An Intercomparison of Hydrogen and Cesium Frequency Standards

Intercomparisons of average frequency and of frequency stability were made among one Hewlett-Packard 5060A cesium beam, two Varian Associates H-10 atomic hydrogen masers, and the National Bureau of Standards NBS III cesium beam designated as the United States Frequency Standard. Each of the standards displayed a white noise frequency fluctuation behavior with a transition into an approximate flicker of frequency fluctuation behavior for longer time intervals. The rms fractional frequency fluctuation between adjacent samples, σ(τ, N = 2), was 6 × 10-11τ-1/2 down to a flicker level of about 3×10-13 for the hp 5060A cesium beam (102 ≤ τ ≤ 104s), 1 × 10-11τ-1/2 down to a flicker level of less than 1×10-13 for NBS III cesium beam (102 ≤ τ ≤ 104s), and 5×10-13τ-1/2 down to a flicker level of about 1×10-14 for the H-10 hydrogen masers (1 ≤ τ≤ 104s). The accuracy capabilities of NBS III and H-10 #4 are now 1.1×10-12 and 0.47×10-12, respectively (1σ estimate). A discrepancy of only 1.1 parts in 1012 was observed between the average frequencies of the hp 5060A cesium beam and the NBS III cesium beam, with the former being higher in frequency. In terms of the frequency of the Cs133 hyperfine transition (F=4, mF = 0)↔(F=3, mF = 0), defined as 9 192 631 770.0000 Hertz, the measured frequency of the H1 hyperfine transition (F=1, mF = 0) ↔-F = 0, mF = 0) was vH=1 420 405 751.7864±0.0017 Hertz.