Anomalous Optical-Model Potential for Sub-Coulomb Protons for89<A<130

The ($p, n$) cross sections for fourteen nuclei from $A=89\mathrm{}$ to $A=130\mathrm{}$ were measured from about 2.5 to 5.8 MeV in order to obtain total reaction cross sections. These cross sections disagree with optical-model predictions in that the predicted $3p$ resonance is missing near $A=105\mathrm{}$ and the peak near $A=90\mathrm{}$ is replaced by a valley. The data can be described by introducing an anomalous $A$ dependence into the depth of the absorptive potential.