A scientist is investigating a radioactive sample in a laboratory. The sample emits alpha, beta and gamma radiation. Describe how the scientist could identify which type of radiation is being emitted by using different absorbing materials, and explain why each material is chosen.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Radioactive materials can emit alpha particles, beta particles and gamma rays. Each type of radiation has different penetrating properties.
Model answer (5 marks)
1. Place a sheet of paper (or a few centimetres of air) between the source and the detector. If the radiation is stopped, the source emits alpha particles.
2. Alpha radiation is the least penetrating; a thin barrier such as paper or air is sufficient to absorb it.
3. Place a few millimetres of aluminium between the source and the detector. If the radiation is now stopped, the source emits beta particles.
4. Beta radiation has greater penetrating power than alpha but is stopped by a thin metal such as aluminium.
5. Use several centimetres of lead (or thick concrete) to reduce the radiation. If the radiation is still detected, it is gamma radiation.
6. Gamma rays are the most penetrating; only a thick shield of lead or concrete can attenuate them.
2. Alpha radiation is the least penetrating; a thin barrier such as paper or air is sufficient to absorb it.
3. Place a few millimetres of aluminium between the source and the detector. If the radiation is now stopped, the source emits beta particles.
4. Beta radiation has greater penetrating power than alpha but is stopped by a thin metal such as aluminium.
5. Use several centimetres of lead (or thick concrete) to reduce the radiation. If the radiation is still detected, it is gamma radiation.
6. Gamma rays are the most penetrating; only a thick shield of lead or concrete can attenuate them.
Examiner tips
- Use the order of penetration (alpha < beta < gamma) to structure your answer. Show why each material is chosen by linking it to the radiation’s penetrating power. Include the specific thicknesses (paper/air, mm of aluminium, cm of lead).
- Keep the answer concise and in a numbered list to match the 5 marks.
Mark scheme (5 marks)
- Place a sheet of paper (or a few centimetres of air) between the source and detector — if radiation is stopped, alpha is present
- Alpha radiation is chosen because it has the least penetrating power / is the least penetrating type of radiation
- Place a few millimetres of aluminium between the source and detector — if radiation is now stopped, beta is present
- Beta radiation is chosen because it has greater penetrating power than alpha but is stopped by aluminium
- Several centimetres of lead (or thick concrete) is needed to reduce gamma radiation, as it is the most penetrating type and cannot be fully stopped
Key terms in this question
gamma radiation · absorbing material
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