cesium

or cae·si·um

[ see-zee-uhm ]

noun

1. a rare, highly reactive, soft, metallic element of the alkali metal group, used chiefly in photoelectric cells. : Cs; : 132.905; : 55; : 1.9 at 20°C; melts at 28.5°C.

cesium

/ ˈsiːzɪəm /

noun

1. See caesium
   the usual US spelling of caesium

cesium

/ sē′zē-əm /

1. A soft, ductile, silvery-white element of the alkali group. It is liquid at room temperature and is the most reactive of all metals. Cesium is used to make photoelectric cells, electron tubes, and atomic clocks. Atomic number 55; atomic weight 132.905; melting point 28.5°C; boiling point 690°C; specific gravity 1.87; valence 1.
2. See Periodic Table

Word History and Origins

Origin of cesium¹

1930–35; < New Latin, special use of Latin caesium, neuter of caesius bluish-grey; -ium

Example Sentences

After these fuel assemblies work for a couple of years in the reactor core, they accumulate an enormous amount of fission products which are very radioactive, such as iodine, cesium, and strontium.

From MIT Technology Review

Cutting-edge atomic clocks such as these use neither cesium nor quartz.

From Popular-Science

Scientists delved into atoms of the element cesium, where a process called the hyperfine transition emits and absorbs microwaves, which scientists could time very precisely with the help of a vibrating quartz crystal.

From Popular-Science

So in terms of metallic character, cesium and fluorine are polar opposites.

From Science News For Students

The levels of radioactive cesium and potassium were elevated, and the source was unmistakable.

From The Daily Beast

Even at the Chernobyl meltdown in 1986, he pointed out, cesium and iodine were the problem.

From The Daily Beast

Of particular concern: cesium-137 in the pool, at levels Alvarez estimates at 20 million to 50 million curies.

From The Daily Beast

It was established that strontium-90 and cesium-137, important in fallout on land, enter the marine cycles only in minute amounts.

From Project Gutenberg