Projectile fragmentation reactions and production of nuclei near the neutron drip line

The reaction mechanism of projectile fragmentation at intermediate energies has been investigated by observing the target dependence of the production cross sections of very neutron rich nuclei. Measurement of longitudinal momentum distributions of projectile-like fragments in a broad range of fragment mass and charge was performed using a 100 MeV/nucleon Ar40 beam incident on Be and Ta targets. By measurement of the fragment momentum distribution, a parabolic mass dependence of the momentum peak shift was observed in the results of both targets, and light-fragment acceleration was found only in the Be-target data. The analysis of production cross sections revealed an obvious enhancement of the target dependence except for a target size effect when the neutron excess is increased. This result implies the breakdown of factorization of production cross sections for very neutron rich nuclei near the drip line.