Lifetime measurements in ¹³¹Sb at LOHENGRIN

Abstract

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 T½=3(2) ps and T½=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.