cesiumatomikellot
Cesiumatomikellot, or cesium atomic clocks, are highly precise timekeeping devices that rely on the microwave transition between hyperfine levels of cesium-133 atoms to realize the SI second. In 1967 the second was defined as exactly 9,192,631,770 cycles of this cesium-133 transition, establishing a universal reference for timekeeping.
Most cesium clocks operate by preparing a sample of cesium atoms, exposing them to a microwave field
Cesium clocks underpin national time standards and time scales such as International Atomic Time (TAI) and