  A microscopic calculation of the reaction cross-section for nucleon-nucleus
scattering has been performed by explicitly coupling the elastic channel to all
particle-hole (p-h) excitation states in the target and to all one-nucleon
pickup channels. The p-h states may be regarded as doorway states through which
the flux flows to more complicated configurations, and subsequently to
long-lived compound nucleus resonances. Target excitations for 40,48Ca, 58Ni,
90Zr and 144Sm were described in a QRPA framework using a Skyrme functional.
Reaction cross sections calculated in this approach were compared to
predictions of a fitted optical potential and to experimental data, reaching
very good agreement. Couplings between inelastic states were found to be
negligible, while the couplings to pickup channels contribute significantly.
For the first time observed reaction cross-sections are completely accounted
for by explicit channel coupling, for incident energies between 10 and 40 MeV.
