Rescattering effects and the validity of the sequential-decay model

A steady-state point of view is used to examine the conditions under which rescattering corrections to the sequential-decay model are important in considering direct reactions to unbound states. Expressions are derived which can give semiquantitative estimates of the size of these effects. A qualitative interpretation is provided for the factors which enter these expressions, and they are evaluated for two specific cases, one where the rescattering effects are expected to be large, and one where they are expected to be small.