Cross sections for 170° backscattering of 4He from oxygen, aluminum and argon for 4He energies between 1.8 and 5.0 MeV
Cross sections for 170° backscattering of 4He ions incident on oxygen, aluminum and argon target atoms at energies in the range 1.8 to 5.0 MeV have been measured using 4He beams from a 6 MV Van de Graaff. The targets were thin (850, 1950 Å) films of Ar-sputtered Al 2O 3 (on C substrates) which incorporated up to 6% Ar. Cross sections at a particular energy were determined by comparing the measured apparent thicknesses (in atoms/cm 2) of O, Al and Ar in the film at the particular energy with those measured for 4He energy near 2 MeV (where the cross sections were assumed to be Rutherford). The cross sections were measured at maxium intervals of 50 keV, with uncertainties of ± 4%. The cross section for HeAr is nearly Rutherford over the entire range, that for HeAl shows small deviations from Rutherford above 4.2 MeV, while that for HeO is strongly non-Rutherford above 2.4 MeV. Results are presented in graphical and tabular form.