  The structure of the neutron rich sodium isotopes 31,32,33Na was investigated
by means of in-beam gammaray spectroscopy following one-neutron knockout and
inelastic scattering of radioactive beams provided by the RIKEN Radioactive Ion
Beam Factory. The secondary beams were selected and separated by the fragment
separator BigRIPS and incident at ~240 meV/u on a natural carbon (secondary)
target, which was surrounded by the DALI2 array to detect coincident
de-excitation gammarays. Scattered particles were identified by the
spectrometer ZeroDegree. In 31Na, a new decay gammaray was observed in
coincidence with the known (5/2+)-> 3/2(+) transition, while for 32,33Na
excited states are reported for the first time. From a comparison to
state-of-the-art shell model calculations it is concluded that the newly
observed excited state in 31Na belongs to a rotational band formed by a 2p2h
intruder configuration within the "Island of Inversion".
