Describe what alpha radiation is and explain why it is not considered a hazard when a radioactive source emitting only alpha radiation is kept several centimetres away from the body in open air.

Eduqas GCSE Physics — 9.2 Absorption and emission of ionising radiations · Describe and Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Alpha radiation consists of a helium nucleus (two protons and two neutrons). It has a very short range in air, only a few centimetres, and is stopped before it can reach the body. Because it cannot penetrate the skin, it is not a hazard when the source is kept several centimetres away in open air. If it did reach body tissue it would be highly ionising and therefore very dangerous.

Examiner tips

  • Use the exact definition of alpha particles (helium nucleus).
  • State the short range in air and that it is stopped by the skin.
  • Explain that the lack of penetration makes it safe at a few centimetres.
  • Mention the high ionising power as a potential hazard if it entered tissue.

Common mistakes

  • Confusing alpha radiation with beta or gamma radiation.
  • Failing to mention the short range or that it is stopped by the skin.
  • Using vague terms like "small" instead of "a few centimetres".

Mark scheme (4 marks)

  1. Alpha radiation consists of two protons and two neutrons (a helium nucleus)
  2. Alpha radiation has a very short range in air (a few centimetres)
  3. Alpha radiation is stopped before it reaches the body / does not penetrate to the skin
  4. Alpha radiation is highly ionising so if it did reach body tissue it would be very dangerous / hazardous internally

Key terms in this question

alpha radiation · radioactive source

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