Reaction mechanisms of the O-16 + Cu-65 system

Abstract

We have measured a precise quasielastic excitation function for the 16O + 65Cu system, at θLAB = 161◦, and at bombarding energies near the Coulomb barrier. A quasielastic barrier distribution for this system was deduced from the experimental quasielastic excitation function. An α-stripping excitation function has also been measured at the same experimental conditions. These new data have been used to investigate the relative importance of several reaction channels in the reaction mechanism of the 16O + 65Cu system. Large-scale coupled-channel calculations and coupled-reaction-channel calculations have been performed. No imaginary potential was used at the barrier region because many channels have been explicitly included in the calculations. Only an inner short-range potential was used to account for the fusion process. We did not fit data by varying potential parameters, and our theoretical results were compared directly to data. Good agreement was found between data and calculations. Owing to the high sensitivity of the barrier distribution, important results have been obtained. The first excited state (1/2−) of 65Cu has less influence in the reaction mechanism than the second (5/2−) and third (7/2−) states, which are the most relevant among all the investigated ones. We have also observed a striking influence of the reorientation of the ground-state spin of the 65Cu nucleus on the elastic scattering at backward angles. In addition, calculations have shown that the excitation of the states 3− , 2+ , 1−, and 2− of the projectile 16O are also important for excellent agreement obtained with both the excitation function and the distribution of barriers. The α-stripping data have been compared to the results of coupled-reaction-channel calculations and good agreement was obtained with the inclusion of the first excited state of 12C in the coupling scheme. However, the α-transfer process has a small influence on the reaction dynamics of this system at the investigated energies.