Europium, discovered in 1896, is an element in the lanthanide series. It is the most reactive of the rare earths. Shown above is a sample of europium photographed in argon.

Europium had virtually no practical use until the atomic age. Europium can absorb more neutrons than any other elements, making it very valuable in control rods for nuclear reactors.

BCIT Chemistry Resource Center
http://nobel.scas.bcit.ca/resource/