How do smoke detectors use radioactivity?

Smoke detectors use radioactivity by employing a small amount of Americium-241, which ionises the air, detecting smoke particles.

Smoke detectors are a common household item designed to alert us to the presence of smoke, and thus, potential fire. The key component in these devices is a small amount of a radioactive material called Americium-241. This substance emits alpha particles, a type of ionising radiation. These alpha particles have the ability to ionise the air molecules in the detector's sensing chamber, meaning they knock electrons off the air molecules, creating ions.

The ionised air molecules allow a small electric current to flow within the detector. When smoke enters the detector, it absorbs the alpha particles. This reduces the ionisation of the air and interrupts the electric current flow. The drop in current triggers the alarm, alerting the occupants of the potential danger.

The amount of Americium-241 used in smoke detectors is very small, typically about one microgram, and is safely contained within the detector. It poses little risk to human health unless it is directly inhaled or ingested. The alpha particles it emits cannot penetrate a sheet of paper or the outer layer of human skin. Therefore, as long as the detector is not tampered with or damaged, it is safe to use.

In summary, the radioactivity in smoke detectors plays a crucial role in their operation. The alpha particles emitted by the Americium-241 ionise the air, allowing an electric current to flow. When smoke enters the detector, it disrupts this current, triggering the alarm. This clever use of radioactivity helps to keep us safe from the dangers of fire.