Systematics of Some Nucleon Transfer Reactions of Complex Nuclei

Nucleon transfer reactions between ${\mathrm{In}}^{115}$ and ${\mathrm{N}}^{14}$ and ${\mathrm{C}}^{12}$ projectiles have been studied at energies up to 10.5 MeV/amu. Radiochemical techniques were used to characterize products resulting from nucleon loss or gain by the target nucleus. Three types of measurements were made: (1) excitation functions; (2) recoil range distributions in the forward direction, by use of stacks of thin catcher foils; (3) average recoil ranges in the forward direction, using thick catcher foils. The recoil measurements provide a clear distinction between transfer and mechanisms involving evaporation from a compound nucleus formed by complete fusion of target and projectile (CFCN). Cross sections are appreciable for transfer of several nucleons, including protons, to the target nucleus. By contrast, reactions in which two protons are lost by the target were not found, although there is considerable probability for loss of as many as five neutrons. A general trend favoring neutron-deficient species is consistent with some secondary neutron evaporation from more highly excited products of primary transfer events. The data indicate that a considerable diversity of transfer reactions occur with appreciable cross section. They thus complement earlier work in which products derived from the projectile were studied. Results are consistent with a concept of grazing reactions in which the Coulomb barrier is penetrated without formation of a compound nucleus by fusion of the raction partners. The energy dependence of the recoil range of single-nucleon transfer products accords closely with a simple quasielastic collision model. Modification of this model to take mass transfer into account can approximate the recoil behavior of multinucleon pickup products. However, a detailed understanding of multinucleon transfer in grazing reactions is still lacking.