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

TL;DR

This study uses advanced proton and gamma-ray coincidence spectroscopy to investigate low-spin states, lifetimes, and shape coexistence in $^{112}$Sn and $^{114}$Sn, revealing evidence of quantum shape coexistence and intruder configurations.

Contribution

It introduces a novel $(p,p' ext{ } extgamma)$ DSA coincidence technique for measuring sub-ps nuclear lifetimes and provides new evidence for shape coexistence and intruder states in tin isotopes.

Findings

74 level lifetimes measured in $^{112,114}$Sn

First identification of QOC quintuplet members in $^{114}$Sn

Support for shape coexistence and intruder configurations

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 $(p,p'\gamma)$ 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 $J \neq 1$.