Centrality dependence of isospin effect signatures in Sn124+64Ni and Sn112+Ni58 reactions

Signatures of isospin effects were investigated for neutron-rich (Sn124+Ni64) and neutron-poor (Sn112+Ni58) systems at 35 MeV/nucleon for noncentral collisions. The centrality dependence of these signatures was tested for several impact parameter estimators. Our main observations are (i) the yields of H1 and He3 particles in the neutron-poor system are strongly enhanced with respect to the neutron-rich system, and the yields of H3, He6, and Li7,8 are suppressed at all impact parameters, (ii) the yields of H2, He4, and Li6 particles are almost the same for both systems, (iii) the N/Z ratio of intermediate mass fragments is correlated with the neutron richness of the system and is weakly dependent on the centrality of the collision, and (iv) the neutron richness of the detected fragments increases strongly with decreasing rapidity in the range from that of the projectile-like fragment to the c.m. region. The gross features of experimental data are reproduced by quantum molecular dynamics model calculations. A comparison between model calculations and the data indicates that the fragments produced in the c.m. regions are weakly excited.