Quasi-free scattering with 6,8He beams

This paper presents the results of experimental investigations of (p, pn), (p, p alpha) and (p, p He-6) reactions with relativistic He-6 and He-8 beams impinging on a hydrogen target. Information on the structure of extremely neutron-rich nuclei was obtained by using the unique characteristic of quasi-free scattering processes and inverse kinematics. For the first time, momentum distributions of complex clusters inside He-6 and He-8 were measured. Spectroscopic factors for valence neutrons, alpha- and He-6 clusters were deduced from the experimental data. They demonstrate that the filling of the p 1/2 shell is the essential feature of the He-8 structure. It is shown that the 8He cluster structure can be considered as a He-6 core plus two valence neutrons. (c) 2005 Elsevier B.V. All rights reserved.