Stopping power and energy straggling for swift protons

Calculations and measurements of energy dissipation by protons at energies above ∼ 100 keV are presented. The calculations, which make use of a statistical model of the atom, are based on a refinement of a procedure suggested by Lindhard and Scharff. The theoretical section of the present paper is concerned with energy straggling, as stopping powers were dealt with in an earlier publication. Measurements of stopping power and energy straggling for 100-500-keV protons have been made in various gases, viz. hydrogen, helium, air, neon, argon, and krypton. The stopping-power data are in good agreement with theory and earlier experimental work. For the heavy gases, the experimental straggling values are seen to be an increasing function of energy, as expected from theory. In a more quantitative comparison, however, some discrepancy between theory and experiment is observed.