Usually atomic bombs are composed of Uranium-235, Uranium-238, and Plutonium (if I am wrong, please correct me), all of which have an alpha decay. However, if alpha particles have the least penetrating power, and can be stopped through something a thin as a piece of paper, how is it so dangerous?
edit: Sorry for the confusion, I meant how is the radiation from it dangerous, not the initial explosion. However it seems my question has been answered on both accounts. Thank you to everyone who answered! I have a better understanding of it now.
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Alpha decay is irrelevant in a bomb. It happens once in a while but that’s not relevant for their use.
If the nucleus of uranium-235 or plutonium-239 gets hit by a neutron then it is likely to split into two smaller nuclei. The process releases a lot of energy: These two small nuclei are now very fast. They’ll heat up your bomb material. It also releases 2-3 new neutrons. They can then be captured by other nuclei, splitting them as well, releasing even more neutrons. That way you can get a chain reaction, splitting a significant fraction of your uranium or plutonium before everything flies apart from the produced heat. Each single reaction doesn’t release that much energy, but you can easily get 1000000000000000000000000 of these reactions, releasing a lot of energy overall.
To store bombs, the material is arranged in such a way that each reaction is unlikely to trigger another reaction. To explode a bomb the material is compressed, making it more likely that a reaction triggers another reaction, and then a few neutrons are shot into the material to start that chain reaction at just the right time.
Most of the damage comes from that initial release of energy, superheating the bomb and the surrounding atmosphere and producing a lot of radiation and a giant shockwave through the air. As side effect you also end up with various radioactive stuff – the atoms produced from the fission reaction, other stuff that captured a neutron and became radioactive due to that, and the remaining uranium or plutonium.
You get a mixture of alpha, beta and gamma decays from all that stuff. If people inhale that, or eat stuff contaminated with it, then it can decay inside a human body where alpha decays are a problem.
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