Study of the $\beta^{-}$ β - decay of 116m1In: A new interpretation of low-lying 0+ states in 116Sn

Abstract

The 116Sn nucleus contains a collective rotational band originating from proton $\pi$ 2p-2h excitations across the proton $Z=50$ shell gap. Even though this nucleus has been extensively investigated in the past, there was still missing information on the low-energy interband transitions connecting the intruder and normal structures. The low-lying structure of 116Sn was investigated through a high-statistics study of the $\beta^{-}$ decay of 116m1In with the $8\pi$ spectrometer and its ancillary detectors at TRIUMF. These measurements are critical in order to properly characterize the $\pi$ 2p-2h rotational band. Weak $\gamma$ -decay branches are observed utilizing $\gamma$ - $\gamma$ coincidence spectroscopy methods, leading to the first direct observation of the 85 keV $2_{2}^{+}\rightarrow 0_{3}^{+}$ $\gamma$ ray with a transition strength of $B(E2) = 99.7(84)$ W.u. The analysis of these results strongly suggests that the 2027 keV $0_{3}^{+}$ state should replace the previously assigned 1757 keV $0_{2}^{+}$ state as the band-head of the $\pi$ 2p-2h rotational band.