First complete description of low-lying spectroscopy in ²⁵⁴No

In this work, we report the first complete shell-model description of low-lying structures of $^{254}$No. Employing the Kuo-Herling effective interaction, the calculations are performed within the Discrete Non-Orthogonal Shell Model recently implemented with the angular-momentum Variation After Projection applied on non-axial wavefunctions. Our calculations show a striking agreement with the experimentally known spectroscopy: the \textit{Yrast} band, the $8^{-}$ ($K=8$), $3^{+}$ ($K=3$) and $10^+$ ($K=10$) isomers together with associated $K$ bands. We reproduce the recently measured Gallagher-Moszkowski splitting between the $3^+$ ($K=3$) and $4^+$ ($K=4$) band heads. We predict the appearance of a second $0^+$ state, in excellent agreement with recent new observation. In addition, we systematically examine the ground state spectra, dipole and spectroscopic quadrupole moments of even-even, odd-even, odd-odd nuclei from $A=251$ to $A=256$, which are favourably reproduced. The present description of $^{254}$No shows the ability of the Shell Model framework to describe the low-lying properties for such an exotic nucleus at the frontier of modern experimental nuclear physics research.