Unveiling the Intruder Deformed02+State inSi34

Abstract

The ${0}_{2}^{+}$ state in $^{34}\mathrm{Si}$ has been populated at the GANIL-LISE3 facility through the $\ensuremath{\beta}$ decay of a newly discovered ${1}^{+}$ isomer in $^{34}\mathrm{Al}$ of 26(1) ms half-life. The simultaneous detection of ${e}^{+}{e}^{\ensuremath{-}}$ pairs allowed the determination of the excitation energy $E({0}_{2}^{+})=2719(3)\text{ }\text{ }\mathrm{keV}$ and the half-life ${T}_{1/2}=19.4(7)\text{ }\text{ }\mathrm{ns}$, from which an electric monopole strength of ${\ensuremath{\rho}}^{2}(E0)=13.0(0.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ was deduced. The ${2}_{1}^{+}$ state is observed to decay both to the ${0}_{1}^{+}$ ground state and to the newly observed ${0}_{2}^{+}$ state [via a 607(2) keV transition] with a ratio $R({2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}/{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{2}^{+})=1380(717)$. Gathering all information, a weak mixing with the ${0}_{1}^{+}$ and a large deformation parameter of $\ensuremath{\beta}=0.29(4)$ are found for the ${0}_{2}^{+}$ state, in good agreement with shell model calculations using a new sdpf-u-mix interaction allowing $np\mathrm{\text{\ensuremath{-}}}nh$ excitations across the $N=20$ shell gap.