Geometrical effect on the measurement of stopping power: Angle-dependent energy loss of 7-MeV protons in metallic and organic thin foils

Abstract

Energy losses of 7-MeV protons in metallic and organic thin foils have been obtained as a function of emergence angles. Angular distributions due to multiple scattering have been also measured. The energy loss is found to increase for all targets with increasing emergence angles. The increase of the energy loss cannot be explained by the following three effects: (1) the increase of the target thickness caused by the deflection of the particle, (2) the increase of the path length due to multiple scattering with atomic nuclei, and (3) the energy transfer to the recoil nuclei during the multiple-scattering process. From this consideration, the observed increase of the energy loss with increasing emergence angle is concluded to be due to a hitherto unknown effect. This effect is very likely the dependence of the energy loss on the average impact parameter with the atomic nucleus.