20 July 2009
The invention: Popularly known as the “H-Bomb,” the hydrogen bomb differs from the original atomic bomb in using fusion, rather than fission, to create a thermonuclear explosion almost a thousand times more powerful. The people behind the invention: Edward Teller (1908- ), a Hungarian-born theoretical physicist Stanislaw Ulam (1909-1984), a Polish-born mathematician Crash Development Afew months before the 1942 creation of the Manhattan Project, the United States-led effort to build the atomic (fission) bomb, physicist Enrico Fermi suggested to Edward Teller that such a bomb could release more energy by the process of heating a mass of the hydrogen isotope deuterium and igniting the fusion of hydrogen into helium. Fusion is the process whereby two atoms come together to form a larger atom, and this process usually occurs only in stars, such as the Sun. Physicists Hans Bethe, George Gamow, and Teller had been studying fusion since 1934 and knew of the tremendous energy than could be released by this process—even more energy than the fission (atom-splitting) process that would create the atomic bomb. Initially, Teller dismissed Fermi’s idea, but later in 1942, in collaboration with Emil Konopinski, he concluded that a hydrogen bomb, or superbomb, could be made. For practical considerations, it was decided that the design of the superbomb would have to wait until after the war. In 1946, a secret conference on the superbomb was held in Los Alamos, New Mexico, that was attended by, among other Manhattan Project veterans, Stanislaw Ulam and Klaus Emil Julius Fuchs. Supporting the investigation of Teller’s concept, the conferees requested a more complete mathematical analysis of his own admittedly crude calculations on the dynamics of the fusion reaction. In 1947, Teller believed that these calculations might take years. Two years later, however,the Soviet explosion of an atomic bomb convinced Teller that America’s ColdWar adversary was hard at work on its own superbomb. Even when new calculations cast further doubt on his designs, Teller began a vigorous campaign for crash development of the hydrogen bomb, or H-bomb. The Superbomb Scientists knew that fusion reactions could be induced by the explosion of an atomic bomb. The basic problem was simple and formidable: How could fusion fuel be heated and compressed long enough to achieve significant thermonuclear burning before the atomic fission explosion blew the assembly apart? A major part of the solution came from Ulam in 1951. He proposed using the energy from an exploding atomic bomb to induce significant thermonuclear reactions in adjacent fusion fuel components. This arrangement, in which the A-bomb (the primary) is physically separated from the H-bomb’s (the secondary’s) fusion fuel, became known as the “Teller-Ulam configuration.” All H-bombs are cylindrical, with an atomic device at one end and the other components filling the remaining space. Energy from the exploding primary could be transported by X rays and would therefore affect the fusion fuel at near light speed—before the arrival of the explosion. Frederick de Hoffman’s work verified and enriched the new concept. In the revised method, moderated X rays from the primary irradiate a reactive plastic medium surrounding concentric and generally cylindrical layers of fusion and fission fuel in the secondary. Instantly, the plastic becomes a hot plasma that compresses and heats the inner layer of fusion fuel, which in turn compresses a central core of fissile plutonium to supercriticality. Thus compressed, and bombarded by fusion-produced, high-energy neutrons, the fission element expands rapidly in a chain reaction from the inside out, further compressing and heating the surrounding fusion fuel, releasing more energy and more neutrons that induce fission in a fuel casing-tamper made of normally stable uranium 238. With its equipment to refrigerate the hydrogen isotopes, the device created to test Teller’s new concept weighed more than sixty tons. During Operation Ivy, it was tested at Elugelab in the Marshall Islands on November 1, 1952. Exceeding the expectations of all concerned and vaporizing the island, the explosion equaled 10.4 million tons of trinitrotoluene (TNT), which meant that it was about seven hundred times more powerful than the atomic bomb dropped on Hiroshima, Japan, in 1945. A version of this device weighing about 20 tons was prepared for delivery by specially modified Air Force B-36 bombers in the event of an emergency during wartime. In development at Los Alamos before the 1952 test was a device weighing only about 4 tons, a “dry bomb” that did not require refrigeration equipment or liquid fusion fuel; when sufficiently compressed and heated in its molded-powder form, the new fusion fuel component, lithium-6 deutride, instantly produced tritium, an isotope of hydrogen. This concept was tested during Operation Castle at Bikini atoll in 1954 and produced a yield of 15 million tons of TNT, the largest-ever nuclear explosion created by the United States. Consequences Teller was not alone in believing that the world could produce thermonuclear devices capable of causing great destruction. Months before Fermi suggested to Teller the possibility of explosive thermonuclear reactions on Earth, Japanese physicist Tokutaro Hagiwara had proposed that a uranium 235 bomb could ignite significant fusion reactions in hydrogen. The Soviet Union successfully tested an H-bomb dropped from an airplane in 1955, one year before the United States did so. Teller became the scientific adviser on nuclear affairs of many presidents, from Dwight D. Eisenhower to Ronald Reagan. The widespread blast and fallout effects of H-bombs assured the mutual destruction of the users of such weapons. During the Cold War (from about 1947 to 1981), both the United States and the Soviet Union possessed H-bombs. “Testing” these bombs made each side aware of how powerful the other side was. Everyone wanted to avoid nuclear war. It was thought that no one would try to start a war that would end in the world’s destruction. This theory was called deterrence: The United States wanted to let the Soviet Union know that it had just as many bombs, or more, than it did, so that the leaders of the Sovet Union would be deterred from starting a war.Teller knew that the availability of H-bombs on both sides was not enough to guarantee that such weapons would never be used. It was also necessary to make the Soviet Union aware of the existence of the bombs through testing. He consistently advised against U.S. participation with the Soviet Union in a moratorium (period of waiting) on nuclear weapons testing. Largely based on Teller’s urging that underground testing be continued, the United States rejected a total moratorium in favor of the 1963 Atmospheric Test Ban Treaty. During the 1980’s, Teller, among others, convinced President Reagan to embrace the Strategic Defense Initiative (SDI). Teller argued that SDI components, such as the space-based “Excalibur,” a nuclear bomb-powered X-ray laser weapon proposed by the Lawrence- Livermore National Laboratory, would make thermonuclear war not unimaginable, but theoretically impossible.