[noo-klee-er, nyoo- or, by metathesis, -kyuh-ler]
disarmament, nuclear, the reduction and limitation of the various nuclear weapons in the military forces of the world's nations. The atomic bombs dropped (1945) on Japan by the United States in World War II demonstrated the overwhelming destructive potential of nuclear weapons and the threat to humanity posed by the possibility of nuclear war and led to calls for controls on or elimination of such weapons.

Public Pressure

Some of the scientists who helped make the bomb started the Union of Concerned Scientists, and since then many public groups have formed to campaign for disarmament, including the Campaign for Nuclear Disarmament (CND) in Great Britain, SANE and the Nuclear Freeze in the United States, and the worldwide Physicians for Social Responsibility. In addition, many local antiwar, ecological, and women's groups have focused on nuclear issues. Disarmament advocates have used political campaigns, mass rallies, blockades of facilities where weapons are manufactured or stored, and even attacks on nuclear weapons themselves, called "ploughshare actions." Disarmament groups have long opposed nuclear testing, beginning with the protests leading up to the Moscow Agreement of 1963, a partial test ban. More recently, the international ecological group Greenpeace tried to disrupt French nuclear testing in the Pacific, and there were coordinated protest campaigns against testing in Kazakhstan and in Nevada.

International Agreements

Official efforts at arms control have made some progress, but only very slowly. The first resolution (1946) of the General Assembly of the United Nations set up an Atomic Energy Commission to make proposals for the peaceful uses of atomic energy and for the elimination of weapons of mass destruction. The commission concentrated debate on the Baruch Plan for an international agency to control atomic power and weapons and passed it, but the plan was vetoed by the USSR in the Security Council. As the cold war progressed, the commission reached an impasse (1948). With the proliferation of nuclear weapons, concern over the situation became more acute.

In 1952 a UN Disarmament Commission was formed under the Security Council. It became the repository for all disarmament proposals under UN auspices. In 1953 a commission subcommittee was set up, consisting of Canada, France, Great Britain, the United States, and the USSR. In this subcommittee, which met intermittently from 1954 to 1957, there was basic disagreement between East and West. The West held that an international control system and on-site inspection must be developed before disarmament could proceed; the USSR stated that the Western position would result in inspection without disarmament and proposed instead an immediate ban on nuclear weapons, without inspection but with possible later, but unspecified, controls. Conferences among the United States, Great Britain, and the Soviet Union on the formulation of a treaty to ban nuclear testing began in Geneva in 1958. The same year these three powers agreed to suspend nuclear testing for one year. The voluntary moratorium continued until it was broken by the Soviet resumption of testing (1961).

The UN Disarmament Commission, expanded (1958) to include all members of the United Nations, was reduced in 1962 to 18 members. Soon afterward, France withdrew. In 1963 the United States, Great Britain, and the Soviet Union reached the Moscow Agreement, which banned testing in the atmosphere, in outer space, and underwater. Other discussions were conducted simultaneously by the 18-member UN Disarmament Commission. No agreement was reached on arms limitation, although the Soviet Union and the United States moved closer together on the issue of the proliferation of nuclear weapons. The two countries proposed (1968) to the commission a 25-year nonproliferation agreement that was later approved by the UN General Assembly and took effect in 1970; it was made permament in 1995. By the end of the century the treaty had been ratified by all nations save Cuba, Israel, Pakistan, and India. North Korea threatened to withdraw in the 1990s and did so in 2003. Pakistan and India have tested nuclear weapons, North Korea has conducted a subkiloton nuclear test, and Israel is believed to have nuclear weapons. Argentina, Brazil, Iran, Iraq, Libya, and South Africa are known to have or are suspected of having attempted to develop nuclear weapons; South Africa actually produced a small nuclear arsenal but later disarmed.

A comprehensive test ban treaty was approved by the UN General Assembly and signed in 1996; over 170 nations have now signed. The treaty prohibits all nuclear testing, establishes a worldwide network of monitoring stations, and allows for inspections of suspicious sites. Conservative opposition to the treaty in the United States led the Senate to reject ratification in 1999; it was ratified by Russia in 2000.

The Soviet Union and the United States began Strategic Arms Limitation Talks (SALT) in the late 1960s, and in 1972 agreed to limit antiballistic missiles (ABMs) and reached an interim accord limiting intercontinental ballistic missiles (ICBMs). Another interim SALT agreement was reached in Nov., 1974, that limited ballistic missile launchers. SALT II, which banned new ICBMs and limited other delivery vehicles, was signed in 1979. It was never ratified, but both countries announced they would adhere to it.

In 1982 the United States and Soviet Union began a new set of negotiations, called START (Strategic Arms Reduction Talks). In 1987, President Reagan and Soviet leader Mikhail Gorbachev signed the INF treaty to eliminate intermediate-range nuclear forces, and a START treaty, signed by President George H. W. Bush and Gorbachev in 1991, called for additional reductions in U.S. and Soviet nuclear arsenals and on-site inspections. In response to increasing Soviet political instability, Bush announced (1991) the elimination of most U.S. tactical nuclear arms, took strategic bombers off alert status, and called for further reductions in ballistic missiles.

With the USSR's disintegration, its nuclear arms passed to Belarus, Kazakhstan, Russia, and Ukraine. The republics pledged to abide by existing treaties and remove outlying weapons to Russia for destruction. In 1993, Bush and Russian president Yeltsin signed a START II treaty that called for cutting nuclear warheads by two thirds by 2003 and eliminating those weapons most likely to be used in a first strike. Ukraine, fearing Russian domination, did not ratify START and the 1970 nonproliferation treaty until 1994, but by 1996 the nuclear arsenals of Belarus, Kazakstan, and Ukraine had been dismantled.

In 1997, Yeltsin and U.S. president Bill Clinton set a goal of further reducing the number of each nation's warheads to 2,500 or less, less than half that permitted under START II. President George W. Bush, regarding earlier arms agreements and the need for them as cold war relics, in 2001 agreed with Russian president Putin to reduce the number of warheads over the next decade to roughly two thirds that called for in START II, while at the same time essentially abandoning that agreement (which was still unratified by the United States) and its restrictions on the types of weapons permitted. This agreement was formalized in the May, 2002, Moscow Treaty. However, under the treaty, both nations are allowed to store the weapons that they remove from deployment, and the accord has been criticized for its lack of a mechanism to verify compliance. Following the U.S. abandonment of the ABM treaty (see below), Russia announced that it would no longer be bound by START II. In 2009, however, the United States and Russia agreed in outline to further nuclear weapons cuts under a new, unfinalized treaty intended to replace START I before its expiration in Dec., 2009, but as negotiations continued past the treaty's lapse both nations pledged to continue to observe START I.

In 1983, President Reagan proposed the development of a U.S. space-based defensive system to act as a shield against a missile attack. The Strategic Defense Initiative, or "Star Wars" as it was popularly known, was ultimately abandoned by the United States, but a more limited missile-defense system using ground-based missiles to provide protection against an accidental launching of a ballistic missile or against a missile attack from a "rogue" nation was proposed in 1991 by President G. H. W. Bush. Such a system would contravene the 1972 ABM treaty and was objected to by Russia, but development and testing proceeded during the 1990s. In 2001, President George W. Bush proposed accelerating and expanding the development and deployment of the system and called for the ABM treaty to be replaced by a new "framework" that would permit such defenses. The United States announced that it would withdraw from the ABM treaty in Dec., 2001, and officially withdrew in June, 2002.


See W. Epstein and B. Feld, New Directions in Disarmament (1981); J. Schell, The Abolition (1986); M. Thee, Arms and Disarmament (1987).

reactor, nuclear: see nuclear reactor.
test-ban treaty, nuclear: see disarmament, nuclear.
or weak nuclear force

Fundamental interaction that underlies some forms of radioactivity and certain interactions between subatomic particles. It acts on all elementary particles that have a spin of 12. The particles interact weakly by exchanging particles that have integer spins. These particles have masses about 100 times that of a proton, and it is this relative massiveness that makes the weak force appear weak at low energies. For example, in radioactive decay, the weak force has a strength about 1/100,000 that of the electromagnetic force. However, it is now known that the weak force has intrinsically the same strength as the electromagnetic force, and the two are believed to be only different manifestations of a single electroweak force (see electroweak theory).

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or strong nuclear force

Fundamental force acting between elementary particles of matter, mainly quarks. The strong force binds quarks together in clusters to form protons and neutrons and heavier short-lived particles. It holds together the atomic nucleus and underlies interactions among all particles containing quarks. In strong interactions, quarks exchange gluons, carriers of the strong force, which are massless particles with one unit of intrinsic spin. Within its short range (about 10−15 m), the strong force appears to become stronger with distance. At such distances, the strong interaction between quarks is about 100 times greater than the electromagnetic force.

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Environmental devastation that some scientists contend would result from a nuclear war. The basic cause, as hypothesized, would be huge fireballs created by exploding nuclear warheads, which would ignite great fires (firestorms). Smoke, soot, and dust would be lifted to high altitudes and driven by winds to form a uniform belt encircling the Northern Hemisphere. The clouds could block out all but a fraction of the Sun's light, and surface temperatures would plunge for as much as several weeks. The semidarkness, killing frosts, and subfreezing temperatures, combined with high doses of radiation, would interrupt plant photosynthesis and could thus destroy much of the Earth's vegetation and animal life. Other scientists dispute the results of the original calculations, and, though such a nuclear war would undoubtedly be devastating, the degree of damage to life on the Earth remains controversial.

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or atomic weapon or thermonuclear weapon

Bomb or other warhead that derives its force from nuclear fission, nuclear fusion, or both and is delivered by an aircraft, missile, or other system. Fission weapons, commonly known as atomic bombs, release energy by splitting the nuclei of uranium or plutonium atoms; fusion weapons, known as hydrogen bombs or thermonuclear bombs, fuse nuclei of the hydrogen isotopes tritium or deuterium. Most nuclear weapons actually combine both processes. Nuclear weapons are the most potent explosive devices ever invented. Their destructive effects include not only a blast equivalent to thousands of tons of TNT but also blinding light, searing heat, and lethal radioactive fallout. The number of nuclear weapons reached a peak of some 32,000 for the United States in 1966 and some 33,000 for the Soviet Union in 1988. Since the end of the Cold War, both countries have decommissioned or dismantled thousands of warheads. Other declared nuclear powers are the United Kingdom, France, China, India, Pakistan, and North Korea. Israel is widely assumed to possess nuclear weapons. Some countries, such as South Africa, Brazil, Argentina, and Iraq, have acknowledged pursuing nuclear weapons in the past but have abandoned their programs. Seealso Nuclear Non-proliferation Treaty; Nuclear Test-Ban Treaty.

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Device that can initiate and control a self-sustaining series of nuclear-fission reactions. Neutrons released in one fission reaction may strike other heavy nuclei, causing them to fission. The rate of this chain reaction is controlled by introducing materials, usually in the form of rods, that readily absorb neutrons. Typically, control rods made of cadmium or boron are gradually inserted into the core if the series of fissions begins to proceed at too great a rate, which could lead to meltdown of the core. The heat released by fission is removed from the reactor core by a coolant circulated through the core. Some of the thermal energy in the coolant is used to heat water and convert it to high-pressure steam. This steam drives a turbine, and the turbine's mechanical energy is then converted into electricity by means of a generator. Besides providing a valuable source of electric power for commercial use, nuclear reactors also serve to propel certain types of military surface vessels, submarines, and some unmanned spacecraft. Another major application of reactors is the production of radioactive isotopes that are used extensively in scientific research, medical therapy, and industry.

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Medical specialty using radioactive elements or isotopes for diagnosis and treatment of disease. A radioisotope is introduced into the body (usually by injection). The radiation it emits, detected by a scanner and recorded, reflects its distribution in different tissues and can reveal the presence, size, and shape of abnormalities in various organs. The isotopes used have short half-lives and decay before radioactivity causes any damage. Different isotopes tend to concentrate in particular organs (e.g., iodine-131 in the thyroid). Radioactive substances are also implanted to treat small, early-stage cancers. This yields a slow, continuous dose that limits damage to normal cells while destroying tumour cells. Seealso computerized axial tomography; diagnostic imaging; positron emission tomography; radiation therapy; radiology.

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Selective absorption of very high-frequency radio waves by certain atomic nuclei subjected to a strong stationary magnetic field. Nuclei that have at least one unpaired proton or neutron act like tiny magnets. When a strong magnetic field acts on such nuclei, it sets them into precession. When the natural frequency of the precessing nuclear magnets corresponds to the frequency of a weak external radio wave striking the material, energy is absorbed by the nuclei at a frequency called the resonant frequency. NMR is used to study the molecular structure of various solids and liquids. Magnetic resonance imaging, or MRI, is a version of NMR used in medicine to view soft tissues of the human body in a hazard-free, noninvasive way.

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One of two or more substances with identical molecular formulas but different configurations, differing only in the arrangement of their component atoms. It usually refers to stereoisomers (rather than constitutional isomers or tautomers; see isomerism, tautomerism), of which there are two types. Optical isomers, or enantiomers (see optical activity), occur in mirror-image pairs. Geometric isomers are often the result of rigidity in the molecular structure; in organic compounds, this is usually due to a double bond (see bonding) or a ring structure. In the case of a double bond between two carbon atoms, if each has two other groups bonded to it and all are rigidly in the same plane, the corresponding groups can be on the same side (cis) of the CdoublehorzbondC bond or across the CdoublehorzbondC bond (trans) from each other. An analogous distinction can be made for ring structures that are all in a plane, between isomers whose substituent groups are on the same side and isomers whose substituent groups are on both sides of the plane. Diastereomers that are not enantiomers also fall into this category. Most cis-trans isomers are organic compounds.

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Process by which nuclear reactions between light elements form heavier ones, releasing huge amounts of energy. In 1939 Hans Bethe suggested that the energy output of the sun and other stars is a result of fusion reactions among hydrogen nuclei. In the early 1950s American scientists produced the hydrogen bomb by inducing fusion reactions in a mixture of the hydrogen isotopes deuterium and tritium, forming a heavier helium nucleus. Though fusion is common in the sun and other stars, it is difficult to produce artificially and is very difficult to control. If controlled nuclear fusion is achieved, it might provide an inexpensive energy source because the primary fuel, deuterium, can be extracted from ordinary water, and eight gallons of water could provide the energy equivalent to 2,500 gallons of gasoline.

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Top: Uranium-235 combines with a neutron to form an unstable intermediate, which quickly splits elipsis

Division of a heavy atomic nucleus into two fragments of roughly equal mass, accompanied by the release of a large amount of energy, the binding energy of the subatomic particles. The energy released in the fission of one uranium nucleus is about 50 million times greater than that released when a carbon atom combines with oxygen atoms in the burning of coal. The energy appears as kinetic energy of the fragments, which converts to thermal energy as the fragments collide in matter and slow down. Fission also releases two or three free neutrons. The free neutrons can bombard other nuclei, leading to a series of fissions called a chain reaction. The energy released from nuclear fission is used to generate electricity, to propel ships and submarines, and is a source of the vast destructive power of nuclear weapons.

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Descent of radioactive materials from the atmosphere to the earth. Radioactivity in the atmosphere may arise from natural causes such as cosmic rays as well as from nuclear explosions and atomic reactor operations. The explosion of nuclear weapons leads to three types of fallout: local, tropospheric, and stratospheric. The first, intense but relatively short-lived, occurs as larger radioactive particles are deposited near the site of the explosion. Tropospheric fallout occurs when the finer particles enter the troposphere, and it spreads over a larger area in the month after the explosion. Stratospheric fallout, made of fine particles in the stratosphere, may continue years after the explosion, and the distribution is nearly worldwide. Many different radioisotopes are formed during a nuclear explosion, but only long-lived isotopes (e.g., cesium-137, strontium-90) are deposited as stratospheric fallout.

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or atomic energy

Energy released from atomic nuclei in significant amounts. In 1919 Ernest Rutherford discovered that alpha rays could split the nucleus of an atom. This led ultimately to the discovery of the neutron and the release of huge amounts of energy by the process of nuclear fission. Nuclear energy is also released as a result of nuclear fusion. The release of nuclear energy can be controlled or uncontrolled. Nuclear reactors carefully control the release of energy, whereas the energy release of a nuclear weapon or resulting from a core meltdown in a nuclear reactor is uncontrolled. Seealso chain reaction, nuclear power, radioactivity.

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Property exhibited by certain types of matter of emitting radiation spontaneously. The phenomenon was first reported in 1896 by Henri Becquerel for a uranium salt, and it was soon found that all uranium compounds are radioactive due to the uranium's radioactivity. In 1898 Marie Curie and her husband discovered two other naturally occurring, strongly radioactive elements, radium and polonium. The radiation is emitted by unstable atomic nuclei (see nucleus) as they attempt to become more stable. The main processes of radioactivity are alpha decay, beta decay, and gamma decay. In 1934 it was discovered that radioactivity could be induced in ordinary matter by artificial transmutation.

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U.S. independent regulatory agency that oversees the civilian use of nuclear energy. Established in 1974 to replace the Atomic Energy Commission, the NRC licenses the construction and operation of nuclear reactors and other facilities and the ownership and use of nuclear materials. It issues standards, rules, and regulations for the maintenance of licenses, and it regularly inspects nuclear facilities to ensure compliance with public health and safety, environmental quality, national security, and antitrust laws. The NRC also investigates nuclear accidents, conducts public hearings, and reviews power-plant operations. Its commissioners are appointed by the president of the U.S.

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in full Organisation Européenne pour la Recherche Nucléaire formerly Conseil Européen pour la Recherche Nucléaire.

International scientific organization established for collaborative research into subnuclear physics. Headquartered in Geneva, CERN includes extensive facilities at sites on both sides of the Swiss-French border. The results of its experimental and theoretical work are made generally available. It was established in part in order to reclaim European physicists who had emigrated to the U.S. as a result of World War II. In 2000 it had 20 European member nations and several nations with observer status.

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