Nuclear weapon

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The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the hypocenter.

Nuclear weapons
History of nuclear weapons
Nuclear warfare
Nuclear arms race
Weapon design / testing
Nuclear explosion
Delivery systems
Nuclear espionage
Proliferation
Countries
Nuclear weapons states US · Russia · UK · France China · India · Pakistan · Israel

A nuclear weapon is a weapon which derives its destructive force from nuclear reactions of either nuclear fission or the more powerful fusion. As a result, even a nuclear weapon with a relatively small yield is significantly more powerful than the largest conventional explosives, and a single weapon is capable of destroying or seriously disabling an entire city.

In the history of warfare, nuclear weapons have been used only twice, both during the closing days of World War II. The first event occurred on the morning of August 6, 1945, when the United States dropped a uranium gun-type device code-named "Little Boy" on the Japanese city of Hiroshima. The second event occurred three days later when a plutonium implosion-type device code-named "Fat Man" was dropped on the city of Nagasaki. The use of these weapons, which resulted in the immediate deaths of around 100,000 to 200,000 individuals (mostly civilians) and even more over time, was and remains controversial — critics charged that they were unnecessary acts of mass killing, while others claimed that they ultimately reduced casualties on both sides by hastening the end of the war (see Atomic bombings of Hiroshima and Nagasaki for a full discussion).

Since that time, nuclear weapons have been detonated on over two thousand occasions for testing and demonstration purposes. The only known countries to have detonated such weapons are the United States, Soviet Union, United Kingdom, France, People's Republic of China, India, and Pakistan. These countries are the declared nuclear powers (with Russia inheriting the weapons of the Soviet Union after its collapse).

Various other countries may hold nuclear weapons, but they have never publicly admitted possession, or their claims to possession have not been verified. For example, Israel has modern airborne delivery systems and appears to have an extensive nuclear program with hundreds of warheads (see Israel and weapons of mass destruction); North Korea has recently stated that it has nuclear capabilities (although it has made several changing statements about the abandonment of its nuclear weapons programs, often dependent on the political climate at the time) but never conducted a confirmed test and its weapons status remains unclear; and Iran currently stands accused by a number of governments of attempting to develop nuclear capabilities, though its government claims that its acknowledged nuclear activities, such as uranium enrichment, are for peaceful purposes. (For more information see List of countries with nuclear weapons.)

Apart from their use as weapons, nuclear explosives have been tested and used for various non-military uses.

Types of nuclear weapons

The two basic fission weapon designs.

Main article: Nuclear weapon design

There are two basic types of nuclear weapons. The first are weapons which produce their explosive energy through nuclear fission reactions alone. These are known colloquially as atomic bombs, atom bombs, or A-bombs. In fission weapons, a mass of fissile material (enriched uranium or plutonium) is assembled into a supercritical mass—the amount of material needed to start an exponentially growing nuclear chain reaction—either by shooting one piece of subcritical material into another, or by compressing a subcritical mass with chemical explosives, at which points neutrons are injected and the reaction begins. A major challenge in all nuclear weapon designs is ensuring that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range between the equivalent of less than a ton of TNT upwards to around 500 thousand tons (kilotons) of TNT.

The second basic type of nuclear weapon produces a large amount of its energy through nuclear fusion reactions, and can be over a thousand times more powerful than fission bombs. These are known as hydrogen bombs, H-bombs, thermonuclear bombs, and fusion bombs. They work by utilizing the Teller-Ulam design, in which a fission bomb is detonated in a specially manufactured compartment adjacent to a fusion fuel. The gamma and X-rays of the fission explosion compress and heat a capsule of tritium, deuterium, or lithium deuteride starting a fusion reaction. Neutrons emitted by this fusion reaction can induce a final fission stage in a depleted uranium tamper surrounding the fusion fuel, increasing the yield considerably as well as the amount of nuclear fallout. Each of these components is known as a "stage", with the fission bomb as the "primary" and the fusion capsule as the "secondary". By chaining together numerous stages with increasing amounts of fusion fuel, thermonuclear weapons can be made to an almost arbitrary yield; the largest ever detonated (the Tsar Bomba of the USSR) released an energy equivalent to over 50 million tons (megatons) of TNT, though most modern weapons are nowhere near that large.

There are other types of nuclear weapons as well. For example, a boosted fission weapon is a fission bomb which increases its explosive yield through a small amount of fusion reactions, but it is not a hydrogen bomb. Some weapons are designed for special purposes; a neutron bomb is a nuclear weapon that yields a relatively small explosion but a relatively large amount of prompt radiation. The detonation of a nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of radioactive contamination. Most variety in nuclear weapon design is in different yields of nuclear weapons for different types of purposes, and in manipulating design elements to attempt to make weapons extremely small.

Nuclear strategy

The United States' Peacekeeper missile was a MIRVed delivery system. Each missile could contain up to ten nuclear warheads (shown in red), each of which could be aimed at a different target. These were developed to make missile defense very difficult for an enemy country.

Main article: Nuclear warfare

Nuclear warfare strategies is a way for either fighting or avoiding a nuclear war. The policy of trying to ward off a potential attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence. The goal in deterrence is to always maintain a second strike status (the ability to respond to a nuclear attack against your country with a nuclear attack of your own) and potentially to strive for first strike status (the ability to completely destroy an enemy's nuclear forces before they could retaliate). During the Cold War, policy and military theorists in nuclear-enabled countries worked out models of what sorts of policies could prevent one from ever being attacked by a nuclear weapon.

Different forms of nuclear weapons delivery (see below) allow for different types of nuclear strategy, primarily by making it difficult to defend against them and difficult to launch a pre-emptive strike against them. Sometimes this has meant keeping the weapon locations hidden, such as putting them on submarines or train cars whose locations are very hard for an enemy to track, and other times this means burying them in hardened bunkers. Other responses have included attempts to make it seem likely that the country could survive a nuclear attack, by using missile defense (to destroy the missiles before they land) or by means of civil defense (using early warning systems to evacuate citizens to a safe area before an attack). Note that weapons which are designed to threaten large populations or to generally deter attacks are known as "strategic" weapons. Weapons which are designed to actually be used on a battlefield in military situations are known as "tactical" weapons.

There are critics of the very idea of "nuclear strategy" for waging nuclear war who have suggested that a nuclear war between two nuclear powers would result in mutual annihilation. From this point of view, the significance of nuclear weapons is to purely deter war because any nuclear war would immediately escalate out of mutual distrust and fear, resulting in Mutual Assured Destruction. This threat of national, if not global, destruction has been a strong motivation for anti-nuclear weapons activism.

Critics from the peace movement and within the military establishment have questioned the usefulness of such weapons in the current military climate. The use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, according to an Advisory Opinion issued by the International Court of Justice in 1996.

Perhaps the most controversial idea in nuclear strategy is that nuclear proliferation would be desirable. This view argues that unlike conventional weapons nuclear weapons successfully deter all-out war between states, as they did during the Cold War between the U.S. and the Soviet Union. Political scientist Kenneth Waltz is the most prominent advocate of this argument.

Weapons delivery

The first nuclear weapons were gravity bombs, such as the "Fat Man" weapon dropped on Nagasaki, Japan. These weapons were very large and could only be delivered by a bomber aircraft.

Main article: Nuclear weapons delivery

Nuclear weapons delivery— the technology and systems used to bring a nuclear weapon to its target—is an important aspect of nuclear weapons relating both to nuclear weapon design and nuclear strategy.

Historically the first method of delivery, and the method used in the two nuclear weapons actually used in warfare, is as a gravity bomb, dropped from bomber aircraft. This method is usually the first developed by countries as it does not place many restrictions on the size of the weapon, and weapon miniaturization is something which requires considerable weapons design knowledge. It does, however, limit the range of attack, the response time to an impending attack, and the number of weapons which can be fielded at any given time.

More preferable from a strategic point of view are nuclear weapons mounted onto a missile, which can use a ballistic trajectory to deliver a warhead over the horizon. While even short range missiles allow for a faster and less vulnerable attack, the development of intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has allowed some nations to plausibly deliver missiles anywhere on the globe with a high likelihood of success. More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs) allow multiple warheads to be launched at a number of targets from any one missile, reducing the chance of any successful missile defense. Today, missiles are by far the most common among systems designed for delivery of nuclear weapons. To make a warhead small enough to fit onto a missile, though, can be a difficult task.

"Tactical" weapons (see above) have involved the most variety of delivery types, including not only gravity bombs and missiles but also artillery shells, land mines, and nuclear depth charges and torpedoes for anti-submarine warfare. An atomic mortar was also tested at one time by the United States. Small, two-man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty to combine sufficient yield with portability limits their military utility.

History

The aftermath of the atomic bombing of Hiroshima.

Main article: History of nuclear weapons

The first nuclear weapons were created in the United States, by an international team including many displaced émigré scientists from central Europe with assistance from the United Kingdom and Canada, during World War II as part of the top-secret Manhattan Project. While the first weapons were developed primarily out of fear that Nazi Germany would develop them first, they were eventually used against the Japanese cities of Hiroshima and Nagasaki in August 1945. The Soviet Union developed and tested their first nuclear weapon in 1949, based partially on information obtained from Soviet espionage in the United States. Both the USA and USSR would go on to develop weapons powered by nuclear fusion (hydrogen bombs) by the mid-1950s. With the invention of reliable rocketry during the 1960s, it became possible for nuclear weapons to be delivered anywhere in the world on a very short notice, and the two Cold War superpowers adopted a strategy of deterrence to maintain a shaky peace.

US and USSR/Russian nuclear weapons stockpiles, 1945-2005.

Nuclear weapons were symbols of military and national power, and nuclear testing was often used both to test new designs as well as to send political messages. Other nations also developed nuclear weapons during this time, including the United Kingdom, France, and China. These five members of the "nuclear club" agreed to attempt to limit the spread of nuclear proliferation to other nations, though at least three other countries (India, South Africa, Pakistan, and most likely Israel) developed nuclear arms during this time. At the end of the Cold War in the early 1990s, the Russian Federation inherited the weapons of the former USSR, and along with the USA pledged to reduce their stockpile for increased international safety. Nuclear proliferation has continued, though, with Pakistan testing their first weapons in 1998, and the state of North Korea claiming to have developed nuclear weapons in 2004. Nuclear weapons have been at the heart of many national and international political disputes, and have played a major part in popular culture since their dramatic public debut in the 1940s, and have usually symbolized the ultimate ability of mankind to utilize the strength of nature for destruction.

There have been (at least) four major false alarms, the most recent in 1995, that almost resulted in the US or USSR/Russia launching its weapons in retaliation for a supposed attack.^[1] Additionally, during the Cold War the US and USSR came close to nuclear warfare a number of times, most notably during the Cuban Missile Crisis. As of 2005, there are estimated to be at least 29,000 nuclear weapons held by at least seven countries, though 96% of these are in the possession of just two (the United States and the Russian Federation).

Media

See also

• More technical details
  • Nuclear weapon design
  • Nuclear weapon yield
  • Nuclear explosion
• History
  • History of nuclear weapons
  • Manhattan Project
  • Los Alamos National Laboratory
  • Lawrence Livermore National Laboratory
  • Nuclear testing
    • Nevada Test Site
  • Soviet atomic bomb project
  • Stanislav Petrov
  • German nuclear energy project
  • Japanese atomic program
  • List of nuclear accidents (including nuclear weapons accidents)
• Related technology and science
  • Nuclear physics
  • Nuclear fission
  • Nuclear fusion
  • Nuclear reactor
  • Nuclear engineering
• Military strategy
  • Nuclear warfare
  • Civil Defense
  • Nuclear strategy
  • Mutual Assured Destruction
  • Fractional Orbital Bombardment System
• Proliferation and politics
  • Nuclear proliferation
  • Nuclear Non-Proliferation Treaty
  • Comprehensive Test Ban Treaty
  • Nuclear disarmament
  • International Court of Justice advisory opinion on legality of nuclear weapons
  • List of countries with nuclear weapons
  • Nuclear weapons and the United States
  • Nuclear weapons and the United Kingdom
  • List of nuclear weapons
• Popular culture
  • Nuclear weapons in popular culture
• Aftermath
  • Nuclear winter
  • Nuclear summer

References

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External links

Wikimedia Commons has media related to:

Nuclear weapons

Wikinews has news related to:

Nuclear proliferation

General

• Nuclear Weapon Archive from Carey Sublette is a reliable source of information and has links to other sources and an informative FAQ.
• The Federation of American Scientists provide solid information on weapons of mass destruction, including nuclear weapons and their effects
• Alsos Digital Library for Nuclear Issues – contains many resources related to nuclear weapons, including a historical and technical overview and searchable bibliography of web and print resources.
• Everything you wanted to know about nuclear technology — Provided by New Scientist.
• Congressional Research Service (CRS) Reports regarding Nuclear weapons
• The Effects of Nuclear Weapons

Historical

• The Manhattan Project: Making the Atomic Bomb
• "The Race to Build the Atomic Bomb", educational resource.

Effects

• Nuclear weapon simulator for several major cities
• Fallout Calculator for various regions
• Example Scenarios - Two scenarios of a nuclear explosion on two United States Cities

Issues

• "The Nuclear Weapons Debate" - OneWorld.net's Perspectives Magazine, May 2005
• "Nuclear Power and Nuclear Weapons: Making the Connections" – an article about the connections between nuclear power and nuclear weapons development by an anti-nuclear group.
• Nuclear War Survival Skills is a public domain text about civil defense.
• IPPNW: International Physicians for the Prevention of Nuclear War – Nobel Peace Prize-winning organization with information about the medical consequences of nuclear weapons, war and militarization.
• Bulletin of the Atomic Scientists – Magazine founded in 1945 by Manhattan Project scientists. Covers nuclear weapons proliferation and many other global security issues. See this page for comprehensive data on nuclear weapons worldwide.
• 50 Facts About U.S. Nuclear Weapons – Largest, smallest, number, cost, etc.
• Nuclear Files.org covers the history of nuclear weapons and explores the political, legal and ethical challenges of the Nuclear Age.
• Union of Concerned Scientists – Nuclear Policy, weapons, testing, technical issues, and arms control.