Rb85-Rb86Hyperfine-Structure Anomaly

The atomic beam magnetic-resonance method with separated oscillatory fields has been used to measure the hyperfine structure separation and magnetic dipole moment of the isotopes ${\mathrm{Rb}}^{85}$ and 18.6-day ${\mathrm{Rb}}^{86}$ in the ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ electronic ground state. Observation of the separation of a $\Delta F=\pm 1$ doublet in the intermediate field region gives the value of the moment; the minimum value of the mean doublet frequency gives the value of $\Delta \nu$. Observation of another $\Delta F=\pm 1$ doublet in low field also yields a value for $\Delta \nu$.