(P,N) REACTION FOR 89 LESS-THAN A LESS-THAN 130 AND AN ANOMALOUS OPTICAL-MODEL POTENTIAL FOR SUB-COULOMB PROTONS

The (p,n) cross sections were measured from about 2.5 to 5.8 MeV with about 100-keV target resolution for natural Pd, Ag, Cd, In, and Te and for Y89, Nb93, Rh103, Pd105,106,108,110, Ag107,109, Cd111,112,113,114,116, and Te125,126,128,130. Systematic uncertainties are about ±2% for Y89, Nb93, and the natural targets and about ±4% for the other nuclei. The isotopic σp,n are fitted by adjustment in the depth WD and diffuseness aD of the surface imaginary part of a proton optical model potential (OMP) that was chosen previously to describe precision (p,n) data for isotopes of Sn. The diffuseness aD is found to be nearly constant, about 0.4 fm, but the depth WD shows a large and systematic A dependence. A study of the parameter space indicates that at least one OMP parameter must have a strong A dependence and that WD is probably the only such single parameter that will suffice. The explanation of this anomaly is currently unclear. NUCLEAR REACTIONS: Pd, Ag, Cd, In, Te, natural targets; and Y89, Nb93, Rh103, Pd105,106,108,110, Ag107,109, Cd111,112,113,114,116, Te125,126,128,130, enriched isotopic targets, E=2.5 to 5.8 MeV, target resolution ∼ 100 keV. Measured σp,n. Deduced optical model parameters. © 1979 The American Physical Society.