the Am-241 is somewhere between 75-95% pure, very pure considering where it comes from. It is a thin coating on a (sometimes) gold alloy so that it does not corrode. Some much older industrial smoke detectors actually have a thin coating of Ra-226 (Radium 226), but because Am-241 produces 3x the alpha radiation as Ra-226 without the high dosage of Gamma radiation and the fact that Am is less costly to make, Ra was eventually put out of use. smoke detectors usually have a marking that they contain Am-241 in EXTREAMLY SMALL type.
-Am-241