The Rare Earth Elements are of the Lanthanide and Actinide series. Most of the elements in the Actinide series are synthetic or man-made.

Brief Facts about the Discovery and History of the Element Neptunium
Neptunium was discovered by Edwin McMillan and Philip Abelson in the USA in 1940

Occurrence of the element Neptunium
Man-made

Common Uses of Neptunium
Neutron detection equipment

The Properties of the Element Neptunium
Name of Element : Neptunium
Symbol: Np
Atomic Number: 93
Atomic Mass: (237.0) amu
Melting Point: 640.0 °C - 913.15 °K
Boiling Point: 3902.0 °C - 4175.15 °K
Number of Protons/Electrons: 93
Number of Neutrons: 144
Crystal Structure: Orthorhombic
Density @ 293 K: 20.45 g/cm3
Color: Silvery