Mass and charge distributions of Cl-induced heavy-ion reactions.

Abstract

Projectilelike fragments were detected and characterized in terms of A, Z, and energy for the reactions $^{37}\mathrm{Cl}$ on $^{40}\mathrm{Ca}$ and $^{209}\mathrm{Bi}$ at E=7.3 MeV/nucleon, and $^{35}\mathrm{Cl}$ on $^{209}\mathrm{Bi}$ at E=15 MeV/nucleon, at angles close to the grazing angle. Mass and charge distributions were generated in the N-Z plane as a function of energy loss, and parametrized in terms of their centroids, variances, and coefficients of correlation. The results are compared to the predictions of two current models based on a stochastic nucleon exchange mechanism. The drifts of the charge and mass centroids for the system $^{37}\mathrm{Cl}$ on $^{40}\mathrm{Ca}$ are consistent with a process of mass and charge equilibration mediated by nucleon exchange between the two partners, followed by evaporation. The asymmetric systems show a strong drift toward larger asymmetry, with the production of neutron-rich nuclei. It is concluded that this is the result of a net transfer of protons from the light to the heavy partner, and a net flow of neutrons in the opposite direction. Model predictions fail to reproduce in detail the evolution of the centroids for asymmetric systems. The variances for all systems increase with energy loss, as would be expected from a nucleon exchange mechanism. However, the variances for the reaction $^{37}\mathrm{Cl}$ on $^{40}\mathrm{Ca}$ are higher than those expected from that mechanism, and the variances for the reaction $^{35}\mathrm{Cl}$ on $^{209}\mathrm{Bi}$ start decreasing after about 100 MeV of energy loss. The coefficients of correlation indicate that the transfer of nucleons between projectile and target is correlated, as expected from Q-value constraints to the valley of \ensuremath{\beta} stability.