Time scale of breakup of the halo nucleus Be-11

We investigate the post-acceleration of the Be-10 fragment in the Coulomb b reakup reaction of the halo nucleus Be-11, assuming that the excitation of the projectile is to states in the low-energy continuum. The method used re tains all finite-range effects associated with the interactions between the breakup fragments and can use realistic wave functions for the halo nuclei . We apply the method to compute the average momenta of the Be-10 fragment at four different scattering angles following breakup of Be-11 on a Au targ et at 42 MeV/nucleon beam energy. Our results, which are in qualitative agr eement with recent precision experimental data, are consistent with the pic ture of no post-acceleration effect. The implication is that the breakup ta kes place on a time-scale long compared to the collision time. [S0556-2813( 99)04204-1].