Shape coexisistence and collective low-spin states in ${}^{112,114}$Sn studied with the $(p,p^{\prime }\gamma )$ DSA coincidence technique

Abstract

Proton-scattering experiments followed by the coincident spectroscopy of $\gamma$ rays have been performed at the Institute for Nuclear Physics of the University of Cologne to excite low-spin states in ${}^{112}$Sn and ${}^{114}$Sn, to determine their lifetimes and extract reduced transitions strengths $B(\Pi L)$. The combined spectroscopy setup SONIC@HORUS has been used to detect the scattered protons and the emitted $\gamma$ rays of excited states in coincidence. The novel $(p,p^{\prime }\gamma )$ DSA coincidence technique was employed to measure sub-ps nuclear level lifetimes. 74 level lifetimes $\tau$ of states with $J=0-6$ were determined. In addition, branching ratios were deduced which allowed the investigation of the intruder configuration in both nuclei. Here, $sd$ IBM-2 mixing calculations were added which support the coexistence of the two configurations. Furthermore, members of the expected QOC quintuplet are proposed in ${}^{114}$Sn for the first time. The $1^{-}$ candidate in ${}^{114}$Sn fits perfectly into the systematics observed for the other stable Sn isotopes. The $E2$ transition strengths observed for the low-spin members of the so-called intruder band support the existence of shape coexistence in ${}^{112,114}$Sn. The collectivity in this configuration is comparable to the one observed in the Pd nuclei, i.e. the 0p-4h nuclei. Strong mixing between the $0^{+}$ states of the normal and intruder configuration might be observed in ${}^{114}$Sn. The general existence of QOC states in ${}^{112,114}$Sn is supported by the observation of QOC candidates with $J\ne 1$.

Manuscript has been published in Phys. Rev. C 97, 054319 (2018). This is the preprint version