An americium smoke detector is a smoke detector that uses americium-241 to detect the changes in the flow of ions that indicates the presence of smoke. A smoke detector that uses americium-241 to detect smoke contains an amount of elemental americium-241 so small that it is not harmful to the human body (cause cancer or radiation sickness).
As seen in the image to the right, the americium is placed towards the edge of the smoke detector and is powered by a standard 9V battery. Since americium is only the third transuranic element[1] it is relatively stable and can be placed in a smoke detector.[2]
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The amount of americium-241 used is less than 1 μg. This enables the smoke detector to be able to detect smoke while also not causing diseases among human beings who come into close vicinity to it on regular basis. The amount may be tiny but it is still required to be disposed of correctly.[3] The presence of americium-241 means that every decommissioned smoke detector must be properly disposed of lest it constitute an environmental hazard.
The radioactive element, americium-241, is used in smoke detectors despite the fact that there are other options available. The use of americium-241 is cheaper compared to other smoke detectors such as ones that look for smoke. Ionisation detectors are more sensitive to flaming fires than optical detectors, while optical detectors are more sensitive to smouldering fires.[4]
The radioactive isotope americium-241 in the smoke detector emits ionizing radiation into a chamber that is open to the air. The air molecules in the chamber become ionized and these ions allow the passage of a small electric current between charged electrodes placed in the chamber. If any smoke particles pass into the chamber the ions will attach to the particles and so will be less able to carry the current. An electronic circuit detects the current drop, and sounds the alarm.[5]