NON-RUTHERFORD HE-4 CROSS-SECTIONS FOR ION-BEAM ANALYSIS

Increasing use of He-4 analysis beams with energies between 2 and 10 MeV for depth profiling and backscattering analysis of thin films and near-surface materials requires accurate measured values of non-Rutherford cross sections for scattering of He-4 by the lighter elements. Cross sections for scattering of He-4 through large angles deviate from Rutherford at He-4 laboratory energy approximately 2.2 MeV for target nuclei C-12 and O-16; deviations for target atomic numbers Z = 20 and 40 occur at He-4 energies of about 5 and 10 MeV, respectively. We review the experimental cross section data currently available for large angle scattering of He-4 from the light elements (4 less-than-or-equal-to Z less-than-or-equal-to 20) for incident He-4 laboratory energies 1.5-10 MeV. For each target element, we indicate energy regions with smooth cross section variation suitable for use for simple backscattering anaysis as well as strong narrow resonances that may be used for depth profiling light elements in heavy-element matrices.