Which of these household appliances commonly uses the radioactive element americium?

Americium-241 is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of 432.2 years. It is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is also commonly found in ionization type smoke detectors.

The ionization type smoke detector – widely used in domestic settings -- uses a americium-241 to ionize air. A difference due to smoke is detected and an alarm is generated. Ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smouldering stage.

The smoke detector has two ionization chambers, one open to the air, and a reference chamber which does not allow the entry of particles. The radioactive source emits alpha particles into both chambers, which ionizes some air molecules. There is a potential difference (voltage) between pairs of electrodes in the chambers; the electrical charge on the ions allows an electric current to flow. The currents in both chambers should be the same as they are equally affected by air pressure, temperature, and the ageing of the source. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm.