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|
Neptunium, 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
|Standard state||Solid at 298 ºK|
|CAS Registry ID||7439-99-8|
|Group in periodic table||N/A|
|Period in periodic table||7 (Actinoid)|
|Block in periodic table||f-block|
|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|