Variation of peak energy for energy loss with angle of observation

The energy loss for protons on Al, Cu, and Ag thin foils around the maximum of the stopping have been measured at two different exit angles. The bombardment energy $E_{\max }$ where such a maximum occurs is found to depend on the angle of observation, $E_{\max }$ being greater when the detector is positioned off beam than when measured downstream in the beam direction. These results are discussed in terms of a varying participation of different electrons in the target. The effect of foil inhomogeneities on $E_{\max }$ is also evaluated.