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…
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