Breakup Threshold Anomaly Of Weakly Bound Nuclei Optical Potentials

It is one of the most frontal fields of nuclear physics to study nuclear structure and reaction mechanism in extreme conditions.When studying nuclear reactions at energies well above the Coulomb barrier between the two ions, frequently it is adequate to ignore specific effects due to reaction channels other than the one of particular interest.These channel-coupling effects are then sufficiently featureless that they can be represented by phenomenological optical potentials which describe scattering and simply models of the transition potentials for nonelastic scattering. These effective potentials vary slowly with energy, even when the coupling between two channels is either sufficiently strong or sufficiently weak. But these features no longer remain true when bombarding energies approach the vicinity of the top of the Coulomb barrier. The couplings between various channels increase in importance. When using the optical potential to interpret the observations, it is found that the parameters of the model begin to vary rapidly with energy, which become necessary to take account of the coupling explicity.The weakly bound nuclei have a high probability of breakup during the colliding processes, which has a strong effect on the fusion around the Coulomb barrier. But the problem is still open whether the cross section would be enhanced or decreased in experiment and theory.The experiments were performed at the HI-13 tandem Van-de Graff accelerator of China Institute of Atomic Energy, Beijing. The angular distributions of elastic scattering have been measured for the ⁹Be+²⁰⁸Pb system at the near- and sub-barrier energies by a group of fiveΔE-ER detectors. We have obtained the energy-dependent potential by the program PTOLEMY. There is a strong absorbing potential at the sub-barrier. The result accord with the forecast of Kelly, that the two weakly bound nuclei 6Li,9Be reaction system have the unusual threshold anomaly.Because the result is opposite to the Woolliscroft's result, it's necessary to do more research to find whether the differentiations are due to the experiment data or other reasons and whether the ⁹Be+²⁰⁸Pb system have the breakup threshold anomaly. If we can measure the breakup an fusion cross sections at the sub-barrier, it's clear that whether the ⁹Be+²⁰⁸Pb system have a strong absorbing cross sections at the sub-barrier.