Core-proton coupled nature of the 11/2⁺ state in ¹³¹ Sb probed by lifetime measurements

The structure of the $11/{2}_{1}^{+}$ state in ¹³¹Sb was investigated at the LOHENGRIN spectrometer of Institut Laue-Langevin via neutron-induced fission of ²³⁵U and lifetime measurements, yielding ${{\rm{T}}}_{1/2}=3(2)$, at the edge of the sensitivity of the experimental method. This first result for the $11/{2}_{1}^{+}$ state half-life in neutron-rich Sb isotopes provides a quadrupole reduced transition probability to the ground state of $\text{B}(\text{E}2)={1.4}_{-0.6}^{+1.5}$ W.u., very close to the $\text{B}(\text{E}2;{2}_{1}^{+}\to {0}_{1}^{+})$ in ¹³⁰Sn. Realistic shell-model calculations reproduce well both the experimental level scheme of ¹³¹Sb and the $\text{B}(\text{E}2;11/{2}_{1}^{+}\to 7/{2}_{1}^{+})$ value, indicting a dominant ${2}^{+}{(}^{130}\text{Sn})\otimes \pi {g}_{7/2}$ core-proton coupled configuration for the $11/{2}_{1}^{+}$ state.