Magnetic-Field Dependence of Polarized Helium Light Excited by Electrons

The polarization of light resulting from the excitation of helium atoms by an electron beam has been measured as a function of magnetic field parallel to the electron beam. Results are presented which show that the polarization of the radiation arising from the diffuse singlet transitions in helium is magnetic-field dependent. The polarization of the radiation of the diffuse triplets is not field dependent. Since the magnetic field (parallel to the direction of the electron beam) cannot lead to a reorientation of the atom in its excited state, the polarization of the emitted radiation should not be altered by the magnetic field subsequent to the excitation impact. It would appear, then, that the inelastic scattering of electrons by helium atoms is independent of magnetic field for triplet-state excitation, but dependent for singlet-state excitation.Since theory, as presently developed, predicts that the population probabilities to diffuse singlet and triplet states should depend only on the orbital angular momentum magnetic quantum numbers, one must conclude that the inelastic scattering that is involved is probably more complicated than is usually assumed.