Energy loss and energy straggling of light ions in fullerite

To determinate the stopping cross section in fullerite a feasible approach, taking into account the high radiation sensitivity and mechanical Fragilit y of Fullerite films, should be employed. In this work, the stopping cross sections of H-1, H-3, He-4 and Li-7 ions for several selected energies were measured by Rutherford backscattering, neutron depth profiling and alpha s pectroscopy using sandwich structures of samples composed of fullerite depo sited on a firm substrate (Si, steel) with an intermediate marker (Au, N, L i, B, Pu). In addition, ion transmission through a thin C film supporting a fullerite layer was also utilized. The measured stopping cross sections fo llow the theoretical predictions calculated for carbon, but are systematica lly (10-35%) higher than the theoretical ones (with the exception of 5 - 5. 5 MeV He-4). The observed deviation of the experimental data can partly be explained by the chemical state effects in fullerite, which accounts for ab out 20-50% of the difference. The measured energy straggling exceeds Bohr's value by a Factor of about 2 for alpha spectroscopy and ion transmission, and 2.5 or 9.5 for Rutherford backscattering and neutron depth profiling, r espectively. The discrepancy can be explained by a thickness variation, suc h as surface roughness of the fullerite films.