Fusion and transfer reactions in the ¹⁹F+¹⁶⁵Ho system at energies near the Coulomb barrier

Abstract

Results of the measurements of fusion cross sections and average angular momenta in the ¹⁹F + ¹⁶⁵Ho system, for center-of-mass energies ranging from 7 MeV below to 13 MeV above the Coulomb barrier are presented. The average angular momenta of the compound system were obtained using three independent methods, namely, the γ-ray multiplicity, the ratios of the evaporation residues, and the fusion excitation function. The transfer probabilities for various one- and two-particle channels have also been measured at a beam energy of 110 MeV, an energy much higher than the Coulomb barrier. The measured Q-integrated one- and two-proton transfer probabilities have been analyzed in terms of an earlier suggested semiclassical calculation taking into account the nuclear branch in addition to the usual Coulomb branch of the classical deflection function. It is seen that the "slope anomaly" in the measured one- and two-proton transfer probabilities as a function of the distance of closest approach can be explained within this framework. The strengths of the form factors, required in a coupled channel calculation of fusion, for the important transfer channels were obtained from the data within such a semiclassical analysis. The observed enhancement of the fusion cross sections and average angular momenta is discussed in terms of the coupled channel model using static deformation for the target, inelastic excitations in the projectile, and couplings to the transfer channels. The data are also compared with the neutron flow model suggested by Stelson.