plutonium
noun
plu·to·ni·um
plü-ˈtō-nē-əm 
: a radioactive metallic element similar chemically to uranium that is formed as the isotope 239 by decay of neptunium and found in minute quantities in pitchblende, that undergoes slow disintegration with the emission of an alpha particle to form uranium 235, and that is fissionable with slow neutrons to yield atomic energy see Chemical Elements Table
Examples of plutonium in a Sentence
Recent Examples on the Web
Despite these changes, experts have long warned that the original design could allow the production of weapons-grade plutonium if restored.
—
Sujita Sinha, Interesting Engineering, 30 Mar. 2026
Over the weekend, the IDF struck two steel plants in Iran, including one that uses radioactive material, the UN’s nuclear watchdog said, as well as a heavy water plant in Arak, which includes key production sites for plutonium.
—Sophie Tanno, CNN Money, 29 Mar. 2026
Heavy water is used in nuclear power plants as well as for weapons-grade plutonium.
—Patrick Sykes, Fortune, 29 Mar. 2026
The tests explode small quantities of weapons-grade plutonium but do not initiate a nuclear chain reaction within the material, according to weapons experts NPR interviewed at the time.
—Geoff Brumfiel, NPR, 17 Feb. 2026
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Sujita Sinha, Interesting Engineering, 30 Mar. 2026
Over the weekend, the IDF struck two steel plants in Iran, including one that uses radioactive material, the UN’s nuclear watchdog said, as well as a heavy water plant in Arak, which includes key production sites for plutonium.
—Sophie Tanno, CNN Money, 29 Mar. 2026
Heavy water is used in nuclear power plants as well as for weapons-grade plutonium.
—Patrick Sykes, Fortune, 29 Mar. 2026
The tests explode small quantities of weapons-grade plutonium but do not initiate a nuclear chain reaction within the material, according to weapons experts NPR interviewed at the time.
—Geoff Brumfiel, NPR, 17 Feb. 2026
See All Example Sentences for plutonium
Cite this Entry
“Plutonium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/plutonium. Accessed 2 Apr. 2026.
Copy CitationKids Definition
plutonium
noun
plu·to·ni·um
plü-ˈtō-nē-əm
: a radioactive metallic element that is formed by decay of neptunium and found in minute quantities in pitchblende and that produces atomic energy by fission see element
Medical Definition
plutonium
noun
plu·to·ni·um
plü-ˈtō-nē-əm
: a radioactive metallic element similar chemically to uranium that is formed as the isotope 239 by decay of neptunium and found in minute quantities in pitchblende, that undergoes slow disintegration with the emission of an alpha particle to form uranium 235, and that is fissionable with slow neutrons to yield atomic energy
—symbol Pu
see Chemical Elements Table
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