Radioactive sources emit different types of nuclear radiation. Explain how the properties of alpha, beta and gamma radiation differ in terms of their penetrating power and what materials can stop each type.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A technician in a nuclear laboratory needs to select the correct shielding material to protect workers from three different radioactive sources. The sources emit alpha particles, beta particles and gamma rays respectively.
Model answer (5 marks)
Alpha particles have the least penetrating power – a few centimetres of air or a thin sheet of paper will stop them. They are highly ionising because they are relatively large and carry a 2+ charge.
Beta particles have intermediate penetrating power – a few millimetres of aluminium (or an equivalent metal sheet) will stop them. They are less ionising than alphas.
Gamma rays have the greatest penetrating power – they can only be reduced, not fully stopped, by thick lead or several centimetres of concrete. They are electromagnetic waves with no charge or mass, making them the least ionising of the three.
Thus, alpha: stopped by paper/air; beta: stopped by aluminium; gamma: requires lead or concrete.
Beta particles have intermediate penetrating power – a few millimetres of aluminium (or an equivalent metal sheet) will stop them. They are less ionising than alphas.
Gamma rays have the greatest penetrating power – they can only be reduced, not fully stopped, by thick lead or several centimetres of concrete. They are electromagnetic waves with no charge or mass, making them the least ionising of the three.
Thus, alpha: stopped by paper/air; beta: stopped by aluminium; gamma: requires lead or concrete.
Examiner tips
- Use the order of penetration (alpha < beta < gamma) to structure the answer.
- Mention the ionising ability to justify the differences.
- Keep each point brief and use the exact wording from the mark scheme.
Common mistakes
- Confusing the order of penetration (e.g., saying beta penetrates more than gamma).
- Using incorrect shielding materials such as steel for alpha particles.
- Omitting the ionising discussion for alpha and gamma radiation.
Mark scheme (5 marks)
- Alpha particles have the least penetrating power / are stopped by a few centimetres of air or a thin sheet of paper
- Beta particles have intermediate penetrating power / are stopped by a few millimetres of aluminium (or equivalent metal sheet)
- Gamma rays have the greatest penetrating power / are only reduced (not fully stopped) by thick lead or several centimetres of concrete
- Alpha particles are the most ionising because they are large / carry a 2+ charge, which explains their low penetrating power
- Gamma rays are the least ionising because they are electromagnetic waves / have no charge / mass, which explains their high penetrating power
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
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- Decode the mark scheme abbreviations →
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