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The Secrets of the Bomb

At Los Alamos there was a brilliant British-born metallurgist named Cyril Smith who had made a career in the brass business, in which alloys are central to making different products. By trial and error he found that if you alloyed plutonium with gallium it stabilized the delta phase, and you could make a plutonium metal. From that day to this, no one knows why gallium works or what the stability of the alloy is over a very long period, something that is important for storing warheads. The use of this alloy is a crucial bit of information that is absolutely essential in the manufacture of plutonium-based nuclear weapons, and Fuchs was in a position to pass it on. When the Russian physicists learned his identity they nicknamed him Santa Klaus.

Fuchs, the son of a Lutheran minister, had been born in Rüsselsheim, Germany, in 1911. As a student he joined the German Communist Party and when the Nazis came to power he left Germany. He managed to get to Bristol University where he got his Ph.D. in 1937. When the war came, he was interned in Canada as an enemy alien but Max Born, one of his professors, got him released. He was then approached by Rudolf Peierls, who made the first calculation of the “critical mass” needed to make a uranium bomb, to work on nuclear weapons. From the time the Germans invaded Russia, Fuchs began giving information to the Soviets about the bomb. When Peierls joined the British delegation to Los Alamos, Fuchs was asked to go along. Recently, a remarkable letter to Peierls from James Chadwick who headed the British delegation to Los Alamos has emerged, in which he describes Fuchs’s reluctance to go. He thought that he could be more useful to the project staying in England. If he had, the subsequent history of the Russian atomic bomb might have been quite different. Once at Los Alamos Fuchs was at the center of the work. He knew everything and transmitted what he knew through the courier named Harry Gold.

The people at Los Alamos liked him. He was a solitary man, worked hard, and was always available as a baby sitter when the more sociable scientists needed one. After the war, the British were not allowed to take classified documents with them. In Fuchs’s case it didn’t matter, since he had a photographic memory and memorized the final design of the gadget, which he saw tested at Alamogordo. This was the same bomb design that destroyed Nagasaki a month later. In October of 1945, a report was delivered to Lavrenty Beria, whom Stalin had put in charge of the Russian bomb program, spelling all of this out. Of the plutonium it says, “The element plutonium of delta-phase with specific gravity 15.8 is the active material of the atomic bomb.”1 It is equally specific about the rest of the design.

How this information aided the Russians is a matter of some disagreement. Beria did not share it freely with the scientists. He probably did not entirely trust the source. There was at least one other source, a young physicist named Theodore Hall who also transmitted material independently from Los Alamos. The Soviet scientists were given information that surely had an effect. What the spies said about plutonium metallurgy and the use of gallium must have saved months of trial and error.

In any event, the first atomic bomb the Russians tested—which they called “First Lightning” and the US called “Joe 1”—was exploded on August 29, 1949. It was a duplicate of the gadget. The US intelligence services were caught completely off-guard. The Americans had no agent on the ground in the USSR and relied on a monitoring system using aircraft alleged to be on routine weather patrols. The planes were equipped to collect radioactive samples of the kind that a reactor accident or a nuclear explosion would produce. Until this data was collected and analyzed, which took several weeks, there was considerable disbelief—including that of President Truman—that the Russians had really tested an atomic bomb. Once it was verified that they had, the cold war nuclear arms race was on. Fuchs was identified in 1950 and served nine years in prison in Great Britain. He was allowed to return to Germany, and died there in 1988.

The reader may wonder why I have not mentioned the hydrogen bomb and any part that Fuchs might have had in the Soviet program to make it. So much of the relevant information is still classified that it is very difficult to arrive at a complete accounting of his contribution. In the case of the fission bomb this is possible because the relevant material is unclassified. We know that what Fuchs did was to supply the Russians with a blueprint of the plutonium implosion bomb that was tested at Alamogordo and dropped on Nagasaki. The Russians then copied this blueprint. Fuchs left Los Alamos in 1946 to return to England where he had an important part in the development of British nuclear weapons.

This took place before there was a breakthrough in the American hydrogen bomb program, owing to the work in 1951 of Stanislaw Ulam and Edward Teller. Nonetheless, Fuchs had been active in hydrogen bomb work before he left the US. In 1946, he and the Hungarian-born mathematician John von Neumann took out a patent on what they thought was a design for a hydrogen bomb.

Such a bomb gets its energy from the fusion of light elements—possibly but not necessarily hydrogen—to make other light elements, with the consequent release of energy. This is the process that makes stars shine. From the beginning of the war, a number of scientists realized that if this process could be duplicated, one could make a weapon of almost limitless energy. The trick was to heat the fusible elements to temperatures like those of the interior of the sun. This was to be done in two steps by using the energy from a fission bomb. First, one had to “ignite” the fusing light elements; second, once ignited, the fusion reaction had to “propagate”—i.e., maintain the ignited state. This latter process was the hard part, and all the designs up to those of Ulam and Teller resulted in a cooling-off before they could propagate. This problem was not solved by Fuchs and von Neumann, but they did propose a novel form of ignition, which was a forerunner of the Teller-Ulam design, and this is what Fuchs gave to the Russians. There is no consensus on the extent to which the Russians used it; but there is increasing agreement that it was of significant help to their program.


I thought of all of this when I read the fascinating new book Spying on the Bomb by Jeffrey T. Richelson, a senior fellow at the privately funded National Security Archive and the author of other books on military intelligence. While some of this material has been available in other sources, it has never been put together so comprehensively. He has also interviewed some of the participants. The book begins with an account of US attempts during World War II to learn what the Germans were doing and goes on to describe its efforts to obtain information about the nuclear programs of the Iraqis, North Koreans, South Africans, Israelis, and Iranians. The one common theme is that if you do not have both agents on the ground and competent people to interpret what they have uncovered, you are playing a game of blindman’s bluff with very high stakes indeed.

So far as I know, the Germans never tried very hard to learn about our nuclear program. I think that they simply did not take seriously the possibility that the US had one. In the early summer of 1945, ten German nuclear scientists were confined in a manor house outside Cambridge, England, and their conversations recorded. When the bombing of Hiroshima was announced, their collective initial reaction was disbelief. On the other hand, we took the possibility of a German program very seriously. It was the British who first concluded from limited intelligence that there was no crash program in Germany to build a bomb. Professor Peierls told me that he was convinced of this because he had got hold of catalogs of courses in German universities and saw that the usual people were teaching the usual physics courses.

However, in the fall of 1943 there was a scare. That summer a German nuclear physicist named Hans Jensen had visited Bohr in Copenhagen. Jensen was not part of the German nuclear program but was close to people who were. He brought to Bohr news of what Werner Heisenberg and the people around him seemed to be doing. Bohr obtained from Jensen a drawing of something that he took to be a nuclear weapon. Who made this drawing was never clear. In October of 1943, Bohr escaped to England carrying with him the information he had learned from Jensen. In December of 1943, Bohr came to the United States and was debriefed by General Leslie Groves, who was in charge of the bomb project. He showed Groves the drawing and Groves became extremely exercised. He insisted that Oppenheimer stop everything he was doing and convene a meeting of experts in Los Alamos as soon as Bohr arrived. In the 1970s I was able to contact the scientists who had attended this meeting and were still alive, including Bohr’s son Aage, Hans Bethe, and Edward Teller. Teller told me that he had no recollection of the meeting but Bethe told me that he took one look at the drawing and saw that it was the drawing of a reactor.2 His first thought was that the Germans must be crazy. Apparently, he thought, they wanted to drop a reactor on London. What neither he nor any of the rest of those at the meeting realized was that the Germans were not crazy at all. By 1940, they understood that you could use plutonium as a nuclear explosive and that this was made in reactors. They never succeeded in making a workable reactor but they knew what to do with one.

In the fall of 1943, General Groves authorized the creation of an intelligence mission that was to follow the troops across Europe and learn once and for all what the Germans had done to produce nuclear weapons. The mission was called Alsos and its scientific leader was the Dutch-born physicist Samuel Goudsmit. By Christmas of 1944, Goudsmit had seen enough to be sure that the Germans never had a workable program. In his book he was somewhat derisive about their efforts. He even, quite incorrectly, chided Heisenberg for failing to realize that plutonium was a possible nuclear explosive. That Goudsmit could make a mistake like this shows just how difficult it is to gather and interpret intelligence.

  1. 1

    For the full text see http://nuclearwea-ponarchive.org/News/Voprosy2.html.

  2. 2

    The late Robert Serber gave me copies of the documents, including a letter from Oppenheimer to Groves that described the meeting and included a list of participants.

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