A number of isotopically enriched light targets were bombarded with ${\mathrm{O}}^{16}$ ions of 36- to 48- MeV energy (lab), and ten elastic angular distributions were measured. All cross sections show strongly destructive interference of nuclear and Coulomb scattering at angles above 30 to 60° c.m., and fall orders of magnitude below the Coulomb cross section. The data were fitted reasonably well with conventional optical-model calculations, and $〈{\chi }^2〉$ values between 0.5 and 5.2 could be obtained for all targets. Typically, four-parameter fits were adequate. For the heavier targets the parameter sets are not unique, but were found to have continuous well-depth—geometry ambiguities, which were investigated in some detail. A procedure to produce in situ clean targets of highly reactive elements is described.

• Received 28 September 1970

DOI:https://doi.org/10.1103/PhysRevC.3.430