Science
What is Nuclear fission?
Nuclear fission is the splitting of a heavy atomic nucleus, such as uranium, into smaller nuclei, releasing a large burst of energy and extra neutrons. Those neutrons can split more nuclei in a chain reaction, which is how nuclear power plants and atomic bombs produce their enormous energy.
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Watch a 2-minute lesson with voice + animation that explains nuclear fission.
Key things to understand
- 1A neutron strikes a heavy nucleus such as uranium-235, making it unstable so it splits into two lighter nuclei.
- 2The split releases energy as heat, plus two or three more neutrons.
- 3Those neutrons can split nearby nuclei, creating a self-sustaining chain reaction.
- 4Power plants control the reaction to boil water into steam; weapons let it run away uncontrolled.
- 5Fission splits heavy atoms apart, whereas fusion joins light atoms together.
Frequently asked questions
- What is the difference between fission and fusion?
- Fission splits a heavy nucleus into lighter ones; fusion fuses light nuclei such as hydrogen into a heavier one. Both release energy, and fusion is what powers the Sun.
- How do power plants control fission?
- Control rods absorb excess neutrons, slowing or speeding the chain reaction so it gives off steady heat instead of running away.
- Why does fission release so much energy?
- A tiny part of the nucleus's mass converts into energy, and by Einstein's E=mc² even a little mass yields a huge amount of energy.