  The reaction mechanism of projectile fragmentation at intermediate energies
has been investigated observing the target dependence of the production cross
sections of very neutron-rich nuclei. Measurement of longitudinal momentum
distributions of projectile-like fragments within a wide range of fragment mass
and its charge was performed using a hundred-MeV/n $^{40}$Ar beam incident on
Be and Ta targets. By measurement of fragment momentum distribution, a
parabolic mass dependence of momentum peak shift was observed in the results of
both targets, and a phenomenon of 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 target size effect when the
neutron excess is increased. This result implies the breakdown of factorization
(BOF) of production cross sections for very neutron-rich nuclei near the drip
line.
