Americium

Americium is a silvery radioactive metal made in nuclear reactors, where it forms from the decay of plutonium. Glenn Seaborg, Ralph James, Leon Morgan and Albert Ghiorso identified it in 1944 at the University of Chicago's wartime Metallurgical Laboratory. Seaborg first revealed it on a children's radio quiz show in 1945. It is named after the Americas, just as europium, above it in the periodic table, is named after Europe.

Americium is one of the few synthetic elements found in ordinary homes. Most ionization smoke detectors hold less than a millionth of a gram of americium-241. Its radiation lets the air in a small chamber carry a tiny current; smoke disrupts the current and sets off the alarm.