How does an ionization smoke detector function?

An ionization smoke detector functions by utilizing a small amount of radioactive material to ionize the air within its sensing chamber. This process involves the radioactive source emitting alpha particles, which collide with air molecules, creating ions. In the normal state, these ions facilitate the flow of electrical current between two electrodes in the detection chamber.

When smoke enters the chamber, it disrupts the flow of this current by attaching to the ions, effectively reducing the number of charged particles available to conduct electricity. This reduction triggers the alarm, indicating the presence of smoke and, potentially, a fire. The key aspect of ionization smoke detectors is their sensitivity to fast-burning fires that produce small smoke particles.

In contrast, the other choices do not accurately describe the operational principle of ionization smoke detectors. Choosing temperature changes to detect smoke, as suggested in one option, is associated more with heat detectors, which operate based on different principles. Measuring light levels disrupted by smoke particles relates to photoelectric smoke detectors, which function through a completely distinct mechanism involving light scattering. Combining methods, as mentioned in another option, is characteristic of dual-sensor smoke alarms but does not reflect the specific function of ionization detectors.