Measurements of Angle-Dependent Energy Losses of 5–10 keV Protons in Collisions with CH4, C2H6, and C3H8 Molecules

Abstract

Angle-dependent energy losses of well-collimated 5–10 keV protons scattered in collisions with CH 4 , C 2 H 6 , and C 3 H 8 molecules have been measured. The thickness of the targets is less than 20 mPa·m, which is determined from the measured neutral fraction in the scattered beam and the charge-transfer cross sections reported by another group. The scattered protons have slightly expanded tails of the angular distribution. The measured energy losses increase with the angle. The stopping cross sections, which are obtained by integrating the angle-dependent energy losses over the square of the angle, agree well with the compilation values of SRIM-2006. The stopping cross sections are found to have a non-linear relationship with the size of target molecules. The contribution of a carbon atom attached by two hydrogen atoms of a heavier molecule becomes relatively small. This molecular size effect is enhanced with the decreasing energy of protons. Meanwhile, for protons that are deflected significantly, the ...