This deep dive covers Nuclear Fission Explained 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 regularly enough that it should still be part of a steady revision cycle. It is section 2 of 18 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 2 of 18
Practice
13 questions
Recall
25 flashcards
💥 Nuclear Fission Explained
Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei. When a slow-moving neutron is absorbed by uranium-235, the nucleus becomes unstable and splits. The products are two medium-sized nuclei (fission fragments), 2–3 free neutrons, and an enormous release of energy.
The energy comes from mass being converted according to E = mc². The products weigh slightly less than the original nucleus — that missing mass becomes energy. Even a tiny mass difference produces a huge amount of energy because c² is so large (9 × 10¹⁶ m²/s²).
The released neutrons can then trigger further fissions — this is the basis of the chain reaction. If uncontrolled, the chain reaction grows exponentially (nuclear bomb). If controlled, it provides a steady supply of heat energy (nuclear power station).
Quick Check: Why do the released neutrons need to be slow to trigger further fission?
Fast neutrons are more likely to escape or bounce off uranium nuclei without being absorbed. Slow neutrons spend more time near the nucleus and are much more likely to be absorbed and trigger fission. The moderator slows them down.