Stopping cross sections for helium and hydrogen in ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, and ${\mathrm{H}}_2$S (0.3-2.5 MeV)

Ion backscattering has been developed recently as a microanalytical technique for depth microscopy and mass analysis in solids. To establish an absolute depth scale in such studies, the energy loss rate of the ion in the constituents of the solid must be accurately measured. Hydrogen, nitrogen, oxygen, and sulphur are often important components of thin solid films; therefore, it is of interest to measure the stopping cross sections of ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, and ${\mathrm{H}}_2$S. A new technique has been developed to accomplish the measurement of the stopping cross sections of high-energy ions (>300 keV) in gases. The technique minimized end-effect problems by passing the ions through a long gas cell and eliminates count-rate difficulties by detecting these ions after they have scattered from a thin Au film. This technique has been used to obtain stopping cross sections for 0.3-2.5-MeV protons and He ions in ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, and ${\mathrm{H}}_2$S to an uncertainty of less than ±2%. The first stopping cross sections for S are derived by means of Bragg's rule and found to be appreciably greater than currently available theoretical or empirical values.