A technician works in a nuclear research facility and is required to handle different radioactive sources. Explain why alpha-emitting sources are considered more dangerous when inhaled or ingested, but less dangerous when the source is held a short distance away from the body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Radioactive sources emit alpha particles, beta particles, or gamma rays. Each type of radiation has different properties that affect how hazardous it is to the human body depending on the situation.
Model answer (4 marks)
Alpha particles are highly ionising and therefore cause significant damage to cells, DNA and tissues when they reach living material. If an alpha‑emitting source is inhaled or ingested the particles are released inside the body and directly irradiate organs and cells, producing large biological effects. In contrast, alpha particles have very low penetration power; a few centimetres of air or a sheet of paper is enough to stop them. Consequently, when the source is held a short distance away the alpha particles are absorbed by the air before they can reach the technician’s body, so no significant irradiation occurs.
Examiner tips
- Use the word ‘highly ionising’ and link to damage of cells/DNA. Mention that inhaled/ingested sources are inside the body. State the low penetration of alpha particles. Explain why a short distance stops them.
Common mistakes
- Confusing alpha particles with beta or gamma radiation. Saying alpha particles are dangerous from a distance. Failing to mention the low penetration of alpha particles.
Mark scheme (4 marks)
- Alpha particles are highly ionising, so inside the body they cause significant damage to cells / DNA / tissues.
- When inhaled or ingested, the source is inside the body so the alpha particles reach living cells / organs directly.
- Alpha particles are weakly penetrating / can be stopped by a few centimetres of air, so they cannot reach the body from a short distance outside.
- Therefore, when the source is held a short distance away, the alpha particles are absorbed by the air before reaching the body, causing no irradiation / no harm to the technician.
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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