Magnetic Moment of Helium in ItsS13Metastable State

The ratio of the electronic $g_J$ value of He in its $1s2s$, ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ metastable state to the $g_J$ of H in its ground state has been redetermined by the atomic beam magnetic resonance method using separated oscillating fields. At magnetic fields of about 540 and 575 gauss the transitions $\Delta m=\pm 1, \pm 2$ in He and $(F, m)=(1, 0)\leftrightarrow (1, -1)$ in H are observed at frequencies of approximately 1570 Mc/sec and 1140 Mc/sec, respectively. The natural line shapes for the separated oscillating fields method are obtained with spacings between the oscillating fields of both 4.2 cm and 2.2 cm. The experimental result is ${\frac{g_J(\mathrm{He}, {}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{})}{g_J(\mathrm{H}, {}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{})}|}_{\exp }=1-(23.3\mathrm{}\pm 0.8)\times {10}^{-6\mathrm{}}$, which agrees with an earlier measurement having an accuracy of 16 ppm, and also with the theoretical value ${\frac{g_J(\mathrm{He}, {}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{})}{g_J(\mathrm{H}, {}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{})}|}_{\mathrm{theor}}=1-(23.3\mathrm{}\pm 1.0)\times {10}^{-6\mathrm{}}$ obtained by Perl and Hughes, which was computed from the Breit equation for He with the addition of a term to represent the interaction of the anomalous spin magnetic moment of each electron with the external magnetic field.