Neptunium

Neptunium, chemical element, symbol Np; for physical constants see Periodic Table. Discovered by Edwin M. McMillan and P.H. Abelson in 1940, it was produced by bombarding uranium with neutrons in a cyclotron. Neptunium was the first synthetically produced transuranium element of the actinide series to be discovered. It is produced in nuclear reactors as a by-product of plutonium production. Neptunium is a silvery, radioactive metal. Neptunium-237 has a long half-life (2.14 million years) and is used in neutron detection instruments.