Possible triaxial shape of even-Amercury nuclei and a phase transition between ≤Hg80196andHg80198,200

Abstract

Evidences for the existence of triaxial shapes in the ground states of even-even nuclei are considered. Most if not all previous reports that support the existence are not definite. The observed decreasing of the energies of the ${2}_{1}^{+}$ and ${4}_{1}^{+}$ states for $^{198,200}\mathrm{Hg}$ compared to the lighter Hg nuclei is opposite to the expected when $N$ increases and deformation decreases. We show that a triaxial model with a phase transition between $N=116 \mathrm{and} 118$ qualitatively can explain the regularities in $B(E2)$ ratios and ${E}_{I}$ for the collective levels with ${I}^{\ensuremath{\pi}}={2}_{1}^{+}, {4}_{1}^{+}, {6}^{+}, \mathrm{and} {2}_{2}^{+}$ in $^{192\ensuremath{-}200}\mathrm{Hg}$.NUCLEAR STRUCTURE Analysis of levels in $^{192\ensuremath{-}200}\mathrm{Hg}$ in triaxial rotor model.