>> At one time, only cesium standards were considered truly primary because > of > >> the definition of the second. However, the quantum mechanical > constants of > >> other atoms such as Rb have been measured to much more accuracy than > the 5071 > >> so that Rb standards can be considered traceable to Cs if they are > otherwise > >> of primary architecture. The key idea is that all Rb atoms are > absolutely > >> identical. Rb gas cells are of course never primary. >
FWIW BIPM just recently started publishing a graph like this that shows monthly TAI-contributions from what BIPM considers primary frequency standards (Cs beam and fountains) as well as 'SRS'-clocks (secondary representation of the second): https://webtai.bipm.org/database/show_psfs.html for these contributions they require a published uncertainty-budget where you calculate 'on paper' all the known shifts and show how you have controlled them to give a total uncertainty of the clock. > > > > Can the physics-nuts calculate the Rb frequency relative to Cs? > > I used to wonder about why there isn't a formula for calculating > the transition frequencies for an atom, at least relative to > another variety, but I know almost nothing about quantum mechanics. > Evidently, if it were possible, we would have heard about it by now. > I think there might be around 12 digits (?) or so of agreement between theory and experiment for Hydrogen (and anti-Hydrogen!?) - but for the complex clock atoms I think there's no theory that predicts the transition frequencies very well. > _______________________________________________ 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.