Cerium: An element of the rare earth family of metals. It has the atomic symbol Ce, atomic number 58, and atomic weight 140.12. Cerium is a malleable metal used in industrial applications.Cerium Radioisotopes: Unstable isotopes of cerium that decay or disintegrate emitting radiation. Ce atoms with atomic weights 132-135, 137, 139, and 141-148 are radioactive cerium isotopes.Cerium Isotopes: Stable cerium atoms that have the same atomic number as the element cerium, but differ in atomic weight. Ce-136, 138, and 142 are stable cerium isotopes.Metal Nanoparticles: Nanoparticles produced from metals whose uses include biosensors, optics, and catalysts. In biomedical applications the particles frequently involve the noble metals, especially gold and silver.Metals, Rare Earth: A group of elements that include SCANDIUM; YTTRIUM; and the LANTHANOID SERIES ELEMENTS. Historically, the rare earth metals got their name from the fact that they were never found in their pure elemental form, but as an oxide. In addition they were very difficult to purify. They are not truly rare and comprise about 25% of the metals in the earth's crust.