Which detectors contain a small amount of radioactive material?

Ionization detectors are designed to detect smoke by using a small amount of radioactive material, typically americium-241. This radioactive element ionizes the air in a sensing chamber, allowing a small electric current to flow between two electrodes. When smoke enters the detector, it disrupts this flow of ions, causing the current to decrease. This reduction in current triggers the alarm, indicating the presence of smoke.

Photoelectric detectors, on the other hand, rely on a light source and a sensor to detect smoke particles. They work by identifying the scattering of light caused by smoke, rather than using radioactive material. Heat detectors are designed to respond to changes in temperature rather than detecting smoke, and smart detectors typically incorporate various technologies for enhanced detection capabilities but do not utilize radioactive materials. Thus, ionization detectors are uniquely identified by their use of radioactivity in smoke detection, making them the correct answer.