A science museum exhibit displays two radioactive samples side by side. A label states that Sample A has an activity of 5 200 Bq and Sample B has an activity of 52 000 Bq. Explain what the unit becquerel means and describe what the difference in activity values tells us about the two samples.

Pearson Edexcel International GCSE Physics (4PH1) — 7.1 Units · Explain · 4 marks · View as Markdown

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

A science museum exhibit displays two radioactive samples side by side. Sample A has an activity of 5 200 Bq and Sample B has an activity of 52 000 Bq.

Model answer (4 marks)

The becquerel (Bq) is the SI unit of radioactive activity. One becquerel equals one nuclear decay per second. Activity is therefore the rate at which unstable nuclei decay, i.e. the number of decays per unit time. Sample B has a higher activity than Sample A – it undergoes about 52 000 decays per second compared with 5 200 decays per second – so its unstable nuclei are decaying roughly ten times faster.

Examiner tips

  • Define Bq and give the conversion to decays per second
  • Explain activity as a rate of decay
  • State the numerical comparison and the implication of higher activity
  • Use correct units and SI notation

Common mistakes

  • Confusing becquerel with curie or using wrong unit (e.g. s⁻¹ instead of Bq)
  • Failing to explain activity as a rate rather than a quantity
  • Not comparing the two activity values or mis‑stating the factor of difference

Mark scheme (4 marks)

  1. The becquerel (Bq) is the unit of (radioactive) activity
  2. One becquerel equals one (nuclear) decay per second
  3. Activity is the rate at which unstable nuclei decay / the number of decays per unit time
  4. Sample B has a higher activity than Sample A, so its unstable nuclei are decaying at a faster rate (ten times faster / 52 000 decays per second compared with 5 200 decays per second)

Key terms in this question

activity · becquerel

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