Validity of spectator core model in neutron knock-out reactions

A few-body model for stripping reactions based on the Glauber approach is presented, which goes beyond the usual spectator core' assumption. The model, which is applied to the one-neutron knockout reactions (Be-12,Be-11) and (C-16,C-15), assumes an incident three-body projectile (core-2n) with an outgoing two-body subsystem (core+n) and includes off-diagonal elements in the transition matrix for the surviving fragment which couple different single particle states. Corrections of less that 10% to the stripping cross sections are found when these dynamical effects are included, implying that the spectator assumption is valid even when the spectator is itself a lossely-bound composite system.