caesium

/ 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

Example Sentences

In 1955, the NPL invented the first atomic clock of the sort that is used today, based on the frequency of radiation from an atom of the element caesium.

From BBC

In 2022, SecDev, a geopolitical risk consultancy based in Canada, conducted an evaluation, which established that Russia had occupied 63% of Ukrainian coal mines, and half of its manganese, caesium, tantalum and rare earth deposits.

From BBC

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

This is because more radioactive caesium from Chernobyl will seep further into the soil, further contaminating the truffles.

From BBC

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