# Radioactive substances undergo nuclear decay, emitting different types of radiation. Explain what happens to the nucleus of an atom when it undergoes alpha decay, and describe two properties of alpha radiation that make it the least penetrating of the three main types of nuclear radiation.

> WJEC A-Level Physics (Wales) — 3.5 Nuclear decay · Explain · 5 marks

## Mark scheme (5 marks)

1. The nucleus loses 2 protons and 2 neutrons (emits a helium nucleus / alpha particle)
2. The proton number (atomic number) decreases by 2
3. The mass number (nucleon number) decreases by 4
4. Alpha particles are relatively large / have a large mass (compared to beta or gamma)
5. Alpha particles are strongly ionising / interact strongly with matter, so they lose energy quickly and are stopped by a few centimetres of air or a thin sheet of paper

## Key terms

- [alpha decay](https://www.gradenine.co.uk/glossary/alpha-decay)

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/radioactive-substances-undergo-nuclear-decay-emitting-d8d3c886) · Published by Druglandscape Ltd.