An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A ductile, silvery radioactive metal, a member of the actinide series; symbol Np. Atomic number 93; atomic weight 237.0482; melting point about 640°C; boiling point 3,902°C (estimated). It was discovered in 1940 by Edwin M. McMillan and Philip H. Abelson, who produced neptunium-239 (half-life 2.3 days) by bombarding uranium with neutrons from a cyclotron at the University of California at Berkeley.

The name derives from the planet → Neptune, since it is the next outer-most planet beyond the planet Uranus in the solar system and this element is the next one beyond uranium in the periodic table.