caesium

British  

/ ˈsiːzɪəm /

noun

1. 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

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Example Sentences

The NPL researchers are perfecting a so-called optical clock to achieve this, which is 100 times more accurate than the most accurate caesium clocks used today.

From BBC • Mar. 2, 2025

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

The small silver cylinder is a 19-becquerel caesium 137 ceramic source commonly used in radiation gauges.

From Seattle Times • Jan. 28, 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 Darwin, Charles