Probabilities For L-Shell Ionization In Intermediate-Velocity Collisions Of Medium-Mass Elements With He-4(2+) Ions

The K alpha and K beta x ray spectra of zirconium, molybdenum, palladium, and praseodymium bombarded by 28-, 40-, 65-, and 100-MeV He-4(2+) ions were measured with a high-resolution transmission curved crystal spectrometer. The K alpha L(1) and K beta L(1) satellite lines were observed and resolved from the parent diagram lines. The deduced satellite energy shifts are very well reproduced by multiconfiguration Dirac-Fock calculations. The experimental average L-shell ionization probabilities for nearly central collisions were obtained from the measured relative yields of the satellites. They are compared with theoretical predictions from the semiclassical independent particle approximation using hydrogenic wavefunctions (SCA-HWF) or Dirac-Hartree-Fock wave functions (SCA-DHF) and with n-body classical trajectory Monte Carlo (CTMC) calculations. A satisfactory agreement is obtained between the experimental probabilities and the SCA-DHF predictions. The variation of the probabilities in function of the projectile reduced velocity is also well reproduced by CTMC calculations although the predictions are in general smaller than the values deduced from our experiment. The same holds for the SCA-HWF calculations for which, in addition, an increasing discrepancy with the projectile reduced velocity is observed.