GCSE Physics resources
AQA GCSE Atomic structure
Fission splits a heavy nucleus; fusion joins light nuclei. Both can release nuclear energy, but their requirements and control mechanisms differ.
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Fission splits a heavy nucleus; fusion joins light nuclei. Both can release nuclear energy, but their requirements and control mechanisms differ.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Fission splits a heavy nucleus; fusion joins light nuclei. Both can release nuclear energy, but their requirements and control mechanisms differ.
Scope: 8463 Physics only · Foundation and Higher
A suitable heavy nucleus such as uranium-235 absorbs a neutron and splits into smaller nuclei, emitting neutrons and gamma radiation and releasing energy. New neutrons can trigger further fissions: a chain reaction. The fragment kinetic energy transfers to the surrounding material. A power station transfers heating to coolant, produces steam and turns a turbine-generator.
Scope: 8463 Physics only · Foundation and Higher
A moderator slows neutrons so they are more likely to cause suitable further fission. Control rods absorb neutrons; inserting them further reduces the chain-reaction rate. Coolant carries away energy and shielding reduces radiation exposure. Do not say that the rods slow neutrons or that the moderator absorbs them to shut down the reactor.
Scope: 8463 Physics only · Foundation and Higher
Fusion joins light nuclei into a heavier nucleus and can release energy. Positive nuclei repel electrically; very high temperature gives enough kinetic energy for close approach and nuclear interaction. Stellar gravity provides conditions sustaining fusion. A fusion fuel is not made by splitting uranium. Fusion and fission are nuclear changes rather than ordinary combustion; radioactive-waste and engineering claims require context.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Slow neutrons without absorbing any.
Use instead: Slowing is the moderator’s role. This controls the chain reaction.
Tempting idea: Nuclei attract electrically at any distance.
Use instead: Like-charged nuclei repel electrically. This links conditions to the barrier.
Retrieval practice
Worked examples
Apply induced fission and a chain reaction in the worked reasoning, then try the changed-context questions below.
Scope: 8463 Physics only · Foundation and Higher
Fewer further fissions occur per second because more emitted neutrons are absorbed.
Exam precision
Do this: Begin induced fission with neutron absorption, then splitting and emitted neutrons. Explain how those neutrons continue or are removed from the chain.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Scope: 8463 Physics only · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): A suitable heavy nucleus absorbs a neutron and splits. Point 2 (1 mark): The fission emits further neutrons. Point 3 (1 mark): These neutrons can be absorbed by other suitable nuclei, causing further fissions. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: A large unstable nucleus absorbs a neutron and splits into two smaller nuclei, releasing energy and two or three neutrons. Some emitted neutrons are absorbed by other large nuclei and cause further fissions, forming a chain reaction. Control rods absorb some neutrons to control the reaction rate.
Scope: 8463 Physics only · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Moderator slows neutrons to make suitable fission more likely. Point 2 (1 mark): Control rods absorb neutrons, reducing the rate of further fission. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: A moderator slows neutrons; control rods absorb them to control the chain reaction.
Useful next steps