Nuclear capable missile?

[Sky Captain]

Often when Russia or some other country with nuclear weapons tests ballistic or cruise missile it gets mentioned in the news outlets that this missile also can carry nuclear warhead. Given that nukes can be made small and durable enough to fire from 150 mm gun are there any constraints on missiles? If missile can carry at least 50 kg high explosive warhead then it also should be able to carry small nuke.
Pretty much every ballistic or cruise missile have payload at least in several hundred kg range. It seems that the term nuclear capable missile often used in the news are meaningless. Any missile capable of carrying useful high explosive payload can carry nuke too.

[Elheru Aran]

Yes and no. There's a world of difference between a low-kT tacnuke warhead, and an ICBM.

That said, it's generally recognized that the vast majority of smaller missiles simply wouldn't carry a nuclear warhead. Tactically nukes aren't great-- sure they'll make one heck of a big bang, even a pretty clean one if you do it right, but it's a lot of trouble for targets that often enough can be addressed conventionally anyway. The fact that they can be used tactically is generally simply not worth mentioning. It'll only ever happen in an all out war, and would almost certainly provoke retaliation in same from the other side if they're capable of such. And if they're not, it could tip the scales for someone who IS...

So that means strategic, which means long range. Which means you're talking about bigger missiles and bigger warheads. And this is pretty much what's usually meant by 'nuclear capable'. So the term isn't quite as meaningless as it would initially seem.

Additionally, it takes awhile to get to the point where you can engineer your nukes small enough to fit on a tactical missile anyway. You're not really going to be able to do it in the early stages of developing nuclear infrastructure unless you're getting serious help from someone else.

[Dominus Atheos]

By 150mm gun, you are referring to the Davy Crockett recoiless rifle, also called the "nuclear bazooka"?



Besides that, the AIM-26 Falcon was a nuclear air-to-air missile.



So yeah, pretty much any missile could probably carry a nuclear warhead.

[Bedlam]

What was the point of the Falcon? Just to show that it could be done? It doesn't seem to me (in no way an expert) that there would be an air based target which would need the power of a nuke to destroy, unless air to air doesn't necessarily mean a flying target.

[Tribble]

Maybe for multiple targets, like nuclear torpedoes for fleets?

[Elheru Aran]

What was the point of the Falcon? Just to show that it could be done? It doesn't seem to me (in no way an expert) that there would be an air based target which would need the power of a nuke to destroy, unless air to air doesn't necessarily mean a flying target.

Think SAC thousand-bomber style attacks. When you just have to swat a LOT of bombers out of the air.

Alternatively, destroying ICBM's, though the Falcon would probably not have been used for something like that, but a nuclear warhead for anti-nuclear-missile purposes has been proposed IIRC. Seems setting off a nuke far overhead to take out multiple nukes that would've otherwise blown up on your heads is acceptable.

[Dominus Atheos]

What was the point of the Falcon? Just to show that it could be done? It doesn't seem to me (in no way an expert) that there would be an air based target which would need the power of a nuke to destroy, unless air to air doesn't necessarily mean a flying target.

The falcon was one of the earliest radar-guided missiles, and wasn't very precise. So the US military's solution, as with most of their solutions, was "more dakka": slap a nuke and a proximity fuse on it, and just make sure that it gets in the same zip-code.

[Sea Skimmer]

Often when Russia or some other country with nuclear weapons tests ballistic or cruise missile it gets mentioned in the news outlets that this missile also can carry nuclear warhead. Given that nukes can be made small and durable enough to fire from 150 mm gun are there any constraints on missiles? If missile can carry at least 50 kg high explosive warhead then it also should be able to carry small nuke.
Pretty much every ballistic or cruise missile have payload at least in several hundred kg range.

The smallest diameter nuclear warhead the US tested was 5in x 24.5in and weighed 96lb, code named Swift. The lightest warhead known to have been tested was ~50lb W54. Several related designs were around this size point, including the Falcon warhead. Declassified British documents indicate they might really have been as light as 45lb, or at least such a weight was feasible with the basic physics package. Swords of Armageddon claims 42lb for the W-54 physics package.

Various math indicates that you might be able to have a physics package significantly lighter then this but it would probably have practical problems concerning durability and triggering if it had to leave the lab bench, and it it wouldn't be physically smaller.

The smallest diameter spherical implosion device the US ever tested was 10in diameter. Linear implosion can fit smaller diameters but it wastes fissile material, and U-235 is awful dense.

Indications are the USN determined that a nuclear projectile was feasible for the 5in 54cal gun family, which is roughly 75% the overall scale of NATO 155mm projectiles. It wouldn't have been too useful as a weapon though given the limited range of the 5/54cal family, Soviet 130mm shore batteries had significantly longer range. NATO 155mm weapons of the era were not better either, but the role was a lot more defensive compared to the intrinsically offensive role of naval shore bombardments. Note that the early 155mm AFAP rounds were extremely heavy for the 155mm caliber and had crappy range for the calibers. The later one's the US never actually fielded like XM-785 were normal weight projectiles.

It seems that the term nuclear capable missile often used in the news are meaningless. Any missile capable of carrying useful high explosive payload can carry nuke too.

No it isn't a useless term. First because on a practical front, while very compact nuclear warheads are possible nobody is known to be building them today, and the various uses oringally intended for them faded due to a combination of factors. For one thing they were always pretty damn impracticable in actual combat in the first place, and presented tremendous positive control problems.

And since they are far from free, tactical weapons cost much more per unit of yield then strategic weapons, the growth of conventional weapons capabilities and lack of a cold war battlefield with literally 15,000 tanks on 300 miles of front leaves little purposeful point to them. The closest you get is India v Pakistan, and even in that environment both sides smallest nuclear systems are still large truck mounted multiple missile launchers.

In terms of larger nuclear systems meanwhile, the big deal is having the security and command structure in place to make it sane to field them in the first place, and the ability to fire them and have them actually work once a nuclear war commences. That you don't just find anywhere, and it's generally desirable to have a decent amount of firing range in the process. At which point logic tends to dictate you also have a significant yield since it will barely cost more then a subkiloton device. And all of this is much easier to implement in a weapon intended from the ground up as a nuclear system. You can always strip out nuclear harndess and the secure communications from a conventional variant. Making a proper nuclear variant of a system never intended to do stuff won't be cheap or easy to do it right.

Back in the 1950s....stuff had little or no hardening and no security in ways nobody would accept today. Such warhead designs also had limited safety, and generally no fire safety at all. Conversely though the lack of security requirements meant they could be designed for assembly/dessembly in the field, and thus be stowed in pieces which was way safer in it's own ways. But not that practical either; it's not exactly a plus to have to put together your ammunition in an nuclear war.

[Sea Skimmer]

What was the point of the Falcon? Just to show that it could be done? It doesn't seem to me (in no way an expert) that there would be an air based target which would need the power of a nuke to destroy, unless air to air doesn't necessarily mean a flying target.

Well keep in mind the original conventional version of the Falcon only had a 7.5lb warhead, it had to be small to be internally carried on fairly small supersonic fighter planes of the era, and that Korean airlines Flight 007 ate two K-8 missiles with 40kg high explosive warheads and still kept flying for something like 15 minutes afterwards. For a while it was maintaining level altitude too. Multiple B-52 bombers were hit by even heavier SA-2 missile warheads and returned to base, though could not always be repaired. Large strategic aircraft are not immune to such weapons by any measure, but they are very large, very strongly built and possess large amounts of redundancy. The jist of design experience has pointed to warheads of more like 100-150lb being required to have a good kill probability on a strategic bomber, though SAMs have been built with warheads as great as 1000lb in the case of Nike Hercules. The Russian S-300 series missiles intended with strategic aircraft as the primary target have warheads around 150kg in contrast.

Later the US went back and took the bigger nuclear Falcon and made a conventional version with a 40lb HE warhead, but it still sucked in every other way.

So you actually you kinda do need a nuke to ensure a single shot kill if your stuck with a relatively small missile. That 15 minutes of KAL 007 flight? At 300 knots average speed (assuming, and it could well be higher for a damaged plane) that's a 75nm flight. So if that was a bomber it could be hit 75nm from the target, and still suicide nuke the target if nothing else stopped it. Which the crew TOTALLY WOULD DO in a nuclear war. That was exactly what US designers were worried about.

Which brings us to the other big reason to use a nuclear anti aircraft missiles. The radiation of the nuclear warhead will destroy the ability of the enemies nuclear bombs to function by contaminating the fissile material. That way even if your shooting the enemy down right over your own city the city won't get nuked by the bomb simply falling with the wreckage.

As the performance of fighter planes and missile systems and particularly radar for long range warning and computerized control (meaning more time to intercept), and people got much more concerned about positive control of nuclear weapons and less concerned about nuclear bomber planes, and bomber tactics shifted to low altitude + stand off missiles the usefulness of nuclear warheads went way down.

Something else to keep in mind is that the effectiveness of HE warheads drops with altitude, because the blast wave has less air to compress. Fragmentation experiences less drag it's true, but the redundancy of bombers makes them hard to kill with fragmentation effects, as the fragments spread out with distance too. Nuclear warheads blast effects are also greatly lessened at high altitude, like 50% the effective radius at 40,000ft vs sea level. But the nuclear radiation effects are increased, meaning the poison the bomb capability only works better.

Obviously though if an enemy bomber is at low altitude over your own territory you really don't want to use a nuke on it. That's a real big factor in why this concept died off.

Oh and at one point the US tried to design a mobile SAM system with only nuclear warheads that had a requirement to defend itself against helicopters low altitude and close range (also ground forces, because why not at that point!). SOMEHOW that program was shitcanned after only 3 years developmental work. Then we spent like 17 years designing Patriot, which actually did have a nuclear option as part of the design until IIRC 1977 when it was dropped purely for cost grounds.

Maybe for multiple targets, like nuclear torpedoes for fleets?

Realistically a nuclear torpedo was still just a weapon to use against a single ship, naval tactical formations are huge in the era of nuclear submarines ect... you need a multi megaton weapon to have much chance of hitting multiple ships and even that's uncertain. Even a 5 megaton warhead will only be certain of killing a ship at a radius of a few miles.

But similar issue at stake as with killing a strategic bomber, a big aircraft carrier will totally survive a conventional torpedo, and plausibly several of them. Even if you crippled the carriers propulsion with under the keel shots it might still be able to launch nuclear armed aircraft with its catapults, and for that matter, anti submarine helicopters with nuclear depth bombs to hunt the damn submarine. So big incentive to make the first attack certain.

But homing torpedoes today are vastly more capable then those of the early and mid cold war, so like missiles and such the actual advantage of a nuclear warhead has gone down. Like the whole point of the US nuclear torpedo was we could not make a conventional one that had a decent chance of hitting a 30 knot nuclear submarine. Add on a nuclear weapon and it had some kind of chance.

The other use for nuke torpedoes is of course to attack ports, but in the cold war that was less then totally plausible because of the limitations of guidance systems and the fact that port approaches are often complex and shallow. The Russian's new fearmongering nuke torpedo project wouldn't have that problem given tech advances, but ultimately it's accomplishing nothing special either.

Think SAC thousand-bomber style attacks. When you just have to swat a LOT of bombers out of the air.

At that point MATH indicated to our glorious forefathers that a much bigger nuke made more sense, thus that Sky Scorcher concept for a 2 megaton air to air missile. Too bad it was proposed right around the time the U-2 overflights proved the Soviets only had about 100 strategic bombers.

The key thing about the nuclear threat to a mass raid wasn't even that nukes could kill a lot of bombers at once. I mean, yeah they could and might. But the enemy would probably just disperse his bombers instead (thus desire for 2 megatons). But if the bombers were dispersed they couldn't support each other with massive amounts of mutual jamming and chaff corridors. The notional 1,000 bomber Soviet MASS RAID threat was predicated on around half the planes being nothing but countermeasure platforms to more or less entirely blind the US radar network. 1950s radars still only had hard wired signal processing and little ability to deal with chaff or barrage jamming. That's one of those 'digital computers changed this by the day in the 1960s' kind of subjects though. And thus the evaporation of interest in nuclear air to air weapons, shift to low level and stand off tactics ect...

Alternatively, destroying ICBM's, though the Falcon would probably not have been used for something like that, but a nuclear warhead for anti-nuclear-missile purposes has been proposed IIRC. Seems setting off a nuke far overhead to take out multiple nukes that would've otherwise blown up on your heads is acceptable.

Falcon was useless for anything but bomber intercepts, assuming it wasn't broken at the the time. Keep in mind it's only the size of a Sidewinder roughly, flew at like mach 1.8, had a range of about 6nm and was less agile then some bombers were! They put a nuke in it because it probably wasn't gonna do anything without one.

All ABM systems that worked before the 1990s used nuclear warheads, often very high yield ones, up to 5 megatons for Spartan. Their effectiveness was largely predicated on the 'poison the warhead' concept, which is super effective in an exp-atmopsheric intercept where no air exists to stop the radiation flux. The US formally stopped developing nuclear ABMs in 1983 because the alternatives were finally becoming plausible, which turns into modern hit to kill missiles. The big problem with nuke ABM was it would fuck up all satellites in space, and while HTK is expensive, nuclear ABM was super expensive too because of the warhead costs, weight (meaning you need a bigger booster for the same range as a HTK missile, and thus even more cost) and all the extra security you needed. Plus the practical problem that any use meant NUCLEAR WAR, while a non nuclear system could be given much looser ROE without causing WW3, meaning it was more likely to actually do it's job in a war as opposed to be told 'hold fire, we gotta ask the president or head of NORAD for permission to shoot first!' kind of problems.

[Sky Captain]

Thanks Sea Skimmer, that was very informative. So essentially no technical issue to field small tactical missiles with nuclear warheads or even have possibility to swap high explosive warhead for a nuke in the field, but it is bad idea when considering security. You don't want some field comander shooting a nuke and triggering nuclear war just because enemy tanks are getting too close to his position.

[Simon_Jester]

Well, under some circumstances you MIGHT, but that's when you want to explicitly draw a line on the map and say "Cross this line and it means nuclear war. Because our ground troops will fire their nukes at your advancing columns to avoid being overrun, regardless of whether you've already started nuking our forces."

And it's kind of a risky thing to do even then.

[Sea Skimmer]

One of the basic problems is minimal safe distance, for protected troops, from a 1kt bomb is still 2,000 yards. For a 20 ton nuke like Davy Crocket it was 600 yards, yet the rapidly lethal radius of said bomb against an enemy MBT was only about 100 yards.

A tank traveling cross country at 25mph covers 2,000 yards in 2.8 minutes. That's faster then an artillery crew will realistically be able to receive a mission to fire, load, aim and fire. That's part of why Crocket was the way it was, a battalion level nuclear system that could direct lay on the target. Though actually the US Army had wanted 11,000 yard range for the system, not 2000 or 4,000, but technology of the time would not allow them to design such a recoilless rifle in just 18 months. Still the desire for low level control was the same, cut out the middle man.

Still in a little under 3 minutes you can go from a non nuclear situation to the enemy being too intermixed with your own forces to employ even the smallest nuclear weapon!

If you delegate control of nuclear weapons to a battalion commander (so that's a dozen mid grade officers a division gaining nuclear release...) that still isn't much time to decide to employ them. And if you don't, then it's certainly too little time to get even a brigade or divisional level authority. And if you don't have nuclear release authority or a secure means to get it..then the nuclear system is just wasted manpower and assets. Maybe if you had more conventional weapons you wouldn't HAVE an enemy breakthrough to nuke!

With aircraft you have an even worse problem because by nature it's hard to keep combat planes loaded for alert duty around the clock, and the time to scramble to intercept an incoming enemy jet bomber or cruise missile attack is pretty much just as short as that tank to doom time. It might take you a while to fly out an actually make the intercept, but your time on the ground is critical.

Scrambling nuclear armed jets without approval to use nuclear weapons is basically unacceptable. It's certainly a bad policy.

The same thign tended to affect nuclear ground units. The nuclear option was not a piece of ammo, it meant entire firing units were dedicated to the task, and simply did not conduct conventional missions. They had to wait ready, but not able, at all times, so they could suddenly unleash that nuclear mission on no warning. If it came. That gets detrimental to overall combat effectiveness when you add in the physical security units guarding them and multiply it across a military. Both the US and USSR decided by the earely 1970s that low level nuclear weapons just didn't make sense, and became more focused on higher level control, slightly higher yields, and basically using the nukes on an operational rather then tactical level of war. Such as the notional tank breakthrough. Rather then firing a single nuke to stop the breakthrough thinking was more on the lines of using twenty nuclear shells to obliterate a whole tank division that had already broken through your own lines.

But at that point you could just go a little further and fire a smaller number of higher yield nuclear missiles to blowup the enemy command posts, artillery and supply system and you've accomplished most of what you really need. For a lot less trouble, manpower and money.

And that sort of thinking is how you get the statement that a tactical nuclear war is just one where the first nukes exploding Germany. And what became important was having enough conventional forces to avoid hostile forces getting too deep into your own lines too quickly, which is thus the conventional buildup of the 1980s, and by the 1990s a new twist in the form of smart weapons that for very high cost finally could counter massed armor attacks.

I can say more on the nuts and bolts of security and warhead control for tactical units later, need to go to bed now. Generally though once your nukes no longer rely on two man control and are being moved by helicopters you might not have any real control of them anymore.

[Shroom Man 777]

How does "poison the bomb" work?

[Simon_Jester]

If the fissionable materials inside the bomb get zapped with enough of the 'wrong' kind of radiation, their material properties change slightly. They stop being so fissionable. This means the bomb is rendered unable to produce a full-sized nuclear explosion. It might produce a much smaller explosion, or a 'fizzle' that causes purely localized damage, or even no explosion at all for all I know. Thus, one nuclear explosion can render a nearby nuclear weapon unable to function.

[My brain spontaneously generated the Shroomy version of this explanation, because I remember the old days, but I went with the Simony version anyway. ]

[Lord Revan]

Basically you can't just take a bunch of uranium or plutonium and tell it to "go boom!".

For example natural uranium is mostly U-238 (as in about 99% of it) which while highly toxic (it is a heavy metal after all), is practically speaking harmless when it comes to radiation and is for all intents and purposes useless as nuclear fuel for reactors or bombs.

The isotype used in nuclear reactors and bombs in called U-235 that is only 0.7038% (by mass) of natural uranium, when you make nuclear fuel or bombs you use a process called enrichment to increase the amount of U-235 in you clump of uranium. low enriched uranium that's used in reactors but is useless in bombs has less then 20% of it's mass in U-235 (typically around 5%) to control the reaction, while weapons grade (or highly enriched) has more then 20%, typically around 80% to ensure a run away reaction.

If there's not enough U-235 in the bomb the reaction won't reach a critical mass and what you get is alot of hot and toxic metal, bad for sure but not an nuclear explotion.

By the way this is why nuclear powerplants will never produce an nuclear explotion, they don't have the critical mass to do so.

Oh and I'm aware there's some specialized reactors that can use U238 but my point stands and those had to be specially built to use it due to how hard it is to get U-238 to have sustained nuclear reaction.

[Simon_Jester]

Well, the key point here is that even knowing that it takes specially enriched uranium to act as a bomb-grade material, it's not obvious why the radiation of one nuclear device going off should "poison" the bomb-grade material of a second device and make it, well... not bomb-grade anymore.

[fnord]

Off top of my head, and subject to correction from those (eg Sea Skimmer) who know a hell of a lot more than I do:

- Prompt radiation from other devices initiating could melt, derange or otherwise sod up the high-explosive initiators or firing mechanisms therefor.

- A stray neutron in wrong place (assembled device core that is supercritical but not yet ready to initiate) at wrong time (when you don't want it there) could make the fission reaction misfire, fissioning a small amount of fissile and physically destroying or deranging the core - eg blowing it apart with a militarily-insignificant yield (a fizzle) and spreading vapourised fissile material around. I think boosted-fission weapons are largely immune to this problem.

- Neutron capture in enough of the fissile core (eg Pu-239 being transmuted to Pu-240) to gum up works - this is probably a very long shot

Edit: remove goof

[Shroom Man 777]

HYPOTHETICALLY then if I'm in an episode of a technothriller or sci-fi thing, we've uncovered a nuke that's on a timer that can't be disarmed, how could I technobabble a way to irradiate and "poison" said nuke's fissible materials? What can be a good substitute for the radiation of a proximity nuclear blast? Chuck it in a big enough X-ray machine? Expose it to the innards of a nuclear reactor?

Of course, that won't stop the conventional "trigger" warheads from exploding and causing a fizzle that'll still scatter radioactive crap all over the place, but still...

ALSO then... is a poisoned nuke gonna be a total fizzle, or if there's still some un-poisoned fissible matter, what happens then? Would a 500KT warhead that's just partially poisoned then still be able to pop to a few KTs? Or is it a really delicate and intricate all or nothing thing when it comes to the fissible stuff inside warheads?

[Lord Revan]

HYPOTHETICALLY then if I'm in an episode of a technothriller or sci-fi thing, we've uncovered a nuke that's on a timer that can't be disarmed, how could I technobabble a way to irradiate and "poison" said nuke's fissible materials? What can be a good substitute for the radiation of a proximity nuclear blast? Chuck it in a big enough X-ray machine? Expose it to the innards of a nuclear reactor?

Of course, that won't stop the conventional "trigger" warheads from exploding and causing a fizzle that'll still scatter radioactive crap all over the place, but still...

ALSO then... is a poisoned nuke gonna be a total fizzle, or if there's still some un-poisoned fissible matter, what happens then? Would a 500KT warhead that's just partially poisoned then still be able to pop to a few KTs? Or is it a really delicate and intricate all or nothing thing when it comes to the fissible stuff inside warheads?

honestly with Uranium the problem isn't so much that it's radioactive (it is but so low as to be practically harmless) but rather that it's toxic, plutonium is slightly more active but we're talking about a half life of 6550 a at the lowest on something that would be used as nuclear fuel.

as for what would come of a "poisoned" warhead I honestly can't say, it depends on so many factors.

[The_Saint]

HYPOTHETICALLY then if I'm in an episode of a technothriller or sci-fi thing, we've uncovered a nuke that's on a timer that can't be disarmed, how could I technobabble a way to irradiate and "poison" said nuke's fissible materials? What can be a good substitute for the radiation of a proximity nuclear blast? Chuck it in a big enough X-ray machine? Expose it to the innards of a nuclear reactor?

...

I'm rusty on the physics but I can't see x-raying the weapon doing much more than giving you large blank images.

HYPOTHETICALLY ... if you did not care for your future chances of cancer (or living at all) getting a crowbar and pulling the high explosive casing and/or core apart would suffice to fizzle the weapon. An example (good, bad or otherwise) is the ending of the film The Peacemaker (1997).

[Lord Revan]

HYPOTHETICALLY then if I'm in an episode of a technothriller or sci-fi thing, we've uncovered a nuke that's on a timer that can't be disarmed, how could I technobabble a way to irradiate and "poison" said nuke's fissible materials? What can be a good substitute for the radiation of a proximity nuclear blast? Chuck it in a big enough X-ray machine? Expose it to the innards of a nuclear reactor?

...

I'm rusty on the physics but I can't see x-raying the weapon doing much more than giving you large blank images.

HYPOTHETICALLY ... if you did not care for your future chances of cancer (or living at all) getting a crowbar and pulling the high explosive casing and/or core apart would suffice to fizzle the weapon. An example (good, bad or otherwise) is the ending of the film The Peacemaker (1997).

dispite what Hollywood or mass media wants to tell as far as radioactivity goes even weapon grade Uranium or plutonium is actually "mostly harmless" as you'd most like use pu-239 as much as you can due the longer half-life (and thus self-life for the warhead) 2.411*104 a to be exact, while U-235 has half-life of 7.038*108 a.

In both cases the half-life is so long that for a short term exposure (like disabling the warhead) you can for all intents and purposes ignore the radiation as a factor (remember longer the half-life is weaker the radiation is) that said both Uranium and Plutonium are highly toxic so you wouldn't want to touching the metal with your bare hands but it's due the chemical properties of the metal not the radiation.

[The_Saint]

Oh that part I get, I was still presuming detonation of the initiating high explosive and possibly some part of the core going critical. Given all the other inherent risks not spoken of here handling the core is trivial, receiving any dose form a fizzled nuclear warhead is just a hazard. At least if you stuff up or it goes off ... you won't know :/

[Lord Revan]

Oh that part I get, I was still presuming detonation of the initiating high explosive and possibly some part of the core going critical. Given all the other inherent risks not spoken of here handling the core is trivial, receiving any dose form a fizzled nuclear warhead is just a hazard. At least if you stuff up or it goes off ... you won't know :/

To be honest if the bomb goes partially off just not at intended yield you getting cancer is still least of your worries as you'll be at ground zero. the thing is that nuclear warheads are designed so that don't have critical mass until it's time to go boom and won't get critical mass accidently (or at least won't easily get it accidently) for safety reasons. With modern nuclear bombs it's easier to make duds then to have an accidental detonation.

Radiation hazzard are generally least of the worries but it's still a powerful bomb with highly toxic materials inside so, if it doesn't go critical it's still a "dirty" bomb, but that's mostly due the chemical properties of the materials not radiation.

[Sea Skimmer]

A couple people got it, the poisoning I mentioned is when neutron flux from an attacking warhead transmutes the fissile material f the target warhead into forms that will not sustain a chain reaction. Functionally it's being dpurified, and on early nuclear weapons purity wasn't too absolute to begin with which is part of why they all always had some fissile risk, and limited total efficiency. Purity limitations of early British bombs for example created such a high risks of fizzling, apparently 18%, that they limited the yield of all field service warheads to 10kt to mitigate the risk until access to US materials and research improved the situation. British traded the US extensive work on nerve gas for this BTW, in IIRC 1958 or such. All else being equal higher purity nuclear materials will be less vulnerable to poisoning. A bomb that marginally works obviously has no margin for error in sustaining a chain reaction.

In theory a poisoned warhead could still produce some nuclear yield as a fizzle, dependent on distance/purity/yield of the attacking warhead, but you would be talking about a 100 ton to say 4lb kind of nuclear yield. This won't destroy a city, and if said warhead air burst it might not kill anyone in the target area at all. The fallout would be annoying but that's life.

Some real chance exists that you'd get no nuclear yield or if any was produced, it would be produced immediately by the neutron attack inducing a fizzle into the target bomb itself.

However there is basically no way one nuke could ignite another nuke with any significant yield, because of geometry. Ignoring gun type devices for reasons, and because a OpenOffice crash nuked my firsts reply on this, nuclear bombs are implosion devices. Even linear implosion is still a symmetrical two point initiation.

An external neutron supply from another nuclear bomb meanwhile is functionally a point source of neutrons. It will unevenly hit the target bomb, and thus ruin it's geometry out of hand. Even if fission commences in the target bomb, which it certainly could given enough of the proper type of neutrons, because it is asymmetrical it will immediately blow the fizzle material apart and stop any chance of a chain reaction. Implosion devices rely not just on geometric initiation, but their own tamper momentum to prevent this in a successful full yield explosion.That really limits the possible yield. It's actually a little more complex then this but better sources exist on that then anything I could type readily. Anyway it makes no difference to the issue at hand.

This is also related to the fact that making nuclear implosion work is more complex then just having a sphere of Pu-239, just lookup wikipedia fat man for more details on that if you want concerning the need for interial triggers. Which is why even in the 2010s people like the North Koreans needed a serious amount of effort to actually engineer a working bomb.

As far as attacking the wiring an electronics on a nuclear bomb goes, it'd be possible to damage them but those kind of parts are deliberately hardened, and were rather simple in early nukes anyway. They aren't a reliable target to attack, and the most complex parts are small and thus much easier (weight issue) to radiation shield then the overall nuclear device is.

Official data for the Bomarc missile, which had a 10kt warhead, say that it would kill the nuclear bomb on a target plane at 300ft distance. This is much less then the maximum 3000ft kill distance for the bomber, but far superior to any conventional missile warhead's kill radius on such a target.

Keep in mind though that neutrons really hate traveling through an atmosphere. So the effective radius scales much slower then yield, so a much smaller nuke might have nearly as high of a bomb poisoning radius, and megaton yield range wouldn't be radically bigger either.

But in space in the ABM context no air exists to stop the neutrons, and the kill radius can be much larger, limited only by actual neutron density vs expanding distance. Also all else being equal, an ICBM RV is just not going to be as well protected as a big ass nuclear gravity bomb inside a bomber can be.

Certain kinds of particle beam weapons should also be able to screw over the guts of a nuke remotely.

[Sea Skimmer]

HYPOTHETICALLY then if I'm in an episode of a technothriller or sci-fi thing, we've uncovered a nuke that's on a timer that can't be disarmed, how could I technobabble a way to irradiate and "poison" said nuke's fissible materials? What can be a good substitute for the radiation of a proximity nuclear blast? Chuck it in a big enough X-ray machine? Expose it to the innards of a nuclear reactor?

You'd either need a huge amount of time or a nuclear reactor with the lid open.

Of course, that won't stop the conventional "trigger" warheads from exploding and causing a fizzle that'll still scatter radioactive crap all over the place, but still...

The best thing to do would be to fire a shaped charge into the center of the the nuclear primary. That should wreck it in a manner which would produce no nuclear yield what so ever. Even if the high explosives in the nuke are detonated by this the shaped charge will be blowing the thing apart before they can induce the necessary compression. Depending on the nuke design AP bullets would work too.

ALSO then... is a poisoned nuke gonna be a total fizzle, or if there's still some un-poisoned fissible matter, what happens then? Would a 500KT warhead that's just partially poisoned then still be able to pop to a few KTs? Or is it a really delicate and intricate all or nothing thing when it comes to the fissible stuff inside warheads?

At some narrow range of reality a kiloton range fizzle should be possible, but generally nukes gone wrong at the initial fission stage yielded really low, stuff measured in tons or pounds. Also this depends somewhat on how the nuke is supposed to make 500kt. The British built a pure fission bomb that frigging big at one point, but typically any nuke trying to yield over say 50kt is using boosted fission or fission-fusion configurations. The more complex the bomb probably the more likely an extremely low yield fizzle is, or no nuclear yield at all.

It's not like these things are simple.

On the other hand a linear implosion nuke yielding 100 tons virtually is a fizzle by design, but it's apparently very hard to make this happen reliably because of how ultra precise it has to be. The failure mode being no nuke at all.

HYPOTHETICALLY ... if you did not care for your future chances of cancer (or living at all) getting a crowbar and pulling the high explosive casing and/or core apart would suffice to fizzle the weapon. An example (good, bad or otherwise) is the ending of the film The Peacemaker (1997).

Umm, I'd say unless the enemy built the nuke inside a wooden packing crate you probably aren't going to be able to damage it with a crowbar. I mean these sorts of devices if nothing else need to not break if they get dropped by the nuclear bomb forklift, the steel casing is going to be tough independent of specific physical security measures. Terrorists would do the same. Most nukes had the ability to impact fuse with the ground, which requires very non trivial toughness even if they can't survive any earth penetration. Some earth penetrating nukes like the B53 had built in crush structures to protect the nuke guts.

If you had no power tools or explosives or serious guns another option would be just to set the nuke on fire with a lot of gasoline. It's definitely not going to like being cooked.