Aspects of Shape Coexistence in the Geometric Collective Model of Nuclei

We examine the coexistence of spherical and $\gamma$-unstable deformed nuclear shapes, described by an SO(5)-invariant Bohr Hamiltonian, along the critical-line. Calculations are performed in the Algebraic Collective Model by introducing two separate bases, optimized to accommodate simultaneously different forms of dynamics. We demonstrate the need to modify the $\beta$-dependence of the moments of inertia, in order to obtain an adequate description of such shape-coexistence.