Below is the initial preparation of metallic cæsium by reduction of CsCl with lithium metal.
Here is more information on cæsium, element 55, which despite its reputation as an exotic metal (it is liquid near room temperature, reacts violently with water and is pyrophoric in air, has the largest atomic radius of any known element, and is the least electronegative of all elements) is more common in the Earth’s crust than tin and more than 100 times as abundant as mercury or silver. The hyperfine structure of cæsium-133 is used to define the second, and employed in atomic clocks that provide the world’s time and frequency standards.
The radioactive cæsium-137 isotope was used by Fourmilab’s HotBits random number generators from 1996 until their retirement at the end of 2022.