The Nuclear Magnetic Moment of Caesium from the Polarization of Resonance Radiation

Measurements on the polarization of resonance radiation in a magnetic field have been used to obtain the hyperfine separation constants of the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and $7{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ levels of caesium I. For a nuclear spin of $\frac{7}{2}$ the hyperfine separation constant is 1.42×${10}^{-3\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ level and 4.86×${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for the $7{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ level. From these values the nuclear magnetic moment is calculated as $\frac{2.40}{1840}$ and $\frac{2.41}{1840}$ Bohr magnetons, respectively. These agree well with the value $\frac{2.52}{1840}$ obtained from the splitting of the lower $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ level. The theoretical and experimental curves for the polarization as a function of the magnetic field agree within experimental error when the shape of the exciting line in the source is taken into account.