High-resolution study of ion-inducedKα1,2x-ray spectra from high-Zelements

Abstract

The $K{\ensuremath{\alpha}}_{1,2}$ x rays emitted from La, Tb, Ta, and U targets induced by proton nitrogen, and neon ion bombardment at incident energies between 15 and 28 MeV/nucleon have been measured with a high-resolution crystal spectrometer. The spectra reflect the decay of a K vacancy in the presence of multiple L, M, N,\dots{} shell ``spectator'' vacancies. The L-shell ionization probabilities for impact parameters in the interior of the target's K shell are extracted from the measured spectra and compared with extensive theoretical calculations of ionization probabilities, based on the semiclassical separate-atom perturbation theory [semiclassical approximation (SCA)]. The projectile velocity varies from 60% to 125% of the target L electron velocity, so we can compare experimental data with theoretical predictions as a function of the relative velocity. We find that wave-function effects play an important role for an accurate calculation of the ionization probability. The experimental results agree well with the SCA predictions when Hartree-Fock-type wave functions are used [variationally determined optimized potential (SCA-OPM)]. Relativistic hydrogenic wave functions (SCA-HYD) provide a reliable description of experimental data only in the case of the uranium target. The influence of electron capture and intrashell coupling is also calculated and discussed. An independent comparison of theoretical constructed spectra with the experimental ones confirms the validity of the SCA-OPM. The hole-hole angular momentum coupling between ``active'' and ``spectator'' holes has been observed as predicted.