# A radioactive isotope used in smoke detectors undergoes alpha decay. Explain why an alpha emitter with a long half-life is suitable for use in a smoke detector, and why a gamma emitter would not be suitable for this application.

> Pearson Edexcel International GCSE Physics (4PH1) — 7.2 Radioactivity · Explain · 4 marks

> Smoke detectors contain a small radioactive source that produces a continuous current inside the detector. When smoke enters the device, the alarm is triggered.

## Mark scheme (4 marks)

1. Alpha particles are highly ionising, so they cause a current to flow inside the detector.
2. A long half-life is needed so that the source remains active / does not decay significantly over the lifetime of the detector.
3. Gamma radiation is lowly ionising, so it would not produce enough ionisation to maintain the current inside the detector.
4. Gamma radiation is highly penetrating, so it would pass through the casing of the detector and pose a radiation hazard to people nearby.

## Key terms

- [half-life](https://www.gradenine.co.uk/glossary/half-life)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-radioactive-isotope-used-in-smoke-132a4597) · Published by Druglandscape Ltd.