E2 transitions between positive- and negative-parity states of the ground-state alternating-parity bands

Abstract

Experimental transition probabilities between states of the ground-state alternating-parity bands of 144Ba and their theoretical analysis are presented. Lifetimes of states in 144Ba have been measured using the recoil distance method following spontaneous fission of 252Cf. The experiment was performed at the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. The experimental data show a significantly larger value of the E2 transition probability between the negative-parity states compared to the positive-parity ones. It is shown that this effect can be explained by a higher weight of the deformed component in the wave functions of the odd-I states. In the framework of the cluster approach it is explained by a higher weight of the alpha-cluster component in the wave function of the negative-parity states compared to the positive-parity ones. In the framework of the traditional collective model with the quadrupole and octupole degrees of freedom the same effect is explained by a higher value of the quadrupole deformation at the minima of the potential energy as a function of β20 and β30 compared to its value at the top of the barrier separating two physically equivalent minima, having opposite signs of the octupole deformation. Additionally, the dependence on parity of the E2 transition probability is analyzed qualitatively in nuclei with a minimum at β30 = 0 in the collective potential energy and compared to experimental data for 148Nd.