Fusion and direct reactions around the Coulomb barrier with the neutron-rich 8He

GANIL Guest House - 9h45

Radioactive ion beams like ⁸He, open new possibilities to investigate the influence of new and exotic structures on reaction mechanisms. This thesis presents the first investigations of reactions of the weakly bound, Borromean nucleus, ⁸He, at energies around the Coulomb barrier. The low intensity of radioactive ion beams (~10⁵pps) necessitated the development of a new sensitive and selective technique for the precise and accurate measurement of fusion cross sections. In the ⁸He+¹⁹⁷Au system, excitation functions for fusion and neutron(s) transfer were measured. In the ⁸He+⁶⁵Cu system, differential and integral cross sections for various processes like elastic scattering, neutron transfer and fusion were measured using both, inclusive and exclusive measurements of characteristic gamma-rays, charged particles and neutrons. These experimental results combined with coupled reaction channels calculations demonstrated the inter-connectivity among the various reaction processes. The internal structure of ⁸He influenced the tunneling process and neutron(s) transfer and interestingly, revealed an unexpected behavior within the Helium isotopic chain. Further, a systematic analysis of the known fusion excitation functions showed that the increase in sub-barrier fusion cross sections associated with the internal structure of nuclei, is in fact much larger for ``normal'' nuclei than for light, weakly-bound ``exotic'' nuclei.