Americium-241 is an isotope of americium.It is the Americium isotope used in some smoke detectors. atomic mass: 241.056823 u excess mass: 52930 keV beta decay energy: -767 keV spin: 5/2- half life: 432 y possible parent nuclides: beta from Pu-241, electron capture from Cm-241, alpha from Bk-245… (More on Americium-241)