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

Minor actinides, including neptunium, americium, and curium, are transuranic elements produced in nuclear fuel during reactor operation. — Aman Tripathi, Interesting Engineering, 1 May 2026

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

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

The team created 30 atoms of element 115 by firing a beam of calcium atoms at a piece of americium foil. — Shannon Palus, Discover Magazine, 19 Dec. 2013

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