# A hospital medical physicist states that a sample of technetium-99m has an activity of 800 000 Bq. State what is meant by the unit becquerel and explain what happens to the activity of this sample over a period of several days.

> Pearson Edexcel International GCSE Physics (4PH1) — 7.1 Units · State and Explain · 4 marks

> Technetium-99m is a radioactive isotope widely used in medical diagnosis. It has a half-life of approximately 6 hours.

## Mark scheme (4 marks)

1. One becquerel is one (radioactive) decay per second / the unit of activity equal to one nucleus decaying per second
2. Activity is the number of decays per unit time / the rate at which unstable nuclei decay
3. The activity decreases / reduces over time
4. This is because the number of unstable nuclei in the sample decreases (as they decay), so there are fewer nuclei available to decay / the activity halves every half-life

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "State and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-hospital-medical-physicist-states-that-64b195cf) · Published by Druglandscape Ltd.