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
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
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
Cite this Entry
“Americium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/americium. Accessed 7 Jul. 2026.
Copy CitationKids 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
Love words? Need even more definitions?
Merriam-Webster unabridged
