Complete fusion excitation functions for 9 Be 1 208 Pb have been measured to high precision at near barrier energies. The experimental fusion barrier distribution extracted from these data allows reliable prediction of the expected complete fusion cross sections. However, the measured cross sections are only 68% of those predicted. The large cross sections observed for incomplete fusion products support the interpretation that this suppression of fusion is caused by 9 Be breaking up into charged fragments before reaching the fusion barrier. Implications for the fusion of radioactive nuclei are discussed. [S0031-9007(99)08474-4] PACS numbers: 25.70.Jj, 25.70.Mn
Excitation functions have been measured for the fusion of the weakly bound nuclei 6 Li and 7 Li with 209 Bi. The complete-fusion cross sections are lower than those predicted by fusion models, being only 65% and 75% for 6 Li and 7 Li, respectively. Within the uncertainties, this suppression is independent of beam energy. Distinguishing complete fusion from incomplete fusion, both experimentally and in theoretical models, is essential to understand the fusion process of weakly bound nuclei. A simple classical trajectory model which makes this distinction is presented. Further developments of the concepts of this model could be used for realistic predictions for the fusion of unstable weakly bound nuclei.
A new technique to analyze fusion data is developed. From experimental cross sections and results of coupled-channel calculations a dimensionless function is constructed. In collisions of strongly bound nuclei this quantity is very close to a universal function of a variable related to the collision energy, whereas for weakly bound projectiles the effects of breakup coupling are measured by the deviations with respect to this universal function. This technique is applied to collisions of stable and unstable weakly bound isotopes.
The elastic scattering of the radioactive halo nucleus 6He on 27Al target was measured at four energies close to the Coulomb barrier using the RIBRAS (Radioactive Ion Beams in Brazil) facility. The São Paulo Potential (SPP) was used and its diffuseness and imaginary strength were adjusted to fit the elastic scattering angular distributions. Reaction cross-sections were extracted from the optical model fits. The reduced reaction cross-sections of 6He on 27Al are similar to those for stable, weakly bound projectiles as 6,7Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al
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