It is uncommon only because it combines so easily with other common elements. A gram of cesium could be found in about a cubic foot of ordinary granite. Cesium-133 atoms are sent from end to end in the vacuum tank of an atomic clock, as shown in this cutaway view. Some internal parts are illustrated below. Some magnetized atoms are set spinning by microwaves in the Ramsey cavity.
Magnetic shielding isolates the atoms from outside magnetic fields.
The spinning of the cesium atoms is stopped by the microwaves at the other end of the Ramsey cavity . The B magnet deflects the in-step atoms towards a detector, the hot wire cesium ionizer and ion collector . The other atoms are absorbed by another carbon getter . The quartz oscillator is adjusted automatically by the servo control to maximize the number of cesium ions collected, keeping the microwaves in step with the spinning of the cesium atoms. Hz, accurate to about 5 parts in one hundred thousand billion when averaged over a day.