AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Nuclear fission is the splitting of a large and unstable nucleus (eg…
Full specification wording
Nuclear fission: Nuclear fission is the splitting of a large and unstable nucleus (eg uranium or plutonium).
Nuclear fission is the splitting of a large, unstable nucleus into two smaller ones.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 1 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Nuclear fission is the splitting of a large, unstable nucleus into two smaller ones. The fuels are heavy nuclei such as uranium-235 and plutonium-239, whose nuclei hold so many protons and neutrons that they are only just held together. When such a nucleus splits, the two fragments are roughly equal in size, two or three neutrons are released, gamma rays are emitted, and energy is transferred to the kinetic energy store of the products. Notice that this is a change to the nucleus, not to the electrons: fission is nothing like burning, and it releases far more energy per atom than any chemical reaction. In a power station this energy heats the fuel, the coolant and eventually the water that drives the turbines.
What earns the marks
- Naming a large unstable nucleus such as uranium or plutonium.
- The nucleus splitting into two smaller nuclei, roughly equal in size.
- Two or three neutrons being released by the split.
- Energy being released by the fission reaction.
Common mistakes and how to put them right
Describing fission as two nuclei joining together, which is fusion.
Saying the atom splits into protons and electrons rather than into two smaller nuclei.
Writing that the uranium burns or reacts chemically.
Locating the process in the electron shells rather than in the nucleus.
Calling the two products 'atoms' when at the moment of fission they are nuclei.
Exam tips
- Use the word 'nucleus' throughout; answers written about atoms often lose the mark for the products.
- Name a specific fuel, uranium or plutonium, rather than saying 'a big atom'.
- Keep fission and fusion vocabulary separate in your mind: splitting large, joining light.
Try the lesson
The start of the Nuclear fission: Nuclear fission is the splitting of a large and unstable nucleus (eg uranium or plutonium). lesson, made from checked teaching notes for this specification point.
Have a go first
Which process describes a large and unstable nucleus splitting into smaller nuclei?
Listen
Nuclear fission is the splitting of a large, unstable nucleus into two smaller ones. The fuels are heavy nuclei such as uranium-235 and plutonium-239, whose nuclei hold so many protons and neutrons that they are only just held together. When such a nucleus splits, the two fragments are roughly equal in size, two or three neutrons are released, gamma rays are emitted, and energy is transferred to the kinetic energy store of the products. Notice that this is a change to the nucleus, not to the electrons: fission is nothing like burning, and it releases far more energy per atom than any chemical reaction. In a power station this energy heats the fuel, the coolant and eventually the water that drives the turbines. A strong answer earns marks for these points. naming a large unstable nucleus such as uranium or plutonium. the nucleus splitting into two smaller nuclei, roughly equal in size. two or three neutrons being released by the split. energy being released by the fission reaction. Exam tip: Use the word 'nucleus' throughout; answers written about atoms often lose the mark for the products.
See it
Key words
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nuclear fission
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uranium and plutonium
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neutrons released
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nuclear not chemical
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See every definition
- nuclear fission
- The splitting of a large and unstable nucleus into two smaller nuclei that are roughly equal in size.
- uranium and plutonium
- Heavy nuclei used as fuels whose nuclei hold so many protons and neutrons that they are only just held together.
- neutrons released
- Two or three of these particles are released when a large unstable nucleus splits.
- nuclear not chemical
- The change is to the nucleus, not to the electrons, so it is nothing like burning and releases far more energy per atom than any chemical reaction.
Label the diagram
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1Box 1
2Box 2
3Box 3
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