# Explain why alpha radiation is used in smoke alarms rather than beta or gamma radiation.

> Edexcel GCSE Physics (1PH0) — 6.1 Radioactivity · Explain · 4 marks

> Smoke alarms contain a small amount of the radioactive isotope americium-241, which has a half-life of 432 years. Under normal conditions the alarm remains silent, but it sounds when smoke enters the device.

## Mark scheme (4 marks)

1. Alpha particles are highly ionising / ionise air particles to create a current
2. When smoke enters, it absorbs/blocks the alpha particles, reducing the ionisation and causing the current to drop, triggering the alarm
3. Alpha radiation is weakly penetrating / stopped by a few centimetres of air, so it is contained safely within the device
4. Beta or gamma radiation would be too penetrating to be blocked by smoke / would pass straight through, so the alarm would not work / would present a greater radiation hazard outside the device

## Related

- [Revision notes for Edexcel GCSE Physics (1PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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