Gibble Quantum Scattering 2 (of 2) (IMAGE) Penn State Caption Schematic of Fountain Clock Juggling Cesium Atoms. Two clouds of cesium atoms are tossed upward with a short time delay so that they collide after passing through the microwave cavity (silver) on the way up and before they return down through the cavity. The microwaves in the cavity excite and probe the atoms, resulting in an atomic fountain clock. Credit Kurt Gibble, Penn State Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.