plutonium

American  

[ploo-toh-nee-uhm] / pluˈtoʊ ni əm /

noun

Chemistry, Physics.

1. a transuranic element with a fissile isotope of mass number 239 plutonium 239 that can be produced from non-fissile uranium 238, as in a breeder reactor. Pu; 94.

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plutonium British  

/ pluːˈtəʊnɪəm /

noun

1. a highly toxic metallic transuranic element. It occurs in trace amounts in uranium ores and is produced in a nuclear reactor by neutron bombardment of uranium-238. The most stable and important isotope, plutonium-239 , readily undergoes fission and is used as a reactor fuel in nuclear power stations and in nuclear weapons. Symbol: Pu; atomic no: 94; half-life of ²³⁹ Pu: 24 360 years; valency: 3, 4, 5, or 6; relative density (alpha modification): 19.84; melting pt: 640°C; boiling pt: 3230°C

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plutonium Scientific  

/ plo̅o̅-tō′nē-əm /

1. A silvery, radioactive metallic element of the actinide series that has the highest atomic number of all naturally occurring elements. It is found in minute amounts in uranium ores and is produced artificially by bombarding uranium with neutrons. It is absorbed by bone marrow and is highly poisonous. Plutonium is used in nuclear weapons and as a fuel in nuclear reactors. Its longest-lived isotope is Pu 244 with a half-life of 80 million years. Atomic number 94; melting point 640°C; boiling point 3,228°C; specific gravity 19.84; valence 3, 4, 5, 6.

2. See Periodic Table

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plutonium Cultural  

1. A radioactive chemical element that is artificially derived from uranium.

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Discover More

Plutonium is used in nuclear reactors.

Etymology

Origin of plutonium

1940–45; < Greek Ploútōn Pluto + -ium

Compare meaning

How does plutonium compare to similar and commonly confused words? Explore the most common comparisons:

• plutonium vs. uranium

Example Sentences

Kim Jong Il, the son of Kim Il Sung, expelled inspectors, withdrew from the NPT and resumed plutonium work.

From The Wall Street Journal • Apr. 3, 2026

These are where the regime was pursuing a bomb via uranium and plutonium.

From The Wall Street Journal • Mar. 15, 2026

After listing Oppenheimer’s wartime accomplishments, including overseeing the invention of the plutonium bomb, Rabi asked the inquisitors, “What more do you want, mermaids?”

From Los Angeles Times • Feb. 6, 2026

Spent fuel from heavy water reactors contains plutonium suitable for a nuclear bomb.

From BBC • Jun. 19, 2025

When S-l reconvened the next day, Compton was awarded responsibility for supervising the theoretical research on U-235 and plutonium.

From "Big Science" by Michael Hiltzik