# Explain why alpha decay causes a change in both the mass number and the atomic number of a nucleus, but gamma decay causes a change in neither.

> AQA GCSE Physics (8463) — 4.4.2 Atoms and nuclear radiation · Explain · 4 marks

## Mark scheme (4 marks)

1. An alpha particle consists of two protons and two neutrons, so it has a mass number of 4.
2. Emitting an alpha particle removes 2 protons from the nucleus, so the atomic number decreases by 2.
3. Gamma radiation is electromagnetic radiation (not a particle), so no protons or neutrons are emitted.
4. Because no protons or neutrons leave the nucleus during gamma decay, the mass number and atomic number both remain unchanged.

## Key terms

- [mass number](https://www.gradenine.co.uk/glossary/mass-number)
- [atomic number](https://www.gradenine.co.uk/glossary/atomic-number)

## Related

- [Revision notes for AQA GCSE Physics (8463)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-alpha-decay-causes-a-59eed1f8) · Published by Druglandscape Ltd.