νi_13/2 Structure in ¹⁵⁹Gd: Supporting Evidence of a Z = 60 Deformed Subshell Gap

While ground-state deformation should maximize at mid-shell in either the proton or neutron Fermi surfaces, subshell gaps can exist that stabilize large deformation at other values. Indeed, a gap at Z = 60 may be present in the rare-earth region as the energy of the first 2⁺ states in even-even nuclei are often lowest in an isotonic chain for neodymium rather than the midshell isotopes of dysprosium (Z = 66). Further evidence of this deformed gap has now been observed by investigating the signature splitting systematics of the νi_13/2 bands in the odd-N, rare-earth nuclei. These were aided by the recent observation of the νi_13/2 band in ¹⁵⁹Gd resulting from a multi-nucleon transfer reaction utilizing Gammasphere at Argonne National Laboratory's ATLAS Facility.