Inner-shell-electron capture byH+,He2+, andLi3+projectiles from CH4, Ne, and Ar

Abstract

The authors have measured cross sections for the capture of $K$-shell electrons from Ne and C (in C${\mathrm{H}}_{4}$) by ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{2+}$, and ${\mathrm{Li}}^{3+}$ projectiles, and of $L$-shell electrons from Ar by ${\mathrm{H}}^{+}$ in an energy range from 0.4 to 3 MeV/amu. Detection of $K$- or $L$-Auger electrons from the target in coincidence with charge-changing projectiles was used to obtain the ratio of capture to total vacancy-production cross sections from the inner shell of interest. This ratio was found to become as high as 43% for the case of ${\mathrm{He}}^{2+}$ on C${\mathrm{H}}_{4}$, giving direct evidence that inner-shell capture becomes an important inner-shell vacancy-production mechanism as one approaches symmetric collisions. Independent measurements of total inner-shell vacancy production were performed, allowing the capture cross sections to be deduced. The capture cross sections increase slightly less rapidly with projectile charge than would be expected on the basis of first-order perturbation-theory Oppenheimer-Brinkman-Kramers (OBK) scaling rules, while scaling from one target shell or nuclear charge to another shell seems better described by these rules at high velocity. Breakdown of the OBK scaling rules occurs at low velocities. A comparison of experimental cross sections with various theoretical results is presented and discussed.