How to create a nuclear explosion localized to only a few square feet?

Question

Is there a way to create a nuclear explosion that only destroys things within a few feet of the bomb?

The point is to completely eradicate something relatively small, leaving no trace. Let's assume that this is taking place on Earth. The government that is using this procedure has access to lots of funds, so cost isn't a problem.

I'm imagining that the explosion would have to be done using a tiny bomb with only a little bit of fission/fusion (i have no idea) in a controlled and protected environment, to prevent both the impact and nuclear radiation from leaking out and harming the surrounding people and environment.

How would someone go about doing this?

(See Should we be mindful of potentially dangerous questions? on meta.)

If this can't be done using a nuclear explosion, another method of near-total destruction of a contained area would be a valid answer.

Answer 1

Continuing on the theme of chemical solutions (ba-dum-bum-CHING - I'm here all night folks)...

One way to rid yourself of unwanted objects or personnel is to liquefy or vaporize them and allow nature to clear them away. For this sort of operation, I eschew explosions because although they deliver a lot of energy, they tend to apply it indiscriminately to everything around them.

So let's try a more focused approach: thermite

Grind up metallic aluminum and rust into a fine dust. Perhaps combine them with a combustible binder material and apply liberally to the object (person) that absolutely, positively has to go away.

Size of thing to be destroyed?          Unknown
Composition of thing to be destroyed?   Non-refractory materials
Level of destruction?                   Burn, liquify, or vaporize
Proximity to nearby objects?            a couple of feet
How affects nearby things?              Don't hurt things beyond a couple of feet
How much time?                          Seconds to minutes

Thermite burns at temperatures of thousands of degrees. It will burn, liquefy, or vaporize many materials as shown in this video of thermite on dry ice:

Thermite Vs. Dry Ice

It won't have this effect on most refractory materials (tungsten, carbon-carbon, etc.).

Bad Stuff
While thermite most certainly will rid you of some offensive materials, unless you are extremely liberal and careful with its application there almost certainly will be evidence left.

Answer 2

The smallest warhead created for the US military was the W54 Davy Crocket which used 23kg of Pu239 and had a yield equivalent to 10-20 tons of TNT.

Video of the Davy Crocket being fired.

According to other research, the smallest amount of Pu239 you can use to make a bomb is 10kg, which still has the power of several tons of TNT, plus the thermal effects. So even that small of an amount would take out a normal city block.

I don't know if it would completely vaporize the target, but none of the pieces would be very big, and they would be pretty spread out.

Edit: So, after a lot more reading, I found that there are ways to lower the threshold for critical mass: shaping the pit, neutron reflectors, the type of explosives used to compress the mass, etc. With all the right tricks you can get it down to about 4kg.

Fatman only used 6.2kg of Pu 239, and it had a yield of 20 kilotons. So you would have to find ways to lower the efficiency.

Apparently it's harder to go smaller with a nuke than it is to go bigger.

Answer 3

If you want to limit the damage to a few feet, any type of explosion is right out. Large firecrackers, bottle rockets, and even non-chemical explosions like the "dry ice bomb" can throw shrapnel a dozen feet or more. Scaling up a little more, a hand grenade can be fatal at up to 15 feet. Nuclear explosions are right out.

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What you want is a concentrated release of energy, unlike an explosion which disperses energy outward. My first instinct is thermite, an extremely hot-burning metal powder. Typically it's used for welding railroad tracks, but you can also use it to, say, melt through the engine block of a car.

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If 2 thousand degree molten metal doesn't fulfill your appetite for destruction though, then let's move on to something else. Since you asked about nuclear devices, let's start with some radiation. In particular, electron beams. Most of the electron beams (originally named 'cathode rays') we encounter today are in the form of CRT monitors, but these only deliver a minuscule amount of power. However, there are a number of more... industrial uses of electron beams:

• Electron irradiation, used to sterilize materials or process plastics. Here's a video of what happens to a camera passing through an irradiator used for industrial plastics processing. The beam used in that video delivers around 25 kW of beam power.
• Electron beam welding. Here's a video showing an electron beam welder making a 74" joint in 1 3/4" steel in just four minutes. A similar technique uses an electron beam to fuse metal powder into 3d printed shapes.
• Finally, the most powerful of these devices is an electron beam furnace. These are huge and highly specialized machines, so information on them is hard to find. Here's an article describing the process of melting iridium with an electron beam furnace. Iridium melts at almost 2500 degrees Celsius.

What a megampere electron beam would do to an unprotected target in open air... I leave that to your imagination.

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Wait, you still want more? Well, we can step up to a proton beam, the type used in proton therapy. The reason I'm limiting myself to charged particle beams is that, unlike neutron radiation or gamma radiation, charged particles interact strongly with matter, so the radiation is short-ranged (which will prevent collateral damage). The type of beams used in cancer treatment penetrate on the order of ten centimeters before stopping abruptly.

Like electron beams, a powerful proton beam would melt or vaporize the target. However, it would also do significant damage to the target on a nuclear level. Individual protons have thousands of times more energy and momentum than electrons, possibly enough to fuse with the nuclei of atoms and increase their mass, or knock out other nucleons and reduce the mass. After you're through with it, the target won't even be identifiable by its isotopes.

I don't have any videos for you here; proton beams don't have many industrial uses, since they're hard to produce. (Good thing "cost isn't a problem.") Again, what you do with such a beam is up to your imagination.

Answer 4

Alright, I'm done with the little stuff, let's move on to explosions.

The problem with explosions (as I stated elsewhere) is that they apply their energy indiscriminately and tend to damage what you want damaged along with everything else around it.

Size of thing to be destroyed?          Scale explosion to target size
Composition of thing to be destroyed?   Scale explosion to target composition
Level of destruction?                   Blast
Proximity to nearby objects?            More than 10s of yards to a mile or more
How affects nearby things?              Don't hurt things beyond this range
How much time?                          milliseconds

If done with careful planning and placed with care, it is possible to create things like shaped charges or direct the explosive force of an explosion. This does indeed focus the explosion and direct the majority of its fury at the intended target, but it is still unhealthy for anything near the explosion.

Consider the case of a self-forging projectile trying to penetrate the armor of a tank. Whether the projectile penetrates the armor or not, the area around the tank is extremely unhealthy for infantry soldiers. Other armored vehicles could shrug off the explosion and/or fragments, but the explosion would likely kill any soldiers near the tank.

The same thing happens when directing an explosion with the intent of destroying high-rise buildings without damaging nearby buildings. The focus of the blast does indeed hit the desired target, but if you stood near the explosion, you'd very likely be killed. Construction materials are MUCH tougher than your typical human being.

We are faced by another quandry with this too. Even with 500 lbs of high explosives, there was plenty of the cement truck left to identify in this Mythbuster's explosion.

https://www.youtube.com/watch?v=Gxm_qpKh7Jw

So in order to really destroy something so that no trace is left, you would need a truly enormous explosion and it just isn't safe to be around those, if you wish to live.

Even with the Mother of all Bombs (MOAB) 18,000 lbs of fuel (it uses atmospheric oxygen as the oxidizer), there would be plenty of material left to identify objects destroyed in the blast.

https://www.youtube.com/watch?v=HsQdeAeOEg4

Oh yeah, and you wouldn't want to be anywhere near the detonation point.

Just a point of interest here. Explosions typically don't break all chemical bonds in the target. The blast tends to fragment the target. Individual fragments of target and bomb usually contain enough information to figure out quite a bit about both.

Answer 5

Go with Californium:

It can used in a small nuclear device due to the much smaller critical mass needed to produce a nuclear chain reaction when using Californium.

According to wikipedia, the critical mass of Plutonium-239 is 10kg, and circa 10-15kg (23kg minus mass of casing etc) was used to make the W54 Davy Crokett recoiless nuclear cannon. A Californium-252 based version would weight much less. Major problem is that Californium is not cheap. At 2.7Kg critical mass, this means a 3-7kg nuclear weapon, but costing at least 10 Million dollars each round.

Answer 6

This will likely be buried under the other answers, but you can have tiny fusion explosions. There is a current real project to produce them. Each fusion capsule is pinhead-sized and detonated by a warehouse-sized laser. All you need to do is scale this up a bit and you can have yourself a fusion explosion capable of destroying a few cubic feet around it with a large "bang". However, it wouldn't be particularly more powerful than a conventional explosion of the same size. The fundamental thing about explosions is that they're not containable.

Or you could just use the warehouse-sized laser directly. Or a plasma torch.

Answer 7

OK, my last entry. This one includes large & unconventional methods of getting rid of things.

Nuclear
if you absolutely positively have to make it go away, nuclear is the sure fired way to ensure that happens.

The problem of course is how do you keep it from destroying the nearby stuff that you don't want destroyed. Well the US Air Force as an app (project) for that, it's called Casaba Howitzer and it is a freaking nuclear shaped charge.

Size of thing to be destroyed?          Roughly human sized
Composition of thing to be destroyed?   Most non-refractory materials
Level of destruction?                   Burn, melt, or vaporize
Proximity to nearby objects?            Minimum of tens of feet,
                                        maximum out to hundreds of yards
How affects nearby things?              Combustion to dozens of feet,
                                        blindness to anyone who can  view the target
How much time?                          Microseconds

I am tired and don't want to get into all the gory details (but find the topic terribly interesting). Scientists felt they could focus about 80% of the destructive power of the bomb.

That still leaves 20% of a nuclear bomb to annihilate everything else not in path of the directed shot.

Within some (very short) distance of the bomb, the gamma rays and neutrons are powerful enough to cause transmutation (fission & fusion reactions). All chemical bonds will be broken all atoms will be ionized (possibly multiple times).

Within a longer (but still short) distance of the bomb, the heat caused by absorbed gamma rays and neutrons will ensure most chemical bonds are broken and many atoms are ionized (but no nuclear shenanigans will be going on).

In an atmosphere these two zones combine and form the fireball region which absorbs most gammas, causing the air to heat and generate the blast wave.

In space, the gammas just keep going and kill people directly.

Regardless of the direction of the blast, the bomb will spew neutrons about. Neutrons are not stopped very well by most shielding (it's better to use large quantities of water to shield you instead of dense metals, for instance). Neutrons will kill people so even if infrastructure survives the 20% of the bomb that escapes the directed blast, the nearby people will die anyway.

Kinetic Projectiles
I want to throw one final thought out there.

You could do it with a hypersonic kinetic projectile. If shot from space, it would look like a shaft of light shot down from the sky and simply left a crater where the offensive tidbits were left. The blast from any bombardment which creates a crater will also damage the things around the crater rim. But this sort of strike does not cause radiation damage (but does cause a blast).

Kinetic weapons scale better than conventional or nuclear weapons. They can be as small as a .22 bullet to as large as the dinosaur killing asteroid (~6 miles in diameter). You can also adjust the speed of the projectile.

Kinetic projectiles have the added benefit of not emitting lethal radiation, so if you survive the impact and subsequent blast, you'll survive the encounter.

This a video of the meteor that fell over Russia. Imagine a targeted strike intended to take out a building. It would damage nearby buildings but leave most of the city untouched (sans windows, of course).

Video of meteor over Russia

Answer 8

I think the only way to make a really small nuclear explosion (for a given value of 'nuclear') is to use a very small quantity of antimatter. But as already pointed out, that won't completely obliterate the object: even with thermite, there would still be chemical traces.

No, the only way to completely obliterate an object is to utilize a quantum black hole.

Answer 9

Forget explosives, too much hassle and not very effective. The proper way of dealing with this, as touched on in another answer, is fire. Lots and lots of lovely fire.

The point is to completely eradicate something relatively small, leaving no trace. Let's assume that this is taking place on Earth. The government that is using this procedure has access to lots of funds, so cost isn't a problem.

Oh baby, lets have fun.

So, since cost isn't an issue, the first thing you're going to need is a ridiculously expensive burn box. How expensive? Basically you need a safe made of high purity tungsten, the thicker the better. Elemental tungsten has one of the highest melting points around at 3695K, plus it is fairly resistant to various forms of corrosion. For suitable tungsten you're probably talking at least \$300-\$400 per kg, at $19250kg/m^3$ a suitable box is not going to be cheap.

Next up is a fuel. Your best bet here is a oxy-acetylene, although you'd need to avoid running it with too much oxygen as the peak temperatures for acetylene burning in pure oxygen are around the same as the previously mentioned melting point of tungsten.

This contraption will melt just about anything. Organic material will be incinerated, most metals will be reduced to liquid (most will actually start to boil), even things like silicon and stone will be an unrecognisable puddle. You're also probably going to need some kind of exhaust capture system, since the fumes would likely be extremely toxic, and a really good cooling system to get rid of the heat.

If you're careful in selecting the materials used to make whatever is being destroyed you should be able to completely incinerate it. Organics and lower temp metals like gold, tin and copper should be little or no traces left. Worst case is a completely unrecognisable bit of slag.

The basic principles involved are not that different to those involved in crematoriums, since there are similar constraints like exhaust capture. This kind of system also works best in smaller scale, suiting your "couple of feet" scale.

As a plus, you could probably slap a heat exchanger on the thing and heat your government offices with it.

Answer 10

How to create a nuclear explosion localized to only a few square feet?

Make it controlled. Nuclear reactors are controlled nuclear reactions. They're controlled to the point where there is no explosion.

A nuclear bomb is an uncontrolled nuclear reaction.

I'm likely stretching physics here, but one could perhaps have an incredibly tiny amount of fissionable material and then control it with a really tiny reactor (nano-sized rods?)

Answer 11

If its that small and needs to be disposed of with no evidence, I'd suggest firing it into the Sun or Jupiter. Trying to destroy it on the spot to that level is going to be tricky and will almost certainly at least leave some traces.

I think about the best you could achieve without major damage to nearby areas would probably be a plasma jet, formed by a large number of shaped charge explosives. Forget nuclear, its not directed enough to achieve the level of destruction you want without major damage to the surrounding area.

Basically surround the object in a number of shaped charge warhead, the conflagration of plasma-jets should pretty much annihilate it with at worst minor damage to surronding areas (you could stand 20' or so away). If the shaped charges are set-up correctly, you could probably reduce nearly anything to dust/vapour. (Shaped charged warheads often vaporise the armour they are penetrating).

Answer 12

I'm going to assume a nuclear weapon is absolutely essential - maybe you need some method to kill Godzilla's eggs, and can only trust in the psudo-magical power of nuclear explosions. Regardless of the reason, it has to be a nuclear bomb.

The Bomb

The smallest nuclear weapon, and very nearly the smallest possible nuclear explosive yield ever constructed, would be the Davy Crockett, which carries the distinction of being the only nuclear weapon ever conceived for infantry use.

The weapon delivers the equivalent explosive force of 10 to 20 tons of TNT, but the actual radius of the blast is less well-documented. However, it apparently delivers an instantly lethal dose of radiation within 500 feet of the blast (and a less lethal but at least equally tragic dose up to 4 miles out), so if radiation is the reason you need a bomb, then it'll definitely do.

Containment

If you have any type of control over the explosion area, your best bet to limit the damage would be to construct an entirely-lead encasing compound, specifically designed to contain the radiation damage AND explosive damage of the bomb. Inner chambers would be constructed to collapse and absorb as much of the explosive force as possible, while the rest of it would simply contain the radiation.

It's hard to say how large the facility would need to be, since most nuclear explosion tests were carried out in large, open, barren areas rather than elaborate lead shielded constructs. If you can mitigate the risk of hitting groundwater, and can control the exact location of the explosion, doing it underground would be even better.

Practicality

Realistically, a nuclear explosion is a poor method of ensuring the absolute destruction of an object. The explosive damage can be replicated with much safer, more practical explosives, and the radiation damage doesn't require a nuclear explosion to create - any nuclear reactor would be able to furnish you with enough toxic radiation to do whatever you need to do to whatever you need destroyed.

The only reason you'd ever need it to specifically be a nuclear blast is if you need both a large amount of kinetic explosive force and high levels of radiation, in an immediate dose and at the same time.

Answer 13

You could, maybe, use an explosively pumped flux compression generator (I swear I didn't take that from an unproduced Back to the Future IV script -- http://en.wikipedia.org/wiki/Explosively_pumped_flux_compression_generator ) to create a really small fusion explosion without the fission stage ( http://en.wikipedia.org/wiki/Pure_fusion_weapon ). But that's not just a matter of cost, there are engineering details that I think we're far from having solved -- you'd probably need Tony Stark, Mr. Spock, and Samantha Carter to design the damn thing.

But if it can be done, then you could make fusion explosions smaller than the minimum practical fission explosion (see AndyD273's answer for that ).

There are also supposed to be ways to trigger very small nuclear fission or fusion explosions using anti-matter, but I (just intuitively -- not based on actually having to go through the trouble of, you know, getting knowledge) think that'd be harder to scale down.

Answer 14

Your question doesn't provide a bunch of very important bounding parameters about the size of the thing to be destroyed, the level of destruction required, the composition of the thing to be destroyed, the proximity of things to not be destroyed, what level of "untouched" is really required, and how much time we're allowed to take.

So I'm going to provide you with several answers. I hope one satisfies your needs.

Size of thing to be destroyed?          1 human body
Composition of thing to be destroyed?   1 human body
Level of destruction?                   must flush down the bathroom tub drain
Proximity to nearby objects?            a couple of feet
How affects nearby things?              Don't hurt things out of bathtub
How much time?                          Days

Use extremely caustic materials like $ LiOH $ or $ H_2SO_4 $ that work well on organic chemicals.

I figured out the quantity once but don't feel up to doing that today. Just remember the acid/base is consumed in the reaction and some of the weight of the acid/base is the water in which it is in solution.

So estimate the weight of chemicals required at 150% of the body weight.

Bad Stuff
The problem is this will not dissolve all the bits of the human body. I assume someone looking for this method of "disposing of evidence" would know what to look for if they found several empty drums of caustic chemicals.

You could do the same thing with metals and other materials. However, the best caustic chemicals for a given task change depending upon the composition of the object to be destroyed and the container in which you plan to do the destruction.

Also, as stated above, this will take days to complete and it will stink to high heaven. You'll probably need a gas mask to enter the room during the destruction.

Answer 15

Still avoiding explosives...

Another way to rid yourself of unwanted possession (or people) would be to burn them. This poses a problem when the object (person) is not flammable. Interestingly, most things that are not already oxidized will burn when exposed to a 100% oxygen environment (things like human flesh).

So acquire a tank of pure oxygen and set that garbage on fire. You may need to keep the flow of oxygen going while you're eradicating the object (evidence).

Size of thing to be destroyed?          Unknown
Composition of thing to be destroyed?   Most non-oxidized materials
Level of destruction?                   Burn or vaporize
Proximity to nearby objects?            Tens of feet?
How affects nearby things?              Don't hurt things beyond tens of feet
How much time?                          Minutes

I've never actually played with this but I would guess that it won't be as carefully contained as the previous two.

Answer 16

How about another twist before we go nuclear...

Directed energy weapons.

Directed energy weapons are very able to apply energy to a very focused source. The amount of energy they can deliver is pretty pitiful when compared with the energy of explosions but it still may be sufficient for your needs.

Size of thing to be destroyed?          Roughly human sized
Composition of thing to be destroyed?   Most non-refractory materials
Level of destruction?                   Burn, melt, or vaporize
Proximity to nearby objects?            Minimum of tens of feet,
                                        maximum out to hundreds of yards
How affects nearby things?              Combustion to dozens of feet,
                                        blindness to anyone who can  view the target
How much time?                          Seconds to minutes

It is easy to focus and direct the beam to hit the intended target without directly hitting anything else. However, such powerful beams will momentarily reflect off objects breaking off the target or floating in the air. This will send stray beams of high powered coherent light flying in all directions.

You'll have to assume anyone standing in the line of sight with the target will be permanently blinded.

Furthermore, if the beam heats the target up enough to burn, melt, or vaporize the target, the target is going to be radiating enormous amounts of heat. My guess is nearby combustibles will combust, including hair & clothing.

Answer 17

A weapon that consists of 2 devices, one is installed in north pole and emits a very narrow (1 nanometer diameter) beam of neutrinos and the other one is installed in the south pole and emits a beam anti-neutrinos. Neutrinos and anti-neutrinos do not interact with either matter or anti-mater so both fluxes can pass through anything and everything.

A super precise technology allows the beams to be directed with incredible precision. When both beams crosses the neutrinos and anti-neutrinos reactive with each other releasing a great amount of energy.

The project is kept in secret so nobody know such devices exist. When they want to kill someone all they need to know is their precise location in the world and make the beams cross in the target. Doesn't matter if the target is inside a box of steel with 10m thickness walls, there is no safe place.