Radioactive decay and nuclear radiation — AQA GCSE Physics
Test yourself on Radioactive decay and nuclear radiation with AQA GCSE practice questions.
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Radioactive decay and nuclear radiation explained
The measurement of radioactive decay focuses on how frequently unstable nuclei emit radiation, quantified in becquerels (Bq), where 1 Bq equals one decay per second.
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This frequency depends on the total number of unstable nuclei present and the specific isotope's half-life. Given identical starting quantities of two isotopes, the one with a shorter half-life exhibits a higher initial frequency of decay events. For example, a sample of polonium-210 (half-life 138 days) registers significantly more counts per second on a detector than an equal sample of polonium-209 (half-life 125 years). As unstable nuclei deplete over time, the frequency of decay events naturally decreases, meaning the sample becomes less radioactive.
Your focus
- State the unit of activity and define it in terms of decays per second.
- Explain why the activity of a radioactive source decreases over time.
- Compare the activities of two different isotopes present in equal numbers, based on their half-lives.
Radioactive decay and nuclear radiation exam tips
Marking Points
- Identifies that the activity of a radioactive source is measured in becquerels (Bq)
- States that one becquerel is equivalent to one nuclear decay per second
- Explains that activity decreases over time as the number of unstable nuclei in the sample reduces
- Compares two sources to conclude that for an equal number of nuclei, a shorter half-life results in a higher activity
Examiner Tips
- 💡When defining activity, always include the unit becquerel (Bq) and state that 1 Bq equals 1 decay per second.
- 💡If asked to compare the activity of two samples, check both the number of unstable nuclei and their respective half-lives before concluding which is more active.
Common Mistakes
- Confusing activity with the total number of undecayed nuclei remaining in a sample; activity is the rate of decay (decays per second), not the absolute number of unstable nuclei present.
- Assuming that a longer half-life means a higher activity; a longer half-life means the nuclei are more stable and decay less frequently, resulting in a lower activity for a given number of nuclei.
- Believing that the activity of a specific radioactive source remains constant over time; as unstable nuclei decay, there are fewer left to decay, so the activity decreases over time.