Which type of detector utilizes radioactive material?

The correct answer is ionization detectors, which utilize radioactive material to detect smoke and gases indicative of a fire. These detectors contain a small amount of radioactive material that ionizes the air in a sensing chamber. When smoke or other particles enter the chamber, they disrupt the flow of ions, causing a reduction in the current flow between two electrodes. This change in current is detected by the detector's circuitry, which triggers an alarm.

This method is particularly effective for detecting fast-flaming fires that produce little visible smoke, making ionization detectors more responsive to certain types of fires compared to other types. Understanding the mechanism by which ionization detectors operate illustrates their unique capability within fire detection systems.