Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive metallic element, neptunium is the first transuranic element and belongs to the actinide series. Its most stable isotope, 237Np, is a by-product of nuclear reactors and plutonium production and it can be used as a component in neutron detection equipment. Neptunium is also found in trace amounts in uranium ores due to transmutation reactions.
Silvery in appearance, neptunium metal is fairly chemically reactive and is found in at least three allotropes:
α-neptunium, orthorhombic, density 20.45 g/cm3
β-neptunium (above 280 °C), tetragonal, density (313 °C) 19.36 g/cm3
γ-neptunium (above 577 °C), cubic, density (600 °C) 18 g/cm3
19 neptunium radioisotopes have been characterized, with the most stable being 237Np with a half-life of 2.14 million years, 236Np with a half-life of 154,000 years, and 235Np with a half-life of 396.1 days. All of the remaining radioactive isotopes have half-lives that are less than 4.5 days, and the majority of these have half-lives that are less than 50 minutes. This element also has 4 meta states, with the most stable being 236mNp (t½ 22.5 hours). The isotopes of neptunium range in atomic weight from 225.0339 u (225Np) to 244.068 u (244Np). The primary decay mode before the most stable isotope, 237Np, is electron capture (with a good deal of alpha emission), and the primary mode after is beta emission. The primary decay products before 237Np are element 92 (uranium) isotopes (alpha emission produces element 91, protactinium) and the primary products after are element 94 (plutonium) isotopes.
The base value of each unit of ranges between 70 and 130Ð per unit, with up to 2 units being found at any one time.
Presence on Mars: Very Rare
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