caesium

British

/ ˈsiːzɪəm /

noun

a ductile silvery-white element of the alkali metal group that is the most electropositive metal. It occurs in pollucite and lepidolite and is used in photocells. The radioisotope caesium-137 , with a half-life of 30.2 years, is used in radiotherapy. Symbol: Cs; atomic no: 55; atomic wt: 132.90543; valency: 1; relative density: 1.873; melting pt: 28.39±0.01°C; boiling pt: 671°C

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

See Examples For:

caesium

The clean air, untainted food and clean water helped to lower the levels of caesium and other radiation stored in the children's bodies.

From BBC ● Aug. 1, 2026

Within the sensors, the light passes through a small glass container containing a caesium gas, which absorbs the light at the right light frequencies.

From Science Daily ● May 2, 2024

It contains the caesium 137 ceramic source, commonly used in radiation gauges, which emits dangerous amounts of radiation, equivalent of receiving 10 X-rays in an hour.

From Seattle Times ● Feb. 1, 2023

The radioactive strontium, caesium and plutonium mainly affected Ukraine and neighboring Belarus, as well as parts of Russia and Europe.

From Reuters ● Feb. 25, 2022

We see, also, that caesium causes inflection, and rubidium does not; and these two metals are allied to sodium and potassium.

From Insectivorous Plants by Charles Darwin

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023