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4 Arzamas-16—The Secret Installation To facilitate the task of assessing the progress Zeldovich and his colleagues were making on the construction of a Soviet hydrogen bomb, Sakharov, Tamm, and two other physicists who were part of this project, Vitalii Ginsburg and Iurii Romanov, were moved to different offices and given new calculators. Because their task was by no means an easy one, Sakharov found himself working longer and harder than he ever had before, remaining in his laboratory late into the night.1 Inevitably, Tamm’s group began to do more than merely check on what Zeldovich’s group had accomplished, and their suggestions for improvement eventually superseded, rather than merely complemented, the work the latter was doing. While in their offices Tamm and his colleagues were guarded closely by security personnel.2 Given their assignment, this is hardly surprising. By the late 1940s, building thermonuclear weapons was an objective of critical importance to Stalin and the rest of the Soviet leadership, no less so than the concurrent development of nuclear weapons (commonly referred to as atomic bombs). The most obvious reason for this was that both of these weapons, especially thermonuclear ones, are militarily effective. They kill far larger numbers of people and inflict more collateral damage than do conventional weapons, and because their use in war requires only a bomber crew or ground-based missile technicians, they are cheaper as well. Sakharov played no role in the development of Soviet nuclear weapons. But both he and other Soviet scientists who were tasked with building thermonuclear weapons proposed that the energy that is released in the fission of atomic nuclei—which occurs when nuclear weapons are detonated—be used to trigger the fusion of atomic nuclei that occurs when thermonuclear weapons explode. For this reason the reader should know how nuclear weapons work.3 When detonated, nuclear weapons release enormous amounts of explosive energy, far more than is released by conventional weapons, which are based on chemical reactions. In the case of nuclear weapons, this is because the amount of energy released when an atomic nucleus is split (or fissioned) is directly proportional to the amount of energy required to overcome the nuclear force that binds the components of the nucleus—protons and neutrons—together. Because the nuclear force is many times stronger than the electromagnetic force that binds atoms that are altered in purely chemical reactions, greater amounts 1. Pariiskaia, “On vsegda budet samim soboi,” 474. 2. Ibid. 3. An explanation of nuclear fission nonscientists can understand is Kip Thorne’s in Black Holes and Time Warps, 221–22. For an explanation of nuclear fusion, see chap. 5. Arzamas-16—The Secret Installation 47 of energy are required to trigger nuclear reactions than are needed to trigger chemical ones. But the greater investment of energy in initiating nuclear reactions results in the production of much more energy than that produced in chemical reactions. Nuclear reactions begin when the nucleus of a heavy element such as uranium or plutonium is bombarded by a stream of neutrons that has been triggered externally. These neutrons hit the nucleus of the heavy element with sufficient force or energy to overcome the nuclear force (or “glue”) holding it together. The nucleus splits, forming smaller and lighter elements, and in the process releases energy. The nuclei of a few heavy elements, such as uranium-238 (U-238), split naturally and spontaneously. But while U-238 is fairly plentiful, its fission does not trigger a chain reaction: its nuclei split, lighter elements are formed, and energy is released—but because a chain reaction is not triggered by this, not enough energy is released to be useful militarily. Uranium-235 is better. When its nucleus splits, it generates more neutrons than are produced by a U-238 nucleus fission, so there are additional, unattached neutrons even after light elements have formed. These additional neutrons smash into other U-235 nuclei, releasing additional energy as well as additional neutrons; these neutrons smash into yet other U-235 nuclei; and this chain reaction based on nuclear fission continues until the original nuclear fuel (the U-235) has fissioned entirely. But because U-235 is rare in nature, American scientists in the early 1940s transmuted U-238 into a new element, plutonium, with an atomic weight of 239, which could, like U-235, trigger a chain reaction when its nucleus was bombarded with neutrons.4 The key to using nuclear fission militarily, once...

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