High-accuracy measurement of the ground-state hyperfine splitting in an atomic fountainS. Bize, Y. Sortais, M. S. Santos, C. Mandache, A. Clairon and C. SalomonEurophys. Lett., 45 5 (1999) 558-564DOI: https://doi.org/10.1209/epl/i1999-00203-9