Promethium

Promethium, chemical element, symbol Pm; for physical constants see Periodic Table. Branner, in 1902, predicted the existence of an element between neodymium and samarium. This element, promethium, was discovered by J.A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell in 1945 by fission of uranium and neutron bombardment of neodymium with neutrons. This was the first chemical identification by use of ion-exchange chromatography. Promethium is not found in the earth's crust but is obtained from nuclear reactors as a fission byproduct. Promethium-145, the most stable isotope, has a half-life longer than 17.7 years. Promethium, a metallic element, has been prepared by the reduction of the fluoride with lithium metal. It is a member of the rare-earth series of metals. Promethium isotopes are used in thickness gauges, self-luminous compounds, nuclear-powered batteries, portable X-ray sources, and auxiliary power sources.