Talk:Nuclear weapon design
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Edited Advanced thermonuclear weapons designs on the issue of salted weapons not being developed or tested. The US conducted an atmospheric test of a salted weapon during Operation Redwing. Information can be found on http://www.nuclearweaponarchive.org/Usa/Tests/Redwing.html under the Flathead shot.
- Everything I've seen on Flathead (which isn't much) suggests that it was just a typical Fission-Fusion-Fission. The "salted" designation by the gov't just means the uranium jacket, as far as I can tell, which isn't the same thing meant by "salted" in the context of this article (which means adding some sort of non-fissile material which will absorb neutrons and so forth). So I've changed it to reflect this a bit more -- Flathead doesn't look like anything special, though it was messy. --Fastfission 05:22, 19 May 2005 (UTC)
- Yea I thought about it afterwards and realized that there wasnt enough information to make a solid claim, specifically no information on the material used as the salt. I was going to revert it back to the original page, but I have been busy the last few days, thanks for fixing it up! If I can find any more information about Flathead I will add it to this discussion page.
I moved all that stuff about neutron bomb tactics, uses, etc. over to neutron bomb. I left the technical description here, but duplicated it in the neutron bomb article. Is this ok? how else should this be covered? -- lommer 04:11 16 May 2003 (UTC)
- I deleted that section from this article. This one is too long anyway. jni 14:02, 21 Sep 2004 (UTC)
I have three comments on the text, but I wont make changes as I am not a native english speaker.
- Fusion releases even more energy per reaction than fission: There are many fusion reactions and some of them must proceed simultaneously, but the largest energy released by a single reaction is about 18MeV [1] (http://gawain.membrane.com/hew/Library/Fusion.html), which is much less than the energy released by a fission process (180MeV [2] (http://gawain.membrane.com/hew/Library/Fission.html)). Even combined fusion reactions will certainly not reach this value.
- The radiation pressure of the X-rays heats and pressurizes the deuterium enough to fuse into helium, and emit copious neutrons. The article does not mention the "spark plug", which is a second fission bomb in the centre of the lithium deuteride. It is needed to reach the high temperature after compression [3] (http://gawain.membrane.com/hew/Library/Teller.html).
- The Tsar Bomba was not a fission-fusion-fission bomb. The fusion tamper was made of lead. Moreover I doubt that it is appropriate to call a fission-fusion-fission bomb "advanced", because uranium is a natural choice for the fusion tamper and its use does not cause additional technical diffuculties in comparison to lead.--El 18:36 26 Jul 2003 (UTC)
"Fusion releases even more energy per reaction than fission, and can also be used as a source for additional neutrons."
"The amount of energy released through fusion is very small compared to the energy from fission, so the fusion chiefly increases the fission efficiency by providing a burst of additional neutrons."
There seems to be a contradiction there. Which is accurate? Omegatron 17:59, 15 Jan 2004 (UTC)
I think the idea is that fusion has more bang for the buck, but not as many bucks. That is, while fusion releases more energy per reaction, there's a lot less of it going on. Furrykef 07:16, 19 Feb 2004 (UTC)
Theres a few small gaps in this article:
"The milling machines used are so precise that they could cut the polished surfaces of eyeglass lenses" Clarification in 1/1000's of an inch or microns or whatever tolerance? This description doesnt actually give a good suggestion of just how tolerant that is. 1/100th of a human hair? or...?
In the first bombs ... (Explosive Lenses). And what is more common now, since then, as explosive lenses?
The largest modern fission-fusion-fission weapons... (Advanced thermonuclear weapons designs) This term is suddenly introduced, so there's a sense that somewhere between "staged tehrmonuclear weapons" and "advanced design", either a stage is missed out, or a description of F-F-F is needed, or some such?
Last, a lot of the latter part of the article isn't about weapons design at all. It should be moved to something like Nuclear Weapons Tactics or some such, its nothing to do with design.
Hope this helps FT2 10:50, Aug 21, 2004 (UTC)
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Images
The images of the gun-type and implosion bombs seem to be taken from globalsecurity.org (http://globalsecurity.org/wmd/intro/nuke-design.htm) and are probably not GPFL. The image of the Teller-Ulam bomb is pretty abysmal and likely from whyfiles.org (http://whyfiles.org/186ed_teller/3.html), again probably not GPFL. I'm happy to work on new versions at some point but I thought I would point out why I was doing it. --Fastfission 18:53, 21 Nov 2004 (UTC)
- Okay, they are all replaced, let me know if you'd like any modifications done to them. --Fastfission 19:17, 13 Feb 2005 (UTC)
Prompt criticality
It is worth incorporating some information from prompt critical into this article. Essentially, when a neutron is absorbed by a fissile nucleus, the nucleus may undergo fission immediately or it may take some time. Nuclear reactors are difficult and dangerous to build because they must remain critical but not prompt critical. Fission bombs are difficult to build because they must go from being subcritical to prompt critical before the heat from being merely critical destroys them. --Andrew 00:03, Dec 14, 2004 (UTC)
Slight Correction
Fusion releases even more energy per reaction than fission,
This is inherently incorrect. As aforementioned fission reactions actually convert significantly more mass into energy then fusion reactions do in a single reaction. The correct analogy is, fusion reactions release more energy per mass then fission reactions do. Fusion reactions are more powerful simply because exponentially more occur in the same space that a single fission reaction occurs in. Veloren 15:03, Mar 20, 2005 (UFT)
Old text from nuclear weapon
Common types
Fission bombs
Fission_bomb_assembly_methods.png
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 nuclear chain reaction). With each of those splits, an amount of energy thousands of times greater than that available from a chemical reaction is released. These are historically called atom bombs or A-bombs, though this name is not precise due to the fact that chemical reactions release energy from atomic bonds too, and fusion is no less atomic than fission. Despite this possible confusion, the term atom bomb has still been generally accepted to refer specifically to nuclear weapons, and most commonly to pure fission devices.
In general, fission bombs are powered by using chemical explosives to compress (implode) a sub-critical 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. A more crude design for such a weapon is to have two sub-critical amounts of uranium-235 simply shot into each other inside a gun barrel. This approach, used in the weapon dropped on Hiroshima during World War II, is conceptually easier but inefficient and inherently more dangerous to maintain than an implosion weapon.
One pound of U-235 can release over 37 million million joules of energy. This is 82 terajoules per kilogram (TJ/kg). A typical duration of the chain reaction is 1 μs, so the power is 82 EW/kg (30 μW or 200 MeV/s per atom; related to the duration of one generation of the chain reaction: 3mW/atom, i.e., the power of a chain reaction just at criticality is 3mW in the case of consecutive fissions, one at a time).
Fusion bombs
Teller-Ulam_device.png
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 or H-bombs because their fusion fuel is often a form of hydrogen, or thermonuclear weapons because fusion reactions require extremely high temperatures for a chain reaction to occur. This latter name can be somewhat confusing, as thermonuclear reactions can take place in nuclear weapons which are not considered "true" 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.
Thermonuclear devices can be phenomenally energetic; easily capable of releasing a thousand times the energy of a fission bomb (megaton range). Consequently, the power of a fusion bomb can achieve staggering levels, representing the highest power levels achievable by humans. For instance, the Tsar bomba released 50 megatons of energy, almost all produced by its final fusion stage. Since 50 Mt is 2.1x1017 J the power produced during the burn is around 5.3x1024 watts (5.3 yottawatts). This represents a power just greater than one percent of the entire power output of the Sun (3.86x10^26 watts)!
Dirty bombs
- Main article: Dirty bomb
Dirty bomb is now 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. One of the most publicly stated fears of Western governments since the September 11, 2001 attacks has been the terrorist detonation of a dirty bomb in a populated area. 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. In the estimation of most analysts, though, the effect would be primarily psychological, and potentially economic if a costly clean-up effort was called for.
Nomenclature
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. Finally, a fusion weapon may include a fission core (in addition to being externally compressed by fission explosion) in order to achieve more complete fusion (see nuclear weapon design for some description of all these variants). 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".
Advanced thermonuclear weapons designs
The most powerful modern weapons include a fissionable outer shell of uranium. The intense fast neutrons from the fusion stage of the weapon will cause natural (that is unenriched) uranium to fission, increasing the yield of the weapon many times.
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, which produces major radioactive contamination. In general this type of weapon is 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). To be useful for salting, the parent isotopes must be abundant in the natural element, and the neutron-bred radioactive product must be a strong emitter of penetrating gamma rays.
The primary purpose of this weapon is to create extremely radioactive fallout to deny a region to an advancing army, a sort of wind-deployed mine-field. No cobalt or other salted bomb has ever been atmospherically tested, and as far as is publicly known none has ever been built. In light of the ready availability of fission-fusion-fission bombs, it is unlikely any special-purpose fallout contamination weapon will ever be developed. The British did test a bomb that incorporated cobalt as an experimental radiochemical tracer (Antler/Round 1, 14 September 1957). This 1 kt device was exploded at the Tadje site, Maralinga range, Australia. The experiment was regarded as a failure and not repeated.
The thought of using cobalt, which has the longest half-life of the feasible salting materials, caused Leó Szilárd to refer to the weapon as a potential doomsday device. With a 5yr half-life people would have to remain shielded underground for many years, effectively wiping out humanity. However this would require a massive (unrealistic) amount of such bombs, yet the public heard of it and there were numerous stories involving a single bomb wiping out the planet.
Neutron bombs
- Main article: Neutron bomb
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, and this knowledge led some to envision a weapon that would do little physical damage while killing all the people in a certain area (a so-called "landlord bomb"). This appears to be somewhat of an exaggeration, as the bomb would still create at least some significant blast and fire damage. The term "enhanced radiation" refers only to the burst of ionizing radiation released at the moment of detonation, not to any enhancement of residual radiation in fallout (as in the salted bombs discussed above).