# A technician is testing three different radioactive sources in a laboratory. Source A emits alpha particles, Source B emits beta particles, and Source C emits gamma rays. The technician places each source near a Geiger-Müller tube and then places different materials between the source and the tube. Explain how the technician could use paper, a few millimetres of aluminium, and thick lead to identify which type of radiation each source emits.

> WJEC A-Level Physics (Wales) — 6.1 Radioactivity · Explain · 5 marks

> Radioactive sources can emit three types of ionising radiation: alpha particles, beta particles, and gamma rays. Each type has a different penetrating power and is stopped by different materials.

## Mark scheme (5 marks)

1. Alpha particles are stopped by paper (or a few centimetres of air)
2. Beta particles pass through paper but are stopped by a few millimetres of aluminium
3. Gamma rays pass through both paper and aluminium but are reduced/stopped by thick lead
4. The source whose count rate drops to background when paper is placed in front is alpha (Source A)
5. Gamma rays are the most penetrating / alpha particles are the least penetrating, so the order of penetrating power is alpha < beta < gamma

## Key terms

- [alpha particles](https://www.gradenine.co.uk/glossary/alpha-particles)
- [beta particles](https://www.gradenine.co.uk/glossary/beta-particles)
- [gamma rays](https://www.gradenine.co.uk/glossary/gamma-rays)
- [Geiger-Müller tube](https://www.gradenine.co.uk/glossary/geiger-m-ller-tube)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-technician-is-testing-three-different-154e1c9e) · Published by Druglandscape Ltd.