Rubens Lichtenthaler

The ${}^8\mathrm{Li}+{}^{120}\mathrm{Sn}$ collision has been investigated at laboratory energies of 21.7 and 25.8 MeV ($V_{\mathrm{CB}}^{\mathrm{lab}}=20.5$ MeV). The ${}^8\mathrm{Li}+{}^{120}\mathrm{Sn}$ elastic scattering and the ${}^7\mathrm{Li}$ fragment angular and energy distributions from the ${}^{120}\mathrm{Sn}({}^8\mathrm{Li},{}^7\mathrm{Li})X$ reaction have been measured. The elastic scattering angular distributions were analyzed by optical model and coupled reaction channels (CRC) calculations considering the coupling with the neutron stripping channel. The effect of the projectile breakup on the elastic scattering distributions has been studied via continuum-discretized coupled-channels (CDCC) calculations. The experimental ${}^7\mathrm{Li}$ energy distribution presents characteristics similar to a neutron transfer reaction populating a wide range of excited states in the recoil system, from the ground state up to states above the neutron threshold, with a maximum in the excitation energy predicted by $Q$-optimum arguments. These energy distributions, as well as the corresponding ${}^7\mathrm{Li}$ angular distributions, are well described using the Ichimura, Austern, and Vincent (IAV) model, which includes the neutron transfer to bound and unbound states of the target nucleus. The total reaction cross sections from the elastic scattering angular distributions and total breakup cross sections have been obtained from the IAV plus CDCC and CRC calculations. A comparison with previous measurements of the ${}^8\mathrm{Li}$ scattering on ${}^9\mathrm{Be}$ and ${}^{58}\mathrm{Ni}$ targets is presented. A dominance of the transfer to bound states over the breakup channel is seen in the present case.

Measurements of the ${}^6\mathrm{Li}+{}^9\mathrm{Be}$ collision above the Coulomb barrier ($E_{\mathrm{lab}}=11.2$ MeV; $V_{\mathrm{Cou}}^{\mathrm{lab}}=3.2$ MeV) were performed using the ${}^6\mathrm{Li}$ secondary beam selected by the RIBRAS (Radioactive Ion Beams in Brasil) first solenoid. The total reaction cross section was obtained from the ${}^6\mathrm{Li}+{}^9\mathrm{Be}$ elastic scattering angular distribution, measured in the same experiment and analyzed by optical model calculations [U. Umbelino et al., Phys. Rev. C 106, 054602 (2022)]. Proton, deuteron, triton, and $\alpha$ yields were measured at angles around ${45}^{\circ }$ in the laboratory and total fusion cross sections were deduced from the comparison between compound nucleus calculations and the measured light particle yields. The difference between the total reaction cross section and the obtained total fusion cross section provided an estimation of the contribution from other direct reaction mechanisms such as elastic and nonelastic breakup.

A geometric model for the direct contribution of the reaction cross section induced by light ions on different targets is presented. The model separates the total reaction cross section into two components, one for total fusion and another for direct reactions. We show that the direct part scales as $2 πRa$, where $R$ is related to the nuclear radius and $a$ is the width of a ring, which is related to the nuclear diffuseness. A simple expression is presented to calculate the radius $R$ and the width parameter $a$ in terms of the masses and charges of the system. The method is applied to experimental data of exotic, weakly bound, and strongly bound projectiles on several targets. Different diffuseness parameters were obtained for different types of projectiles: exotic n-rich, stable weakly bound, stable strongly bound and exotic p-rich exotic projectiles.

Quasielastic scattering angular distributions of radioactive $({}^8\mathrm{Li},$ ${}^{7,10}\mathrm{Be}, \mathrm{and} {}^{8,12}\mathrm{B})$ and stable $({}^{6,7}\mathrm{Li},$ ${}^9\mathrm{Be}, \mathrm{and} {}^{11}\mathrm{B})$ projectiles on a ${}^9\mathrm{Be}$ target are presented. The angular distributions have been analyzed by the optical model using Woods-Saxon form factor and São Paulo potential. Total reaction cross sections have been obtained from the optical model analysis and a comparison between different systems is presented. Coupled channels (CC), coupled reaction channels (CRC), and continuum-discretized coupled channels (CDCC) calculations have been performed to investigate the effect of the cluster configuration in the projectile inelastic excitation, breakup, and stripping reactions on the quasielastic angular distributions.

The ${}^8\mathrm{Li}+{}^{58}\mathrm{Ni}$ collision is investigated at 23.9, 26.1, 28.7, and 30 MeV bombarding energies. Quasielastic angular distributions and the singles ${}^7\mathrm{Li}$ angular and energy distributions are presented. Coupled-reaction channels (CRC) calculations, which include the coupling of the elastic channel to ${}^{59}\mathrm{Ni}={}^{58}\mathrm{Ni}+n$ states above and below the neutron threshold, provide a simultaneous description of the quasielastic and transfer distributions and evidence the strong effect of the one-neutron transfer/breakup channels on the quasielastic scattering. The ${}^7\mathrm{Li}$ angular and energy distributions have been also successfully analyzed combining the continuum discretized coupled channels (CDCC) method, for the elastic breakup, and the IAV model of Ichimura, Austern, and Vincent [ Phys. Rev. C 32, 431 (1985)], for the nonelastic breakup. These calculations indicate that most of the ${}^7\mathrm{Li}$ yields are due to nonelastic breakup contributions (transfer), whereas elastic breakup plays a minor role.