Elastic and Inelastic Scattering of 13- to 19-MeV Protons byO16

Abstract

Closely spaced differential cross sections have been obtained for elastic and inelastic scattering of protons by ${\mathrm{O}}^{16}$ ($0>~Q>~-8.88\mathrm{}$ MeV). At laboratory angles of 80, 100, 120, 140, and 160°, continuous elastic excitation curves over the energy range from 13 to 19 MeV were obtained by a thick-target technique. For proton energies between 14.8 and 19.2 MeV, additional measurements with about 200-keV energy resolution were made by conventional thin-target techniques. Numerical values of cross sections for elastic and inelastic scattering are presented for the angular range from 15 to 160° at typically 10° angular and 200-keV energy intervals. Differential cross sections often change by a factor of 2 within 200-500 keV for large as well as small angles. The largest resonance is found at 14.9 MeV, but fluctuations at the upper end of the energy scale (≈ 19 MeV), particularly for inelastic scattering, are not significantly smaller. Some, but not all of these strong fluctuations occur slightly above the five reaction thresholds ($p, 2p$), ($p, d$), ($p$, ${\mathrm{He}}^3$), ($p, \mathrm{pn}$), ($p, n$) in the 12-to 19-MeV region. Previously, nine of the elastic angular distributions reported here had been made available for analysis by the use of an optical-model search code. Fits to within 10% were obtained, but the optical-model parameters for good fits showed strong energy dependence. It is suggested that simple potential scattering provides an insufficient explanation for ${\mathrm{O}}^{16}(p, p){\mathrm{O}}^{16}$ for the energy region investigated. The interference of potential scattering with compound nuclear scattering is discussed and shown to be very noticeable, even for 200-keV energy resolution. Data and analysis emphasize the need for a theoretical approach to scattering which takes explicit account of easily formed states in light nuclei.