Nuclear weapon

The mushroom cloud of the atomic bombing of Nagasaki, Japan, in 1945 lifted nuclear fallout some 60,000 feet (18 km) above the epicenter.

A nuclear weapon is a weapon that derives its energy from nuclear reactions and has enormous destructive power - a single nuclear weapon is capable of destroying a city. Nuclear weapons have been used only twice for war, by the United States against the Japanese cities of Hiroshima and Nagasaki during World War II. They have been used many hundreds of times, however, for the nuclear testing u

Non-weaponized nuclear explosives have also been proposed for various civilian uses.

Types of weapons

Common types

In a burst at high altitudes, where the air density is low, the soft X-rays travel long distances before they are absorbed. The energy is so diluted that the blast wave may be half as strong or less. The rest of the energy is dissipated as a more powerful thermal pulse.

Yield

The explosive yield of a nuclear weapon is expressed in the equivalent mass of trinitrotoluene (TNT):

Davy Crockett - variable yield 0.01 - 1 kt - mass only 23 kg (51 pounds), lightest ever deployed by the United States
Special Atomic Demolition Munition - variable yield 0.01 - 1 kt
Hiroshima’s "Little Boy" 12-15 kt
Nagasaki’s "Fat Man" 20-22 kt
W-76 warhead 100 kt (10 of these may be in a Trident II missile)
B-61 Mod 3 gravity bomb: 4 yield options ("dial-a-yield"): 0.3 kt, 1.5 kt, 60 kt, and 170 kt
W-87 warhead 300 kt (10 of these are in a LG-118A Peacekeeper)
W-88 warhead 475 kt (8 of these may be in a Trident II missile)
Castle Bravo 15 Mt - largest tested by the US
EC17/Mk-17, the EC24/Mk-24, and the B41 (Mk41) (largest nuclear weapons ever built by the United States) 25 Mt - gravity bombs carried by B-36 bomber; retired by 1957
Tsar Bomba 50 Mt - largest tested, Russian, mass of 27 ton

Compare Oklahoma City bombing: 0.002 kt.

The yield per ton was e.g. for the Davy Crocket 40 kt and for the Tsar Bomba 2 Mt.

Blast damage

Much of the destruction caused by a nuclear explosion is due to blast effects. Most buildings, except reinforced or blast-resistant structures, will suffer moderate to severe damage when subjected to moderate overpressures. The blast wind may exceed several hundred km/h. The range for blast effects increases with the explosive yield of the weapon.

Two distinct, simultaneous phenomena are associated with the blast wave in air:

Static overpressure, i.e., the sharp increase in pressure exerted by the shock wave. The overpressure at any given point is directly proportional to the density of the air in the wave.
Dynamic pressures, i.e., drag exerted by the blast winds required to form the blast wave. These winds push, tumble and tear objects.

Most of the material damage caused by a nuclear air burst is caused by a combination of the high static overpressures and the blast winds. The long compression of the blast wave weakens structures, which are then torn apart by the blast winds. The compression, vacuum and drag phases together may last several seconds or longer, and exert forces many times greater than the strongest hurricane.

Thermal radiation

Nuclear weapons emit large amounts of electromagnetic radiation as visible, infrared, and ultraviolet light. The chief hazards are burns and eye injuries. On clear days, these injuries can occur well beyond blast ranges. The light is so powerful that it can start fires that spread rapidly in the debris left by a blast. The range of thermal effects increases markedly with weapon yield.

Since thermal radiation travels in straight lines from the fireball (unless scattered) any opaque object will produce a protective shadow. If fog or haze scatters the light, it will heat things from all directions and shielding will be less effective.

When thermal radiation strikes an object, part will be reflected, part transmitted, and the rest absorbed. The fraction that is absorbed depends on the nature and color of the material. A thin material may transmit a lot. A light colored object may reflect much of the incident radiation and thus escape damage. The absorbed thermal radiation raises the temperature of the surface and results in scorching, charring, and burning of wood, paper, fabrics, etc. If the material is a poor thermal conductor, the heat is confined to the surface of the material.

Actual ignition of materials depends on the how long the thermal pulse lasts and the thickness and moisture content of the target. Near ground zero where the light is most intense, what can burn, will. Farther away, only the most easily ignited materials will flame. Incendiary effects are compounded by secondary fires started by the blast wave effects such as from upset stoves and furnaces.

In Hiroshima, a tremendous fire storm developed within 20 minutes after detonation. A fire storm has gale force winds blowing in towards the center of the fire from all points of the compass. It is not, however, a phenomenon peculiar to nuclear explosions, having been observed frequently in large forest fires and following incendiary raids during World War II.

Electromagnetic pulse (EMP)

Gamma rays from a nuclear explosion produce high energy electrons through Compton scattering. These electrons are captured in the earth's magnetic field, at altitudes between twenty and forty kilometers, where they resonate. The oscillating electric current produces a coherent EMP (electromagnetic pulse) which lasts about 1 millisecond. Secondary effects may last for more than a second.

The pulse is powerful enough so that long metal objects (such as cables) act as antennas and generate high voltages when the pulse passes. These voltages, and the associated high currents, can destroy unshielded electronics and even many wires. There are no known biological effects of EMP. The ionized air also disrupts radio traffic that would normally bounce off the ionosphere.

One can shield electronics by wrapping them completely in conductive mesh, or any other form of Faraday cage. Of course radios cannot operate when shielded, because broadcast radio waves can't reach them.

The largest-yield nuclear devices are designed for this use. An air burst at the right altitude produces continent-wide effects.

Radiation

About 5% of the energy released in a nuclear air burst is in the form of initial neutron and gamma radiation. The neutrons result almost exclusively from the fission and fusion reactions, while the initial gamma radiation includes that arising from these reactions as well as that resulting from the decay of short-lived fission products.

The intensity of initial nuclear radiation decreases rapidly with distance from the point of burst because the radiation spreads over a larger area as it travels away from the explosion. It is also reduced by atmospheric absorption and scattering.

The character of the radiation received at a given location also varies with distance from the explosion. Near the point of the explosion, the neutron intensity is greater than the gamma intensity, but with increasing distance the neutron-gamma ratio decreases. Ultimately, the neutron component of initial radiation becomes negligible in comparison with the gamma component. The range for significant levels of initial radiation does not increase markedly with weapon yield and, as a result, the initial radiation becomes less of a hazard with increasing yield. With larger weapons, above 50 kt, blast and thermal effects are so much greater in importance that prompt radiation effects can be ignored.

Nuclear fallout

The residual radioactive contamination hazard from a nuclear explosion is in the form of radioactive fallout and neutron-induced activity. Residual ionizing radiation arises from:

Fission Products. These are intermediate weight isotopes which are formed when a heavy uranium or plutonium nucleus is split in a fission reaction. There are over 300 different fission products that may result from a fission reaction. Many of these are radioactive with widely differing half-lives. Some are very short, i.e., fractions of a second, while a few are long enough that the materials can be a hazard for months or years. Their principal mode of decay is by the emission of beta and gamma radiation. Approximately 60 grams of fission products are formed per kilotonne of yield. The estimated activity of this quantity of fission products 1 minute after detonation is equal to that of 1.1 × 10²¹ Bq (30 million kg of radium) in equilibrium with its decay products.
Unfissioned Nuclear Material. Nuclear weapons are relatively inefficient in their use of fissionable material, and much of the uranium and plutonium is dispersed by the explosion without undergoing fission. Such unfissioned nuclear material decays slowly by the emission of alpha particles and is of relatively minor importance.
Neutron-Induced Activity. If atomic nuclei capture neutrons when exposed to a flux of neutron radiation, they will, as a rule, become radioactive (neutron-induced activity) and then decay by emission of beta and gamma radiation over an extended period of time. Neutrons emitted as part of the initial nuclear radiation will cause activation of the weapon residues. In addition, atoms of environmental material, such as soil, air, and water, may be activated, depending on their composition and distance from the burst. For example, a small area around ground zero may become hazardous as a result of exposure of the minerals in the soil to initial neutron radiation. This is due principally to neutron capture by various elements, such as sodium, manganese, aluminum and silicon in the soil. This is a negligible hazard because of the limited area involved.

In an explosion near the surface large amounts of earth or water will be vaporized by the heat of the fireball and drawn up into the radioactive cloud. This material will become radioactive when it condenses, mixed with fission products and other radiocontaminants that have become neutron-activated. The larger particles will settle back to the earth's surface near ground zero (depending on wind and weather conditions of course) within 24 hours, while fine particles will rise to the stratosphere and be distributed globally over the course of weeks or months.

Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations. In detonations near a water surface, the particles tend to be lighter and smaller and produce less local fallout but will extend over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding affect causing local rainout and areas of high local fallout.

The radiobiological hazard of worldwide fallout is essentially a long-term one due to the potential accumulation of long-lived radioisotopes, such as strontium-90 and caesium-137, in the body as a result of ingestion of foods incorporating these radioactive materials. The hazard of worldwide fallout is much less serious than the hazards which are associated with local fallout.

Blast and thermal injuries in many cases will far outnumber radiation injuries. However, radiation effects are considerably more complex and varied than are blast or thermal effects and are subject to considerable misunderstanding. A wide range of biological changes may follow the irradiation of animals, ranging from rapid death following high doses of penetrating whole-body radiation to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.

For more technical details see: nuclear explosion

Weapons delivery

The term strategic nuclear weapons is generally used to denote large weapons which would be used to destroy large targets, such as cities. Tactical nuclear weapons are smaller weapons used to destroy specific military, communications, or infrastructure targets. By modern standards, the bombs that destroyed Hiroshima and Nagasaki in 1945 were tactical weapons (with yields between 13 and 22 kilotons), although modern tactical weapons are considerably lighter and more compact.

Basic methods of delivery for nuclear weapons are:

Free-fall bombs: Early weapons were so big and heavy that they could only be carried by bombers such as the B-52 and V bombers, but by the mid-1950s smaller weapons had been developed that could be carried and deployed by fighter-bombers. Air-dropping of gravity bombs can use various techniques, including toss bombing, parachute-retarded delivery, and laydown modes, intended to give the dropping aircraft time to escape the ensuing blast.
ballistic missiles: Missiles using a ballistic trajectory, usually to deliver a warhead over the horizon. Mobile ballistic missiles may have a range of tens to hundreds of kilometers, while larger ICBMs or SLBMs may use suborbital or partial orbital trajectories for intercontinental range. Early ballistic missiles carried a single warhead, often of megaton-range yield. Since the 1970s modern ballistic weapons often use multiple independent reentry vehicles (MIRVs) with up to a dozen warheads, usually of kiloton-range yield. This allows a single launched missile to strike a handful of targets, or inflict maximum damage on a single target by encircling the target with warheads.
cruise missiles: A jet engine or rocket-propelled missile that flies at low altitude using an automated guidance system (usually inertial navigation, sometimes supplemented by either GPS or mid-course updates from friendly forces) to make them harder to detect or intercept. Cruise missiles have shorter range and smaller payloads than ballistic missiles. At present most do not have multiple warheads, although conventional cruise missiles sometimes use cluster munition payloads. Cruise missiles may be launched from mobile launchers on the ground, from naval ships, or from aircraft.

Other potential delivery methods include artillery shells, mines such as Blue Peacock, and nuclear depth charges and torpedoes for anti-submarine warfare. In the 1950s the U.S. developed small nuclear warheads for air defense use. Most of the air-defense weapons were out of service by the end of the 1960s, and nuclear depth bombs were taken out of service by 1990. Small, man-portable tactical weapons ("suitcase bombs") capable of being carried by an individual, such as the Special Atomic Demolition Munition, have been developed, although the difficulty of balancing yield and portability limits their military utility.

See list of nuclear weapons for a list of the designs of nuclear weapons fielded by the various nuclear powers.

Nuclear weapons in culture

Nuclear weaponry has become a part of pop culture; the decades post-WWII can be termed the atomic age. The stunning power and the astonishing visual effects have been the topic of art including Andy Warhol's silkscreen Atomic Bomb (1965) and James Rosenquist's F-111 (1964-65) to Gregory Green's mockups of atomic devices and the efforts of artist James Acord to use uranium in his sculptures.

Films featuring nuclear war or the threat of it include Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964), Fail-Safe (1964), On the Beach (1959), The Day After (1983), The War Game (1966), When the Wind Blows (1982), Testament (1983), The Terminator (1984), Threads (1985), WarGames (1983), Miracle Mile (1988), By Dawn's Early Light (1990), The Sum of All Fears (2002),Taiyo o nusunda otoko / The Man Who Stole the Sun (1979), True Lies (1994), Broken Arrow (1996), The Peacemaker (1997), and the Planet of the Apes and Mad Max movies. Godzilla (1954) is considered by some to be an analogy to the nuclear weapons dropped on Japan, and was the start of a more general genre of movies about creatures mutated or awakened by nuclear testing.

A memorable episode of The Bionic Woman featured the threat of a cobalt bomb. A main character in Repo Man was a designer of the neutron bomb.

Nuclear weapons are a staple element in science fiction novels. The chain reaction type nuclear bomb was predicted in a 1944 science fiction story by Cleve Cartmill titled "Deadline" which caused him to be investigated by the FBI, concerned that there had been a breach of security on the Manhattan Project. The phrase "atomic bomb" dates back even further to H. G. Wells's The World Set Free from 1914, when scientists had discovered that radioactive decay implied potentially limitless energy locked inside of atomic particles (Wells's atomic bombs, however, were only as powerful as conventional explosives, but would continue exploding for days on end). Many of the characteristics of nuclear weapons themselves have played on ages-old human themes and tropes (penetrating rays, persistent contamination, virility, and, of course, apocalypse), giving their standing in popular culture and politics a particularly emotional valence (both positive and negative).

Nuclear weapons are also one of the main targets of peace organisations. The CND (Campaign for Nuclear Disarmament) was one of the main organisations campaigning against the 'Bomb'. Its symbol, a combination of the semaphore symbols for "N" (nuclear) and "D" (disarmament), entered modern popular culture as an icon of peace.

References

Glasstone, Samuel and Dolan, Philip J., The Effects of Nuclear Weapons (third edition), U.S. Government Printing Office, 1977. PDF Version
NATO Handbook on the Medical Aspects of NBC Defensive Operations (Part I - Nuclear), Departments of the Army, Navy, and Air Force, Washington, D.C., 1996.
Hansen, Chuck. U.S. Nuclear Weapons: The Secret History, Arlington, TX: Aerofax, 1988.
Hansen, Chuck. The Swords of Armageddon: U.S. nuclear weapons development since 1945, Sunnyvale, CA: Chukelea Publications, 1995 [1].
Smyth, Henry De Wolf. Atomic Energy for Military Purposes, Princeton University Press, 1945. (The first declassified report by the US government on nuclear weapons)
The Effects of Nuclear War, Office of Technology Assessment (May 1979).
Rhodes, Richard. Dark Sun: The Making of the Hydrogen Bomb. Simon and Schuster, New York, (1995 ISBN 0684824140)
Rhodes, Richard. The Making of the Atomic Bomb. Simon and Schuster, New York, (1986 ISBN 0684813785)
Weart, Spencer R. (1988). Nuclear Fear: A History of Images. Cambridge, Mass.: Harvard University Press.

External links

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
The Nuclear War Survival Skills is a public domain text and is an excellent source on how to survive a nuclear attack.
Step by step scenario of a 150 kiloton bomb exploding in Manhattan - click on the Next >> button at the bottom of each slide.