Characterization of long-lived isomers in the odd-odd heavy actinide Md254

Abstract

Bandhead energies of all the physically admissible low-lying two-quasiparticle configuration states in the doubly-odd heavy actinide $_{101}^{254}\mathrm{Md}_{153}$ are evaluated using the well-tested two-quasiparticle rotor model with explicit inclusion of the residual proton-neutron interaction. A critical examination of these results, aimed at characterization of the long-lived (${t}_{1/2}=10$ min and 28 min; $%\ensuremath{\varepsilon}\ensuremath{\le}100$) isomer pair, conclusively rules out a high-spin ($J\ensuremath{\ge}5$) assignment for either of the isomers. Our analysis leads to ${J}^{\ensuremath{\pi}}K={1}^{\ensuremath{-}}0{p:1/{2}^{\ensuremath{-}}[521]\ensuremath{\bigotimes}n:1/{2}^{+})[620]}$ and ${3}^{\ensuremath{-}}3{p:7/{2}^{\ensuremath{-}}[514]\ensuremath{\bigotimes}n:1/{2}^{+}[620]}$ assignments, respectively, to these isomers and designates the 10-min isomer as its ground state. Our study reveals a ``landmark'' position for $^{254}\mathrm{Md}$ in the decay path of super heavy elements. The as-yet unobserved electron capture decay branches from each of the two $^{254}\mathrm{Md}$ isomers to $^{254}\mathrm{Fm}$ levels are specified.