Radioactive substances emit radiation that can be alpha, beta or gamma. Explain why gamma radiation is the most penetrating of the three types, and describe one use and one hazard of gamma radiation.

WJEC A-Level Physics (Wales) — 6.1 Radioactivity · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Radioactive sources emit ionising radiation. The ability of each type of radiation to pass through materials depends on its nature and properties.

Model answer (5 marks)

Gamma radiation is electromagnetic and has no mass or charge, so it interacts only weakly with matter. Consequently it can penetrate far, being stopped only by thick lead or several centimetres of concrete, whereas alpha particles are stopped by paper and beta particles by a few millimetres of aluminium. Because gamma rays are weakly ionising, they lose energy slowly as they pass through materials, allowing them to travel further.

A useful application is radiotherapy, where high‑energy gamma rays are used to destroy cancer cells. A hazard is that gamma radiation can damage biological cells, causing mutations and increasing the risk of cancer.

Examiner tips

  • Use the term ‘electromagnetic radiation’ and note lack of mass/charge; mention lead/concrete as shielding; give one clear use and one clear hazard; keep answer concise to fit 5 marks

Common mistakes

  • Confusing alpha or beta with gamma in shielding details; not specifying that gamma is weakly ionising; giving a non‑radiation use such as ‘laser cutting’ instead of a valid gamma application

Mark scheme (5 marks)

  1. Gamma radiation has no mass (and no charge) / is electromagnetic radiation, so it interacts very little with matter
  2. Gamma radiation can only be stopped / significantly absorbed by thick lead or several centimetres of concrete (whereas alpha is stopped by paper and beta by a few mm of aluminium)
  3. Because gamma is weakly ionising, it loses energy slowly as it passes through materials, allowing it to travel further
  4. One valid use of gamma radiation: detecting or treating cancer (radiotherapy) / sterilising medical instruments or food / medical imaging using gamma cameras
  5. One valid hazard of gamma radiation: it can cause cell damage / mutations / cancer

Key terms in this question

gamma radiation · penetrating

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