Stopping power and energy straggling of protons in graphite and amorphous carbon obtained from a resonance in BS spectra

Backscattering (BS) spectra with a sharp 4.8-MeV resonance for carbon targets have been measured using proton beams in an energy range 4.85-6.1 MeV per 100-keV step. By systematic analyses of the resonance peak profiles, values of stopping power and energy straggling have been deduced for proton energies from 0.8 to 3.4 MeV which corresponds to a penetration depth of 88 μm. In particular, to investigate the difference in stopping power and straggling caused by target inhomogeneity, we used two target materials which were highly oriented pyrolytic graphite (HOPG, 2.26 g/cm³) as a homogeneous material and amorphous carbon (1.73 g/cm³) as an inhomogeneous material. We describe a method of measuring stopping power and straggling using a resonance in the BS spectra. The stopping powers obtained are compared with the values determined by SRIM-2006. Moreover, collision straggling and a density straggling due to the inhomogeneity of the target materials are evaluated from the width broadening of resonance peaks.