Which type of smoke detector uses a small amount of radioactive material to make the air within a sensing chamber conduct electricity?

• A. Photoelectric Smoke Detector
• B. Smoke Detector
• C. Ionization Smoke Detector
• D. Heat Detector

Answer: (C)

Ionization-based smoke detectors work by using a small sealed radioactive source to ionize the air inside a sensing chamber, creating a tiny electrical current between two electrodes. When smoke enters the chamber, the smoke particles attach to the ions and reduce the current, which triggers the alarm. This relies on the radioactive material to create free ions and conduct electricity in the air.

This is different from photoelectric detectors, which use a light beam and a sensor to detect smoke by light scattering; heat detectors, which respond to heat rise; and a generic “smoke detector” term that doesn’t specify the ionization mechanism. So the type that uses radioactive material to make the air conduct electricity is the ionization smoke detector.