Impact parameter dependence of projectile-electron excitation and loss in relativistic collisions with atomic targets

Abstract

The semiclassical approximation is extended to relativistic collisions of two composite atomic particles. Electron excitation and loss of relativistic ion-projectiles colliding with atomic targets are studied. A general expression is derived for the semiclassical transition amplitude. In the limit of nonrelativistic collision velocities this expression goes over into the known nonrelativistic formula. The main focus of this study is on the projectile-electron excitation, for which numerical calculations have been performed. Our calculations for ultrarelativistic collisions between a heavy single-electron projectile and light atomic targets show the importance of the shielding effects, which reduce transition probabilities at larger impact parameters, and a considerable contribution from the antiscreening mode in collisions with few-electron atoms. Further, the antiscreening probabilities are shown to extend to much larger impact parameters than do the screening probabilities. An enhancement in probabilities for the dipole-allowed transitions and a reduction of the probabilities for transitions to the 2s state are found compared with relativistic collisions at low . For electronic cross sections the semiclassical treatment is shown to be equivalent to the plane-wave Born approximation.