They are both basically nuclear bombs.
A simple nuclear bomb is a “fission” bomb. This detonated by splitting apart huge, unstable atoms like types of Uranium or Plutonium. The heavy materials are hard to create, but the bomb itself If pretty simple.
A Thermonuclear Bomb is a “fusion” bomb. It creates energy by fusing together two smaller atoms, like hydrogen or helium. Those elements are super easy to create, but they require a lot of energy to create that fusion reaction.
To detonate a thermonuclear or “fusion” bomb, basically you need to start with a fission bomb as a primer to create the energy to start the chain reaction.
They are significant more complicated, but they yield a LOT more energy – like 1000x or more than a fission bomb.
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