${\hat{I}}^2$ and ${\hat{I}}^2$-delayed neutron decay of the $N=82$ nucleus ${}_{49}^{131}$In${}_{82}$

Abstract

The half-lives of three ${\hat{I}}^2$ decaying states of ${}_{49}^{131}$In${}_{82}$ have been measured with the GRIFFIN ${\hat{I}}^3$-ray spectrometer at the TRIUMF-ISAC facility to be $T_{1/2}(1/2^{-})=328(15)$~ms, $T_{1/2}(9/2^{+})=265(8)$~ms, and $T_{1/2}(21/2^{+})=323(55)$~ms, respectively. The first observation of ${\hat{I}}^3$-rays following the ${\hat{I}}^{2}n$ decay of ${}^{131}$In into ${}^{130}$Sn is reported. The ${\hat{I}}^2$-delayed neutron emission probability is determined to be $P_{1n}=12(7)\%$ for the $21/2^{+}$ state and $2.3(3)\%$ from the combined $1/2^{-}$ and $9/2^{+}$ states of ${}_{49}^{131}$In${}_{82}$ observed in this experiment. A significant expansion of the decay scheme of ${}^{131}$In, including 17 new excited states and 34 new ${\hat{I}}^3$-ray transitions in ${}_{50}^{131}$Sn${}_{81}$ is also reported. This leads to large changes in the deduced ${\hat{I}}^2$ branching ratios to some of the low-lying states of ${}^{131}$Sn compared to previous work with implications for the strength of the first-forbidden ${\hat{I}}^2$ transitions in the vicinity of doubly-magic ${}_{50}^{132}$Sn${}_{82}$.

14 pages, 15 figures, 5 tables