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neptunium

From The Collaborative International Dictionary of English v.0.48:

Neptunium \Nep*tu"ni*um\, n. [NL.]
   A radioactive metallic element of atomic number 93, produced
   in nuclear reactors from Plutonium or Uranium. Symbol Np; The
   atomic weight of the most stable isotope is 237.0482.
   [PJC]

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