how can splitting a tiny piece of an even tinier atom create such a vast explosion?
In: Physics
The bonds that hold atoms together is incredibly powerful. Breaking that bond releases energy.
The best ELI5 analogy would be a spring. If you had a powerful spring and a force kept that compressed until the force was removed, all that potential energy is released. Except the spring is really tiny and really confusing physics keeps is compressed.
Even though they are tiny, the amount of energy holding those atoms together is really strong (relatively). When the atom is split that energy is released. Lots of atoms get split in an almost instant chain reaction, lots of energy gets released, and boom!
You don’t need to actually know math, I promise. Bear with me:
The relevant equation is
E=mc^2 (yes, *that* E = mc^2 )
Energy = mass x the speed of light *squared*
Splitting atoms in a nuclear explosion converts a tiny bit of matter (mass) into energy. But the speed of light is a huge number. The speed of light *squared* is so utterly gigantic that multiplying a small mass by this HUGE amount means you release a ton of energy in a very small space – aka a vast explosion.
This answer brought to you by a man. That man’s name? Albert Einstein.
If you have a small piece of uranium, it decays by itself and releases small bursts of energy. That energy is powerful for its size, but it’s not explosive and would not really hurt you unless you spend time with the uranium. And even then, it is cell damage and cancer risk that will hurt you, not an explosion.
When you get to a nuclear reactor, you have a lot of radioactive material with the impurities reduced. The energy released from one of the radioactive atoms causes the atom near it to release its energy. If one atom causes one other atom to release it’s energy, you have a sustained reaction. And one of the side effects is decay heat, which can be harnessed for energy.
Now a reactor can become explosive when one atom sets off more than 1 other atom. Those atoms set off multiple other atoms and now, you have a dramatic increase in heat. Heat causes liquids to turn to gas and causes gases to expand which can cause an explosion. But even then, it’s not really a nuclear explosion per se… It’s an explosion caused by heat build up. (The heat can also set things on fire but those also aren’t really nuclear explosions either. Additionally, nuclear reactors can trigger chemical explosions, like splitting water into hydrogen, which goes boom, but that’s not a nuclear explosion either.)
An intentional nuclear blast is an even more extreme version of this. It requires momentarily packing so many radioactive atoms next to each other in a high energy environment that many of the atoms release their energy all at once: that is, the chain reaction of atoms starts with many atoms going off and they set off many other atoms all at once (like the run away reactor but with a huge starting number of atoms and huge number of nearby atoms set-off by each atom.)
But the main point is the power of a single atom is not explosive per se. Nuclear bombs can only become explosive because many atoms are releasing their bonding energy at once in a chain reaction.
How much energy does it take to use a knife to cut a ratchet strap under a LOT of tension? (very small)
How much energy does it release? (very big)
The amount of energy contained in each molecule is by proportion tiny, but by scale, massive
Take 1 uranium 235 molecule. Break it apart, it sends out a tiny pop.
That tiny pop triggers other uranium around it to break up, releasing their tiny pops
Take 235 grams or about half a pound of a certain kind of uranium, let those molecules pop, that adds up to what’s called avagadro’s number of molecule pops. Avagadro’s number is 6×10^23. Boom
The thing here is it is the chain reaction that your missing. While splitting one individual atom does not release a lot of energy, the splitting of that atom splits two more. That splits 8, 16, 32, 64, 128, 256, 532, 1064, 2128. This all happens in a fraction of a second and as you can see ten reactions later we can now splitting two thousands of atoms at a time. In ten more reactions we will be splitting two million atoms at a time.
If we can control the reaction so each atom only splits one other atom we have a very good source of power. But if it splits two instead of one it can quickly get out of control and explode.
On a related note I’d also like to know why the inverse is true for lighter elements like fusion for hydrogen. Why does THAT *release* so much energy when we require to input a lot of energy to fuse atoms??
It doesn’t. Splitting an atom releases some energy and some free neutrons. Those free neutrons can then go and split more atoms. This is what powers a nuclear power plant. You have a slow, controlled reaction to produce heat. The nuclear fuel is slowly used up over a period of years.
A bomb tries to split as many atoms as it can at once. The combined energy of the fission of all of those atoms at once is what produces such a massive explosion.
When you cut through something with a knife (an onion, piece of paper, lump of lithium, a log, whatever), aren’t you sometimes purely by chance slicing through atoms? Why isn’t there a reaction when splitting these atoms?
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