Talk:Nuclear weapon design

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Contents 1 2 Images 3 Prompt criticality 4 Slight Correction 5 Old text from nuclear weapon 5.1 Common types 5.1.1 Fission bombs 5.1.2 Fusion bombs 5.1.3 Dirty bombs 5.1.4 Nomenclature 5.2 Advanced thermonuclear weapons designs 5.2.1 Cobalt bombs 5.2.2 Neutron bombs 6 Atom Bomb 7 Efficiency 8 Impracticality of the needed amount of cobalt 9 Possible mistake in the cobalt article 10 Stuff which needs to get added 11 Duration? 12 Possible Inter-Disciplinary Applications of (Emerging) Technologies and Classification of Weapons Designs by Innovative Usage of Such Technologies 13 Data and Computational Requirements for Effective Nuclear Weapon Design Analysis and Simulation 14 Common causes for nuclear weapons testing failures and Design Philosophy 15 Article misleading emphasis 16 salted bomb 17 SI Units 18 Purified Hydrogen Bomb, is that real? 19 this is one of the best articles on wiki 20 Foam vs. Ablation 21 Tamper

[edit]

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.

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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)

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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], which is much less than the energy released by a fission process (180MeV [2]). 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].

• 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)

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"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)

The second statement refers to the few grams of fussion material inserted into the pit more as a source of neutrons to amplify the fission reaction than as a source power in itself. The fussion reaction of a few grams is indeed swamped by the fission of many kilos of material. LiamE

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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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Practical limitations of fission bombs

"A pure fission bomb is practically limited to a yield of a few hundred kilotons by the large amounts of fissile material needed to make a large weapon."

In light of the 700kt+ fission weapon test by the UK in the 50's (Orange Herald, 31 May 1957) shouldn't that be revised up a bit?

LiamE

• According to [4], Orange Herald/Grapple 2 was a quasi-fusion/booster device along the lines of Joe 4, not a pure fission weapon. --Fastfission 17:45, 15 July 2005 (UTC)

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[edit] Images

The images of the gun-type and implosion bombs seem to be taken from globalsecurity.org and are probably not GPFL. The image of the Teller-Ulam bomb is pretty abysmal and likely from whyfiles.org, 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)

[edit] 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)

[edit] 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)

[edit] Old text from nuclear weapon

[edit] Common types

[edit] 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 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).

[edit] 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 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)!

[edit] 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.

[edit] 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".

[edit] 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.

[edit] 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.

[edit] 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).

[edit] Atom Bomb

It is a precise enough term, in that atom bombs _alter_ atoms into other atoms and this is their unique feature. The bit about chemical bonds is really not relevant.

All explosives are "atomic" -- they "alter atoms" in a variety of ways, whether it be their configurations, how they are bonded, how many electrons they have, etc. Nuclear weapons are unique in that they specifically alter the nucleus of the atoms, which is what you mean by "atoms into other atoms". Even in 1945 "nuclear" was seen as the correct terminology (Henry DeWolf Smyth was forced to refer to them as "atomic weapons" in the Smyth Report against his will), but "atomic" resonated more with early public knowledge about radiation (from, i.e. radium). It is in the same league as another proposition from the time which didn't take off, William Laurence's reference to them as "cosmic" weapons. --Fastfission 13:49, 16 July 2005 (UTC)

[edit] Efficiency

65.241.94.2 edited the text to read:

The most efficient pure fission bomb possible would still only consume ~25% of its fissile material before being blown apart, and can often be much less efficient (Fat Man only had an efficiency of 14%).

The changes were from 20% to ~25% (which sounds reasonable) and also from 1.4% to 14% (which is an order of magnitude!). Are the new numbers more correct?

Atlant 12:46, 3 October 2005 (UTC)

The 14% figure seems to be plausible. this estimate, and this estimate, and this estimate state that each weapon contained only about 6.5 kilograms of plutonium, of which roughly 1.1 kilograms fissioned (as can be calculated from the bomb yield, see this reference desk question doing that calculation for Little Boy. Therefore 14% seems reasonable. Little Boy was much, much less efficient. --Robert Merkel 13:38, 3 October 2005 (UTC)

Thanks for checking!

Atlant 19:08, 3 October 2005 (UTC)

Looking at it, the point is perhaps more effectively illustrated by using Little Boy as an example of inefficiency (and it was only about 1.4% efficient). I'll make the change. --Robert Merkel

~~Mike Velasquez~~

I believe this has already been pointed out, but a comment could probably be added to the cobalt bomb mention since many stories speak about a single bomb wiping out the planet. It should be mentioned that the amount of cobalt would be enormous and not technologically practical.

I also want to point out that the Flathead test seems to have been a "salted" test, meaning a "dirty" weapon or a high-fission weapon. In this link, it is mentioned as being a 73% fission weapon, therefore "dirty". I think it must be taken into account that the Redwing tests were testing the Mk-28 warhead, a three-stage weapon and considered "dirty" or "salted" high fission weapons. It doesn't seem to be talking about a salting agent, besides the ones produced by high fission. Consider this:

"The configuration fired in this test was a "clean" (low fallout) version that used a lead tamper around the thermonuclear third stage. Only 15% of the energy yield was from fission. A "dirty" version of this design, the Bassoon Prime device, was later fired in Redwing Tewa. The predicted yield for Zuni was 2-3 Mt. In the dirty version,the fission yield was 87%, the highest known fission yield in any U.S. thermonuclear test"

http://nuclearweaponarchive.org/Usa/Tests/Redwing.html

The context of these tests seem to have been contrast betwe high fission and low-fission weapon and the amount of fallout they produced.

• As the article notes, there have been a number of relatively "dirty" thermonuclear tests, with a big final fission stage. But this is not the same thing as a cobalt bomb. My understanding is that the doomsday device idea would not be limited by size, ala Strangelove's "When you

merely wish to bury bombs, there is no limit to the size," but beyond that I don't know the physical details. I've never seen anything about Flathead that suggested in convincing terms that it utilized anything other than a final fission stage. --Fastfission 20:24, 1 February 2006 (UTC)

• As an aside, many of the other sources for cobalt bomb fantasy (such as On the Beach) considered that many bombs would be dropped by both sides, not a single doomsday bomb. --Fastfission 20:40, 1 February 2006 (UTC)

[edit] Impracticality of the needed amount of cobalt

~~Mike Velasquez~~

That's true. I don't think I have the authority to make a change in the article, though. Maybe you can talk about the impractical amount of cobalt that would be needed in the article. I think it would be appropriate, since I have seen some people from doomsday websites advocate that a few bombs could get the enough amount, regardless of the enormous amount needed of cobalt, uneven distribution and so on.Nowadays, a good amount of info on nuclear weapons has been declassified and the miniaturization of devices obviously showed that weapons are not intended to have a "doomsday" effect. The article should probably be a little more specific, since it does not offer details and gives the impression that one or few of the current devices could get that effect. People from rense.com and other websites have cited this place as proof.I think the article should probaly be as scientfic as possible.

[edit] Possible mistake in the cobalt article

I have seen in the article of "cobalt", there is a mention that emissions of neutrons will convert iron into cobalt 60. If that were the case, many nuclear weapons tested that had steel cases such as Ivy Mike, would have produced nightmarish amounts of cobalt 60. Probably, it was meant to say that cobalt 59 turns into Cobalt 60 by the emission of neutrons, not iron or steel. Can somebody tell me if steel or iron really turns into cobalt 60 by neutron emission? I doubt that is the case.

Mike Velasquez 04:09, 23 February 2006 (UTC)

The version I'd heard was that cobalt 59 was transmuted to cobalt 60. Dusting off my copy of the rubber bible, I find that cobalt 59 represents virtually all naturally-occurring cobalt, and has a relatively large neutron capture cross-section (just shy of 20 barns), while most iron is iron 56, which would require four neutron captures to transmute, and which has a much lower neutron capture cross-section (2.5 barns). The heaviest naturally-occurring iron isotope is iron 58, which would still require two captures, and which has an even smaller capture cross-section and occurs in very minute quantities. So, I think it's safe to say it's a typo (though you'll still get _activation_ of the casing, as some of the iron and some of the alloying materials will get transmuted). --Christopher Thomas 17:19, 23 February 2006 (UTC)

Yeah, that's what I meant in my comment in the cobalt article when I said some iron would probably be transmuted into cobalt 60 as part of the fission products, but it would not be a significant amount as the article gave the idea of. I agree some cobalt 60 would be produced, although no significant amounts and would not be a more abundant and significant risk than other fission products. The biggest problem and cause of fallout is the debris being kicked up by a groundburst. If significant amounts of Cobalt 60 were produced from the activation of the steel casing, that would be considered more dangerous than the activation of debris due to the metals in the ground. The fact that it is not so, clearly shows that cobalt 60 is not produced significantly from steel and why a cobalt bomb would require the use of natural cobalt in the case, not steel or iron that cannot produce cobalt 60 in great amounts.

Mike Velasquez 17:33, 23 February 2006 (UTC)

Rather than re-editing your previous comments, it's generally considered good form to add a new comment instead. Otherwise it gets a bit tricky telling who said what and when. --Christopher Thomas 19:51, 24 February 2006 (UTC)

Sorry for the mistake, did not know it was not recommendable to edit comments. In any case, I think we have reached an agreement that there would be some cobalt 60 produced although not in significant amounts.You will find my previous comment in the "talk:cobalt" page. We could improve the cobalt article. Would you consider changing the article of the "metal" cobalt or should I go and make an specification into the small amount that would be produced from steel in contrast to a cobalt bomb?

MIke Velasquez 01:00, 25 February 2006 (UTC)

I just caught up on this... something seems wrong here. You can't change the atomic number (number of protons and electrons) in an isotope by neutron capture. Neutron capture changes one isotope (say, Co-59) into another isotope (Co-60) of the same atomic number. Other elements are formed from that then decaying (say, emitting an alpha and dropping two units of atomic number and four of weight, to Mn-56).

The only way Iron will get turned into Cobalt is if it fuses with a hydrogen, deuterium, or tritium atom. For which, the activation energy level is truly insane (far higher than the fusion energy of D-T fusion). Heavier elements get made by large research particle accellerators, or inside of supernova star explosions. Nuclear weapons are generally D-T fusion to Helium on the Fusion side, and neutron capture and subsequent fission or decay on the fission side.

I need to go read the article in detail and see what it's really saying right now. Georgewilliamherbert 01:10, 25 February 2006 (UTC)

You very frequently end up changing the proton number, because the isotope produced by neutron capture will usually beta decay. In the case of iron, you'd get the miniscule fraction of iron 58 transmuted to iron 59, which beta decays to cobalt 59 with a half life of about 45 days. This doesn't help you get cobalt 60 from iron, of course (that would require absorbing two neutrons during the explosion, to iron 60, and would produce cobalt 60 very slowly, as iron 60 is much more stable than iron 59). Neutron capture followed by beta decay is the process by which breeder reactors turn uranium 238 into plutonium. --Christopher Thomas 07:08, 25 February 2006 (UTC)

I should have been clearer. I know about beta decay and the production of Pu-239. The statement "The only way..." should have been followed by "...during the nuclear explosion process..." as the dual neutron capture scenario appears statistically improbable due to the initial small (0.3%) quantity of Fe-58 and the capture cross sections of Fe-58 and Fe-59, and the equally improbable triple neutron capture from Fe-57 to get up there. Beta decay of both fission daughter isotopes and neutron activated bomb materials following the detonation will give you a wide range of various isotopes including some Co-60, but is useless as a mechanism to produce a Co-60 radiological device. I should have been more precise to start with. Georgewilliamherbert 23:37, 25 February 2006 (UTC)

Sorry for the re-editing, won't do it again. In the discussion of iron, you mention iron 58, however, the biggest amount of it in natural abundance are iron 56,then iron 54 and then 57. What is the possibility of these capturing the necessary neutrons? I remember you mentioned that they have a much lower neutron capture crosssection, would they not capture the necessary amount or would they capture it but in a very insignificant amount (due to how unlikely it is) as to be negligible?

Mike Velasquez 19:09, 25 February 2006 (UTC)

As User:Georgewilliamherbert notes, the amount produced would be extremely low due to the low probability of two neutrons being absorbed by a single iron 58 atom during the explosion. If you want back of the envelope numbers, I can pull numbers out of thin air, but as they depend strongly on assumptions, they won't be very accurate.

For example, we can blindly assume that the absorption cross-section for iron 59 is about the same as that of iron 58 (on the order of 1 barn), as this is pretty typical for isotopes that are neither good absorbers nor neutron reflectors, but the real value could be off by orders of magnitude. We could assume that you'd get about one neutron produced per hundred iron atoms, based on assumed amounts of iron vs. fissile material in the bomb, but this depends strongly on construction of the bomb. We can assume that the neutron capture cross-section for the several-MeV neutrons emitted will be roughly of the same order as that for thermal neutrons, but resonances make this a very bad assumption. We can assume that the iron casing is about 1 cm thick, giving about 0.1 atom per barn of cross-sectional area, but this too can vary. This means we get about 0.001 neutron per barn of cross-sectional area. Given all of these questionable assumptions, any given iron 58 atom has a probability of 0.001 of absorbing a neutron being bred into iron 59, and that has a 0.001 probability of being bred into iron 60, for a total of one atom in a million of iron 58 turning into iron 60, which amounts to one atom out of about 300 million of all of the iron in the casing. Each year, only about one in 300,000 of these will beta decay into cobalt 60, meaning that if you set off your bomb, and checked every iron atom produced a year later, you'd find about one in 100 trillion turned into cobalt 60. Disclaimer: This could be off by at least three or four orders of magnitude due to all of the assumptions made, as indicated above. --Christopher Thomas 07:36, 26 February 2006 (UTC)

Thanks for taking your time to answer my question I see. Even though these numbers may not be accurate,the amount produced would be very low and still comparable to other fission products due to the low probability of the absorption of two neutrons by an atom of iron 58.This without considering the miniscule amount of iron 58. I take it then, that the absorption of three, four or more neutrons as would be necessary for iron 57, iron 56 and iron 54 would be a lot more improbable.

Mike Velasquez 17:30, 26 February 2006 (UTC)

Absorption of more neutrons would be extremely improbable, yes. If the bomb specced out above exploded in vacuum (no other matter around to activate), most of the radioactive byproducts would be the fission products themselves, not anything activated by neutrons (the neutrons would eventually decay into proton/electron pairs). In practice, you'll get some of the alloying materials in the casing (like manganese, nickel 62, and vanadium) being activated as beta emitters with lifetimes in a problematic range, and for a detonation in or near the ground, perhaps some activation of the material there, depending on rock composition and presence of other materials. A detonation high in the air mostly just rains down fission products and activated casing materials, as neither nitrogen nor oxygen can be easily activated by neutron radiation. Short-lived beta emitters are a considerable radiation hazard even when produced in fairly small quantities. --Christopher Thomas 20:09, 26 February 2006 (UTC)

I think I just realized something. Even if the absorption of two neutrons happened, the half-life of iron 60 is 1.5E6 y. A significant amount of cobalt 60 would take many years to be produced from the iron 60 as the beta decay to cobalt 60 would be very slow and cobalt 60 produced would decay while more iron is decaying into cobalt. Considering the half-life of iron 60, its beta decay is not dangerous due to its long half-life and even the miniscule amount of iron 60 produced turning into cobalt 60, would be no danger at the pace it would be produced, compared to other activated materials and fission products, right?

Mike Velasquez 19:59, 27 February 2006 (UTC)

According to my (1975) copy of the Rubber Bibble, the half-life is 3e5 years, and I already factored that in (that's why I divided by 300,000 to find out how much would be transmuted after waiting one year, though this number is off by ln(2) now that I think about it). The other casing materials I noted above have much shorter half-lives (from tens of minutes to something like 90 years), and so are indeed much more of a problem in the fallout from an air burst (what little fallout there is). In practice you mostly run into problems when a bomb is let off near the ground with geology containing easily-activated elements. This can give you tons of radioactive ash raining down over a large area. --Christopher Thomas 20:14, 27 February 2006 (UTC)

As a point of information, modern bomb casings are probably high-Z (high atomic number) x-ray opaque material liners with a lightweight aluminum outer structural casing. Iron / steel aren't really the best engineering choice... Georgewilliamherbert 21:30, 27 February 2006 (UTC)

If iron 60 has 3e5 years of half-life, I would think a mistake was probably made in the iron page. When it describes isotopes, it says that iron 60 has a half-life of 1.5E6 y.

http://en.wikipedia.org/wiki/Iron

I will check in other sources and then post a comment on what I find.

Mike Velasquez 21:42, 27 February 2006 (UTC)

The T2 site agrees with 1.5E6 years. Georgewilliamherbert 22:01, 27 February 2006 (UTC)

Yes, I have seen other sources with similar results.

60 1.5×10+6 years Beta-minus Decay 100.00

http://education.jlab.org/itselemental/iso026.html

Iron-60, a radioactive isotope with a half-life of just under 1.5 million years, can be readily produced only by high-mass stars just before they self-destruct in supernova explosions.

http://www.looksmartscience.com/p/articles/mi_m1134/is_5_112/ai_102275167

and from Phil Plait's site:

There are two amazing things about this finding, if it turns out to be correct. One is that iron-60 is radioactive, with a half-life of roughly a million years.

http://www.badastronomy.com/bitesize/stardust.html

I think the iron page is correct in the half-life of iron 60

Mike Velasquez 22:23, 27 February 2006 (UTC)

It's quite possible that the longer half-life value is correct; my copy of the Rubber Bible is very old (hence the date citation). However, be advised that web page sources may be repeating inaccurate information as well (though T2 looks reputable). This doesn't change my numbers much, compared to the other uncertainties. Re. casing materials, aluminum mostly scatters neutrons, and is transmuted into stable isotopes of silicon that do an even better job of scattering, but it's usually alloyed with copper (which activates with a half-life of minutes for one isotope and hours for another) and other metals. --Christopher Thomas 22:39, 27 February 2006 (UTC)

I hope T2 is reputable; they and JAERI are the reference sources of record for most isotope data these days... and the source of the data tables for computer modeling... Georgewilliamherbert 22:45, 27 February 2006 (UTC)

Sorry for being a pain on you Chris. I have been discussing some of this stuff with some rense.com folks and want to have knowledgeable answers, I myself can't come up with. I thought that the division by 1.5E6 rather than 3e5 would certainly make a big difference as well as the other uncertainties, since the beta decay of iron 60 would be slower(although a half-life of 3e5 years would probably still make the amount of Cobalt 60 transmuted each year small and negligible). Therefore I presume, an slow conversion rate (3e5 or 1.5E6 years) seems to eliminate the danger of the produced Cobalt 60 ,even if hypothetically, there were huge amounts of iron 60 to be eventually converted in Cobalt 60, as in any given year only small amounts would be transmuted and since there would be decaying of a good amount of cobalt 60 each year as more is produced) , therefore the danger of cobalt 60 would be negligible unlike other activated materials or fission products. But hey, I am not sure if my conclusions are right, math is not my forte and so I have to hope others will bear with me.

Mike Velasquez 01:19, 28 February 2006 (UTC)

The change in half-life means that you get about one fifth the amount I'd originally estimated transmuted per year. This is a significant change, but the other fudging I was doing in the calculation could cause far greater changes. The math I gave is at best used as a hand-waving argument illustrating how 1) most of the iron would take more than two absorptions to activate, 2) two neutron absorptions doesn't happen for the vast majority of atoms (about one in ten million absorbs two with the fudged numbers I gave), and 3) the amount that's transmuted decays very slowly. Any actual numbers added to these handwaved points aren't terribly important, but only illustrate that the calculations can be performed and give you something in roughly the right ballpark. The values I used were _not_ trustworthy for most steps. --Christopher Thomas 09:37, 28 February 2006 (UTC)

Yeah, I think I see your point now. As you mention, actual numbers would not be terribly important when the points could be made with the calculations you made. the fact that most iron would take more than two absorptions of neutrons, the absorptions of two neutrons don't happen often and that the amount transmuted decays slowly seem to point out to a conclusion: that the Cobalt 60 produced each yeat would be a negligible danger and not noticeable due to its extremely small production, and also that any amount transmuted eventually will not be noticeable due to its long half-life, in comparison to other fission products and activated materials. That's why iron couldn't be any significant source of Cobalt 60. I hope I understood your conclusion. If not, feel free to point out the mistake in my conclusion.

Mike Velasquez 15:18, 28 February 2006 (UTC)

[edit] Stuff which needs to get added

There needs to be a basic introduction to linear implosion here in the design article; I have covered the basics in the W48 and W79 pages, but it should really be here.

There should be a better introduction or overview of levitated pit and hollow core pit designs; they're currently mentioned in several places in passing.

Georgewilliamherbert 02:06, 14 April 2006 (UTC)

[edit] Duration?

How long can an atomic bomb lay in abeyance before it becomes rusty and out of order? 50 years? 100 years? A thousand years? In theory, would the US be able to defend itself against an alien attack of green little men in the year 2525 with today's weapons? XavierTheGreat 20:24, 30 April 2006 (UTC)

'Depends on what type of bomb we're discussing. For a plain-old atomic (single-stage fission) bomb, the main fuel (uranium or plutonium) is sufficiently stable to let the bomb detonate even a long time later. But if the "initiator" is passive (polonium and gold foil, IIRC), the polonium has a very short half life and won't work after something like < 1 year. And if the initiator is electronic, the batteries will need changing. (Certain extremely-primitive gun-type fission bombs will probably detonate without an initiator; they would probably remain viable for a long, long time [in the scale of human politics].) Also, the high-explosives may degrade, either becoming more sensitive to an accidental detonation (which would probably be a fizzle, atomic-bomb-wise) or lead to screwed-up timing (which would cause an implosion-style bomb to fizzle).

For a boosted fission bomb or a thermonuclear (fusion) bomb, you've also got the constraint that the tritium has a pretty short half life and would probably need replacement in <10 years.

Atlant 00:32, 1 May 2006 (UTC)

Nobody uses polonium anymore; electrical neutron generators have been standard since slightly after the invention of the nuclear bomb, usually short particle acellerators firing deuterium and/or tritium into a D or T target (there are commercial neutron generators for industrial use which are longer lifetime/lower output, but the same concept).

Plutonium metal's behavior changes over long periods of time. The lifetime of existing US nuclear warheads past 40 or 45 years is in question due to Plutonium aging effects.

The lifetime and stability of the explosives used is also uknown for hundreds-of-years duration. Some older explosives used had safe shelf lives of less than five years; modern ones have lasted for 35 years or more. We still have W62 warheads from 1970-1976 production in service today, and other models of nuclear weapon were in service for more than 30 years as well... the B61 design has been in production for 40 years, but the earliest models produced have all been retired.

It's hard to predict how long one could push designs; 50 years should be practical. Using Uranium instead of Plutonium should extend the fissile material lifetime. There are probably explosives which can be stable for 50+ years, and plastic bonded TATB seems likely to fit into that category based on what I know. Nobody's actually stored it for 50+ years to see what happens, though, so we don't know for sure (it's not that old a material....).

Gun type bombs could conceivably last for a very very long time.

For all weapons, the lifetime of the electronics would be a major limit.

Is this book project research, or just an idle question? Georgewilliamherbert 06:19, 1 May 2006 (UTC)

They started making new plutonium pits a few years back (2003, I believe, about 15 years after Rocky Flats got tube steaked). This may idicate that the friendly folks at Sandia and Lawrence Livermore believe that replacement parts are needed. (You could also argue that new designs are in the works, or that they are making them just to keep a skilled workforce in case of future need). Give Peace A Chance 06:38, 1 May 2006 (UTC)

As has been noted, there are a lot of variables in this. Our stockpile stewardship article is pretty bare at the moment, but if you Google "stockpile stewardship" you'll find a lot of official and unofficial reports about the research done on the reliability of the U.S. nuclear stockpile as time goes on, which gets at your question. It is also a politically controversial issue as well, which you should watch out for: some people use the uncertainty as a way to argue for more testing of weapons components and even of the weapons themselves. --Fastfission 15:29, 1 May 2006 (UTC)

[edit] Possible Inter-Disciplinary Applications of (Emerging) Technologies and Classification of Weapons Designs by Innovative Usage of Such Technologies

It would be good to have some way of trying to find out how emerging technological areas (such as nanotechnology) might have something of an effect on the nature of advanced nuclear designs. Further areas of progress in regards to theoretical limitations of the design of nuclear weapons - together with possible suggestions for various methods for improving nuclear design might also be interesting. Specifically, I imagine that *theoretical limitations* on current nuclear designs would be an interesting topic for the wiki.

One idea that crossed my mind would certainly be how nanotechnologically derived materials could alter the nature of the lensing apparatus associated with the guidance of shock waves for the initiation of the fission process.

It is also obvious that an aesthetic classification system that analyses how some of the weapons designs depend on other technologies (for example, guidance systems) would be interesting.

While potentially interesting, this looks like it is wading directly into the area of Wikipedia:No original research. --Fastfission 16:07, 22 June 2006 (UTC)

[edit] Data and Computational Requirements for Effective Nuclear Weapon Design Analysis and Simulation

Here is a quote from the article : "Weapons systems that require relatively small thermonuclear weapons, such as MIRVed missiles, are thought to be achievable only with large amounts of test result data."

Perhaps some elucidation would be useful in these regards? What aspect of weapons design requires access to what types of data? Specifically what critical data is measured and obtained from direct nuclear tests and how does this reveal efficacy of nuclear design? Could I determine the type of nuclear weapon used/deployed during a nuclear war with satellite information? Surely advances in computational simulation methods and techniques replace at least a significant amount of what may have been historically required in terms of 'on the field experimental validation' of nuclear weapons design?

Well I'm not sure a lot of those details on what exactly the test data tells you are public (in fact I am sure much of it is not). My rough guess is that in the end it all comes down to intricacies regard the behavior of the materials with very small tolerances for error, but that is an almost meaninglessly general statement. As for detection of type used via satellite information, you could probably tell a lot about the weapon from various types of post-blast information, and I imagine the sort of information you can get from Vela satellites probably would help with that. As for the computer simulations, generally speaking, yes, they are trying to rely on them, but my understanding of it is that it is hard to have confidence in the simulations without the test data to go along with it. With a large set of test data, though, you can apparently make fairly useful and reliable computer simulations, which is why the U.S. was so afraid of Chinese spies stealing old test data (because they could use the simulations to leapfrog without having testing themselves). --Fastfission 16:20, 22 June 2006 (UTC)

[edit] Common causes for nuclear weapons testing failures and Design Philosophy

Here it might be a nice idea to analyse (briefly) some of the common causes of the *failures* of any particular nuclear tests (this includes analysis of those tests that were touted as being successes). This may link into the above section about data and how it feeds back into the nuclear design process and philosophy. What extra equipment might I choose to integrate with any particular nuclear design system (and how might I conveniently integrate such equipment) to ensure that I can maximise the amount of information that I would gain from the deployment of a given nuclear weapon (whether or not such a deployment would succeed or fail).

This links into sensors for nuclear weapons and how those sensors might place constraints on the original intention of the nuclear weapons design (namely destruction) - clearly, when designing a nuclear weapon (though having a large amount of informational and theoretical background in regards to nuclear weapons design, at least from textbooks), it would possibly be a prudent investment of time and effort to ensure that some design alterations are made in such a way as to maximise 'practical' data obtained from a single deployment - that way any further tests would stand a greater chance of success, especially if the given test deployment is your first one. This includes both internal and external sensor technology methods for test data retrieval. Perhaps emphasis should be given to the issue that it is not so much the data that is obtained from the nuclear weapons testing that is of relevance (so it is!) but what you do with that data (specifically, how it can be incorporated into softwares to aid in design and error detection).

Basically want a better approximation to the perfect nuclear weapons system design and systems design approach. Philosophically speaking - how would I design the perfect nuclear weapon *and* nuclear weapons infrastructure? Are there any error detection methods and techniques that are required in nuclear weapons design that are not commonly used in regards to the design of other more mundane technologies?

Failures: I'm not sure there is a uniform reason for failures other than "they made certain theoretical assumptions that proved to be wrong." But a description of some of the notable failures and errors might be useful, since it does highlight the somewhat absurd nature of nuclear design (that even after dumping millions of dollars into something as important as a nuclear weapon, they can still be quite wrong about the science and not realize it until they accidentally irradiate a thousand people). The biggest failures that I know of are the first three tests for Lawrence Livermore (all fizziles) and the under-estimations of the yields of the Operation Castle shots (175% of expectation in one shot, 150% off in another). There are other issues like bombs being dropped in the wrong place (i.e. in the Crossroads Able shot) but those aren't design-related problems.

Sensors: I don't quite think I understand what you are getting at. I think you are mixing the question of warhead design and test design up a bit. The test design (i.e. design of the nuclear test shots themselves) was no doubt often arranged to give lots of different types of practical knowledge from any given shot, but I don't think that the warhead design was likely affected by this in any way.

Design and systems: I imagine there are many things which are technically specific to nuclear weapons designs, primarily because nuclear weapons designs deal with lots of things that "mundane" technologies do not (a simple example of that is the extreme levels of heat and pressure they create). As for the "perfect" weapon/infrastructure, it depends what you define "perfect" as. There is no "perfect" nuclear weapon design -- it depends what characteristics you want in a weapon (i.e. must it be very high yield or not? must it fit onto a missile or not? must it use only plutonium or not? must it be able to survive for decades without maintenance or not?), which history has shown to be very context-sensitive (hence many in the U.S. think that what was "perfect" for the Cold War is no longer "perfect" in the post-Cold War). --Fastfission 16:29, 22 June 2006 (UTC)

And... Wikipedia is not a nuclear proliferation how-to guide.

It's one thing to examine the past in detail. Cookbooks for how to design nukes and nuclear development or materials production programs are something else. These things are examined by unclassified experts in the field all the time, but people don't publish the details openly. Georgewilliamherbert 20:55, 22 June 2006 (UTC)

I very much doubt that there's anything we could publish here that would be of use to any would-be proliferator. --Robert Merkel 00:09, 23 June 2006 (UTC)

This is an actual problem with, for example, the Nuclear Weapons FAQ that Carey Sublette maintains. There is significant openly known information which has been left out of the FAQ to date, as detailed analytical treatments of it would be a proliferation risk. Even the level of detail in the FAQ and related materials is sufficient for a suitably bright and educated person with physics and engineering background to build compact reliable weapons, and have a fair chance at designing a functional moderately compact thermonuclear weapon on the first try. Georgewilliamherbert 00:36, 27 June 2006 (UTC)

Anything that would be seriously of use to them would fail WP:V and WP:NOR. Anything which meets WP:V and WP:NOR is already in the public domain somewhere and not our proliferation problem. I know there is at least one person who edits on here who probably knows some hard facts which would be useful for a proliferator of some sort, but he is smart enough not to post it, since the personal penalties would be high. --Fastfission 01:54, 23 June 2006 (UTC)

[edit] Article misleading emphasis

• Expanding on my http://en.wikipedia.org/w/index.php?title=Nuclear_weapon_design&oldid=81247579 edit:

Lithium does not actually take part in the thermonuclear reactions. Lithium is used in the form of lithium deuteride (a solid) to compactly store deuterium within the second stage of the H-bomb. It is the deuterium that takes part in the thermonuclear reaction not the lithium. I'm surprised this hasnt been picked up before. Troll at work? LochVoil 18:05, 13 October 2006 (UTC)

Disclaimer: I'm no expert.

But are you sure the lithium itself plays no part? I note that in ITER, it's the torus's lithium liner (blanket) that is transmuted by the neutron bombardment to create the tritium that will fuel the on-going reaction.

Atlant 18:20, 13 October 2006 (UTC)

From http://nuclearweaponarchive.org/Library/Fusion.html

The most important fusion reactions for thermonuclear weapons are given below:

1. D + T -> He-4 + n + 17.588 MeV
2. D + D -> He-3 + n + 3.268 MeV
3. D + D -> T + p + 4.03 MeV
4. He-3 + D -> He-4 + p + 18.34 MeV
5. Li-6 + n -> T + He-4 + 4.78 MeV
6. Li-7 + n -> T + He-4 + n - 2.47 MeV

[D and T stand for deuteron or deuterium (H-2), and triton or tritium (H-3) respectively.]

Reactions 5 and 6 are not thermonuclear reactions, strictly speaking. They are neutronic reactions, like fission, and do not require heat or pressure, just neutrons in the correct energy range. This distinction is usually ignored in the literature about nuclear weapons however. The Li-6 + n reaction requires neutrons with energies is the low MeV range or below. The Li-7 + n reaction is only significant when the energies are above 4 MeV.

Note the magnitude of the various MeV releases, the D+T and D+D are the primary energy release mechanisms. As I understand it equation 4 makes a smaller contribution although its MeV release is large, because all the reactions are exponentially sensitive to the plasma temperature i.e. complex reaction kinetics.

From Lithium:

6Li content may be as low as 3.75% in natural samples. 7Li would therefore have a content of up to 96.25%.

Note that the Li-7 reaction is endothermic. AFAIK "enriched" Li with a higher proportion of Li-6 is not used in HBombs?

All in all, the original wording implies to a layman that gaseous D combined with metallic Li "spontaneously" results in a thermonuclear reaction which is obviously not the case. Perhaps the wording could be: "... deuterium and tritium (via lithium transmutation) ..."

If you sum over the reaction set, Li + D -> ... is strictly correct, but stating it that way really seems to obscure whats really driving the energy release. LochVoil 21:04, 13 October 2006 (UTC)

The edit you made was surely the correct one; I'm not sure how it slipped beyond for so long though honestly I rarely read over the intro to articles carefully after awhile. The only other place lithium appears in the article seems to be correct (it does not fuse itself, but is a convenient way to store deterium and to create tritium). Apparently the sentence used to say "hydrogen and helium" which was more correct than lithium though itself somewhat misleading; I think someone must have changed it to "deterium" and "lithium" because they were confused about the role in the latter. --Fastfission 17:31, 14 October 2006 (UTC)

[edit] salted bomb

A salted bomb is a nuclear weapon constructed like fission-fusion-fission weapons, but instead of a fissionable jacket around the secondary stage fusion fuel, a blanket of a specially chosen isotope of a non-fissionable element is used, (cobalt-59 in the case of the cobalt bomb). This blanket captures the escaping neutrons from the secondary to breed a radioactive isotope that maximizes the radiation hazard from the weapon rather than generating additional explosive force from fast fission of U-238. The primary purpose of this weapon is to create extreme radioactive fallout to deny a region to an advancing army, a sort of wind-deployed mine-field.

Salting agents

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). Arsenic and Sodium could also be used for very short-term fallouts. To be useful for salting, the blanket element must be abundant in the natural isotope, so that expensive purification is not needed. Also, the neutron-bred radioactive product must be a strong emitter of high energy penetrating gamma rays, either directly or through indirect decay pathways.

I found this description with www.ask.com It is from wikipedia, but where is it now? Wandalstouring 21:29, 26 October 2006 (UTC)

See this section near the end of the article: Nuclear weapon design#Advanced thermonuclear weapons designs

I hope that helps answer your question. Georgewilliamherbert 23:54, 26 October 2006 (UTC)

[edit] SI Units

I can suggest changing to SI units in the Miniaturization part, or maybe adding them in brackets to comply with international standards. Lack of meters and kilograms and presence of inches and pounds confuses European readers.

Fixed. Next time, feel free to fix it yourself. I have gone for using SI units as the primaries, as this is a physics/engineering article of global interest. --Robert Merkel 06:55, 28 October 2006 (UTC)

George, could you please point out precisely what section of the policy I violated by changing to using SI units as the primary units? I understand your loss of concern with precision in the estimates, but look at the context: it's not providing precise engineering details, it's giving handwavy figures (which are of dubious accuracy anyway) making the point that nuclear weapons got a lot smaller in the 1950s. --Robert Merkel 14:42, 29 October 2006 (UTC)

[edit] Purified Hydrogen Bomb, is that real?

In the game Metal Gear Solid 2, I heard something about a purified Hydrogen bomb. Does this kind of nuclear device really exists, or it´s just an invention?

• Most likely just a weird game-specific issue. Hydrogen bombs usually use Lithium-6 Deuteride, sometimes mixed with 'regular' Lithium-7, wrapped in natural uranium as a tamper with a hollow plutonium 'spark plug' in the center of a cylindrical assembly with an aspect ratio greater than 1.  E. Sn0 =31337= ^{Talk to me :D} 02:57, 10 November 2006 (UTC)

You could ideally interpret it as meaning that the fusion fuel was especially refined but it is likely just nonsense. It is not a common term, anyway. --Fastfission 03:02, 16 November 2006 (UTC)

It's probably referring to a pure fusion weapon, which appears to be impossible with present technology despite considerable research in the area. --Robert Merkel 12:30, 16 November 2006 (UTC)

[edit] this is one of the best articles on wiki

which is fairly disturbing!

[edit] Foam vs. Ablation

Under "Staged thermonuclear weapons" there is a graphic illustrating the "foam theory" of compression. Beneath this graphic, the text points out that this is a disputed theory. I think it is worth informing the reader that the foam theory is more than disputed; it has been essentially discredited in favor of ablation pressure.

[edit] Tamper

Here is a quote from the article.

While the effect of a tamper is to increase the efficiency both by reflecting neutrons and by delaying the expansion of the core, the effect on the efficiency is not as great as the effect on the critical mass. The reason for this is that the process of reflection is relatively time consuming and may not occur extensively before the chain reaction is terminated.

Is this correct? It is saying that the tamper affects the critical mass more than the efficiency. From the second sentence, I would think that the reverse would be true. Also, by affecting the critical mass, does that mean it causes a reduction in the critical mass? I think that it should be stated explicitly. -- Kjkolb 17:22, 19 November 2006 (UTC)

The reduction in critical mass is a consequence of the reflected neutrons and of compression so this section is wrong in implying that the reduction in critical mass is a separate thing. The time issue is relevant in that it means you can't reduce the critical mass with reflectors too much before the chain reaction slows down enough for efficiency to suffer. Man with two legs 10:20, 20 November 2006 (UTC)

What is probably necessary here is to better define "efficiency". --Fastfission 14:01, 20 November 2006 (UTC)

That is already covered in that section (Tamper reflector): efficiency, i.e. the fraction of the fissile material that actually fissions. Man with two legs 15:10, 20 November 2006 (UTC)