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

noun, Chemistry, Physics.
a transuranic element produced in nuclear reactors by the neutron bombardment of U-238: decays rapidly to plutonium and then to U-235. Symbol: Np; atomic number: 93.
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, 237Np: 2.14 × 106 years; valency: 3, 4, 5, or 6; relative density: 20.25; melting pt: 639±1°C; boiling pt: 3902°C (est)

1941, from Neptune + element ending -ium. Named for its relative position in the periodic table, next after Uranium, as the planet Neptune is one beyond Uranus. Cf. also plutonium.

neptunium nep·tu·ni·um (něp-tōō’nē-əm, -tyōō’-)
Symbol Np
A metallic radioactive element found in trace quantities in uranium ores or synthesized; its longest-lived isotope is Np 237 with a half-life of 2.1 million years. Atomic number 93.
Symbol Np
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. See Periodic Table.


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  • Neral

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    abbreviation 1. Natural Environment Research Council

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