  neptunium is a chemical element with symbol np and atomic number 93. a radioactive actinide metal, neptunium is the first transuranic element. its position in the periodic table just after uranium, named after the planet uranus, led to it being named after neptune, the next planet beyond uranus. a neptunium atom has 93 protons and 93 electrons, of which seven are valence electrons. neptunium metal is silvery and tarnishes when exposed to air. the element occurs in three allotropic forms and it normally exhibits five oxidation states, ranging from +3 to +7. it is radioactive, pyrophoric, and can accumulate in the bones, which make the handling of neptunium dangerous. although many false claims of its discovery were made over the years, the element was first synthesized by edwin mcmillan and philip h. abelson at the berkeley radiation laboratory in 1940. since then, most neptunium has been and is still produced by neutron irradiation of uranium in nuclear reactors and the vast majority is generated as a by-product in conventional nuclear power reactors. while neptunium itself has no commercial uses at present, it is widely used as a precursor for the formation of plutonium-238, used in the radioisotope thermal generators that power some spacecraft. neptunium has also been used in detectors of high-energy neutrons. the most stable isotope of neptunium, neptunium-237, is a by-product of nuclear reactors and plutonium production, and it and the isotope neptunium-239 are also found in trace amounts in uranium ores due to neutron capture reactions and beta decay. __toc__ ==characteristics== ===physical=== neptunium is a hard, silvery, ductile, radioactive actinide metal. in the periodic table, it is located to the right of the actinide uranium, to the left of the actinide plutonium and below the lanthanide promethium. neptunium is a hard metal, having a bulk modulus of 118&nbsp;gpa, comparable to that of manganese. neptunium metal is similar to uranium in terms of physical workability. when exposed to air at normal temperatures, it fo
Actinides Chemical_elements Neptunium Synthetic_elements