The gettering in the tube is only for capturing any stray Cesium atoms that don't get caught in the main gettering patch. If the gettering fails or gets too loaded up then the Cesium background level will get too high causing poor SN.
The ion pump is for any gases. When a tube is off for extended times any gas atoms lingering or leaking slowly into the tube than happen to impinge on either the mass Spectrometer filament or the Cs oven filaments get capture by the filaments. They function as excellent getters! (this even if the ion pump is on) Now this is not by design but results in the filaments being "loaded" with the gas atoms. Then when you turn the tube on the filaments light up and expell a burst of gas. This of coarse causes the ion pump current to rise and trips off the filaments, Once the ion pump removes the burst the cycle repeats until the filaments have expelled the trapped gases. Then the ion pump can handle the load and pump the tube down completely. Cheers, Corby _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
