Hydrogen Bomb
Even as work on the first atomic bomb was going ahead, some scientists were thinking about an even more powerful weapon, the hydrogen, or fusion bomb. As far back as the 1920s, scientists had been exploring the possibility that small nuclei might join together--or fuse--to make larger nuclei. Ernest Rutherford (1871-1937) and his colleagues at Cambridge UniversityÕs Cavendish Laboratory had observed the hydrogen fusion reaction in 1934. In 1938, the German-Austrian physicist, Hans Bethe (1906-), summarized much previous work on fusion in a theory that explained the production of energy in the stars. Bethe showed how four hydrogen nuclei--protons--might fuse to produce a single helium nucleus, with the release of enormous amounts of energy. A Japanese physicist, Tokutaro Hagiwara, had delivered a lecture in 1941 on the possibility of using uranium fission to ignite a hydrogen fusion reaction. So the theoretical groundwork for a fusion bomb had been laid even before concrete work on the atomic fission bomb began.
Many scientists realized that nuclear fusion could be used as a source of energy on earth, for either military or peacetime applications, if a method could be found to carry out and control the reaction. But that "if" was a very large one. For one thing, nuclear fusion reactions require temperatures in the range of 40 million degrees Celsius. Because of these high temperature requirements, fusion reactions are also referred to as thermonuclear reactions. The task of working at such high temperatures was a daunting one.
One scientist, Edward Teller, an emigré from Hungary, began arguing for the development of a fusion weapon, or " super" atomic bomb, during the Manhattan Project. He pointed out that such a weapon would be many times more powerful than a fission (atomic) bomb and would provide the United States with an unmatched military superiority.
Teller's ideas were largely ignored, however, as the United States endeavored to complete the bombs it later dropped on Hiroshima and Nagasaki. The technical requirements for the hydrogen bomb were staggering, and production of the crude first atomic bombs was already difficult enough. For example, an important raw material needed for the hydrogen bomb, tritium (hydrogen-3) had to be made synthetically. It would have taken eighty times the effort the U.S. was already spending on the manufacture of plutonium for the atomic bomb to make the required tritium. There was not enough time, manpower, or equipment to work on a fusion bomb when the fission bomb had not even been developed.
After World War II ended, many scientists, appalled at the damage done in Hiroshima and Nagasaki, rejected the idea of building even more powerful weapons. Furthermore, there seemed to be no challenge to the United States' military superiority, based as it was on its possession of fission bombs. However, other scientists, particularly Edward Teller, were sure that the so-called Super bomb was possible, and they continued their research. Then in September1949, the Soviet Union exploded its first atomic bomb. The Manhattan Project reseach on the atomic bomb had been kept secret from the Soviets, though that country had been allied with Britain and the United States to defeat German and Japan. But with the help of materials stolen through espionage, Soviet scientists duplicated the atomic weapon, and let the world know they had it by testing it above ground. A few months after the Soviet test, in January 1950, President Harry S. Truman (1884-1972) ordered the Atomic Energy Commission to begin work on developing a fusion bomb.
The general concept for such a bomb is a two-part explosion, where a fission bomb then sets off a fusion reaction. The first Super design relied on the heat from the primary fission bomb to set off the secondary fusion explosion. Edward Teller, in conjunction with the mathematician Stanislaw Ulam (1909-1984), came up with a more workable idea (that became the basis for subsequent weapons) of using radiation from the primary fission bomb to generate a shock wave that would compress the thermonuclear fuel and thus set off the fusion reaction. The greatest technical problem scientists faced was finding a way to pack hydrogen isotopes together tightly enough to allow fusion to occur and to make the bomb small enough to be transportable. One of the first solutions to this problem was to surround the fission bomb with crystalline lithium hydride, made of lithium-6 and hydrogen-2. When the fission bomb explodes, tritium (hydrogen-3) is produced. This isotope then fuses with hydrogen-2.
The first thermonuclear test was carried out by the United States in May 1951. The landmark full-scale thermonuclear explosion was at Bikini Atoll on November 1, 1952. It had the destructive power of about seven million tons of TNT, roughly 500 times greater than that of the first fission bombs. Meanwhile the Soviet Union had also developed nuclear fusion bombs, the product of intensive research by the countryÕs top scientists, supplemented by ongoing espionage. In 1948 Andrei Sakharov (1921-1989) had independently derived a fusion bomb design analogous to one Teller had described in 1946. (TellerÕs design was called the Alarm Clock, SakharovÕs the Layer Cake.) Soviet scientists in 1953 tested the first transportable fusion bomb, one that could be air-dropped and was designed for mass production. A transportable fusion bomb was not tested by the United States until 1956.
The ability of both countries to deploy fusion bombs led to an arms race that did not effectively end until the collapse of the Soviet Union in 1989. Bombs were made small enough to be delivered from long-range missiles, and with over a thousand times the destructive power of the bomb dropped on Hiroshima. Other countries too developed thermonuclear weapons, including India and Pakistan, who aggressively tested their arsenals in May 1998. However, the drastic horror of actually using the bombs had up through that time held any country back from waging nuclear war. In the best light, the development of the hydrogen bomb had been a deterrent to conflict, an ominous stabilizing force.
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