Element Neptunium, Np, Actinide or Actinoid

Neptunium had been discovered in 1940 and had become the first transuranium element produced synthetically. Active investigations of artificial radioactive elements ran in 1930-s included examination of the products of uranium neutron bombardment. Chemical analysis of such elements revealed the existence of new elements heavier than uranium. In 1939 Edwin M. McMillan discovered a new radioactive isotope with 2.3 day half-life during their research ran at the Berkeley Laboratory of the University of California by irradiation of uranium with slow movement neutrons. It was examined by Emilio Segre who found out that its properties are similar to those of rare-earth elements. In 1940 Edwin M. McMillan and Philip Abelson investigated the reaction which produced the isotope during which uranium-238 transmutes into uranium-239 with 23 minutes half-life by neutron capturing; uranium-239 in its turn transforms into neptunium-239. Neptunium was named after Neptune, the next planet out from Uranus in Solar system.

Traces of member of actinide or actinoid group of chemical elements - Neptunium-237 and Neptunium-239 were found in uranium ores in which these isotopes are formed continuously by of uranium neutron irradiation.