Discovered by E.A. Demarçay in 1901 in Paris, France. The most reactive member of the lanthanide group of elements and one of the less abundant (2.1 ppm in the Earth's crust), europium is a ductile silvery metal which reacts rapidly with air and water. As a result of its reactive nature, the metal has limited applications, but some is used in the manufacture of thin-film superconductor alloys. Europium is also used as control rod material in nuclear reactors due to its ability to absorb neutrons.Rod - A straight length of circular section material.