Nature of Isomerism in Exotic Sulfur Isotopes

We clarify the origin of the anomalously hindered $E2$ decay from the $4_1^{+}$ level in ${}^{44}\mathrm{S}$ by performing a novel many-body analysis in the shell model. Within a unified picture about the occurrence of isomerism in neutron-rich sulfur isotopes, the $4_1^{+}$ state is demonstrated to be a $K=4$ isomer dominated by the two-quasiparticle configuration $\nu {\mathrm{\Omega }}^{\pi }=1/2^{-}\otimes \nu {\mathrm{\Omega }}^{\pi }=7/2^{-}$. The $4_1^{+}$ state in ${}^{44}\mathrm{S}$ is a new type of high-$K$ isomer which has significant triaxiality.

Figure 1

Energy levels and $B(E2)$ values (in $e^2{\mathrm{fm}}^4$) in ${}^{43,44}\mathrm{S}$ compared among experiments (Expt.), the full shell-model calculation (Full Calc.), and the AM-VAP approximation to the shell model (AM-VAP). The spin-parity is denoted as $J^{\pi }$ for ${}^{44}\mathrm{S}$ and $2J^{\pi }$ for ${}^{43}\mathrm{S}$. Experimental data are taken from [2, 5, 6, 9, 23, 24].

Figure 2

Possible low-lying neutron configurations for ${}^{44}\mathrm{S}$ and ${}^{43}\mathrm{S}$.