We have used the atomic-beam magnetic-resonance technique to measure the nuclear spin and the hyperfine-structure separation of 18-min ${}_{}{}^{88}{}_{}{}^{}\mathrm{Rb}$ in the ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ electronic ground state. These results, combined with the Fermi-Segrè formula, yield the nuclear magnetic moment. Our results are: $I=2\mathrm{}$, $\Delta \nu =\pm 1186.084\left(18\right)\mathrm{}$ MHz, ${\mu }_I\left(\mathrm{uncorr}\right)=\pm 0.506\left(5\right)\mathrm{}$ nm, ${\mu }_I\left(\mathrm{corr}\right)=\pm 0.508\left(5\right)\mathrm{}$ nm. Present nuclear theory favors assignment of the negative sign to the value of the moment.

• Received 8 September 1967

DOI:https://doi.org/10.1103/PhysRev.166.1131