A new determination of the Rb85 unperturbed hyperfine transition frequency

The unperturbed hyperfine transition frequency of the Rb85 atoms has been measured using a beam maser device operating under pulsed conditions. Population inversion is achieved through optical pumping in a storage cell. Using a double conversion receiver, frequency measurements were made to a few tenths of a hertz. Magnetic-field effect, cavity pulling, wall shift, and density dependent shift, are the main frequency shifts discussed and evaluated. The unperturbed frequency obtained is 3 035 732 440 ± 3 Hz, which is in agreement with previously published results. The absolute-wall frequency-shift coefficient for Paraflint is measured to be: −176 ± 25 Hz · cm at 72°C. The uncertainties reported are mostly attributed to the reproducibility of the maser storage cell coating.