  A microscopic calculation of reaction cross sections for nucleon-nucleus
scattering has been performed by explicitly coupling the elastic channel to all
particle-hole excitations in the target and one-nucleon pickup channels. The
particle-hole 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 $^{40,48}$Ca, $^{58}$Ni,
$^{90}$Zr and $^{144}$Sm were described in a random-phase framework using a
Skyrme functional. Reaction cross sections obtained agree very well with
experimental data and predictions of a state-of-the-art fitted optical
potential. Couplings between inelastic states were found to be negligible,
while the pickup channels contribute significantly. The effect of resonances
from higher-order channels was assessed. Elastic angular distributions were
also calculated within the same method, achieving good agreement with
experimental data. For the first time observed absorptions are completely
accounted for by explicit channel coupling, for incident energies between 10
and 70 MeV, with consistent angular distribution results.
