Lifetime measurements in 131Sb at LOHENGRIN

The neutron-rich 131Sb nucleus was studied at Institut Laue-Langevin, with the LOHENGRIN spectrometer, via neutron-induced fission of 235U and lifetime measurements using LaBr3(Ce) detectors. The lifetimes of the 11/2+1 and 19/2+1 states were measured with the generalized centroid difference and the decay slope methods, yielding T1/2=3(2) ps and T1/2=1347(171) ps, respectively. The measured value for the 11/2+1 is at the limit of the fast-timing technique. The level scheme of 131Sb and the decay properties of the 11/2+1 state were described by realistic shell-model calculations, which reproduce well both the experimental spin and energy sequences of 131Sb and the measured B(E2;11/2+1 → 7/2+1 ) value, pointing to an almost pure 2+(130Sn) ⊗ πg7/2, core-proton coupled configuration for the 11/2+1 state.