Actinium is a soft, silvery-white radioactive metal. It glows blue in the dark because its intense radioactivity excites the air around it. Actinium is a very powerful source of alpha rays, but is rarely used outside research. Actinium has no known biological role.

What makes actinium unique?

One of the more noteworthy actinium facts is that the element glows blue in the dark. The blue color comes from the ionization of gases in the air by radioactivity. Actinium is a silver-colored metal that has properties similar to those of lanthanum, the element located directly above it on the periodic table.

Why is actinium so rare?

Actinium-225 is unique among alpha emitters because it only has a 10-day half-life. (An isotope's half-life is the amount of time it takes to decay to half of its original amount.) In fewer than two weeks, half of its atoms have turned into different isotopes.