Reactive Content of the Proton-Nucleus Impulse-Approximation Dirac Optical Potential

The total reaction cross sections for intermediate-energy proton scattering on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are calculated within the Dirac-eikonal formalism. Comparison with data indicates that the recently proposed impulse-approximation Dirac optical potential for nucleon-nucleon scattering is quite adequate, and accounts for 90% of the measured total reaction cross section.