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We present the results of a high-precision quasi-elastic excitation function measurement for the 48Ca + 120Sn system at θLAB=160° at near-barrier energies in steps of 1.0 MeV. The corresponding quasi-elastic barrier distribution is derived. A large-scale coupled-channel calculation was performed to investigate the role of several reaction channels in the reaction mechanism. An excellent agreement between theory and data was obtained for the barrier distribution. The first quadrupole vibrations of the 48Ca + 120Sn, the 2n, and the 4He transfers have a strong influence on the reaction mechanism and are responsible for the good agreement achieved. The 1n transfer has a minor importance in the result when compared with the 2n transfer, which suggests that the pairing correlation might play an important role in the 2n-neutron transfer process. However, if the octupole vibration of the projectile is included in the coupling scheme, the agreement with the data gets worse. The comparison of the coupled-channel calculations with experimental data leads to the conclusion that the nuclear matter diffuseness of the 48Ca nucleus is 0.56 fm in agreement with most of the double-magic nuclei. [ABSTRACT FROM AUTHOR]

The precise quasielastic excitation function for the 18O+64Zn system was measured at energies near and below the Coulomb barrier at θlab=161∘, from which its correlated quasielastic barrier distribution was derived. The excitation functions for the two-neutron, α, and tritium transfer reactions have also been measured at the same conditions. These data were well described by the coupled channel and coupled reaction channel calculations. The comparison of the data with theoretical calculations shows the strong influence of three inelastic channels in the coupling process: the quadrupole and octupole vibrational states of 64Zn, 2+1 and 3-1, and the quadrupole vibrational state of 18O, 2+1. In addition, theoretical calculations indicate that the two-neutron stripping is mostly due to a one-step process, which has a striking effect on the reaction mechanism of this system. [ABSTRACT FROM AUTHOR]

Precise quasielastic experimental excitation function for the 18O+65Cu system has been measured and its barrier distribution has been derived. Several reaction channels have been observed on the experimental spectra, revealing the presence of two-neutron and α-stripping processes, as well as the proton pickup transfer, for which excitation functions were also measured. Extensive coupled channel and coupled reaction channel calculations have been performed to describe the experimental data. The inelastic couplings of target and projectile, and the ground state reorientation of the target, were important to the proper description of data. The transfer data were well described by calculations; however, it was shown that they almost do not affect the excitation function of 18O+65Cu quasielastic scattering. Whenever possible, structure shell model calculations have been performed to obtain the spectroscopic amplitudes of projectile and target overlaps. The two-neutron and α-transfer reactions have been calculated considering the transferred particle as a cluster with spin 0. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A precise quasielastic excitation function for the 18O+63Cu system has been measured at energies around the Coulomb barrier at θLAB=161°. The corresponding quasielastic barrier distribution has been derived. Two-neutron-, one-proton-, and a-transfer-excitation functions have also been measured at the same energies and angle. Coupled reaction channels calculations were performed to describe the experimental data. Large-scale shell-model calculations were performed to derive most of the spectroscopic amplitudes. No surface imaginary potential was necessary for the interaction potential because almost all relevant reaction channels were explicitly included in the calculation. The theoretical results were compared to the experimental quasielastic barrier distribution and a very good agreement was achieved. The comparison of the coupled reaction channel calculations and data has put in evidence several important details of the reaction mechanism of the 18O+63Cu system. The collectivity of the 63Cu nucleus has important contribution to the reaction mechanism of this system, mainly due to its first 5/2+ and 7/2+ states. It was also observed a striking influence on the reaction dynamics of the 18O(2+) state, the two-neutron transfer and the reorientation of the target ground-state spin. The best agreement to data was achieved when the nuclear matter diffuseness for the 18O was assumed equal to 0.60 fm, value that we have derived in a previous paper and that is 10% greater than the 16O diffuseness. Another significant result was that the two-neutron transfer process is much more relevant than the one-neutron-transfer process, which suggests that the pairing correlation could play an important role in the transfer process of this system. [ABSTRACT FROM AUTHOR]

An elastic backscattering experiment has been performed at energies below the Coulomb barrier to investigate static and dynamic effects in the interaction of 6He with 209Bi. The measured cross sections are presented in terms of the dσ/dσRuth ratio, as a function of the distance of closest approach on a Rutherford trajectory. The data are compared with a three-body CDCC calculation and good agreement is observed. In addition, the critical distance of interaction was extracted. A larger value was obtained for the exotic 6He nucleus as compared with the weakly bound 6Li and 9Be nuclei and the tightly bound 4He, 12C, and 16O nuclei. [ABSTRACT FROM AUTHOR]

Fusion cross sections were measured for the exotic proton-halo nucleus ⁸B incident on a ⁵⁸Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a proton-halo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section., (© 2011 American Physical Society)