Peripheral fragmentation of a 240 MeV/nucleon beam of the halo nucleus ${}^6\mathrm{He}$ incident on carbon target has been studied in a kinematically complete experiment. It is found that one-neutron stripping to the unbound nucleus ${}^5\mathrm{He}$ is the dominant fragmentation mechanism and that it leads to a spin alignment of ${}^5\mathrm{He}$ in a plane perpendicular to the ${}^5\mathrm{He}$ momentum vector. This is expected to be a common feature for all neutron halo nuclei.

• Received 7 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.201