Ionization smoke detectors operate by detecting ionization of air due to radioactive material. Which option best describes this principle?

Ionization smoke detectors operate by detecting ionization of air due to radioactive material. Which option best describes this principle?

• A. Ionization of air due to radioactive material
• B. Photoelectric light scattering
• C. Thermal rise
• D. Electrical current change

Answer: (A)

Ionization smoke detectors use a small amount of radioactive material (typically americium-241) to ionize the air in a detection chamber, creating a steady electrical current between two electrodes. When smoke enters, the smoke particles attach to the ions, reducing the current. When the current drops enough, the alarm sounds. This is the principle described by ionization of air due to radioactive material. The other methods rely on detecting smoke by different means—light scattering for photoelectric detectors or a heat rise for thermal detectors—so they don’t describe the ionization-based mechanism.

Ionization smoke detectors use a small amount of radioactive material (typically americium-241) to ionize the air in a detection chamber, creating a steady electrical current between two electrodes. When smoke enters, the smoke particles attach to the ions, reducing the current. When the current drops enough, the alarm sounds. This is the principle described by ionization of air due to radioactive material. The other methods rely on detecting smoke by different means—light scattering for photoelectric detectors or a heat rise for thermal detectors—so they don’t describe the ionization-based mechanism.