Linear polarization of the characteristic x-ray lines following inner-shell photoionization of tungsten

The linear polarization of the characteristic lines L alpha(1) (3d(5/2) -> 2p(3/2)) and L alpha(2) (3d(3/2) -> 2p(3/2)), following inner-shell photoionization of neutral tungsten, is analyzed both experimentally and theoretically. In the experiment, a tungsten target is photoionized by the primary emission of an x-ray tube with incident photon energies in the range of 10.2-30 keV. The sigma and pi components of the emitted fluorescence are measured by using a spectropolarimeter, based on x-ray diffraction at Bragg angles close to 45 degrees. The degree of linear polarization of the L alpha(1) and L alpha(2) lines is determined to be +(1.6 +/- 0.5)% and -(7 +/- 2)%, respectively. In addition, this degree of polarization is calculated within the framework of the density-matrix theory as a function of the incident photon energy. These calculations are in good agreement with the experimental results and show only a weak dependence of the degree of polarization on the energy of the incident photoionizing photon.