Remnants of spherical shell structures in deformed nuclei: The impact of an N=64 neutron subshell closure on the structure of N≈90 gadolinium nuclei

Odd-mass gadolinium isotopes around N=90 were populated by the (p,d) reaction, utilizing 25-MeV protons, resulting in population of low-spin quasineutron states at energies near and below the Fermi surface. Systematics of the single quasineutron levels populated are presented. A large excitation energy gap is observed between levels originating from the 2d_3/2, 1h_11/2, and 3s_1/2 spherical parents (above the N=64 gap), and the 2d_5/2 (below the gap), indicating that the spherical shell model level spacing is maintained at least to moderate deformations.