americium

noun

am·​er·​i·​ci·​um ˌa-mə-ˈri-shē-əm 

-sē-

: a radioactive metallic element produced artificially by bombarding plutonium with high-energy neutrons see Chemical Elements Table

Examples of americium in a Sentence

Recent Examples on the Web

Meanwhile other nations are pursuing or preserving their own RPS capabilities, with Europe’s sights set on americium 241, a radioisotope with a five-times-longer half-life but a five-times-weaker energy output than plutonium 238. —Hannah Richter, Scientific American, 13 Aug. 2025

If successful, this process could deal with the americium that is the most dangerous and long-lived component of spent reactor fuel. —IEEE Spectrum, 25 Nov. 2024

The energy source is a small amount of the radioactive element americium, embedded in a polymer crystal that converts the radiation into a stable green glow, eerily similar to those old stars everyone had stuck to their childhood bedroom ceiling. —Michael Irving, New Atlas, 19 Sep. 2024

Along with americium, the discovery of curium was related to the top-secret Manhattan Project, so no announcement was made until WWII ended. —Allison Futterman, Discover Magazine, 17 Sep. 2022

Word History

Etymology

New Latin, from America + New Latin -ium

First Known Use

1946, in the meaning defined above

Kids Definition

americium

noun

am·​er·​i·​ci·​um ˌam-ə-ˈris-ē-əm 

-ˈrish-

: a radioactive metallic element produced by bombardment of plutonium with high-energy neutrons see element

Medical Definition

americium

noun

am·​er·​i·​ci·​um ˌam-ə-ˈris(h)-ē-əm 

: a radioactive metallic element produced by bombardment of plutonium with high-energy neutrons

—symbol Am see Chemical Elements Table