Nuclear reactions as a source of energy
2 marks · EasyExplain briefly why a chain reaction can occur in a sample of uranium-235.
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Because each fission produces neutrons which can cause further fission if they hit other U-235 nuclei. This repeats, so the reaction continues.
Also accept: Each fission produces more neutrons that can trigger other U-235 nuclei to split.
Common mistakes: Not mentioning neutrons; not mentioning repeated process.
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Marking points
B1 · 1 mark · Points out that fission events release neutrons.
B2 · 1 mark · Explains these neutrons can cause further fissions (process repeats/continues).
Worked solution
During the fission of uranium-235, neutrons are released. These neutrons can hit other U-235 nuclei and cause them to split, so the process repeats and a chain reaction occurs.