Nuclear fission: The splitting of a large, unstable nucleus (such as uranium-235) into two smaller nuclei, releasing energy and 2–3 neutrons.
Nuclear fusion: The joining of two small, light nuclei to form a larger nucleus, releasing energy. This process powers stars.
Chain reaction: A self-sustaining sequence of fission reactions, where neutrons from each fission trigger further fissions.
Moderator: A material (graphite or water) that slows neutrons down so they can trigger further fission in a nuclear reactor.
Control rods: Rods of boron or cadmium inserted into a reactor to absorb neutrons and control the rate of the chain reaction.
This definitions covers Key Definitions within Nuclear Fission & Fusion for GCSE Physics. Revise Nuclear Fission & Fusion in Atomic Structure for GCSE Physics with 13 exam-style questions and 25 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 12 of 18 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Practice questions for Nuclear Fission & Fusion
What is nuclear fission?
Explain what is meant by a chain reaction in nuclear fission.