Abstract
Energy spectra of keV ions interacting with self-supporting foils of Au and W were recorded with a Time-of-Flight Medium-Energy Ion Scattering system in different backscattering and transmission geometries in an otherwise identical experimental setup. For He ions transmitted through Au spectra of detected particles depending on geometry show two distinct components, i.e. different energy loss distributions in the film, whereas for protons no such phenomenon was observed. The two components in the spectrum of transmitted He could be attributed to impact parameter dependent energy loss, being more prominent for He than for protons. The main origin of the necessary impact parameter selection along different trajectories is expected to be texture in the Au-foils. Electronic stopping powers obtained from both, most probable energy loss in transmission and best fits to spectrum width in backscattering are in agreement within experimental uncertainties. This observation applied for all investigated combinations of projectile and target material.
Highlights
Energetic ions moving in matter lose energy due to interaction with both electrons and nuclei of the target material
The results suggest that the two components in the spectrum of transmitted He ions could be attributed to impact parameter dependent energy loss, being more prominent for He ions than for protons
Electronic energy loss can be deduced from the width of the metal signal
Summary
Energetic ions moving in matter lose energy due to interaction with both electrons and nuclei of the target material. With n being the atomic density of the target material, b the impact parameter, T(b) the impact parameter dependent energy transfer in a single collision and dσ the corresponding differential scattering cross section. For a particle to be detected in backscattering geometry, at least one large-angle scattering event, i.e. small impact parameter, is necessary. This significant difference in the impact parameters probed along the trajectory of the projectile can in principle yield differences in the energy loss [2,3,4]
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