Differential-cross-section and polarization measurements are presented for the elastic scattering of 9.8-MeV protons by ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$. In general, the angular range 17-160° was covered with an accuracy of ±2% for the cross section and ±0.02 for the polarization measurements. The data are analyzed using an optical model in three ways: (1) using individual data sets for each element and either a seven- or a nineparameter model; (2) using all the data simultaneously and a "global" search routine; (3) using individual data sets and the folding version of G. W. Greenlees, G. J. Pyle, and Y. C. Tang. The analysis using procedure (1) suggests the model is overparameterized at 9.8 MeV. These difficulties are overcome to some extent using procedures (2) and (3).

The most surprising result of the analysis is the insensitivity of the fitting to the choice of spin-orbit parameters at this energy even though relatively accurate and extensive polarization data are available. Thus, in the global analysis, spin-orbit radius parameters anywhere in the range 0.7 to 1.2 F give ${\chi }^2$ values within 5% of the optimum. The analysis using the folding version of the model indicates that additional effects are present in the interaction which are not included in the description.

• Received 20 November 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1231