Unbound States in C-17 Probed via Single-Neutron Removal from C-18 at 245 MeV/u

A study of unbound states in C-17 by means of one-neutron knockout from a fast moving 18 C beam at an energy of 245 MeV/nucleon on a carbon target was performed at the RIKEN-RIBF laboratory utilizing SAMURAI. The energy spectrum of unbound C-17 constructed from momentum vectors of the forward going beam velocity C-16 fragment and neutron covered an energy range of the decay neutron below about 6 MeV in the center of mass of C-17*. The relative energy E-rel spectrum was characterized by two resonances at about 1.92 and 3.24 MeV in E rei and a possible multiplet at around E-rel similar to 0.7 MeV. Momentum distributions of the knockout residue for the E-rel= 1.92 and 3.24-MeV states well matched to those of p-wave neutron removal, providing a model independent confirmation of negative parity assignments for these states. The proposed level scheme of C-17 was compared with a range of different shell-model predictions; it turned out that the YSOX shell-model interaction, employing the monopolebased universal interaction for the cross-shell two-body matrix elements and incorporating larger (h) over bar omega excitations, gave a consistent account of it, including the locations of the 1/2(1)(-) and 3/2(1)(-) cross-shell states.