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GCSE Combined Science · key term
The number of nuclear decays occurring in a radioactive source per second, measured in becquerels (Bq). One becquerel means one decay per second.
Used by AQA and Edexcel
Specification 6.4.2.1, 6.4.2.3 · Paper 5
The rate at which a source of unstable nuclei decays, measured in becquerels (Bq).
Revise: Radioactive Decay and Radiation TypesThe activity of a radioactive source is the rate at which its unstable nuclei decay. Its unit is the becquerel, Bq. A source with an activity of 80 Bq undergoes 80 nuclear decays per second.
Paper 5, Paper 6
The number of nuclear decays per second in a radioactive source.
Revise: Activity and half-lifeA radioactive source contains unstable nuclei that can decay and emit radiation. Its activity is the number of nuclear decays per second. Activity is measured in becquerels, symbol Bq: an activity of 800 Bq means that, on average, 800 nuclei decay each second.
Distinguish activity from count-rate: activity concerns decays in the source; count-rate concerns emissions recorded by the detector.
Define half-life using half the undecayed nuclei or half the activity, not half the total number of atoms.
On a graph, find the time interval between an activity and half that activity. It need not start at time zero.
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