Americium 's a synthetic element that's the symbol Am and atomic number 95. A radioactive metallic element, americium's an actinide that was obtained in 1944 by Glenn T. Seaborg who was bombarding plutonium with neutrons and was the fourth transuranic element to be discovered. It was named for the Americas, by analogy with europium. Americium's widely used in commercial ionization-chamber smoke detectors as well as in neutron sources and industrial gauges. Properties Pure americium has a silve… (More on Americium)