neptunium

American  

[nep-too-nee-uhm, -tyoo-] / nɛpˈtu ni əm, -ˈtyu- /

noun

Chemistry, Physics.

1. a transuranic element produced in nuclear reactors by the neutron bombardment of U-238: decays rapidly to plutonium and then to U-235. Np; 93.

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neptunium British  

/ nɛpˈtjuːnɪəm /

noun

1. a silvery metallic transuranic element synthesized in the production of plutonium and occurring in trace amounts in uranium ores. Symbol: Np; atomic no: 93; half-life of most stable isotope, ²³⁷ Np: 2.14 × 10 ⁶ years; valency: 3, 4, 5, or 6; relative density: 20.25; melting pt: 639±1°C; boiling pt: 3902°C (est)

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neptunium Scientific  

/ nĕp-to̅o̅′nē-əm /

1. A silvery, radioactive metallic element of the actinide series. It occurs naturally in minute amounts in uranium ores and is produced artificially as a byproduct of plutonium production. Its longest-lived isotope is Np 237 with a half-life of 2.1 million years. Atomic number 93.

2. See Periodic Table

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Etymology

Origin of neptunium

First recorded in 1940–45; Neptune + -ium

Example Sentences

Hafner: Do we know what nep... excuse my ignorance here, it sounds like it - Neptunium?

From Scientific American • Aug. 24, 2023

Neptunium has 93 electrons, which meant that the list of known elements was growing at the heavy end.

From Time Magazine Archive