Triaxiality and state-dependent shape properties of Xe isotopes

Abstract

The low-lying collective spectra for an extended set of Xe nuclei are described within a phenomenological Bohr model with an exactly separable collective potential. The dependence of the collective potential on the $\ensuremath{\gamma}$ shape variable is chosen to allow the description of a phase transition between axial and triaxial shapes, while the $\ensuremath{\beta}$ excitations are described within the formalism of energy-dependent potentials in order to accommodate the different structure of the excited states. The combined contribution of these effects leads to a high fidelity description of the experimental spectra for $^{118--128}\mathrm{Xe}$ isotopes, especially in the excited rotational bands, which revealed a rapid onset of stable triaxial deformation in the $^{120}\mathrm{Xe}$ nucleus persisting also in the heavier isotopes. The critical nature of $^{120}\mathrm{Xe}$ is also reflected in its very strong state-dependence of the deformation properties.