What is the benefit of using Am-241 in smoke detectors even though it is a radioactive element?
The usage in ionizing smoke detectors requires a radioactive isotope to work.  In addition to a sufficient half-life to make a smoke detector with a suitable service life, Am-241 emits mostly alpha radiation (which is used for the ionizing mechanism) with relatively little of the more hazardous and useless gamma radiation.  See the Applications section in  https://en.m.wikipedia.org/wiki/Americium.