Atomic collisions with relativistic heavy ions. III. Electron capture

Cross sections for the electron capture by 82- , 140- , and 200-MeV/amu ${\mathrm{Xe}}^{54+}$, ${\mathrm{Xe}}^{53+}$, and ${\mathrm{Xe}}^{52+}$ ions incident on thin solid targets from Be to Au were measured. The measurements are compared with calculations of radiative and nonradiative capture. The nonradiative capture calculations are based on the relativistic eikonal approximation which includes transitions from K, L, and M shells of the target to nearly all projectile shells. In high-Z targets, nonradiative capture into excited states of the projectile is dominant, as predicted by the eikonal calculations and confirmed by comparing measured cross sections for bare ${\mathrm{Xe}}^{54+}$ and ${\mathrm{Xe}}^{52+}$ (1$s^2$) projectiles. A simple formula for estimating nonradiative-electron-capture cross sections for relativistic-ion accelerator design and other applications is derived. Double and triple electron capture are also observed in the low-velocity, high-Z collisions.