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I came across this interesting weapon by H.G. Wells, from his novel, The World Set Free, about a special type of atomic bomb that will explode indefinitely.

Here is a description on Wikipedia:

Wells's "atomic bombs" have no more force than ordinary high explosive and are rather primitive devices detonated by a "bomb-thrower" biting off "a little celluloid stud."[9] They consist of "lumps of pure Carolinum" that induce "a blazing continual explosion" whose half-life is seventeen days, so that it is "never entirely exhausted," so that "to this day the battle-fields and bomb fields of that frantic time in human history are sprinkled with radiant matter, and so centres of inconvenient rays."

I doubt such a material as presented here would cause such an effect. However, I wonder if there is a possibility of any type of explosive, as long as it is hard in nature, that can cause an effect of "non-stop explosions".

Assume that all resources are present. However, total Unobtainium or Handwavium will not be appreciated.

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    $\begingroup$ If it makes you feel any better Wells was a terrible writer. He only knew one adjective and used it to DEATH in War of the Worlds. I wrote an essay on it in school called ‘Tom stood upon the tumultuous tomult of toms’. If you don’t understand why that was the title of my essay you haven’t read the book. $\endgroup$ – Darius Arcturus Jan 12 at 13:26
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    $\begingroup$ Wells had some issues with arithmetic here. "Never entirely exhausted..." With a 17 day half life, after 4 years, the fraction remaining is 1.4E-26. Assuming that it's Californium as indicated in one of the answers, then for every 25.3 kilograms grams of the material that started, there is one atom left. I'm prepared to call that "exhausted." $\endgroup$ – puppetsock Jan 12 at 16:15
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    $\begingroup$ @DariusArcturus Well then, let me defend Wells, then. The World Set Free was written in 1913, 19 years before neutrons were discovered. That is, back then, they had no idea how radiation works, and nuclear bomb was about as much a sci-fi as a warp drive is now, and more of a sci-fi than a fusion powerplant is. Yes, really, while they knew that maybe perhaps it could exist(because E= mc^2), they had no idea how a man would even approach building such a device, much less how would nuclear bomb work. The World Set Free is to the Manhattan Project what From the Earth to the Moon is to Apollo 11. $\endgroup$ – Failus Maximus Jan 12 at 19:23
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    $\begingroup$ The science community would treat idea of nuclear bomb as seriously, as FTL is treated now. Then neutrons were discovered, and scientists did a second take. Then somebody (well, Leó Szilárd) noticed that neutrons might be the key to actually making such device, maybe, if such an element existed, which when hit with a neutron, splits, producing more than one neutron during its fission. Then, just before WW2, they discovered one of such element was Uranium. Well, not Uranium actually, only its isotope 235. And thus, that nuclear bomb is really a thing - this is 25 years after The World Set Free. $\endgroup$ – Failus Maximus Jan 12 at 19:32
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    $\begingroup$ Don’t worry Falius, my issue was only with Wells’ limited vocabulary. My ‘tumult’ reference was meant to provide a giggle for anyone who suffered their way through War of the Worlds. $\endgroup$ – Darius Arcturus Jan 12 at 20:31
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Having had a quick read of the source material, it seems clear that the devices do not explode as such, but vigourously emit heat and radiation sufficient to burn and melt their surroundings.

We already know of a way to release the energy stored in a fissile material over a period of time, of course: a nuclear reactor. Regular reactors are limited by their tiresome need to remain solid, and that sharply limits their operating temperatures because even the most refractory kinds of regular matter have a depressing tendency to turn to liquid even before it reaches a puny 4000K. We have a handy term for a reactor whose operating temperature exceeds the temperature limits of its containment vessel and fuel assemblies: a meltdown.

The "continuous bomb" therefore is in fact a naked reactor core that when fired up rapidly reaches criticality and promptly melts down into a blob of radioactive metal. The temperature limit now is the boiling point of the fissile material (because it'll be hard to keep a hot gas dense enough to sustain fission), which is 4400K for uranium and neptunium (though a disappointing 3500K for plutonium) which is hot enough to melt tungsten and sublime carbon so there's no practical armour that will keep the stuff out.

The liquid reactor will melt or burn or otherwise react vigorously with its surroundings, producing copious amounts of radioactive smoke and ash and lava and being too hot to practically cool with water (as you risk the water disassociating into hydrogen and oxygen, with all the excitement that implies). You just have to wait for the nuclear lava to disperse as it melts through the ground underneath the activation point so that it falls below the density required to sustain fission and then cools by itself, or to get so hot that it boils away into dense radioactive vapour and rains out over the surroundings.

This meltdown bomb would probably have a shorter halflife than Wells' weapon, because trying to keep it together to maximise the amount of fission is going to be impractical and so the main energy-releasing reaction seems unlikely to last more than a few hours at the very most, though secondary reactions will keep it hot for a while longer and it will be intensely radioactive for a very long time after it has cooled. In theory the cooled melt (or condense vapour) could be reprocessed to use as nuclear fuel or weapons again, so there's a proliferation risk on top of all the other hazards.

With regards to Wells' ideas, his active ingredient, Carolinum, was a name given to a suspected new element that turned out to be no such thing but was merely the already known thorium. Alas, thorium would be a bad choice for a meltdown bomb, because it must be first transmuted into a useful fissile fuel (such as U233) by neutron capture and subsequent decay in a reactor (which is what happens in thorium reactor designs). By itself, the common isotope is not fissionable, and so could not be used here.

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    $\begingroup$ big problem of course would be the mass of liquid superhot material rapidly expanding to where it loses criticality. It might work as a sort of a plasma lance, where you propel such a device at very high speed where the aerodynamic forces keep it together long enough to be still critical on impact with the target. You'd get a cloud of radioactive debris/fallout but no long term (decades, or whatever) problems with thermal effects. $\endgroup$ – jwenting Jan 13 at 6:53
  • $\begingroup$ With the right choice of materials (amount, element(s), isotope composition), it might be possible to have a liquid puddle of fissile material that maintains criticality, going supercritical when it cools and subcritical as it heats up further. What the proper size and enrichment would be might be a question for the Physics SE. $\endgroup$ – AI0867 Jan 13 at 21:23
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    $\begingroup$ @AI0867 It's definitely possible. This is pretty much exactly how Liquid Fluoride Thorium Reactors work. $\endgroup$ – Ryan_L Jan 13 at 22:31
  • $\begingroup$ A puddle of LFTR liquid wouldn't work unless it was in a graphite bowl though. $\endgroup$ – AI0867 Jan 14 at 10:34
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    $\begingroup$ On further thought, it seems like a puddle of UO2 would be reasonably stable in air (it would burn to U3O8, but then decompose back to UO2 at higher temperatures). If you enrich it far enough that it doesn't need a moderator, a homogenous puddle might work if it's big enough. Boiling point is apparently over 4000 K (much higher than PuO2). Issues that I can think of: minimum thickness for criticality, stability of reaction (it may be closer to a fizzle than a reactor) and dissolving the ground into the melt, diluting it. $\endgroup$ – AI0867 Jan 14 at 12:35
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You can't really have a non-stop explosion, since the explosion by definition violently propells the exploding stuff away. About the closest you could get is something like the fuel pellets used in a radioisotope thermal generator https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator With a high-temperature ceramic container, you could probably have one operate at white heat for quite a while.

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    $\begingroup$ I suspect what is imagined in something like "explosion-like power" - as in wattage - being sustained for a highly perceptible interval of time. For example, a hand grenade with 1 MJ detonation energy that releases it in 1 millisecond has 1 GW of power, and so the idea here is to imagine a 1 GW continuous release of heat/mechanical energy directly into the air and environs from a point source and what it would do. Essentially like a ludicrously-powerful blowtorch. $\endgroup$ – The_Sympathizer Jan 13 at 6:01
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This is quite a coincidence, H. G. Wells having died in 1946.

His Carolinum does not exist (and there is no known way of triggering a sizeable nuclear reaction whatsoever by "pulling a pin" in a hand-throwable device).

However, there is an isotope of Californium - namely 253Cf - which decays into Einsteinium, then to Berkelium 249, then to the much stabler Californium 249, which slowly decays into Plutonium 241 (all are toxic). Meanwhile, the usual chemical actinide reactions take place, never in so large an amount to be definable as "explosions". Flames are possible, "inconvenient rays" a dead - pardon the pun - certainty.

The half-life of 253Cf is approximately 17 days.

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  • $\begingroup$ You could probably create a compact nuclear device if you were able to create a similarly compact long-term antimatter storage system. You don't need more than a few nanograms of antimatter to trigger a useful amount of fission in one of the usual fissile materials. I'd venture that such a thing would probably be A Bad Idea to use as a hand grenade, however. In any case, it wouldn't fit the "continuous explosion" requirement. $\endgroup$ – Starfish Prime Jan 12 at 13:40
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    $\begingroup$ The problem is, there's no way to trigger it. If you have a big lump of Cf-253 it will be decaying. So the old phrase "this hurts me more than you" comes to mind. $\endgroup$ – puppetsock Jan 12 at 16:07
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    $\begingroup$ If the pin contained a neutron absorber that you were removing from a fissil fuel source, you could actually trigger a melt down bomb by pulling a pin $\endgroup$ – Nosajimiki - Reinstate Monica Jan 12 at 16:08
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Willie Pete

AKA white phosphorus. This is a material that burns when exposed to oxygen. This makes it extremely hard to "put out," since oxygen is a major constituent of our atmosphere. Has historically been used in explosives, illumination, and smoke generation.

If you mixed a large amount of WP with some other agent to control the reaction speed and help remove the heat, you could theoretically build a large block of something that would remain very hot for a long time - probably on the order of hours to days, which is not years, but still pretty long for an "explosion."

Bonus points: (if you want to call it that...) If part of the block is isolated from the air - say it breaks off and get buried under ash - it will cease to burn. This chunk will re-ignite when it is next exposed to air, which makes it dangerous over a long period, similar to HG Wells bomb.

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A micro-Black hole might behave like this.

To explain: A Black Hole (BH) is a region of highly-curved space-time bounded by an event horizon. Its high gravitational field draws matter in and anything passing the EH cannot escape, so the BH grows with time. However, Hawking Radiation allows the BH to emit radiation. The rate of emission (the BH's temperature) depends very strongly, and inversely, on its size. So a small BH can have a very high temperature. It is conceivable that a BH could achieve equilibrium where the gain due to infalling matter is equivalent to the loss due to Hawking Radiation. Such a thing would look like a continuous nuclear explosion in a space the size of a proton.

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    $\begingroup$ Black holes will simply drop through any containment they may be in, then through the floor - matter cannot slow them down. -- A charged black hole can be contained, by electrical fields, but you'd need an outrageous voltage differential for that to work, and there would be spectactular side effects. $\endgroup$ – toolforger Jan 13 at 12:30
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    $\begingroup$ @toolforger Also, it would probably be a bit heavy to throw... $\endgroup$ – Oscar Bravo Jan 13 at 12:52
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    $\begingroup$ Well, small-enough BHs would be throwable, but I guess a sub-kilogram BH would evaporate too quickly to fit the H.G. Wells description. $\endgroup$ – toolforger Jan 13 at 13:08
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    $\begingroup$ Unfortunately, a BH with a rest-life of only a single second weights several hundred thousand tons. And it explodes with the force in the range of millions of atomic bombs. This extremely intense radiation is coming from an object with a size comparable to an atomic nucleus. And this intense radiation makes it extremely hard for other matter to actually hit the BH. You simply cannot feed a 1s BH by placing it within other matter, it'll just blow that slap of matter apart. Once you scale up the BH weight to the point where it can be fed, you cannot keep it from falling into earth's core. $\endgroup$ – cmaster - reinstate monica Jan 13 at 22:08
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    $\begingroup$ @cmaster-reinstatemonica Oh dear.. Back to the drawing-board... $\endgroup$ – Oscar Bravo Jan 14 at 8:08
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Usually not without creating a lot of force that needs to go somewhere. This has a tendency to disperse the explosion. It blows not only itself out, but also it's fuel and in the case of nuclear explosions, a lot or real estate. You could use the force for propulsion though. This fact is used by the continuously exploding rear end of a Nuclear Salt Rocket.

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Island of Stability Metals with High Melting Points and Strength, plus radioactivity

Given that we're speculating on a fantasy metal, we can make some assumptions and then deal with the engineering problems. The fantasy is that a metal exists which self-heats, but maintains its strength and doesn't melt. Let's imagine we have a very dense metal, with a very high melting temperatures ( 6000* C, to make it better than all known materials ) and maintains high strength up to that temp. Let's also say that this metal is moderately radioactive, similar to U-235.

Criticality is a complicated dynamic situation, changing as the mass's shape, temperature-based density, and other circumstances change. Let's not model that, because there are many authoritative sources. Instead, let's simplify to say that a 10kg sphere of it simply self-heats up above 5000* C, and atmospheric cooling will suffice to keep it below melting temp at 6000* C.

Let's surround the sphere in a cubic lattice of the same metal, with the masses adjusted not to enrage its criticality further. Let's make the cube structure 2m across, with multiple crossings in every direction. The lattice is there for several reasons : to keep air flowing around the sphere, to keep the sphere from touching and sinking into surfaces, and to provide more conduction surface for heat. The lattice has to be made out of our super-metal, which is the only substance which can withstand the heat.

This 5500* C sphere is pouring out heat and horrible radioactivity. Everything nearby catches on fire, melts, or vaporizes. You can see the approximate heat effects at https://what-if.xkcd.com/35/ , as if it's pouring out about 100 MW.

If you want to go hotter, you need an even more outlandish metal which supports even higher temps, and you need an even bigger indestructible lattice. Otherwise, it sinks into a lake of its own lava in short order. See the XKCD link for higher power levels.

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