The York Research Database

The levels in ²⁶Na with single particle character have been observed for the first time using the d(²⁵Na, pγ) reaction at 5 MeV/nucleon. The measured excitation energies and the deduced spectroscopic factors are in good overall agreement with (0+1)hω shell model calculations performed in a complete spsdfp basis and incorporating a reduction in the N=20 gap. Notably, the 1p_3/2 neutron configuration was found to play an enhanced role in the structure of the low-lying negative parity states in ²⁶Na, compared to the isotone ²⁸Al. Thus, the lowering of the 1p_3/2 orbital relative to the 0f_7/2 occurring in the neighbouring Z=10 and 12 nuclei - ^25,27Ne and ^27,29Mg - is seen also to occur at Z=11 and further strengthens the constraints on the modelling of the transition into the island of inversion.