Normally, this process occurs in some uranium atoms at once. But in an atomic bomb, the atoms split up quickly, releasing large amounts of energy instantly.
Uranium atoms disintegrate inside an atomic bomb because they are hit by subatomic particles or neutrons. When a neutron hits the nucleus of a uranium atom, it causes the nucleus to split.
This produces energy and sends the particles of the uranium atom that crash into other atoms, whose nuclei disintegrate at the same time, sending more energy and particles, and so on. This process is called a chain reaction.
Once the chain reaction starts inside the bomb, the process continues until most of the atoms have split. This happens in a fraction of a second, so all the uranium energy is released.
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