How is americium-241 used in smoke detectors?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — actinoid element Modern version of the periodic table of the elements (printable).

In ionization-type smoke detectors, americium-241 is used to ionize the air molecules between two electrodes within a detection chamber. This process allows a minute electrical current to flow through the air.12

When smoke enters the chamber, the smoke particles attach themselves to the ions, which diminishes the flow of this current. The resulting reduction in current triggers the device's alarm circuit. The use of americium-241 in these devices exploits its alpha-particle emission, and the quantities used are so small that they are considered to pose no significant health hazard.21