Nuclear Weapons
There are two types of nuclear weapons, each of which utilizes a different nuclear reaction: nuclear fission and nuclear fusion. The bomb developed by the Manhattan Project and dropped on Japan during World War II were fission weapons, also known as atomic bombs. Hydrogen bombs are fusion weapons, and these were first developed and produced during the early 1950s.
In fission weapons, the explosive energy is derived from nuclear fission, in which large atomic nuclei are split into two roughly equal parts. Every time a nucleus divides, it releases a large amount of energy. Each fission reaction also produces one or more neutrons, the subatomic particles that are needed to initiate a fission reaction. Thus, once a fission reaction has been started in a few nuclei, it rapidly spreads to other nuclei around it, creating a chain reaction. The two nuclei most commonly used for this type of nuclear reaction are uranium-235 and plutonium-239.
The necessary fission reaction will not occur if an atomic bomb carries any single piece of fissionable material that is more than a few kilograms. The bomb can contain more than one piece of this size, but it seldom contains more than three or four. Thus there is a limit to the size of a fission weapon, as well as the energy it can release. Nuclear weapons and the force of their blasts are measured in kilotons, each of which is equivalent to a thousand tons of TNT. Fission weapons are limited to 20 or 30 kilotons.
Fusion weapons derive their explosive power from a reaction that is the opposite of fission. In fusion, two small nuclei combine or fuse, releasing large amounts of energy in the process. The materials needed to initiate another fusion reaction are produced as a byproduct. Fusion, like fission, is a cyclic reaction.
In contrast to fission weapons, a hydrogen bomb can be of almost any size. Such a bomb consists of a fission bomb at the core, surrounded by a mass of hydrogen isotopes used in the fusion reactions. No limit exists to the mass of hydrogen that can be used, and there is thus no theoretical limit to the size of fusion weapons. The practical limit is simply the necessity of transporting it to a target; the bomb cannot be so large that a rocket or an airplane is unable to carry it effectively. Both fission and fusion weapons are often classified as strategic or tactical. Strategic weapons are long-range weapons intended primarily for attack on enemy land. Tactical weapons are designed for use on the battlefield, and their destructive power is adjusted for their shorter range.
Nuclear weapons cause destruction in a number of different ways. They create temperatures upon explosion that are, at least initially, millions of degrees hot. Some of their first effects are heat effects, and materials are often incinerated on contact. The heat from the blast also causes rapid expansion of air, resulting in very high winds that can blow over buildings and other structures. A weapon blast also releases high levels of radiation, such as neutrons, x rays, and gamma rays. Humans and other animals close to the center of the blast suffer illness and death from radiation exposure. The set of symptoms associated with such exposure is known as radiation sickness. Many individuals who survive radiation sickness eventually develop cancer and their offspring frequently suffer genetic damage. Finally, a weapon's blast releases huge amounts of radioactive materials. Some of these materials settle out of the atmosphere almost immediately, creating widespread contamination. Others remain in the atmosphere for weeks or months, resulting in long-term radioactive fallout.
Because of their destructive power, the nations of the world have been trying for many years to reach agreements on limiting the manufacture and possession of nuclear weapons. Between July 16, 1945, and September 23, 1992, the United States of America conducted (by official count) 1054 nuclear tests, and two nuclear attacks. In 1963, the United States and the former Soviet Union agreed to a Limited Nuclear Test Ban Treaty that banned explosions in the atmosphere, outer space, and underwater. After 1963, both nations continued testing underground. The 1974 Threshold Test Ban Treaty restricted the underground testing of nuclear weapons by the United States and the former Soviet Union to yields no greater than 150 kilotons.
In the 1980s and 1990s, debates over arms control and continued testing of nuclear weapons were affected by a number of international developments. The first was the growing internal weakness and eventual disintegration of the former Soviet Union. After a decade of difficult negotiations, the United States and the Soviet Union signed a bilateral Strategic Arms Reduction Agreement, or START I, on July 31, 1991. Five months later the Soviet Union dissolved. It was succeeded by four states that had nuclear weapons on their territories: Russia, the Ukraine, Belarus, and Kazakhstan. On December 5, 2001, the United States and the Russian Federation succeeded in reducing their number of deployed warheads to the level specified by START I. The Ukraine, Belarus, and Kazakhstan have eliminated or removed from their territory all nuclear weapons left over from the Soviet period. The START II treaty, which specifies further reductions in the number of nuclear weapons possessed by both powers, was ratified by the U.S. Senate on January 26, 1996, and by the Russian Duma on April 14, 2000. On May 24, 2002, President George W. Bush of the United States and President Vladimir Putin of Russia signed the Strategic Offensive Reductions Treaty, which commits both nations to reduce the number of their nuclear warheads to two-thirds of their 2002 levels by December 31, 2012.
The second international development of concern has been the steady increase in the number of states possessing nuclear weapons, and the potential for their use in international conflicts. As of the spring of 2002, the Carnegie Institute's Non-Proliferation Project estimates that 35 nations have some type of nuclear ballistic missile. It is difficult to obtain precise information about the number and location of these weapons because many countries in the so-called "nuclear club" have not openly acknowledged their membership.
The third development since the 1980s is the growing possibility that terrorist groups might acquire the information and materials to build nuclear devices. This fear acquired new prominence after the terrorist attacks of September 11, 2001. As early as 1997 Alexander Lebed, a Russian general, claimed that the former Soviet Union had developed nuclear weapons small enough to fit in a suitcase. Although technical information is lacking on the Russian side, the United States' experimental development of small-sized nuclear weapons suggests that it is technically possible to design a bomb small enough to fit in a large suitcase. In addition, it is known that members of al-Qaeda made several attempts to purchase commercial reactor-grade plutonium during the 1990s. As of 2002, however, the likelihood of a terrorist group's constructing a small portable nuclear device is not high. The construction of a suitcase bomb using plutonium would require a very high degree of sophistication, and would be extremely hazardous to its creators. On the other hand, there are no substantial technical obstacles for a small terrorist group to manufacture a simple but highly destructive nuclear bomb about the size of a truck. One scientific expert has stated, "There is no doubt that if a group like al-Qaeda were to obtain sufficient fissile material—no more than 12 kg of plutonium, or 50 kg of highly enriched uranium, and quite possibly less—a highly destructive [nuclear] bomb could be constructed."
Resources
Books
Dresser, P. D., ed. Nuclear Power Plants Worldwide. Detroit, MI: Gale Research, 1993.
Jagger, J. The Nuclear Lion: What Every Citizen Should Know about Nuclear Power and Nuclear War. New York: Plenum, 1991.
Weinburg, A. M. Continuing the Nuclear Dialogue. La Grange Park, IL: American Nuclear Society, 1985.
Periodicals
Ahearne, J. F. "Nuclear Power after Chernobyl." Science (May 8, 1987): 673–79.
Other
National Academy of Sciences, Committee on International Security and Arms Control. The Future of U.S. Nuclear Weapons Policy. Washington, DC: National Academy Press, 1997.
Robinson, C. Paul. A White Paper: Pursuing a New Nuclear Weapons Policy for the Twenty-First Century. Albuquerque, NM: Sandia National Laboratories, 2002.
Sublette, Carey. "Could Al-Qaeda Go Nuclear?" EnviroWeb. May 18, 2002 [cited July 11, 2002]. <http://www.nuketesting.envirowe b.org>.
Organizations
Federation of American Scientists, 1717 K Street, NW, Suite 209, Washington, DC USA 20036 (202) 546-3300, <www.fas.org>.
National Nuclear Security Administration, Sandia National Laboratories, New Mexico, P. O. Box 5800, Albuquerque, NM USA 87185 (925) 294-3000, <www.sandia.gov>.
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