Question

Am-241 is used in smoke detectors because it has a long half-life (458 y). Given the schematic diagram of a smoke detector below, explain how it works?

• A. it emits $\alpha$-particles which are energetic enough to ionise air molecules
• B. it emits $\beta$-particles which can complete the circuit
• C. it emits $\gamma$-particles which have high penetration
• D. it emits $\alpha$- and $\beta$-particles

Answer 1

The correct option is A it emits $\alpha$-particles which are energetic enough to ionise air molecules

The smoke detector contains Am-241 and emits -particles which are energetic enough to ionize air molecules.
Thus once the smoke enters smoke detector, it is bombarded with -particles and is ionized.
The ions are then detected.