He-8-He-6: a comparative study of nuclear fragmentation reactions

Dissociation of 227 MeV/u He-8 in a carbon target has been studied in kinem atically complete experiments. The data include the relative energy spectru m, angular distributions in the neutron knock-out channel (He-6 + n) as wel l as diffractive dissociation and inelastic scattering into the (He-6 + 2n) channel. The data are compared with corresponding results from the well-kn own halo nucleus He-6. In both cases it is found that neutron knock-out is the: dominating reaction channel. The relative energy spectrum (He-6 + n) s hows a structure, which is interpreted as being due to the I-pi = 3/2(-) re sonance in the He-7 ground state with about equal contribution from its I-p i = 1/2(-) spin-orbit partner. The He-7 resonance shows a spin alignment similar to that observed in He-5, but with a smaller anisotropy indicating that the structure of the He-8 gr ound state is more complicated than that of He-6. The data in the (He-6 + 2n) channel were used to identify resonances in the excitation energy spectrum of He-8. If the spectrum is interpreted as two overlapping resonances, the spin-parity assignment for these is found to be 2(+) and 1(-), respectively. (C) 2001 Elsevier Science B.V. All rights res erved.