# A research team is investigating the suitability of two radioactive isotopes, Isotope P and Isotope Q, for use in treating cancerous tumours using chemotherapy. Isotope P is a gamma emitter with a half-life of 8 hours. Isotope Q is an alpha emitter with a half-life of 200 years. Explain why Isotope P is more suitable than Isotope Q for use in cancer treatment by chemotherapy.

> OCR A-Level Physics A (H556) — 6.2 Electric and magnetic fields · Explain · 5 marks

> Chemotherapy using radioactive materials involves directing radiation onto cancerous cells so they absorb the energy and are destroyed. The radiation source may be placed near the tumour inside the body or directed at the body from outside.

## Mark scheme (5 marks)

1. Gamma radiation is the most penetrating type of radiation, so it can pass through body tissue to reach the tumour
2. Alpha radiation has the least penetrating power / is stopped by a few centimetres of air or skin, so it would not reach an internal tumour
3. A short half-life means the source does not remain strongly radioactive for a long time, reducing long-term risk to the patient
4. A half-life of 200 years means Isotope Q would remain radioactive for a very long time, posing a long-term hazard to the patient
5. Gamma radiation is less ionising than alpha, so it causes less damage to surrounding healthy cells as it passes through the body

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" 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-research-team-is-investigating-the-6563a710) · Published by Druglandscape Ltd.