The Magnetic Moment of the Helium Atom in the Metastable Triplet State

The atomic beam magnetic resonance method has been used to measure the ratio of the g value of the two-electron system in helium in the metastable $1s2s$, ³S₁ state to the g value of the one-electron system in atomic hydrogen in the ground $1s$, ²S1/2 state. The metastable helium and the atomic hydrogen were alternately produced in a dc discharge tube. The helium beam was detected by measurement of the current of electrons ejected when the metastable atoms strike a wolfram wire. The hydrogen beam was detected by a Pirani gauge.The resonance frequencies for the transitions m=±1↔0 of helium and F, m=1, 0↔1, -1 of hydrogen were measured in the same magnetic field. Field values near 520 and 567 gauss were used. By the use of the Breit-Rabi formula for the hydrogen transition frequency, these measurements may be combined with experimental values for gₚgJ(H, ²S1/2) and Δν (hydrogen) to give the result gJ(He, ³S₁)gJ(H, ²S1/2)=1-(11±16)×10^-6. This result may be combined with the experimental value gJ(H, ²S1/2)ₑₓₚ=2(1.001128±12×10^-6) to give gJ(He, ³S₁)=2(1.001117±20×10^-6) or with the theoretical value gJ(H, ²S1/2)ₜₕₑₒᵣₑₜ=2(1.0011276) to give gJ(He, ³S₁)=2(1.001117±16×10^-6).These results are in good agreement with the theoretical values, [gJ(He, ³S₁)gJ(H, ²S1/2)]ₜₕₑₒᵣₑₜ=1-23×10^-6 gJ(He, ³S₁)ₜₕₑₒᵣₑₜ=2(1.001104), calculated to order α² by Perl and Hughes in the accompanying paper. This agreement tends to substantiate the arithmetic additivity of the anomalous magnetic moments of the two electrons and the nonradiative relativistic bound-state correction to the magnetic moment for the two electrons in helium. The mutual radiative correction arising from the Breit interaction is small compared with the experimental uncertainty.