Energy dependence of isovector and isoscalar1+excitations in28Si(p,p’) between 200 and 400 MeV

Forward-angle cross sections for $1^{+}$, T=1 and $1^{+}$, T=0 states in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ excited by the (p,p’) reaction have been measured to determine the energy dependence of important pieces of the effective nucleon-nucleus interaction. The isovector spin-transfer transitions depend on energy as expected from distorted-wave impulse approximation calculations based on the dominant $V_{\sigma \tau }$ part of the Franey-Love interaction. The parts of this interaction responsible for exciting the 9.5 MeV isosca- lar spin-flip transition predict a weaker energy dependence than is observed experimentally. The summed Gamow-Teller strength for isovector transitions below 14.5 MeV is found to be (0.89±0.09) times the result of large-scale shell model calculations.