Types of Nuclear Weapons: Difference between revisions
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The different types of nuclear weapons, delivery systems, and their basic purpose.
With the exception of the Dirty Bomb (below) all nuclear weapons rely on one or both of the following:
* '''Fission:''' This is the name for when a single large nucleus splits into two smaller nuclei. When this happens, some of the energy that had been holding the original nucleus together (and in some cases, left-over parts of the nucleus that end up in neither of the successor nuclei) is released. The materials used for fission bombs are unstable heavy elements that: a) undergo spontaneous fission which releases free neutrons, and b) undergo stimulated fission when exposed to free neutrons. Spontaneous fissions send neutrons into other nuclei, causing them to split and release more neutrons, and so on in a chain reaction
In the vast majority of nuclear weapons, either U-235 or Pu-239 is used as the fissile material. Pu-239 is a synthetic element, essentially, and must be produced in particle accelerators or specialized plutonium-production reactors. Regular nuclear reactors produce it too, but they also produce other isotopes of plutonium that don't work as well. Uranium's quite common, but the vast majority of natural uranium is U-238, a stabler isotope than U-235. U-235 can be extracted from natural uranium to obtain weapons-grade material. This refers to uranium or plutonium which is something like 90-95% U-235 or Pu-239. It's possible to design weapons which use stuff that's enriched to only 80%, but that's a major challenge and only a nuclear power like the US could manage. And they kind of suck, too. By comparison, nuclear fuel in commercial power reactors is enriched to something like 5%.
Finally, a note on terminology: "fissile" nuclei can be split by low-energy 'thermal' neutrons (U-235 and Pu-239 are fissile) and can be 'burned' in reactors. They can sustain a chain reaction. 'Fissionable' materials can be fissioned, of course, but it's much more difficult. They can't be fissioned by low-energy neutrons, but require high-energy 'fast' neutrons to split them.
* '''Fusion:''' The reaction that powers stars. When two small nuclei collide with enough energy the two will combine into a single, larger nucleus, releasing even more energy in the process. It requires both vast pressure and immense temperature to get this kind of reaction started, because the positively charged nuclei must be forced against their electromagnetic repulsion until the strong nuclear force takes over (unlike fission, wherein an uncharged neutron can be made to smash into a nucleus more easily). In bombs or reactors, deuterium<ref>Hydrogen-2, so-called because it has a neutron as well as a proton in its nucleus.</ref> would be made to fuse with tritium.<ref>Hydrogen-3, so-called because it has two neutrons as well as a proton in its nucleus</ref> Depending on the nuclei used as "fuel", this may also release fast neutrons.
Fusion is more efficient than fission in converting mass to energy, but is much harder to initiate, sustain and control. Hence, we do not yet have fusion reactors, though there are ongoing efforts to create workable "tokamak" type reactors in which fusion plasma is contained inside an electromagnetic field, in a toroidal chamber. Fusion for bombs is somewhat simpler—you just need to initiate the reaction, and do not need to worry about sustaining it or containing it.
Just in case you're wondering, stars use the gravity exerted by their tremendous mass to initiate and sustain fusion—even smaller stars like our sun are capable of creating carbon via fusion, while more massive stars can go all the way up to iron (which is the end of the line, given that iron is "inert" when it comes to nuclear reactions). The most massive stars fuse elements above iron, but since this ''costs'' energy rather than releases it, they go through this rather quickly and explode brilliantly—what we call a supernova. This, by the way, is how almost ''all'' atoms of elements heavier than helium and a little bit of lithium (the former was produced in the Big Bang in quantity, and the latter in smaller amounts) originally came into being (leaving heaviest of them for later fission and decay).
Technically, in the correct circumstances any element can experience either fusion or fission. However, fusion only releases energy for elements of lower atomic number than iron and fission only for elements of higher atomic number than iron. Different elements have a different affinity for the two. The best isotopes for use in a fission reaction tend to be Uranium-235 and Plutonium-239 due to their long half-lives and low spontaneous fission rate. Larger elements decay ''very'' quickly, and therefore are absolute nightmares to amass or store sufficient quantities of, and smaller elements require far more effort to start the reaction. Fusion conversely works best with smaller elements: the typical fuel for fusion are two isotopes of Hydrogen (deuterium and tritium).
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Finally, there is a third type of nuclear reaction: [[Antimatter|matter-antimatter annihilation.]] When a particle, like a proton, neutron or electron, collides with its antiparticle, the result is all of their mass converting to energy according to Einstein's mass-energy equivalence equation. (E=mc^2) This energy might be in the form of gamma rays, highly energetic pions or possibly harmless neutrinos. Because antimatter is so hard to get, no matter-antimatter weapon has ever been built, and it seems improbable that any will be in the forseeable future. If they could be built, though, they would have the advantage of producing no radioactive fallout and practically no induced radioactivity. Technically a very small amount might occur due to the photoneutron effect, but it's really hard to find any hard numbers on this.
A slightly more practical use of this is what's called antimatter-catalyzed fusion, which uses a minuscule amount of antimatter as a "spark plug" to set off a fusion reaction, allowing for a relatively clean, fusion-only bomb. This is also beyond present-day technology, but not nearly as far beyond as a pure annihilation device. Both classes of antimatter-based weapons would suffer from the same problem that plagues fission and fusion
'''Atomic bomb (or A-bomb):''' The original nuclear weapon, an atomic bomb is any explosive device where the majority of the energy output comes from a runaway nuclear fission reaction. They're more properly called "nuclear bombs." Two major types exist:
* Pure fission weapons. Obviously, only fission reactions occur when one of these babies detonates. Highly-enriched fissile material is used. Normally, it is kept in a subcritical state inside the bomb; when the time comes, conventional explosives are used to assemble the fissile materials so that they enter a supecritical state. After that comes a tremendous release of energy and a massive explosion. There are two ways to assemble the fissile material, and they're both implementations of this principle.
** The first, and simplest, is a gun-type nuclear device. Two subcritical masses of fissile material are brought together; one is a target, and one is a bullet. The bullet is fired down a tube at the target, conventional explosives acting as a propellant. (Yes, a nuclear bomb built upon the principle of [[More Dakka]].) Only U-235 may be used as the fissile material in a practical device, because of predetonation problems with Pu-239
** There are also implosion bombs. The fissile material is kept together in a single mass, typically a sphere. It may be hollow or solid, depending on the circumstances. This "pit" is surrounded by conventional explosives; there are numerous explosive "lenses". It is necessary to very, very carefully shape the shockwave in order to achieve proper compression of the pit. As such, the lenses must be manufactured to extremely tight tolerances, and the detonators must be triggered with precise timing. Special types of detonators and switches are used as a result. (Look up "explosive bridgewire detonators," "slapper detonators," and "krytrons.")<br /><br />The Trinity device was an implosion-type weapon utilizing Pu-239. It had to be tested because there were far more doubts about implosion-type weapons than gun-type weapons. The Fat Man device, used on Nagasaki, was also an implosion-type weapon. Most nuclear weapons today are implosion-based, for safety and efficiency reasons, although for a time gun-type weapons were stockpiled. They were useful because of their form factor, which made them suited for tactical use. Before they were scrapped, the entire nuclear arsenal of South Africa consisted of gun-type devices.▼
The "Little Boy" device used on Hiroshima was a gun-type device using U-235; it was very simple and needed no testing. Gun-type weapons aren't as safe as implosion-type weapons because it is much easier to accidentally assemble the fissile material in such a way that there is significant nuclear yield; the Enola Gay may have gone up in a multi-kiloton fireball had it crashed carrying the device. They were useful, however, because of their form factor, which made them suited for tactical use. Before it was scrapped, the entire nuclear arsenal of [[South Africa]] consisted of gun-type devices.
▲** There are also implosion bombs. The fissile material is kept together in a single mass, typically a sphere. It may be hollow or solid, depending on the circumstances. This "pit" is surrounded by conventional explosives; there are numerous explosive "lenses". It is necessary to very, very carefully shape the shockwave in order to achieve proper compression of the pit. As such, the lenses must be manufactured to extremely tight tolerances, and the detonators must be triggered with precise timing. Special types of detonators and switches are used as a result. (Look up "explosive bridgewire detonators," "slapper detonators," and "krytrons.")
The Trinity device was an implosion-type weapon utilizing Pu-239. It had to be tested because there were far more doubts about implosion-type weapons than gun-type weapons. The Fat Man device, used on Nagasaki, was also an implosion-type weapon. Most nuclear weapons today are implosion-based, for safety and efficiency reasons, although for a time gun-type weapons were stockpiled. They were useful because of their form factor, which made them suited for tactical use. Before they were scrapped, the entire nuclear arsenal of South Africa consisted of gun-type devices.
* Boosted fission weapons: tritium is injected into the pit. As the fission reaction occurs, this is more than enough to induce fusion of the tritium; the extra neutrons allow more of the pit to be "burned" and converted to useful energy before the pit blows apart and the reaction stops. Efficiency can be increased enormously as a result. By varying the amount of tritium injected into the pit, the yield can be varied. That way, a single device can be made more flexible.
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There is no upper limit on the explosive yield from a Teller-Ulam device; arbitrarily many stages may be added. Remember, when you merely wish to bury bombs, there is no limit to the size! However, scaling beyond a certain point is impractical, as the damage radius is approximately logarithmic with respect to the yield. The current power record is held by the [[wikipedia:Tsar Bomba|Tsar Bomba]], the original design of which was estimated to have a yield of 100 MT. For testing, the U-238 tamper was not used (so as to limit the fallout), thereby reducing the yield to "only" 50 MT. Size, weight and power make this weapon relatively useless. Not to mention the fact that had they dialed it up to the full 100 MT, [[Too Awesome to Use|it would have vaporized the plane that was dropping it]].
'''Dirty bomb:''' These weapons, properly known as radiological dispersion devices, don't actually involve nuclear explosions. Instead, this basically involves setting off a bomb with some radioactive material in. This would only cause direct destruction equivalent to the power of the device itself, but would cover a large area in radioactive nastiness and render much of it uninhabitable.
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It should be noted that the primary intended use of neutron bombs is as a tactical last line of defense against enemy tanks. Among the other uses for depleted uranium is tank armor thick enough to be blast proof, heat proof, EMP proof, impact proof (from small arms or debris), gamma ray proof and gas impermeable. Sounds [[Made of Diamond|invincible, right?]] Wrong. Besides the fact that a powerful enough blast will overwhelm any armor (tactical nukes can take out tanks within about 20 meters of ground zero), depleted uranium is worse than useless at stopping fusion neutrons. So, the tank will survive, but the crew will suffer a rapid onset case of fatal radiation poisoning out to half a mile.
First, there's the tactical/strategic dichotomy. It can be hard to discern the difference between the two when it comes to nuclear weapons, which is part of why there is so much controversy over this. Generally, though, a tactical nuclear weapon is designed to be used on a battlefield, directly against enemy forces. That's fairly broad, though; it may be on land, at sea, or in the air. A strategic nuclear weapon is most everything else.
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This category also sort of includes nuclear land mines. This troper knows of only one specific design, however: the British Blue Peacock. This became famous as the "chicken-powered nuclear bomb" when the relevant documents were declassified in 2004. If it was buried in winter, the thing might have frozen over, so one proposal involved stuffing live chickens into the casing, with a supply of food and water. They'd live for a week, which was the intended buried lifetime of the mine anyway. In the interim, they'd keep everything at operating temperature by virtue of their body heat.
'''Aircraft:''' A wide variety of aircraft can deliver nuclear weapons, and historically, aircraft delivery was the first method. It is also the only method that has [[World War II|actually been used operationally]]. As mentioned previously, these aircraft can be anything from huge multi-engined strategic bombers, to supersonic one-man fighter-bombers.
'''ICBMs:''' Intercontinental ballistic missiles, or ICBMs, are ballistic missiles that have more than 5,500
Various types of ICBMs are, today, the strategic nuclear delivery systems of choice. They're a diverse group, however; for example, there are many possible launch environments. An ICBM may be launched from a fixed land base... of course, it may require a launch pad and large, soft aboveground facilities, it may be stored horizontally in a hardened concrete "coffin" before being raised to the vertical for launch, or it may be stored upright in a hardened underground silo, a large massive silo door sliding open when the time comes. A land-based ICBM may even be mobile; it might be launched from a heavy truck or a railcar. An ICBM may even be air-launched, although air-launched ICBMs have never gotten past the design study phase. ICBMs may be launched from submarines, surfaced or submerged, or even from surface ships.
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Modern ICBMs generally have solid-fuelled lower stages, for the sake of quick reaction times (the flight time from the US to Russia or vice versa is about half an hour), and liquid-fuelled upper stages, as liquid-fuelled engines have superior performance and may be throttled and restarted. They're much smaller than their predecessors, but at the same time so much more capable; they can be on their way within two or three minutes of the launch order being given, they can carry multiple miniaturized high-yield warheads, and they carry penetration aids and countermeasures to defeat anti-ballistic missile defenses.
'''SRBMs:''' Short-range ballistic missiles, or SRBMs, are ballistic missiles designed for use at a tactical or theater level. They tend to far more mobile then their ICBM counterparts, focusing on targets like troop concentrations. The 1987 Intermediate Nuclear Forces Treaty between the US and USSR resulted in them scrapping all land-based ballistic and cruise missiles with a range between 500 and 5,500
'''Missile submarines:''' These are, simply put, submarines capable of launching ballistic nuclear missiles. Their role is not necessarily to launch in the first part of nuclear exchange (although some were, like the Soviet [[Reporting Names|"Yankee"]] class, intended for that role), but as a "second-strike" weapon. Since "boomers" (the US navy slang term for them) are very hard to find, they could wait out for months if need be. They can usually be recognised by a pronounced hump behind the sail, which is where the missiles are stored.
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The ultimate examples of this type are the US ''Ohio'' class (18 built, 14 still in a nuclear role with the others now converted for conventional Tomahawk launching) and the Soviet/Russian Akula/"[[Reporting Name|Typhoon]]" class (6 built, 3 still in service). The latter is a very distinctive design indeed- the largest submarines in the world, with the missile compartment at the front.
'''Anti-shipping cruise missiles:''' This are carried by aircraft and designed to engage naval groups from long distance (200 miles or more). A Russian speciality, these weapons tend to be supersonic, but fly high to seek out their targets. These missiles will need be guided to their targets by a radar
'''Land-attack cruise missiles:''' Similar to the above, except these missiles are used to attack land-based targets, usually with much greater range. The target doesn't move, but much of Earth's land surface is rather less flat than the ocean, so most modern weapons of this type have some variety of terrain-following guidance, which also enhances their ability to fly low enough to stay below the radar horizon of the defenders until (theoretically) it's too late for them to mount an effective defense. Like their anti-shipping cousins, many can be adapted for use as conventional weapons; although by far not the only example, the "Tomahawk" cruise missile is probably the most famous one, thanks to its heavy use in the 1991 campaign against Iraq, and subsequent engagements in and around southwestern Asia.
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