Structure Shape Evolution in Lanthanide and Actinide Nuclei

To give the characteristics of the evolution of the collectivity in even-even nuclei, we studied the behavior of the energy ratios R(4/2) and R(6/4). All chains of lanthanides begins as vibrational with R(4/2) near 2.0 and move towards rotational (R(4/2) ! 3.33) as neutron number increases. A rabid jump in R(4/2) near N=90 was seen. The plot of R(4/2) against Z shows not only the existence of a shape transitions but also the change in curvature in the data for N=88 and 90, concave to convex. For intermediate structure the slopes in E-GOS (E over spin) plots range between the vibrator and rotor extremes. The abnormal behavior of the two-neutron separation energies of our lanthanide nuclei as a function of neutron number around neutron number 90 is calculated. Nonlinear behavior is observed which indicate that shape phase transition is occurred in this region. The calculated reduced B(E2) transition probabilities of the low states of the ground state band in the nuclei 150Nd/152Sm/154Gd/156Dy are analyzed and compared to the prediction of vibrational U(5) and rotational SU(3) limits of interacting boson model calculations.