STUDY OF PHASE TRANSITIONS AND CRITICAL POINTS IN THE RARE-EARTH REGION IN THE FRAMEWORK OF THE INTERACTING BOSON MODEL (IBM-1)

A systematic study of isotope chains in the rare–earth region is presented. For the chains 144 −154 60 , , , and energy levels, E2 transition rates, and two–neutron separation energies (S Nd −16014662
Sm 162148 64 −Gd ) are described by using the most general (up to two–body terms) IBM-1 Hamiltonian. For each isotope chain a general fit is performed in such a way that all parameters but one are kept fixed to describe the whole chain. In this region, nuclei evolve from spherical to deformed shapes and a method based on catastrophe theory, in combination with a coherent state analysis to generate the IBM-1 energy surfaces, is used to identify critical phase transition points.The approach used to fix the Hamiltonian parameters leads to a very good global agreement with the recent available experimental data corresponding to excitation energies, B(E2)’s and S  values. In particular, an excellent agreement with the measured S 2n 2n  values is obtained, which is considered a key observable to locate phase transitional regions. The analysis presented here is consistent with previous CQF studies in the same region. As a result we find that 148 Nd and 150 Sm are the best candidates to be critical,but we should remark that  150 Nd and 152 Sm are not far away from it.