K-shell ionization probability in close collisions of 7-12-MeV protons with targets ofZ=24−83

Abstract

K-shell ionization probabilities were measured by the particle--x-ray coincidence technique for 7-MeV protons of 15 to 39 fm impact parameter on 24 targets from Cr to Bi. For 22 of these targets, total K-shell ionization cross sections are also reported. Additional K-shell ionization probabilities were measured for 7-, 10-, and 12-MeV protons on Mo, Cd, and Sn, at impact parameters down to 2 fm. While the total K-shell cross sections closely follow relativistic semiclassical (RSCA) calculations supplemented by minor binding-plus-polarization corrections, significant discrepancies of up to 70% occur for the K-shell ionization probabilities at small impact parameters, particularly for the targets from Cr to Zr. They can be traced back to the use of hydrogenic wave functions in the RSCA calculation, whereas nuclear recoil may account only for a few percent of the discrepancies. The data on both K-shell total cross sections and ionization probabilities exhibit the pattern characteristic for small distortions of the K-electron binding energy by the projectile charge: adiabatic binding for xi/sub K/ 1. The perturbed-stationary-state approximation somewhat underestimates these distortion effects.