Why Use Americium-241 in Smoke Detectors?
There are two kinds of smoke detectors: ionization detectors and photoelectric detectors. A photoelectric detector does not use radioactive elements and senses smoke by its interference with a light beam. In ionization detectors, collisions between americium-241’s alpha particles and air molecules yield ions that allow a (small) current to flow between two electrodes. Any reduction of this current by smoke or steam (which combine with charged particles) sounds the alarm. The alarm also sounds when a weak battery causes a reduction in the current. How Much Americium-241 Is in a Smoke Detector? About one microcurie, equal to about one five thousandths of a gram. The alpha particles produced are not very energetic and are contained by the shielding in the detector. The more energetic gamma rays are not entirely absorbed by the housing of the detector, but gamma rays from an unshielded smoke detector give a radiation dosage about three thousand times lower than the natural background radia
