tamper, and the difference of pressure of the composition and the tamper would result and would compress and ignite it. And in the report Fuchs elaborated this theory, which showed that the ignition definitely took place under the impact of the spreading radiation. That was the principally new moment contained in this document. As I have written in my article, in my mind this proposal was ahead of its time and beyond the possibilities of mathematical models.

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