93. Neptunium
Name: Neptunium
Symbol: Np
Atomic Number: 93
Atomic Mass: (237.0) amu
Melting Point: 640.0 °C (913.15 °K, 1184.0 °F)
Boiling Point: 3902.0 °C (4175.15 °K, 7055.6 °F)
Number of Protons/Electrons: 93
Number of Neutrons: 144
Classification: Rare Earth
Crystal Structure: Orthorhombic
Density(293 K): 20.45 g/cm3
Color: Unknown
Neptunium is a radioactive rare earth metal and has at least 3 allotropic forms. Np-237 is a by-product from nuclear reactors.
Neptunium (named for the planet Neptune) was first discovered by Edwin McMillan and Philip Abelson in 1940. The discovery was made at the Berkeley Radiation Laboratory of the University of California, Berkeley where the team produced the neptunium isotope Np-239 (2.4 day half-life) by bombarding uranium with cyclotron-accelerated neutrons. It was the first transuranium element produced synthetically and the first actinide series transuranium element discovered.
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