How does the metal ball used in nuclear weapons work, and how can it be handled without constant fear of exploding?
In: Technology
The metal ball contains an amount of nuclear material that will only explode if it’s compressed into a volume smaller than the ball. It’s still Plutonium and super toxic, so you can’t touch or lick the ball, but you can’t make it go off. To make it go off you have to use very specific arrangements of explosives to uniformly compress it into a smaller volume, where it can do its nuclear thing. You can’t compress it that much with your hand, it’s a metal sphere.
Because it won’t explode, it can’t explode without first having another explosion compress it to an insane degree. A subcritical mass can become critical when compressed. So a nuclear weapon uses a subcritical mass of metal, and surrounds it in conventional explosives, which trigger the nuclear explosive.
Not to say that working with the stuff wasn’t dangerous. It still killed plenty of people who worked with it. Just that you’re not dealing with a live bomb until the whole weapon is put together.
you’re probably thinking of the plutonium core. plutonium is a fissile material, which means when a neutron hits a plutonium atom’s nucleus it will split, releasing energy and more neutrons, some of which may hit other plutonium atoms and cause them to split as well. the core is subcritical, which means this reaction isn’t self-sustaining. not enough atoms will be hit in order to keep the reaction going.
you can increase the number of atoms that split by surrounding the core with neutron reflectors or by compressing the core and packing the atoms closer together. when the reaction is fast enough that it sustains itself at a steady rate it’s called critical, and when it begins to accelerate that’s called supercritical
a nuclear explosion requires the core to be so supercritical that most of the atoms in the core are consumed in a tiny fraction of a second, releasing all of that energy in an instant. it takes very specific conditions for that to happen. in old nuclear bombs like the ones dropped on Japan, they achieved those conditions either by pushing two pieces of fissile material together (the gun method) or by using a shell of explosives to compress the core down until it was dense enough to cause the required reaction (the implosion method) [like this](https://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Fission_bomb_assembly_methods.svg/800px-Fission_bomb_assembly_methods.svg.png)
the faster the reaction, the more heat and radiation is released, so a core can be dangerous if it’s used improperly and allowed to go supercritical, but there’s no way for it to cause a nuclear explosion outside of very specific circumstances that will never occur outside of the nuclear bomb itself. that’s why you don’t need to worry about nuclear power plants exploding like nuclear bombs
When certain radioactive elements decay they release high energy neutrons, which can be absorbed by neighboring atoms and cause them to decay immediately. However, the neutrons have too much energy and aren’t likely to be absorbed, so most of the decay happens randomly from other atomic forces.
In a nuclear power plant, a mediator like water is used to slow the neutrons down so they get absorbed and cause immediate decay (releasing more neutrons). Controlling how much of the fuel is exposed to each other through the mediator controls the reaction.
In a nuclear (fission) weapon, the goal is to cause such a large burst of neutrons that even with the low chance of them being absorbed there are just so many in such a tight space that it’s inevitable, causing an uncontrolled reaction.
The fuel alone isn’t dense enough or emitting enough neutrons normally to cause this chain reaction. To get it going, an even more unstable element is smashed into the bomb’s core which releases a ton of neutrons. At basically the same time very carefully balanced conventional high explosives all around the core compress the core so that it becomes far more dense and more likely to absorb neutrons.
In a hydrogen (fusion) bomb, all of that also happens but the small fission bomb is used to compress a hydrogen pellet so much that it fuses and releases far more energy.
The uranium or plutonium core can’t undergo that chain reaction on its own.
A nuclear bomb is actually 2 bombs. A hydrogen bomb is actually three bombs.
First is some conventional explosive like C4 or dynamite if you want to imagine something really basic. This explosion is necessary to cause the “metal ball” to explode. When the metal ball goes off that is basically the second bomb.
The second bomb (the nuclear part) cannot explode unless the first one explodes and does so in a **very** special manner. I wouldn’t recommend this but one way to disable a nuclear bomb is actually to blow it up. If you mess up the special explosive then it cannot go nuclear but it will still be a dirty bomb which is its own thing.
For hydrogen bombs after the second part goes off (nuclear fission) the explosion will cause the third explosion to happen which comes from hydrogen fusion. Again this requires the second part to explode in a very special way to cause the third bomb to go off.
To add on with what other people are saying, a big problem with nuclear weapons is a fizzle, where the material contacts enough to produce a nuclear explosion, but that very explosion blows the material apart, stopping the explosion.
This means that even if nuclear material accidently reached critical mass, without a lot of human interference, it would just blow apart and stop immediately. This effectively stops natural nuclear explosions for occurring, and means that without serious effort, its hard to hurt yourself with material that could be used to create a nuclear explosion (though radiation will still kill you dead).
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