THRESHOLDS OF NON-RUTHERFORD NUCLEAR CROSS-SECTIONS FOR ION-BEAM ANALYSIS

A theoretical model of classical scattering in the presence of combined Coulomb and weakly perturbing nuclear fields predicts the incident ion energies at which elastic backscattering cross sections begin to deviate from their Rutherford values [M. Bozoian et al., Nucl. Instr. and Meth. B51 (1990) 311]. The model, parameterized with two nuclear constants, is in good agreement with experimental data for proton and helium-ion beams. This classical model was revised by including the nature of the Z = 1 and 2 projectiles. In this paper the revised model is applied to Z = 3 projectiles. Although little backscattering data exists, there is consistency among the optical model calculations of departures from Rutherford backscattering for the lithium-target systems considered. The revised model is in good agreement with these calculations. New experimental results for Li-6 and Li-7 ion beams compared with the revised model are presented at this conference [K.M. Hubbard et al., Bull. Am. Phys. Soc. 35 (1990) 1785].