The sudden onset of the band crossing for the aligned πg9/2 orbitals: a possible transition of a triaxial shape from prolate to oblate?

The yrast states were observed up through both the first and second band crossings in both 112Ru and 116Pd using the 238U(α, f) fusion–fission reaction. The rotational alignment of the g9/2 proton-pair is responsible for the second band crossing. This assignment is based on the amount of angular momentum gained in the alignment and a similar crossing frequency is observed for the rotational band based on the h11/2 neutron orbital in both 111Ru and 117Pd. The closeness of the crossing frequency between the first and second band crossings, which happens unexpectedly within a rotational frequency span of ≈50 keV, most likely is caused by a transition of a triaxial shape from prolate to oblate in neutron rich Ru and Pd nuclei.