Actinium

Chemical element with atomic number 89 (Ac)

Actinium is a chemical element; it has symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. The actinide series, a set of 15 elements between actinium and lawrencium in the periodic table, are named for the first member, Actinium. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.

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