# A hospital uses americium-241 in smoke alarms and a gamma-emitting isotope in cancer treatment. Explain why americium-241 is suitable for use in a smoke alarm, and explain why a gamma emitter, rather than an alpha or beta emitter, is used to treat cancerous cells inside the body.

> OCR A-Level Physics B: Advancing Physics (H557) — 6.1 Capacitors · Explain · 5 marks

> Americium-241 is an alpha emitter with a half-life of 432 years. It is used in smoke alarms found throughout a hospital building. Separately, doctors use a gamma-emitting radioactive isotope to treat cancerous tumours located deep inside a patient's body.

## Mark scheme (5 marks)

1. Americium-241 has a long half-life (432 years), so it does not need to be replenished / remains active for a very long time
2. Alpha radiation is the least penetrating / is stopped by a few centimetres of air, so it does not travel far and is not harmful to people nearby
3. When smoke enters the alarm, it reduces / absorbs the alpha particles in the surrounding air, triggering the alarm to sound
4. Gamma radiation is the most penetrating type of nuclear radiation, so it can pass through body tissue to reach tumours deep inside the body
5. Alpha or beta radiation would be absorbed by surrounding healthy tissue before reaching the tumour / would not penetrate deep enough into the body

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