Contribution from close and distant collisions toK-shell excitation in Ge measured using the channeling technique for relativistic protons,π+, andAuthor(s) - J. F. Bak, G. Melchart, E. Uggerhøj, J.S. Forster, Per Jensen, H. Madsbøll, S. P. Møller, G. Petersen, H. E. Schiøtt, R. Regall, P. Siffert

For the first time, the impact-parameter dependence for K-shell ionization was measured for relativistic projectiles, although in an indirect way. Experimentally, channeling of GeV projectiles was used to gradually exclude close-encounter processes. In the present experiment, the Lorentz gamma factor varied between approximately 2 and approximately 100; in this region, the contribution from distant collisions becomes increasingly important and amounts to about 50% of the total yield for gamma approximately 100. The experimental data are compared to theoretical calculations of impact-parameter distributions, and the agreement is fair for both positive and negative particles