OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Recall that some nuclei are unstable and may split, and relate such…
Full specification wording
Uses and hazards: recall that some nuclei are unstable and may split, and relate such effects to radiation which might emerge, to transfer of energy to other particles and to the possibility of chain reactions (to include: knowledge of the term nuclear fission for fission to occur the unstable nucleus must usually first absorb a neutron) (content found only in the physics separate science qualification)
Some nuclei are unstable and may split in a process called nuclear fission.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 4 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Some nuclei are unstable and may split in a process called nuclear fission. For fission to occur, the unstable nucleus usually first absorbs a neutron; the nucleus then splits into two smaller nuclei and releases further neutrons together with energy. The energy is transferred to the surrounding particles and material, raising their kinetic and thermal energy. The neutrons released can be absorbed by other unstable nuclei, causing them to split in turn, so a chain reaction becomes possible. Radiation such as gamma rays may also emerge from the fission products, which are often themselves unstable. In a controlled reactor the chain reaction is regulated; in an uncontrolled situation it can grow rapidly.
What earns the marks
- States that some nuclei are unstable and may split in a process called nuclear fission.
- Recalls that for fission to occur the unstable nucleus must usually first absorb a neutron.
- Describes that fission releases further neutrons and energy, which is transferred to other particles and surrounding material.
- Explains that released neutrons can trigger further fissions, making a chain reaction possible.
- Identifies that radiation such as gamma rays may emerge from the unstable fission products.
Common mistakes and how to put them right
Says fission happens spontaneously without any trigger.
Put it right by stating that the unstable nucleus usually first absorbs a neutron.
Confuses fission with fusion.
Put it right by describing fission as a large nucleus splitting rather than small nuclei joining.
Omits the released neutrons when explaining chain reactions.
Put it right by stating that each fission can release neutrons that trigger further fissions.
Exam tips
- Use the exact term nuclear fission and state the neutron-absorption step explicitly.
- Show the chain reaction as a sequence: neutron absorbed, nucleus splits, more neutrons released, further nuclei split.
Try the lesson
The start of the Uses and hazards: recall that some nuclei are unstable and may split, and relate such effects to radiation which might emerge, to transfer of energy to other particles and to the possibility of chain reactions (to include: knowledge of the term nuclear fission for fission to occur the unstable nucleus must usually first absorb a neutron) (content found only in the physics separate science qualification) lesson, made from checked teaching notes for this specification point.
Have a go first
For nuclear fission to occur in a uranium-235 nucleus, what must usually happen first?
Listen
Some nuclei are unstable and may split in a process called nuclear fission. For fission to occur, the unstable nucleus usually first absorbs a neutron; the nucleus then splits into two smaller nuclei and releases further neutrons together with energy. The energy is transferred to the surrounding particles and material, raising their kinetic and thermal energy. The neutrons released can be absorbed by other unstable nuclei, causing them to split in turn, so a chain reaction becomes possible. Radiation such as gamma rays may also emerge from the fission products, which are often themselves unstable. In a controlled reactor the chain reaction is regulated; in an uncontrolled situation it can grow rapidly. A strong answer earns marks for these points. States that some nuclei are unstable and may split in a process called nuclear fission. Recalls that for fission to occur the unstable nucleus must usually first absorb a neutron. Describes that fission releases further neutrons and energy, which is transferred to other particles and surrounding material. Explains that released neutrons can trigger further fissions, making a chain reaction possible. A common slip: Says fission happens spontaneously without any trigger. Instead, stating that the unstable nucleus usually first absorbs a neutron. Exam tip: Use the exact term nuclear fission and state the neutron-absorption step explicitly.
See it
Key words
Say what each word means before you turn the card.
nuclear fission
Try answering aloud or in your head before turning the card.
neutron absorption
Try answering aloud or in your head before turning the card.
chain reaction
Try answering aloud or in your head before turning the card.
See every definition
- nuclear fission
- A process in which some unstable nuclei may split, usually after first absorbing a neutron.
- neutron absorption
- The step in which an unstable nucleus must usually first absorb a neutron for fission to occur.
- chain reaction
- Released neutrons can be absorbed by other unstable nuclei, causing them to split in turn, so further fissions become possible.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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Test your understanding of Uses and hazards: recall that some nuclei are unstable and may split, and relate such effects to radiation which might emerge, to transfer of energy to other particles and to the possibility of chain reactions (to include: knowledge of the term nuclear fission for fission to occur the unstable nucleus must usually first absorb a neutron) (content found only in the physics separate science qualification)
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