Incident-energy dependence of the fragmentation mechanism reflecting the clustering structure of the 19B nucleus

We investigate how clustering structure of neutron drip-line nucleus 19B is reflected in heavy-ion reactions. We compare 19B fragmentation in 19B+14N reactions with 13B fragmentation in 13B+14N reactions calculated by antisymmetrized molecular dynamics, where 19B has a well developed cluster structure in its ground state while 13B has no clustering features in its structure. The clustering structure of the 19B nucleus is reflected in its fragmentation as the simultaneous breakup of 19B into He and Li isotopes, and we investigate the dependence of this cluster breakup of the 19B nucleus on incident energy. We find that the most adequate incident energy for verification of the clustering structure of the 19B nucleus by the use of the coincident experiment between He and Li isotopes is around 30 MeV/nucleon. This incident-energy dependence can be explained in terms of the competition between the mean-field effect and nucleon-nucleon collision processes. The mean-field effect causes the cluster breakup of the 19B nucleus, while nucleon-nucleon collision processes work to destroy constituent clusters of the 19B nucleus. We also investigate the influence of the neutron-rich property of the 19B nucleus. (author)