The atomic-beam magnetic-resonance method was used to obtain the hyperfine-structure separation $\Delta \nu$, the nuclear magnetic dipole moment ${\mu }_I$, and the hyperfine-structure anomaly $\Delta$ of ${\mathrm{Cs}}^{131}$. Independent values of ${\mu }_1$ and $\Delta \nu$ were obtained by observing one of the $\Delta F=\pm 1$ doublets in a field-independent region. The results of the measurements, made in the ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ electronic ground state, are $\Delta \nu =13181.375\mathrm{}\left(2\right)\mathrm{}$ Mc/sec, ${\mu }_1\left(\mathrm{uncorr}\right)=+3.517\mathrm{}\left(2\right)\mathrm{}$ nm, and ${}_{}{}^{131}{}_{}{}^{}\Delta _{}^{133}{}_{}{}^{}=-0.45\mathrm{}\left(5\right)\%$. Possible nuclear ground states for ${\mathrm{Cs}}^{131}$ are discussed.

• Received 29 July 1965

DOI:https://doi.org/10.1103/PhysRev.140.B1483