Increased energy losses in off-beam directions for MeV protons traversing thin films

This article reports on a negative attempt to understand the experimental data of Ishiwari et al. (Phys. Rev. A25 (1982) 2524) on the angle-dependent energy-loss of MeV protons traversing thin films. They observed an increasing energy-loss with increasing exit angle, and an apparent saturation at large angles. The explanation proposed by Ishiwari et al., as a small angle multiple scattering process which reduces the effective impact parameters in the ion-atom interaction, is investigated. The predictions of multiple scattering theory, with a reasonable impact-parameter dependent inelastic energy loss function, are shown to be at least a factor of three below the reported experimental values.