cesium

noun

ce·​si·​um ˈsē-zē-əm 

 also  -zhē-

: a metallic chemical element that is the most electropositive element known and that is used in photoelectric cells, in atomic clocks, and as a component of drilling fluid see Chemical Elements Table

Examples of cesium in a Sentence

Recent Examples on the Web

Much of the work so far uses rubidium and cesium atoms, but the physicist Jeff Thompson at Princeton University prefers encoding the information in the nuclear spin states of metal atoms such as strontium and ytterbium, which have even longer coherence times. —Philip Ball, Quanta Magazine, 25 Mar. 2024

So, in 1955, scientists started measuring seconds using the resonance of cesium atoms, a more stable timekeeping method. —Will Sullivan, Smithsonian Magazine, 29 Mar. 2024

In 1955, physicist Louis Essen created an atomic clock based on the oscillation of cesium atoms. —Markus Lutz, Forbes, 20 Feb. 2024

Since the accident, TEPCO has been regularly testing surface ocean water samples near the plant for radioactive cesium and iodine levels; Buesseler and his colleagues compiled and analyzed this data for the ES&T report. —IEEE Spectrum, 11 Jan. 2012

By 1967, the resonant frequency of cesium (9,192,631,770 per second) became the international standard for what defines a second. —Markus Lutz, Forbes, 20 Feb. 2024

Today’s most accurate timekeepers are atomic clocks, which count vibrations of a cesium atom—but even these need to be tweaked based on the sun and stars, because the Earth’s spin is gradually slowing. —Bridget Alex, Smithsonian Magazine, 7 Dec. 2023

The stomach and tissue samples of the boars that researchers tested still continued to exhibit unsafe levels of cesium isotopes. —Stephen C. George, Discover Magazine, 7 Nov. 2023

The National Institute of Standards and Technology keeps time with cesium fountain clocks, using lasers, vacuum chambers, clouds of ultracold atoms to nail the natural resonance frequency of the cesium—the basis for the standard second (9,192,631,770 Hz). —WIRED, 27 Sep. 2023

Word History

Etymology

New Latin, from Latin caesius bluish gray

First Known Use

1861, in the meaning defined above

Kids Definition

cesium

noun

ce·​si·​um ˈsē-zē-əm 

: a silver-white soft element used especially in photoelectric cells see element

Medical Definition

cesium

noun

ce·​si·​um

variants or chiefly British caesium

ˈsē-zē-əm 

: a silver-white soft ductile element of the alkali metal group that is the most electropositive element known and that is used especially in photoelectric cells

—symbol Cs see Chemical Elements Table