Bridging the gap between X(5) and the interacting boson model

Phase transitional behavior in the evolution of nuclear structure from spherical to deformed shapes is often investigated in two seemingly different contexts: within the framework of the interacting boson approximation (IBA) model, or using a geometric approach such as the X(5) or E(5) solutions. To study the connection between these two different models, two-parameter IBA-1 calculations were performed and compared to the parameter-free predictions of the X(5) model. The results show that the X(5) solution cannot be exactly reproduced by any point in the two-parameter space and that the best agreement is close to, but does not coincide with, the phase transitional region for a finite number of particles. Comparison of these two approaches with experimental data on X(5)-type nuclei shows that while X(5) and the two-parameter IBA can reproduce characteristic energy ratios in these nuclei, the IBA calculations give better agreement with the experimental electromagnetic transition strengths