Neptunium (Np)

Isotopes of Neptunium 

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
Np-234 234.04289 4.40 days EC to U-234 0 No data available 
Np-235 235.04406 1.058 years EC to U-235;
α to Pa-231
5/2 No data available 
Np-236 236.04657 155,000 years EC to U-236;
α to Pa-232;
β- to Pu-236
6 No data available 
Np-237 237.0481678 2.14 x 106 years α to Pa-233; SF 5/2 3.14
Np-238 238.05094 2.117 days β- to Pu-238 2 No data available 
Np-239 239.05293 2.355 days β- to Pu-239 5/2 No data available 

NpNeptunium, named for the planet Neptune, is a radioactive rare earth metal. It was the first synthetic transuranium element (elements after uranium) of the actinide series. It was discovered in 1940 by Edwin M. McMillan and Philip Hauge Abelson at Berkeley, California, USA, who bombarded uranium with neutrons produced from a cyclotron.

Silvery in appearance, neptunium metal is fairly reactive chemically and is found in at least three allotropes: α-neptunium, orthorhombic, density 20.45 g/cm3 β-neptunium (above 280 °C), tetragonal, density 19.36 g/cm3 at 313 °C; and γ-neptunium (above 577 °C), cubic, density 18 g/cm3 at 600 °C.

Neptunium has the largest liquid range of any element: 3363 °K between its melting and boiling points. It is the densest of all the actinides and the fifth-densest of all naturally occurring elements. Neptunium has no biological role. It is not absorbed by the digestive tract. When injected into the body, it accumulates in bones, from which it is slowly released.

Though neptunium has no commercial uses at present, it is widely used as a precursor for the formation of Plutonium-238, used in radioisotope thermal generators, which are used to power some spacecraft. Neptunium itself can be used in detectors of high-energy neutrons.

Properties of Neptunium

Name Neptunium
Symbol Np
Atomic number 93
Atomic weight [237]
Standard state Solid at 298 ºK
CAS Registry ID 7439-99-8
Group in periodic table N/A 
Group name Actinoid
Period in periodic table 7 (Actinoid)
Block in periodic table f-block
Color Silvery metallic
Classification Metallic
Melting point 910 °K [or 637 °C or 1179 °F]
Boiling point 4300 °K [or ca. 4000 °C or 7232 °F]
Density of solid 20.45 g/cm3
Electron configuration [Rn]5f46d17s2


Isotope Supplier: ISOFLEX logo