Li quasi - free scattering off the α - cluster in 9 Be nucleus

Spectra of coincident charged particles from the reactions induced by a 52 MeV 7 Li beam incident on a beryllium target were measured. Strong contributions of the 7 Li quasi-free scattering off the α-cluster in 9 Be nucleus were observed. This observation supports the conclusions from the study of complete fusion of weakly bound light nuclei at low energies that the " fragility " of the nuclei makes their fusion less probable. PACS. 25.70.-z Low and intermediate energy heavy-ion reactions – 27.20.+n 6 ≤ A ≤ 19 7 Li and 9 Be nuclei are very deformed, loosely bound systems. In the cluster model their ground states are portrayed as having the α-t and α-5 He cluster structure, respectively. It has been recently found [1], that the cross section for fusion of light, weakly bound nuclei at energies ranging from E C to 5E C (E C-Coulomb barrier) is significantly lower than the total reaction cross section and also smaller than the fusion cross section expected from the available systematics. This feature was interpreted to be due to the strong influence of the break-up processes. Among the break-up processes, especially at higher energies , an important role is often played by the quasi-free scattering, a process in which one of the nuclei in collision quasielastically scatters off a cluster and ejects it from the other nucleus. Many different quasi-free processes have been observed and studied with both 7 Li and 9 Be nuclei-from e.g. (p,pα) and (α,2α) reactions on them as target nuclei [2,3,4] to their direct fragmentation as projectiles in interaction with complex nuclei e.g. [5]. However, as far as we know, there is no information about these processes in reactions between these two " fragile " nuclei. Recently we have studied different many-body exit channels of the 9 Be-7 Li reaction at 7 Li energy of 52 MeV [6]. This short note is concerned primarily with the observation of strong contributions of the 7 Li quasi-free scattering on the α-particle cluster in 9 Be nucleus at this relatively low energy. In the experiment a 52 MeV 7 Li +++ beam (I = 60-100 nA) from the SMP Tandem Van de Graaff accelerator (Laboratori Nazionali del Sud) was used to bombard a self-supported beryllium target (400 µg cm −2). Outgoing charged particles were detected and identified in several particle telescopes consisting either of silicon surface barrier (∆E and E) detectors …