On the angular dependence of L x-ray production cross sections following photoionisation at an energy of 59.54 keV

The anisotropy of L x-ray fluorescence induced by 59.54 keV unpolarized photons is investigated by means of an experimental procedure which allows the relative L x-ray production cross section to be evaluated without taking account of the angular set-up and the instrumental efficiency. Thick targets of Yb, Hf, Ta, W and Pb are considered, and the angular trend of the relative experimental ratios, ILα/ILβ, is calculated by simple evaluations of the peak area alone. Within the experimental uncertainties, which are found to be of the order of 1.6% in the worst cases, the results do not show any significant angular dependence of the Lα emission lines if the isotropy of the Lβ lines is assumed. This fact contrasts with the results of some groups, which report evidence of strong angular dependence at this level of photon energy.