Radioactive substances can decay by emitting different types of radiation. Describe the differences between beta decay and gamma emission in terms of what is released and what happens to the nucleus in each case.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Beta decay:
1. A beta particle (fast‑moving electron) is emitted from the nucleus.
2. A neutron in the nucleus converts into a proton, so the atomic number increases by 1 while the mass number stays the same.
Gamma emission:
1. A high‑frequency electromagnetic wave (gamma ray) is released.
2. There is no change to the proton number or mass number of the nucleus.
3. It occurs when the nucleus drops from a higher to a lower energy state, becoming more stable.
1. A beta particle (fast‑moving electron) is emitted from the nucleus.
2. A neutron in the nucleus converts into a proton, so the atomic number increases by 1 while the mass number stays the same.
Gamma emission:
1. A high‑frequency electromagnetic wave (gamma ray) is released.
2. There is no change to the proton number or mass number of the nucleus.
3. It occurs when the nucleus drops from a higher to a lower energy state, becoming more stable.
Examiner tips
- Use the word ‘beta particle’ and ‘gamma ray’. Mention the change in proton number for beta decay. State that gamma emission leaves Z and A unchanged. Explain that gamma is a transition to a lower energy state.
Common mistakes
- Confusing gamma rays with gamma particles; they are electromagnetic waves. Forgetting that beta decay changes the atomic number. Saying gamma emission changes the mass number, which is incorrect.
Mark scheme (5 marks)
- Beta decay involves the emission of a beta particle (fast-moving electron) from the nucleus
- In beta decay a neutron in the nucleus changes into a proton (so the atomic/proton number increases by 1)
- Gamma emission involves the release of a high-frequency electromagnetic wave / high-energy electromagnetic radiation
- During gamma emission there is no change to the proton number or mass number of the nucleus
- Gamma emission occurs when the nucleus loses excess energy (nucleus moves from a higher energy state to a lower energy state / nucleus becomes more stable)
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Nuclear decay questions
- Radioactive materials can be used as tracers in medicine. A doctor injects a pat…
- A radioactive nucleus undergoes beta decay. Explain what happens inside the nucl…
- Explain what happens to the nucleus of an atom when it undergoes alpha decay.
- A smoke detector contains a small amount of americium-241, which is a radioactiv…