R. Liguori Neto

Effect of the breakup on the fusion and elastic scattering of weakly bound projectiles on {sup 64}Zn

We study the behavior of the fusion, breakup, reaction, and elastic scattering of different projectiles on {sup 64}Zn, at near and above barrier energies. We present fusion and elastic scattering data with the tightly bound {sup 16}O and the stable weakly bound {sup 6}Li, {sup 7}Li, and {sup 9}Be projectiles. The data are analyzed by coupled channel calculations. The total fusion cross sections for these systems are not affected by the breakup process at energies above the barrier. The elastic (noncapture) breakup cross section is important at energies close to and above the Coulomb barrier and increases the reaction cross sections. In addition, we show that the breakup process at near and below barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and gives rise to a new type of anomaly.

No evidence of break-up effects on the fusion of 9Be with medium-light nuclei

Abstract Fusion cross sections were measured for the 9 Be + 27 Al and 19 F + 9 Be , 12C systems, at energies above the Coulomb barrier, in order to investigate the possible effect of fusion hindrance due to the break-up of the weakly bound nuclei. Comparisons with one-dimensional barrier penetration models and with other similar systems, where no break-up is expected to occur, show no evidence of fusion hindrance.

Reaction mechanisms in the 6Li + 59Co system

Abstract The reactions induced by the weakly bound 6 Li projectile interacting with the intermediate mass target 59 Co were investigated. Light charged particles singles and α – d coincidence measurements were performed at the near barrier energies E lab = 17.4 , 21.5, 25.5 and 29.6 MeV. The main contributions of the different competing mechanisms are discussed. A statistical model analysis, Continuum-Discretized Coupled-Channels (CDCC) calculations and two-body kinematics were used as tools to provide information to disentangle the main components of these mechanisms. A significant contribution of the direct breakup was observed through the difference between the experimental sequential breakup cross section and the CDCC prediction for the non-capture breakup cross section.

Fusion of 16O + 144Sm at sub-barrier energies

Abstract Fusion cross sections have been measured for the system 16 O+ 144 Sm at bombarding energies in the range 63 MeV ⩽E lab ( 16 O )⩽72 MeV by observation of delayed X-rays emitted by the evaporation residues. Comparison of the present results for the magic nucleus 144 Sm with those already existing for the fusion of 16 O with other samarium isotopes shows that the enhancement of the cross sections at sub-barrier energies can be explained in terms of a one-dimensional barrier-penetration model that incorporates the quadrupole deformation parameter, s 2 . There is no need to invoke the neck degree of freedom.

A new experimental method for precise energy loss measurements

Abstract A new method was developed in order to obtain continuous energy loss curves, combining transmission and backscattering techniques. The method was tested using 16 O projectiles scattered in thick Ta and Nb targets going through a mylar foil. Energy loss curves were obtained for a range from 4 to 25 MeV within 1% precision. Theoretical simulations were performed in order to study the influence of some physical effects in the method.

Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets

An experimental overview of reactions induced by the stable, but weakly-bound nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data on elastic scattering, total reaction cross sections, fusion processes, breakup and transfer channels are discussed in the framework of a CDCC approach taking into account the breakup degree of freedom.

Effect of breakup on elastic scattering for theLi6,7+Co59systems

The elastic scattering for the {sup 6,7}Li+{sup 59}Co systems was investigated in the bombarding energy range 12 MeV{<=}E{sub lab}{<=}30 MeV by means of an analysis using the Sao Paulo potential, through which the behavior of the real and imaginary parts as function of the bombarding energy was established. The experimental results suggest that overall there is an evidence of the usual threshold anomaly for both systems, although for the {sup 6}Li+{sup 59}Co system, an evidence of the breakup threshold anomaly could also be questioned.

External PIGE-PIXE measurements at the São Paulo 8UD tandem accelerator

Abstract An external PIGE–PIXE setup was installed on a beam line of the 8 MV tandem Pelletron accelerator of the Open Nuclear Physics Laboratory (LAFN). Proton beam energy was chosen in the 8–12 MeV range, sufficient to get an acceptable gamma ray yield but not so high as to prevent us from measuring X-rays. This also allowed the use of a thick aluminum exit window (0.5 mm) instead of the usual thin and sometimes fragile plastic windows. This external PIXE–PIGE system was used to analyze trace element concentrations in the enamel of human and animal teeth. The main interest was to find compatible human teeth substitutes for dentistry laboratory practice and chemical tests. In spite of their morpho-histological similarity, trace element concentrations in human and animal teeth have not yet been compared. Teeth from humans, cattle and swine collected primary at Sao Paulo region were analyzed. The elements Cu, K, Zn, Fe, Ti, Sr, V, Mn and Zr were detected by high energy external beam PIXE technique. Though preliminary, the results showed that the trace element concentrations observed in the enamel of human and swine are more similar to each other than to cattle teeth.

Nuclear fusion between heavy ions by the gamma-ray spectroscopy method

Abstract The in-beam and off-beam gamma-ray spectroscopy method, as a tool for the study of nuclear fusion between heavy ions, is described. These methods allow the study of the production and decay of the compound nucleus, inelastic scattering and transfer reactions. In this work we report the determination of fusion cross sections at energies near and below the Coulomb barrier for a series of systems: targets of 46,50 Ti, 59 Co and 64,66 Zn bombarded by 14 N and 16 O projectiles. Cross sections from 0.4 to 1000 mb were measured.

6Li direct breakup lifetimes

Abstract α − d coincidence data are studied for the 6 Li + 59 Co reaction at E l a b = 29.6 MeV . A kinematic analysis is used to identify which process, leading to the same final state, has the major contribution for selected angular regions. The contributions of the 6 Li sequential and direct breakup to the incomplete fusion/transfer process is discussed by considering the corresponding lifetimes obtained by using a semiclassical approach.