L-shell ionization probabilities for near-central collisions of MeV protons with low-Z atoms

摘要

High resolution K _ alpah X-ray spectra of Ca, Cr and Fe induced by 0.7-1.5 MeV protons and of Ti induced by 0.7-4 MeV protons were measured by a flat crystal spectrometer. The experiment was mainly performed at the J. Stefan Institute. STi spectra induced by 2, 3 and 4 MeV protons were measured at the Ruder Boskovic Institute in Zagreb. From the relative yiekds of the KL~1 satellites, which are the result of multiple inner-shell ionization, the average L-shell ionization probabilities in near-central collisions were determined. The effects of the rearrangement of the inner-shell holes prior to the K X-ray emission and the changes of the fluorescence yields due to the multiple ionization were taken into account in the evaluation of the ionization probabilities. It was shown that the rearrangement of the L-shell holes significantly changes the initial inner-shell holes distribution. The change of the K-shell fluorescence yield due to additional L shell hole was estimated to be negligible. The inner shell ionization induced by proton collisons with light atoms is mainly results of the direct Coulomb interaction between the inner shell electron and the moving projectile. The direct Coulomb ionization probabilities in the near-central collisions were determined from the relative yields of the KL~1 satellites after subtracting the shake contribution. The values obtained were compared with semiclassical approximation chalculations exploiting relativistic hydrogenic and Hartree-Fock wave functions. The importance of a realistic atomic description using Hartree-Fock wave functions was demonstrated.