Why is caesium used in atomic clocks?

Question

What makes it the preferred means of measuring time? And I guess, really, how do atomic clocks work?

In: Other

Answer 1

The official, formal definition of a second is:

> The second […] is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.

So cesium is the natural choice.