An atomic clock is a clock whose timekeeping mechanism is based on the interaction of electromagnetic radiation with the excited states of certain atoms.

Why is cesium used for atomic clocks?

And that's where caesium comes in. It has a far higher resonant frequency even than quartz - 9,192,631,770 Hz, to be precise. This is one reason Essen used the element to make the first of the next generation of clocks - the "atomic" clocks.

How does caesium clock work?

Inside a cesium atomic clock, cesium atoms are funneled down a tube where they pass through radio waves . If this frequency is just right 9,192,631,770 cycles per second then the cesium atoms "resonate" and change their energy state. ... Other electronics in the atomic clock count this frequency.