Production of neutron-rich fragments with neutron number N > N-projectile in the reaction Ca-48 (60 MeV/nucleon) plus Ta

The goal of the present paper is to attempt to clarify the nuclear reaction mechanism leading to the production of fragments at zero degree with neutron number larger than that in the Ca-48 projectile, at about 60 MeV per nucleon. The production cross sections of the extremely neutron-rich Si and P isotopes were measured. Concerning the nuclear reaction mechanism leading to the production of these isotopes, one should probably refer to a particular type of transfer mechanism, which results in low excitation energy for the fragments, rather than to the 'genuine' fragmentation mechanism. An upper limit of about 0.05 pb was estimated for the production cross section for the P-47 isotope for which no count was observed.