a soft, silver-white, ductile, metallic chemical element, one of the alkali metals and the most electropositive of all the elements: it ignites in air, reacts vigorously with water, and is used in photoelectric cells: symbol, Cs; at. no. 55: a radioactive isotope (cesium-137) with a half-life of 30.17 years is produced by fission and is used in cancer research, radiation therapy, etc.
Origin of cesiumModL, origin, originally neuter of Classical Latin caesius, bluish-gray (; from Indo-European base an unverified form (s)kai-, bright from source -hood): so named (1860) by R. W. Bunsen because of the blue line seen in the spectroscope
A soft, silvery-white ductile, metallic element that is the most electropositive and alkaline of the elements and is used in atomic clocks and photoelectric cells and to catalyze hydrogenation of some organic compounds. The fundamental unit of time in the International System, the second, is based on the frequency of radiation between two energy states in an atom of the Cs-133 isotope. Atomic number 55; atomic weight 132.905; melting point 28.44°C; boiling point 671°C; specific gravity 1.873; valence 1. See Periodic Table.
Origin of cesiumFrom Latin caesius, bluish gray (from its blue spectral lines).