New perspective of the nuclear structure of $$^{96}$$Ru–$$^{114}$$Ru isotopes

Abstract

The angular momentum induced rigid tri-axiality observed at higher spins in $$^{110}$$Ru–$$^{114}$$Ru, a unique phenomenon, is studied. It is different from the tri-axiality observed in W, Os and Pt isotopes and in the neutron deficient Xe and Ba isotopes, occurring near shell closures. In Ru isotopes, it is enhanced at the middle of the deformed region at $$N=66$$. To understand this, the increasing collectivity in the ground state bands and in the $$\gamma $$-bands, in the full chain of $$^{96}$$Ru–$$^{106}$$Ru and the saturation at $$^{108}$$Ru–$$^{114}$$Ru are studied. The varying odd–even spin staggering displayed in the $$\gamma $$-bands of $$^{108}$$Ru–$$^{112}$$Ru and the formation of odd–even spin doublets and the wobbling motion displayed in $$^{112}$$Ru are illustrated. Microscopic basis of this is also pointed out. Relation with neighboring odd-A isotopes is studied. Comparison is made with the predictions of the Interacting Boson Model-1, as well as of the rigid tri-axial rotor (RTR) model. Distinguishing features of the anharmonic vibrator or U(5), and the $$\gamma $$-soft rotor or O(6) symmetry are illustrated. The different roles of the asymmetry parameter $$\gamma $$ for a $$\gamma $$-rigid nucleus and spherical anharmonic vibrator are explicitly demonstrated from the study of the $$\gamma $$-$$\hbox {g }B(E2)$$ ratios in Ru, for the first time. Limitation of the RTR model for transitions from the higher spin level is illustrated.