We generalize the Goldhaber momentum-dispersion formula to the case of a ‘‘two-fluid’’ nucleus, in which the nucleons of one fluid have a different mean square momentum from those of the other fluid. The model predicts that fragments originated from the core of neutron-rich nuclei have a transverse momentum width which is significantly larger than that of a weakly bound ‘‘halo’’ neutron, and that both are much smaller than the ∼100 MeV/c widths observed in the fragmentation of less exotic nuclei.

• Received 17 May 1993

DOI:https://doi.org/10.1103/PhysRevC.48.2534