Final answer:
A projected beam smoke detector works on the ionization principle, utilizing Americium-241 to ionize air and create a current, which triggers an alarm when disrupted by smoke particles.
Step-by-step explanation:
A projected beam smoke detector operates on the principle of ionization, specifically using alpha particles emitted by Americium-241 (Am-241).
These particles ionize the air between two metal plates, creating a pathway for a small electric current. When smoke enters the ionization chamber, it interferes with the flow of these ions, which reduces the current and triggers an alarm.
This process relies on the presence of smoke particles to disrupt the ionized air, providing a reliable method of fire detection. Solid-state radiation detectors, like those used in smoke detectors, are semiconductors designed to directly convert incident radiation into electrical current.