Nuclear Weapons

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A nuclear weapon is detonated in the atmosphere of a Class M planet

Nuclear weapons derive their energy from nuclear reactions and generally have enormous destructive power — a typical nuclear weapon is capable of destroying a city, and the highest yield weapons in use are capable of reducing entire continents to sheets of glass. For many cultures, nuclear weapons are their first taste of Weapons of Mass Destruction; most planets develop nuclear weapons before entering their respective space ages, often using them in devastating global wars before their civilizations can become spacefaring.

Common types

Fission bombs

Fission bombs derive their power from nuclear fission, where heavy nuclei (uranium or plutonium) split into lighter elements when bombarded by neutrons (producing more neutrons which bombard other nuclei, triggering a chain reaction). These are historically called atom bombs or A-bombs.

In general, fission bombs are powered by using chemical explosives to compress a sub-critical mass amount of either uranium-235 or plutonium into a dense, super-critical mass, which is then subjected to a source of neutrons. This begins an uncontrollable nuclear chain reaction, and produces a very large amount of energy. 0.45kg of U-235 can release over 37 million million joules of energy.

Fusion bombs

Fusion bombs are based on nuclear fusion where light nuclei such as hydrogen and helium combine together into heavier elements and release large amounts of energy. Weapons which have a fusion stage are also referred to as hydrogen bombs, atom smashers or thermonuclear weapons because fusion reactions require extremely high temperatures for a chain reaction to occur. Imperial Concussion Missiles are a form of fusion bombs.

Generally speaking, hydrogen bombs work by having a "primary" device (a fission bomb) detonate and begin the fusion reactions in the "secondary" device (fusion fuel). A virtually limitless number of large "secondaries" can be chained together (each fusion reaction beginning the next) in this fashion, creating weapons with far larger yields than could be achieved with simple fission alone.

Nuclear weapons are often described as either fission or fusion devices based on the dominant source of the weapon's energy. The distinction between these two types of weapon is blurred by the fact that they are combined in nearly all complex modern weapons: a smaller fission bomb is first used to reach the necessary conditions of high temperature and pressure to allow fusion to occur. On the other hand, a fission device is more efficient when a fusion core first boosts the weapon's energy. Since the distinguishing feature of both fission and fusion weapons is that they release energy from transformations of the atomic nucleus, the most accurate general term for all types of these explosive devices is "nuclear weapon."

Dirty bombs

Dirty bomb is a term for a radiological weapon, a non-nuclear bomb that disperses radioactive material that was packed in with the bomb. When the bomb explodes, the scattering of this radioactive material causes radioactive contamination, a health hazard similar to that of nuclear fallout. Dirty bombs, similar to other enhanced fallout weapons of more technologically sophisticated design, are area denial weapons that can potentially render an area unfit for habitation for years or decades after the detonation.

Cobalt bombs

The cobalt bomb uses cobalt in the shell, and the fusion neutrons convert the cobalt into cobalt-60, a powerful long-term (5 years) emitter of gamma rays. In general, this type of weapon is referred to as a salted bomb and variable fallout effects can be obtained by using different salting isotopes. Gold has been proposed for short-term fallout (days), tantalum and zinc for fallout of intermediate duration (months), and cobalt for long term contamination (years). The primary purpose of this weapon is to create excess radioactive fallout making a large region uninhabitable.

Neutron bombs

A final variant of the thermonuclear weapons is the enhanced radiation weapon, or neutron bomb, which is a small thermonuclear weapon in which the burst of neutrons generated by the fusion reaction is intentionally not absorbed inside the weapon, but allowed to escape. The X-ray mirrors and shell of the weapon are made of chromium or nickel so that the neutrons are permitted to escape. This intense burst of high-energy neutrons is a highly destructive mechanism, although the bomb will still produce damaging thermal and shock effects, only with a lower magnitude than a standard thermonuclear weapon. Neutrons are more penetrating than other types of radiation so many shielding materials that work well against gamma rays are less effective against neutrons. They are also more biologically harmful than gamma rays, making it possible to create neutron bombs that do little physical damage while killing all the people in a certain area (a so-called "landlord bomb").

Effects of a nuclear explosion

The energy released from a nuclear weapon comes in four primary categories:

• Blast—40-60% of total energy
• Thermal radiation—30-50% of total energy
• Ionizing radiation—5% of total energy
• Residual radiation (fallout)—5-10% of total energy

The amount of energy released in each form depends on the design of the weapon, and the environment in which it is detonated. The residual radiation of fallout is a delayed release of energy, while the other three forms of energy release are immediate.

The dominant effects of a nuclear weapon (the blast and thermal radiation) are the same physical damage mechanisms as conventional explosives. The primary difference is that nuclear weapons are capable of releasing much larger amounts of energy at once. Most of the damage caused by a nuclear weapon is not directly related to the nuclear process of energy release, but would be present for any explosion of the same magnitude.

The damage done by each of the three initial forms of energy release differs with the size of the weapon. Thermal radiation drops off the slowest with distance, so the larger the weapon the more important this effect becomes. Ionizing radiation is strongly absorbed by most Class M atmospheres, so it is only dangerous by itself for smaller weapons. Blast damage falls off more quickly than thermal radiation but more slowly than ionizing radiation.

When a nuclear weapon explodes, the bomb's material comes to an equilibrium temperature in about a microsecond. At this time about 75% of the energy is emitted as primary thermal radiation, mostly soft X-rays. Almost all of the rest of the energy is kinetic energy in rapidly-moving weapon debris. The interaction of the x-rays and debris with the surroundings determines how much energy is produced as blast and how much as light. In general, the denser the medium around the bomb, the more it will absorb, and the more powerful the shockwave will be.

When a nuclear detonation occurs in air near sea-level, most of the soft X-rays in the primary thermal radiation are absorbed within a few feet. Some energy is re-radiated in the ultraviolet, visible light and infrared, but most of the energy heats a spherical volume of air. This forms the fireball.

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 usually expressed in the equivalent mass of trinitrotoluene (TNT), either in kilotons (thousands of tons of TNT), megatons (million of tons of TNT) or even gigatons. In modern Federation usage, the unit "isoton" is used.

Blast damage

Much of the destruction caused by a nuclear explosion is due to blast effects. Most buildings, except reinforced, shielded, 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 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.

Electromagnetic pulse (EMP)

Gamma rays from a nuclear explosion produce high energy electrons through Compton scattering. These electrons are captured in a planet's magnetic field, 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 electric 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.

Some 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 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.

• 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 planet's surface near ground zero (depending on wind and weather conditions of course) within a day, 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 effect 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. Chemically, both isotopes are recognized as similar to calcium and deposited in bone structure throughout the body. These highly-radioactive substances then interfere with white blood cell production, which is a prime effect of radiation sickness. 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.

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 or continents; this is a euphemism for Weapons of Mass Destruction. Tactical nuclear weapons are smaller weapons used to destroy specific military, communications, or infrastructure targets.

Source Note

• The original version of this article comes from Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Main_Page).
• Glasstone, Samuel and Dolan, Philip J., The Effects of Nuclear Weapons (third edition) (http://www.cddc.vt.edu/host/atomic/nukeffct/), U.S. Government Printing Office, 1977. PDF Version (http://www.princeton.edu/~globsec/publications/effects/effects.shtml)
• NATO Handbook on the Medical Aspects of NBC Defensive Operations (Part I - Nuclear) (http://www.fas.org/nuke/guide/usa/doctrine/dod/fm8-9/1toc.htm), 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] (http://www.uscoldwar.com/).
• Smyth, Henry DeWolf. Atomic Energy for Military Purposes (http://nuclearweaponarchive.org/Smyth/), Princeton University Press, 1945. (The first declassified report by the US government on nuclear weapons) (Smyth Report)
• The Effects of Nuclear War (http://www.fas.org/nuke/intro/nuke/7906/index.html), 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 (http://nuclearweaponarchive.org) is a reliable source of information and has links to other sources and an informative FAQ (http://nuclearweaponarchive.org/Nwfaq/Nfaq0.html).
• The Federation of American Scientists (http://fas.org) provide solid information on weapons of mass destruction, including nuclear weapons (http://fas.org/nuke/) and their effects (http://www.fas.org/nuke/intro/nuke/effects.htm)
• The Nuclear War Survival Skills (http://www.oism.org/nwss/) 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 (http://www.atomicarchive.com/Example/Example1.shtml) - click on the Next >> button at the bottom of each slide.