STRUCTURE OF THE N = 84 ISOTONES XE-138 SM-146

A collective model study using the interacting boson model-2 (IBM-2), as well as an approach explicitly treating both the shell-model and collective-model degrees of freedom, i.e., the particle-core coupling model (PCM), are applied to the N = 84 isotones 138Xe to 146Sm. A new mapping procedure from the PCM onto the IBM-2 model space is developed in order to more fully understand and discriminate between the shell-model and collective-model parts of the nuclear wave functions, and to study the criteria for which the IBM-2 is a valid approximation to the PCM in the N = 84 nuclei. It is shown that the PCM gives the better description of all nuclear properties and that, although an apparently good fit is obtained within the IBM-2, its model space using only s and d bosons is too restricted to provide a comprehensive description of these N = 84 nuclei.