sup 8 He- sup 6 He: a comparative study of nuclear fragmentation reactions 27.20.+n; 24.70.+s; 25.06.-t

Dissociation of 227 MeV/u sup 8 He in a carbon target has been studied in kinematically complete experiments. The data include the relative energy spectrum, angular distributions in the neutron knock-out channel ( sup 6 He+n) as well as diffractive dissociation and inelastic scattering into the ( sup 6 He+2n) channel. The data are compared with corresponding results from the well-known halo nucleus sup 6 He. In both cases it is found that neutron knock-out is the dominating reaction channel. The relative energy spectrum ( sup 6 He+n) shows a structure, which is interpreted as being due to the I suppi=3/2 sup - resonance in the sup 7 He ground state with about equal contribution from its I suppi=1/2 sup - spin-orbit partner. The sup 7 He resonance shows a spin alignment similar to that observed in sup 5 He, but with a smaller anisotropy indicating that the structure of the sup 8 He ground state is more complicated than that of sup 6 He. The data in the ( sup 6 He+2n) channel were used to identify resonances in the excitation energy spectrum of sup 8 He. If the spectrum is interpreted as two overlapping resonances, the spin-parity assignment for these is found to be 2 sup + and 1 sup - , respectively.