# A hospital is considering using iodine-131, a beta and gamma emitter with a half-life of 8 days, to treat thyroid cancer. The thyroid gland absorbs iodine naturally. Explain why iodine-131 is suitable for use as a cancer treatment in this context, and explain one risk associated with its use.

> OCR A-Level Physics B: Advancing Physics (H557) — 6.3 Nuclear and particle physics · Explain · 5 marks

> Iodine-131 is a radioactive isotope that emits both beta particles and gamma rays. It has a half-life of 8 days. When a patient swallows iodine-131, the thyroid gland absorbs it because the thyroid naturally takes up iodine from the bloodstream.

## Mark scheme (5 marks)

1. Gamma radiation is the most penetrating type of radiation and can pass through body tissue to reach the cancerous thyroid cells.
2. The radiation (beta/gamma) ionises and kills the cancerous cells in the thyroid, controlling or destroying the tumour.
3. The thyroid gland naturally absorbs iodine, so the iodine-131 concentrates at the target site (the thyroid), reducing exposure of other organs.
4. The half-life of 8 days is short enough that the activity declines relatively quickly, reducing the long-term radiation risk to the patient.
5. One risk: surrounding healthy tissue may also be irradiated by the gamma radiation, damaging or killing healthy cells and causing harmful side effects.

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-hospital-is-considering-using-iodine-131-5b7546e8) · Published by Druglandscape Ltd.