We propose to measure the angular distribution of L x rays obtained by impact of electrons with energies of 10 to 100 keV, produced by the injector of the Microtron accelerator in elements of varied atomic number. If this distribution is found to be anisotropic, we will determine the degree of alignment of ions with a precision of about 10%. We plan to perform measurements for targets with varying thicknesses, in order to understand better the competing processes that affect the measurements. Some theories predict alignment when the total angular momentum J of the vacancy is larger than 1/2 while others conclude that the angular distribution is isotropic, regardless of the J value. The experimental data found in the literature refer mostly to the alignment by impact of protons or photoionization, are scarce and discrepant: while some authors found a strong anisotropy in the angular distribution parameter and high alignment, others observed an isotropic angular distribution. Although the alignment and orientation of atomic shells in the excitation of outer-shell electrons by electron impact is a well-studied and well-known phenomenon, the alignment by ionization has not yet been conclusively observed. A quantitative explanation of this phenomenon, or its absence, and the resulting angular distribution of the emission of x rays constitute a particularly sensitive test of the atomic structure model.
News published in Agência FAPESP Newsletter about the scholarship: