Progress on reaction mechanisms of the proton drip-line nucleus <sup>17</sup>F at energies around the Coulomb barrier

Abstract

<p indent=0mm>The reaction mechanism of proton drip-line nuclear systems at energies around the Coulomb barrier is one of the most popular topics in the field of nuclear physics. The present status of reactions induced by ¹⁷F at energies around the Coulomb barrier is reviewed in this paper. To make a further investigation of the reaction mechanisms of ¹⁷F, our group performed the measurements of elastic scattering of ¹⁷F+¹²C, ⁸⁹Y and ²⁰⁸Pb, as well as the complete kinematics of ¹⁷F+⁵⁸Ni at energies around the Coulomb barrier. For the elastic scattering, the excitation to the first excited state of ¹⁷F cannot be distinguished, hence the results have to be considered as the quasi-elastic scattering. The continuum-discretized coupled-channels (CDCC) calculations were performed to investigate the couplings to the continuum states on the elastic scattering. Both the calculations with and without the couplings to the continuum states can describe the quasi-elastic scattering data properly. The results indicate that, in a wide target-mass range, the couplings to the continuum states of ¹⁷F are not significant. For the breakup mechanism, breakup fragments of ¹⁷F+⁵⁸Ni and ²⁰⁸Pb were measured at energies above the Coulomb barrier. CDCC calculation could reproduce the breakup angular distribution of ¹⁷F+⁵⁸Ni well. However, it significantly overestimated the results of ¹⁷F+²⁰⁸Pb. The possible reason is that the excitation of the core, ¹⁶O, was not taken into account in the calculation. However, the underlying physics needs a further study. Within the energy region close to the Coulomb barrier, the breakup reactions of ¹⁷F+⁵⁸Ni were measured in single and in coincidence. The CDCC and the newly developed three-body model (the IAV model) were adopted to analyze the breakup data. The coincident data could be described well by the CDCC calculations. The sum of CDCC and IAV, which is referred to be as the total breakup, can reproduce properly the angular distributions of ¹⁶O. Moreover, the results also indicate that the non-elastic breakup dominates the ¹⁶O production. For the fusion measurement, only the results of ¹⁷F+⁵⁸Ni and ²⁰⁸Pb have been reported so far. The total fusion cross section of ¹⁷F+⁵⁸Ni was derived by measuring the fusion-evaporated protons and alphas. Compared with ¹⁶O+⁵⁸Ni, an obvious enhancement was observed at the energy below the Coulomb barrier. CDCC calculation indicates that such an enhancement is mainly due to the couplings to the continuum states. While for ¹⁷F+²⁰⁸Pb, the total fusion cross section was deduced by measuring the fusion-fission fragments in coincidence. The fusion excitation function of ¹⁷F+²⁰⁸Pb is almost identical with the stable system ¹⁹F+²⁰⁸Pb, indicating that the weakly bound nature of ¹⁷F does not play an important role in the fusion of ¹⁷F+²⁰⁸Pb. The underlying physics of the difference between ¹⁷F+⁵⁸Ni and ²⁰⁸Pb strongly deserves a further investigation. Furthermore, to establish the systematics of the reaction dynamics of ¹⁷F, reaction measurements of ¹⁷F on a range of targets at energies around and below the Coulomb barrier will be valuable. The results of ¹⁷F further indicate that the complete kinematics measurement could be the only promising approach to understand the reaction mechanisms of weakly bound nuclear systems comprehensively and provide the convincing data to promote the development of nuclear reaction theory.