Normal and intruder configurations in ${}^{34}$Si populated in the $β^-$ decay of ${}^{34}$Mg and ${}^{34}$Al

Abstract

The structure of ${}^{34}$Si was studied through ${\hat{I}}^3$ spectroscopy separately in the $β^-$ decays of ${}^{34}$Mg and ${}^{34}$Al at the ISOLDE facility of CERN. Different configurations in ${}^{34}$Si were populated independently from the two recently identified ${\hat{I}}^2$-decaying states in ${}^{34}$Al having spin-parity assignments $J^{\ddot{I}}€=4^{-}$ dominated by the normal configuration $\ddot{I}€(d_{5/2}{)}^{-1}\otimes \hat{I}½(f_{7/2})$ and $J^{\ddot{I}}€=1^{+}$ by the intruder configuration $\ddot{I}€(d_{5/2}{)}^{-1}\otimes \hat{I}½(d_{3/2}{)}^{-1}(f_{7/2}{)}^2$. The paper reports on spectroscopic properties of ${}^{34}$Si such as an extended level scheme, spin and parity assignments based on log($ft$) values and ${\hat{I}}^3$-ray branching ratios, absolute ${\hat{I}}^2$ feeding intensities and neutron emission probabilities. A total of 11 newly identified levels and 26 transitions were added to the previously known level scheme of ${}^{34}$Si. Large scale shell-model calculations using the {\sc sdpf-u-mix} interaction, able to treat higher order intruder configurations, are compared with the new results and conclusions are drawn concerning the predictive power of {\sc sdpf-u-mix}, the $N=20$ shell gap, the level of mixing between normal and intruder configurations for the 0${}_1^{+}$, 0${}_2^{+}$ and 2${}_1^{+}$ states and the absence of triaxial deformation in ${}^{34}$Si.