Atomic number: 93

Symbol: Np

Category: actinide 

Density at 25°C: solid: density: 20.45 g·cm−3

Named after the god of the ocean, neptunium tends to be quite a rare element only occurring in trace amounts in uranium ores. It mainly comes from nuclear reactors.

A sphere of neptunium held in a container. image: adapted from wikipedia

Use, natural applications or common combinations: 

  • nuclear reactor radioactive waste
  • military uses

Basic characteristics:

  • Standard atomic weight: 237.048 
  • Melting point: (637) 644 °C
  • Boiling point:  3902 °C
  • Radioactivity: all radioactive
    • 238Np with a half-life of  4.47 billion years emitting alpha particles
    • 235Np  with a half-life of  704 million years, spontaneous fission decay process.