# A radioactive source used in a school laboratory contains an isotope with a half-life of 6 hours. The initial activity of the source is measured at 3200 Bq. A student says: 'After 24 hours, the source will no longer be radioactive and will be safe to handle without any precautions.' Evaluate the student's statement.

> Edexcel A-Level Physics (9PH0) — 6.1 Circular motion and momentum · Evaluate · 5 marks

> Radioactive decay is a random process. Background radiation is present in all environments. The activity of a radioactive source decreases over time as unstable nuclei decay.

## Mark scheme (5 marks)

1. Identifies the correct number of half-lives in 24 hours (4 half-lives)
2. Correctly determines the activity after 4 half-lives is 200 Bq (3200 → 1600 → 800 → 400 → 200 Bq)
3. States that the activity is not zero / the source is still radioactive after 24 hours
4. References background radiation as an additional reason precautions are still relevant / the student's comparison is flawed because background radiation is always present
5. Concludes that the student's statement is incorrect because precautions may still be needed as the source remains radioactive

## Key terms

- [half-life](https://www.gradenine.co.uk/glossary/half-life)
- [activity](https://www.gradenine.co.uk/glossary/activity)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Evaluate" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-radioactive-source-used-in-a-c0c196c1) · Published by Druglandscape Ltd.