Americium-241 is used in smoke alarms. It is an alpha emitter with a half-life of 432 years. Explain why americium-241 is a suitable radioactive isotope for use in a smoke alarm inside a home.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Alpha particles are weakly penetrating and travel only a few centimetres in air, so the radiation from the source does not reach the occupants of the home and poses minimal risk to people nearby.
The isotope has a long half‑life of 432 years, which means its activity remains roughly constant for many years; the source does not need to be replaced frequently.
The activity (count‑rate) of the Americium‑241 source is low enough that it does not present a significant hazard during normal use.
The isotope has a long half‑life of 432 years, which means its activity remains roughly constant for many years; the source does not need to be replaced frequently.
The activity (count‑rate) of the Americium‑241 source is low enough that it does not present a significant hazard during normal use.
Examiner tips
- Use the term ‘alpha particles’ and mention their limited penetration. Explain the long half‑life in terms of source longevity. Show that the low activity keeps the dose below harmful levels.
- common_mistakes
- :
- Confusing alpha radiation with gamma or beta. Claiming the isotope is ‘highly radioactive’ without noting the low activity. Ignoring the long half‑life and its practical advantage.
Mark scheme (4 marks)
- Alpha radiation is weakly penetrating / travels only a few centimetres in air
- So the alpha radiation does not reach the occupants of the home / poses minimal radiation risk to people nearby
- The long half-life means the activity remains roughly constant over many years / the source does not need to be replaced
- The activity / count-rate is low enough that it does not present a significant hazard during normal use
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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