system
Given the following post, respond as if you're commenting on Reddit:
human
The outer electron of a Cesium-133 atom reverses its direction of spin when exposed to microwave radiation of precisely 9.19263177 GHz, which is the basis of the atomic clock. But what happens if the frequency is off slightly? What if it's a Hertz or two too high or too low? How does the atom react?
gpt
Take a stream of cesium is sent past the microwave radiation. the closer the radiation is to the proper frequency, the more cesium atoms will transition to their higher state. The atoms then pass a  filter which removes non-transitioned atoms from the stream, and the rest (the  atoms that did transition) hit a detector. A hgher the signal coming off the detector means moreatoms made the transition which means the microwaves are closer to the correct frequency. Jigger the microwave frequency until you find a peak or maximum in the signal. Now you know the microwaves are very close to the 9.2GHz you are looking for. Split off that input signal, divide it down to 5 or 10 MHz and you got yourself an atomic clock. A cesium beam frequency standard actually. This is a rough approximation to what happens in an HP 5061A.