Alignment of L3 subshell vacancy states in Au, Bi, Th and U following photoionisation and effect of external magnetic field

Alignment of the L3 (J=3/2) subshell vacancy states in the Au, Bi, Th and U elements following photoionisation have been investigated through angular distribution measurements of subsequently emitted L3 subshell X-rays. The 59.54 keV unpolarized γ-rays from the 241Am radioactive point-source were used to ionize the target and the subsequently emitted L X-rays were measured using an HPGe detector. The improved experimental procedure along with correct evaluation scheme permits straight-forward method for investigating anisotropy in photo-excited L X-ray emission. The efficiency of the detector and the absorption correction for the emitted L X-rays in the target remain fairly constant as the target-detector assemblage remains undisturbed in the present measurements at various angles. Isotropically emitted L1 subshell (J=1/2) X-rays measured simultaneously were used to normalize the L X-ray spectra taken at different emission angles. The present measurements clearly support small theoretical predicted values of the alignment parameter; however, it is difficult to infer regarding the predicted anisotropic trends. The angular distribution measurements for the L3 subshell X-ray emission were also performed by placing the target in magnetic field ∼ 0.6 T. The earlier reported large anisotropy in angular distribution of the emitted L3 subshell X-rays and significant effect of external magnetic field on the angular distribution are ruled out. (authors)