COULOMB AND NUCLEAR EFFECTS IN THE FRAGMENTATION OF EXOTIC NUCLEI

The role of the nuclear and the Coulomb interactions in the dissociati on of the neutron-rich exotic nuclei Li-11, Be-11 and Be-14 incident o n a number of targets has been studied. The two-neutron removal cross sections of Li-11 and Be-14 and one-neutron removal cross section of B e-11 have been calculated. The theory of diffraction dissociation and diffraction stripping has been used to account for the nuclear effects . The Coulomb-dissociation cross sections have been calculated within the framework of a direct fragmentation model formulated earlier. The Coulomb dissociation along with the nuclear cross sections explain sat isfactorily the target-mass dependence of the experimental total two-n eutron removal cross sections of Li-11 and Be-14 around 30 MeV/A incid ent energy. The beam-energy dependence of this cross section is also w ell reproduced. The stripping contributions dominate the nuclear cross sections. The dependence of the reaction mechanism underlying the two -neutron removal process on the separation energy of the two-neutron s ystem in the projectile is discussed. The role of the ''post-accelerat ion effect'' on the energy spectra of the produced fragments is invest igated.