Keychain Np Neptunium.

<div>   </div> <div> <strong> Atomic number     <span class = "Apple-tab-span" style = "white-space: pre;"> </span>93</strong></div> <div> <strong> Atomic mass       <span class = "Apple-tab-span" style = "white-space: pre;"> </span>237</strong></div> <div> <strong> Density, kg / m ?     <span class = "Apple-tab-span" style = "white-space: pre;"> </span>20450</strong></div> <div> <strong> Temperature </strong> </div> <div> <strong> melting, ° С         <span class = "Apple-tab-span" style = "white-space: pre;"> </span>640</strong></div> <div>   </div> <div > Neptunium is a silvery white radioactive soft metal. Prior to the adoption of the theory of nuclear fission, which substantiated the existence of a later synthesized real such element, the independent discoveries of element 93, which turned out to be erroneous, were made three times: Ausonium in Italy (Enrico Fermi), Bohemium in Czechoslovakia in 1934 and sequania ( Sequanium) in Romania in 1939. Neptunium was first obtained by E. M. Macmillan and F. H. Abelson in 1940. The name Neptunium is derived from the name of the planet Neptune. Natural sources of neptunium are of no practical importance. Currently, neptunium is extracted from the products of long-term irradiation of uranium in nuclear reactors as a by-product in the extraction of plutonium. </div> <div>   </div>