The proton h11/2 intruder orbital: Evidence for collectivity and a strong proton-neutron interaction

A rotational band based on the proton h11/2 orbital has been observed to high spin (79/2ħ) and high rotational frequency (ħω≃1.0 meV) in the nucleus Sb51113. The measured transition quadrupole moment is Q0=4.4±0.6 e b, consistent with an axial prolate deformation of β2≃0.32. A large interaction strength (360±60 keV) has been measured for the rotational alignment of h11/2 neutrons which, together with a considerable delay in the crossing frequency (Δħω≃0.09 MeV), is construed as the first direct evidence of a large high-j proton-neutron interaction.